Locomotion Sequence

Cross references:     Amphioxus Locomotion   Lamprey Locomotion     
Reticular Activating Sytem   
  Reticulospinal Transmission  
Activity of Reticulospinal Neurons During Locomotion     
Initiation of Locomotion in Lampreys     Inhibition of Locomotion in Lampreys 
GABA/Glycine Inhibition      Tonic Inhibition    Behavioral Disinhibition   
Diencephaloreticular Transmission        Salamander Locomotion              
Lamprey Striatum  
   Tectum      Pretectum      Tectospinal Tract    

Thalamus Tectal Connections       Medium Spiny Neurons    Rhombencephalon 
Neuroethology   Teleost Prey Catching     Anurian Prey Catching    
Thalamus Tectal Connections       Medium Spiny Neurons    Rhombencephalon  
Basal Ganglia   
Cerebellar Neurotransmitters  Dictionary   
GABA      Glutamate   
Current hypothesis of Locomotion Sequence

     excitatory:

       
SI(Glu) >+ Cbl(Glu) >+ Th(Ach) >+ MP              

    inhibitory
                                      
        Str(GABA) >- SNr
(GABA) >-
Th(Ach) >+ MP                                                
        Str(GABA) >- GPi
(GABA) >-
Th(Ach) >+ MP                                                                               
        Str(GABA) >- GPe(GABA) >- STN(Glu) >+ SNr(GABA) >- Th(Ach) >+ MP  
        Str(GABA) >- GPe(GABA) >- STN(Glu) >+ GPi(GABA) >- Th(Ach) >+ MP 


Where - Abbreviation Key:   

Ach = Acetylcholine      
Cbl = Cerebellum  
Ctx = Cerebral Cortex   
DA = Dopamine  
        D1R and D2R - see:   Dopamine Receptors           
GABA = GABA        
Glu =    Glutamate        
GP   = Globus Pallidus  
        GPl = Lateral Globus Pallidus = GPe: globus pallidus externa 
        GPm = Medial Globus Pallidus = GPi: globus pallidus interna  
MLR = Mesencephalic Locomotor Region       
MP = Motor Programs           
NAC = Nucleus Accumbens Septi     ?    aka    Ventral Striatum    ?    
PTc = Pretectum       
RAS = Reticular Activating Sytem    -    Rhombencephalon?    
SI  = Sensory Input 
SLG = Spinal Locomotor Generator  
SN = Substantia Nigra    
        SNc = Substantia Nigra pars Compacta   
        SNr =  Substantia Nigra pars Reticulata   
SpC = Spinal Cord 
        phSC = Posterior Horn of the Spinal Cord 
STN = Subthalamic Nucleus  
Str = Striatum  =  Str/NAC        
Tec = Tectum  
Th   = Thalamus   
        VTh = Ventral Thalamus   
VTA = Ventral Tegmental Area 
VStr = Ventral Striatum     ?  aka     Nucleus Accumbens Septi   ?    



The diagram from   Basal Ganglia

https://upload.wikimedia.org/wikipedia/commons/4/45/Basal-ganglia-classic.png

Connectivity diagram showing excitatory glutamatergic pathways as red, inhibitory GABAergic pathways as blue, and modulatory dopaminergic pathways as magenta. (Abbreviations: GPe: globus pallidus external; GPi: globus pallidus internal; STN: subthalamic nucleus; SNc: substantia nigra compacta; SNr: substantia nigra reticulata) 



I'm changing my notation.  Up until now,   
    "
SNc >+ Str/NAC (DA-D1R)" 
meant that the SNc used the neurotransmitter DA to communicate with the D1R receptor in the Str/NAC.  
I'm going to change that notation to
    "SNc(DA)>+Str/NAC(D1R)" with the same meaning but less ambiguity. 
If the receptor notation is followed by a neurotransmitter notation, then that is the neurotransmitter which carries the input forward to the next receptor. 

    I've used the right arrow, ">" to indicate the input > output relationship.  Thus, in the sequence A > B > C,  A is provides input to B and B provides input to C.   
    When the right arrow ">" is followed by a plus "+" or minus "-", this indicates whether the  input has a excitatory or ihibitory effect on the receiving neuron.  Thus, ">+" indicates excitation and ">-" indicates inhibition. 

    The neurotransmitter specification in parentheses indicates the output neurotransmitter, and the receptor specification in parentheses indicates the input receptor. 
     Thus 
               "SNc(DA) >+ Str/NAC(D1R)(GABA) >- GPi(GABAA)(GABA)>-Th(GABAA) >"    
         indicates excitatory output from SNc to Str/NAC using the neurotransmitter DA at
         the D1R receptor which results in inhibition of GPi by GABA followed by inhibition of Th,
         once again by GABA. 

Note: 
    (GABA) is a neurotransmitter and (GABAA) is a receptor.   (Glu) is sometimes one and sometimes the other. 

    As per Striatum , I've assumed that Str = NAC, and I've begun to write it "Str/NAC".


    from:   Cerebellar Neurotransmitters
    "
Both inhibitory (GABA) and excitatory (glutamate) neurons are present.  However, they play different roles.  The inhibitory, GABAergic, neurons stay within the cerebellum.  They modulate the excitatory, glutamatergic, neurons which extend beyond the cerebellum and function as the over-all output.  Therefore, looking at the larger picture, the cerebellum is excitatory rather than inhibitory. "      


 The two hypothetical direct sequences (via D1R) are now: 

(1)   SI >+ Cbl(Glu) >+ SNc(Glu)(DA) >+ Str/NAC (D1R)(GABA)>-  
            GPi(GABAA)(GABA) >-  
        Th(GABAA) > VTh > MLR > RAS > SLG   

                and    

(2) 
   SI >+ Cbl(Glu) >+ SNc(Glu)(DA) >+ Str/NAC (D1R)(GABA) >- 
            SNr(GABAA)(GABA)>-  
        Th(GABAA) > VTh > MLR > RAS > SLG   


    References from  Medium Spiny Neurons

The two hypothetical indirect sequences (via D2R) are: 

(1)   
SI >+ Cbl(Glu) >+ SNc(Glu)(DA)>- Str/NAC (D2R)(GABA) >-
            GPe(GABAA)(GABA) >-
        STN(GABAA)(Glu) >+ GPi(Glu)(GABA) >-
        Th(GABAA) > VTh > MLR > RAS > SLG   


                and 

(2)   
SI >+ Cbl(Glu) >+ SNc(Glu)(DA) >- Str/NAC (D2R)(GABA) >-
            GPe(GABAA)(GABA) >-
        STN(GABAA)(Glu) >+ SNr(Glu)(GABA) >-
        Th(GABAA) > VTh > MLR > RAS > SLG   


    References from  Medium Spiny Neurons
     
"projections to the globus pallidus showed solely D2-mediated presynaptic inhibition" 

or, more briefly: 

    SNc > Str/NAC (D1R) >- GPm and SNr >- Th  presynaptic facilitation   (direct pathway)

    SNc > Str/NAC (D2R) >- GPl  >- STN >+ GPm and SNr >- Th  presynaptic inhibition  (indirect pathway)


    As per Striatum , I've assumed that Str = NAC, and I've begun to write it "Str/NAC". 

     As briefly mentioned in  Nucleus Accumbens Septi , I have a long standing interest in drugs of abuse.  Since the level of dopamine at the D2 receptors in the NAC seems to be an important determinant of "reward", I'm going to concentrate on the indirect pathway.   

    Diencephaloreticular Transmission  " makes it sound as though behavior is initiated in the  Rhombencephalon, which is way below the NAC, GP, STN, Th, PTc and Tec ".      
     

Substantia Nigra pars Compacta  (SNc)  >  Nucleus Accumbens Septi  (NAC)  

    Substantia Nigra

     Substantia Nigra pars Reticulata  (SNr)    
           
Substantia Nigra pars Compacta  (SNc)   
   "Neurons of the pars compacta receive inhibiting signals from the collateral axons from the neurons of the pars reticulata. [4] All these neurons send their axons along the nigrostriatal pathway to the striatum (NAC?) where they release the neurotransmitter
dopamine."  


Nucleus Accumbens Septi  (NAC)   

   Nucleus Accumbens Septi (NAC)    
http://en.wikipedia.org/wiki/Nucleus_accumbens  
    "From the core, the neurons project to other sub-cortical areas such as the globus pallidus (GP) and the substantia nigra. GABA is one of the main neurotransmitters in the NACc, and GABA receptors are also abundant. [16][18] These neurons are also the main projection or output neurons of the nucleus accumbens.
    While 95% of the neurons projecting from the nucleus accumbens are medium spiny GABA-ergic neurons, other projecting neuronal types are also present, such as large cholinergic interneurons. "  
My comments:   
    1.  As per Striatum , I've assumed that Str = NAC.
    2.  If "95% of the neurons projecting from the nucleus accumbens are medium spiny GABA-ergic neurons", then the NAC is broadly inhibitory.  However, it doesn't say which part of the GP, GPl or GPm, receives the input, and this makes a difference.   

1988  10<13  in   Medium Spiny Neurons  SEARCH # 1 . 
Synaptic organization of the striatum   
http://www.ncbi.nlm.nih.gov/pubmed/3069970 
    "The major physiologic function of striatal efferent activity appears to be inhibition of tonically active GABAergic neurons in the globus pallidus and substantia nigra pars reticulata."  


Nucleus Accumbens Septi   (NAC)  >  Lateral Globus Pallidus (GPl) 
and  Medial Globus Pallidus   (GPm)  
 
1980 
Nucleus accumbens to globus pallidus GABA projection: electrophysiological and iontophoretic investigations.
http://www.ncbi.nlm.nih.gov/pubmed/7370763 
    "Extracellular recordings were obtained from neurons in the nucleus accumbens and globus pallidus of urethane anesthetized rats. Eight neurons in the nucleus accumbens were activated antidromically following stimulation of the globus pallidus. Calculated conduction velocities were 0.4-1.5 m/sec, indicative of small unmyelinated fibers.  
    A total of 74 of 153 neurons in the globus pallidus responded to stimulation of the nucleus accumbens. Of these neurons 4 (2.7%) were excited only, 46 (30.1%) were inhibited only and 24 (15.7%) had sequential effects to excitation and inhibition.  
    Iontophoretic application of picrotoxin was found to attenuate or abolish the poststimulus inhibition in one-half of the neurons examined. The 74 neurons which responded to stimulation of the nucleus accumbens had slower firing frequencies and generally more random firing patterns than neurons which did not respond to stimulation. Fifty-three per cent of all globus pallidus neurons examined had increased spontaneous firing frequencies following the iontophoretic administration of picrotoxin alone. This is indicative of the removal of a tonic GABA input onto these neurons. 
    Most neurons examined had decreased spontaneous firing frequencies following the iontophoretic application of GABA which could be blocked by the iontophoretic application of picrotoxin. The results from antidromic activation, slow conduction velocity, sensitivity to GABA and picrotoxin, and picrotoxin attenuation of the poststimulus inhibitory effect provide evidence of a direct GABAergic projection from the nucleus accumbens to the globus pallidus in the rat."
    262 Related citations:
http://www.ncbi.nlm.nih.gov/pubmed?linkname=pubmed_pubmed&from_uid=7370763     7 Cited by's:
http://www.ncbi.nlm.nih.gov/pubmed?linkname=pubmed_pubmed_citedin&from_uid=7370763   
My comment
    As above,  it doesn't say which part of the GP, GPl or GPm, receives the input, and this makes a difference.         

from: Globus Pallidus      

    Reminder

        GPl = Lateral Globus Pallidus = GPe: globus pallidus externa         
        GPm = Medial Globus Pallidus = GPi: globus pallidus interna    

    Globus pallidus (GP)       
http://en.wikipedia.org/wiki/Globus_pallidus           
    ""In primates, the dorsal pallidum, or globus pallidus, is divided into two parts by the medial medullary lamina. These are often termed "internal" and "external" (the internal globus pallidus [GPi] and the external globus pallidus [GPe]); both are composed of closed nuclei surrounded by myelinic walls.
    The ventral pallidum (VP) lies within the substantia innominata (Latin for unnamed substance) and receives efferent connections from the ventral striatum (the nucleus accumbens and the olfactory tubercle). It projects to the dorsomedial nucleus of the dorsal thalamus, which, in turn, projects to the prefrontal cortex; it also projects to the pedunculopontine nucleus (PPT) and tegmental motor areas."  
    "When it comes to regulation of movement, the globus pallidus has a primarily inhibitory action that balances the excitatory action of the cerebellum."  
    "The two pallidal nuclei and the two nigral (pars compacta and pars reticulata) parts constitute a high-frequency autonomous pacemaker [6]  ... The two parts receive successively a large quantity of GABAergic axonal terminal arborisations from the striatum through the dense striato-pallidonigral bundle. ... The striatal afferents contribute more than 90% of synapses.  The two pallidal nuclei receives dopaminergic axons from the pars compacta of the substantia nigra."  
My comments
1.  The statement that the VP receives "efferent" connections from the NAC is probably a misstatement.  Received connections are generally referred to as "afferent".  If the NAC is broadly inhibitory as concluded in the NAC>GP section, above, then the NAC inhibits the VP. 
2.  Although it says that the VP projects to the dorsomedial nucleus of the dorsal thalamus, it doesn't say whether this projection is excitatory or inhibitory.  It also says that it projects to the PPT, and this implies that some of its output bypasses the TH.      
3.  The statement that "the globus pallidus (GP) has a primarily inhibitory action" is ambiguous.  The GP receives inhibitory input from the NAC.  Since the GP provides an inhibitory output, the inhibition of the GP by the NAC should be excitatory for the structures to which the GP projects.   
    Important
"When it comes to regulation of movement, the globus pallidus has a primarily inhibitory action that balances the excitatory action of the cerebellum."     

    
Ventral pallidum (VP) 
http://en.wikipedia.org/wiki/Ventral_pallidum   
    "The ventral pallidum is a structure within the basal ganglia of the brain. It is an output nucleus whose fibres project to thalamic nuclei, such as the ventral anterior nucleus, the ventrolateral nucleus, and the medial dorsal nucleus."   
    "The ventral pallidum also receives GABAergic inputs from the nucleus accumbens. [2] It is the relay nucleus from the nucleus accumbens to the medial dorsal nucleus. The nucleus accumbens projects to the medial dorsal nucleus via GABAergic medium spiny neurons."  
My comments
1.  Although it says that the VP projects to three thalamic nuclei, it doesn't specify the neurotransmitter or whether it is excitatory or inhibitory. 
2.  Since the VP receives GABA inputs from the NAC, the NAC inhibits the VP.      
3.  If the NAC projects to the thalamus via GABA neurons, is it bypassing the VP?    


Lateral Globus Pallidus    (GPl)  >  Subthalamic Nucleus  (STN)     (indirect pathway)   


Lateral Globus Pallidus    (GPl) 


2011 2<13  in   Medium Spiny Neurons  SEARCH # 1 . 
Targeting neuronal populations of the striatum.
http://www.ncbi.nlm.nih.gov/pubmed/21811438   
    "The dorsal striatum, caudate-putamen, is primarily implicated in motor control and the learning of habits and skills, whereas the ventral striatum, the nucleus accumbens, is essential for motivation and drug reinforcement."  
    "dopamine D(1) receptor-positive (D(1)R) striatonigral MSNs project to the medial globus pallidus and substantia nigra pars reticulata (direct pathway)"  
    "dopamine D(2) receptor-positive (D(2)R) striatopallidal MSNs project to the lateral globus pallidus (indirect pathway)"  


2011  1<13 in   Medium Spiny Neurons  SEARCH # 1 . 
Differential DAergic Control of D1 and D2 Receptor Agonist Over Locomotor Activity and GABA Level in the Striatum.
http://www.ncbi.nlm.nih.gov/pubmed/22110374   
    "The striatum is made up 96% of medium spiny neurons which are GABAergic cells.  GABAergic cells are known to contain DA receptors which divide into two main branches-
    the D1 receptor (D1R)-expressing direct pathway and the  
    D2 receptor (D2R)-expressing indirect pathway. "  


2011   28<77  in   Medium Spiny Neurons  SEARCH # 2 .   
Functional connectome of the striatal medium spiny neuron.
http://www.ncbi.nlm.nih.gov/pubmed/21273403
    " Projections to the globus pallidus showed solely D2-mediated presynaptic inhibition, whereas projections to the substantia nigra showed solely D1-mediated presynaptic facilitation."  


Subthalamic Nucleus  (STN)  >  Substantia Nigra pars Reticulata   (SNr)  


Subthalamic Nucleus  (STN)     

    "The subthalamic nucleus receives its main input from the globus pallidus,[6] ... These afferents are GABAergic, inhibiting neurons in the subthalamic nucleus... The subthalamic nucleus also receives neuromodulatory inputs, notably dopaminergic axons from the substantia nigra pars compacta.[7] It also receives inputs from the pedunculopontine nucleus."    
    "The efferent axons are glutamatergic (excitatory)"   

Searching PubMed for "Subthalamic Nucleus found 5106 references: 
http://www.ncbi.nlm.nih.gov/pubmed/?term=subthalamic+nucleus      


Substantia Nigra pars Reticulata   (SNr) 
    "The neurons of the pars reticulata produce the neurotransmitter gamma-aminobutyric acid (GABA). The neurons of the pars reticulata through the nigrothalamic bundle send axons to a particular part of the motor thalamus. The nigral territory corresponds to the nucleus ventralis anterior (VA) (see also List of thalamic nuclei) (different from the pallidal VO). VA is the origin of one output of the basal ganglia system." 
    "
The neurons of the pars reticulata are fast-spiking pacemakers, generating action potentials in the absence of synaptic input.[3] In primates they discharge at a mean rate of 68Hz in contrast to dopaminergic neurons (below 8Hz).[4] They receive abundant afferrences from the striatum (mainly from the associative striatum) with the same very peculiar synaptology as the pallidum. It receives axons from the subthalamic nucleus and a dopaminergic innervation from the dopaminergic ensemble. The pars reticulata is one of the two primary output nuclei of the basal ganglia system to the motor thalamus (the other output is the internal segment of the globus pallidus)."  

 
Substantia Nigra pars Reticulata  (SNr)  >  Thalamus  (Th)     (indirect pathway)  

Thalamus  (Th)   
    "A major role of the thalamus is devoted to "motor" systems. ... The neuronal information processes necessary for motor control were proposed as a network involving the thalamus as a subcortical motor centre.[16]
    Note:  As of 03-18-15, this article says very little that relates to locomotion.  Its focus is primarily on sensation.  
    
   
Medial Globus Pallidus   (GPm)  >  Thalamus  (Th)     (direct pathway)  

Medial Globus Pallidus   (GPm) 
    "The medial globus pallidus (or internal, GPi) is one of the output nuclei of the basal ganglia (the other being the substantia nigra pars reticulata). The GABA-containing neurons send their axons to specific nuclei of the dorsal thalamus (VA and VL), to the centromedian complex and to the pedunculopontine complex.[1][2]



Thalamus Tectal Connections            

Thalamus Tectal Connections:     


From: Searching PubMed for "thalamus tectal connections" identified 60 references:   
http://www.ncbi.nlm.nih.gov/pubmed/?term=thalamus+tectal+connections     
    Some are considered in the Tec > MLR section, below. 

58<60    1975     
The connections and laminar organization of the optic tectum in a reptile (lguana iguana).   
http://www.ncbi.nlm.nih.gov/pubmed/1176645  
    "The total pattern of projections from the optic tectum in the Iguana and the turtle is similar to that reported for representatives of other vertebrate classes."    
    "Tectotectal connections and several descending pathways were also recognized in each species. 
The descending pathways include ipsilateral tectobulbar and tecto-isthmi pathways and a contralateral predorsal bundle." 
    "A small lesion involving the deep periventricular layers as well as the superficial layers produced degeneration in the predorsal bundle and the ipsilateral tectobulbar tract as well as in the structures receiving input from the more superficial layers. These results are compared to the results of similar analyses of the superior colliculus in mammals."    
    196 Related citations:    
http://www.ncbi.nlm.nih.gov/pubmed?linkname=pubmed_pubmed&from_uid=1176645   
   
My comment:
This reference discusses only the efferent, not the afferent, connections of the tectum.     
57<60 1977
Tectal efferents in the branded water snake, Natrix sipedon
http://www.ncbi.nlm.nih.gov/pubmed/853143  
    "The tectum gives rise to crossed and uncorssed projections to the brainstem reticular formation."
    My comment:
This reference discusses only the efferent, not the afferent, connections of the tectum.      

48<60 1981
Efferent tectal pathways in two chondrichthyans, the shark Scyliorhinus canicula and the ray Raja clavata.
http://www.ncbi.nlm.nih.gov/pubmed/7204648  
    "... a descending projection to the rhombencephalic reticular formation. The last mentioned tract can be subdivided into (a) the ipsilateral tractus tectobulbaris ventralis and intermedius, giving off fibers to the intercollicular nucleus, the nucleus reticularis isthmi, and the medial and median reticular formation of the rhombencephalon and (b) the contralateral tractus tectobulbaris dorsalis, which connects the tectum with the contralateral medial reticular formation."  


47<60  1981   
Organization of extrinsic tectal connections in Goldfish (Caraccius auratus).
http://www.ncbi.nlm.nih.gov/pubmed/7217368     
from the Abstract:   
     "Ipsilateral tectal afferents include ... the nucleus dorsalis lateralis of the thalamus ... Terminals of the ... nucleus dorsolateralis ... are sparse and widely branching."
    See also: Pretectum  for more connections and  Tectum  for full Abstract .   


45<60  1982
The afferent connections of the tectum mesencephali in two chondrichthyans, the shark Scyliorhinus canicula and the ray Raja clavata.
http://www.ncbi.nlm.nih.gov/pubmed/7076889  
    " Diencephalic projections to the tectum originate from the thalamus dorsalis pars medialis, the thalamus ventralis pars lateralis, the nucleus medius infundibuli ..." 
    See also: Pretectum  for more connections and  Tectum  for full Abstract .   


1982  132<143    
    The afferent connections of the tectum mesencephali in two chondrichthyans, the shark Scyliorhinus canicula and the ray Raja clavata . 
http://www.ncbi.nlm.nih.gov/pubmed/7076889   
    "
Rhombencephalic cells projecting to the tectum could be identified in the nucleus cerebelli (only in Scyliorhinus), the nucleus vestibularis superior, the reticular formation, the nucleus funiculi lateralis, the nucleus tractus descendens nervi trigemini, and the nucleus dorsalis and intermedius areae octavolateralis."  
My comments
1.  I am unfamiliar with the nucleus cerebelli, the nucleus vestibularis superior, the nucleus funiculi lateralis, the nucleus tractus descendens nervi trigemini, and the nucleus dorsalis and intermedius areae octavolateralis.  I need to find out more about them.  If any of them receive sensory data, then they are potentially the first step in the sensory > motor locomotion sequence. 
2.  If behavior is initiated in the rhombencephalon, then activity of the ascending connections to the tectum may be simultaneous with activity of the descending connections to the spinal cord.  This would make the rhombencephalon, rather than the SNc, the origin of behavior.  The SNc may just release activity initiated reflexivly by the rhomboencephalon.  
     See:  Thalamus Tectal Connections  for full Abstract and Related citations .  
Note:  The two pages,   Thalamus Tectal Connections  and  Diencephaloreticular Transmission  may be redundant.  If so, I should combine them.   

 

    

29<60  1990
Afferent connections of the optic tectum in channel catfish Ictalurus punctatus.
http://www.ncbi.nlm.nih.gov/pubmed/2078856    
Abstract
    "Horseradish peroxidase was injected unilaterally into the optic tectum of the channel catfish, Ictalurus punctatus. The sources of tectal afferents were thereby revealed by retrogradely labeled neurons in various brain centers. ...  Both the anterior thalamic nucleus and the ventro-medial thalamic nucleus projected to the ipsilateral optic tectum."  
    See also: Pretectum  for more connections and Tectum  for full Abstract .   


14<60    2001
Neural modulation of visuomotor functions underlying prey-catching behaviour in anurans: perception, attention, motor performance, learning.   
    See:  Anurian Prey Catching


10<60   2002 
Mesencephalic and diencephalic afferent connections to the thalamic nucleus rotundus in the lizard, Psammodromus algirus.
http://www.ncbi.nlm.nih.gov/pubmed/12169109   
My comment
    The nucleus rotundus may be reptilian but not mammalian. 


Thalamus  (Th)  >  Pretectum  (PTc)  >  Tectum (Tec) 


Thalamus  (Th)

Thalamus Motor Relay    


Tectum (Tec)  >   Reticular Activating Sytem  (RAS)     (?)   


1998    444<985 
Electrophysiological and neuropharmacological study of tectoreticular pathways in lampreys.
http://www.ncbi.nlm.nih.gov/pubmed/9757053    
"Abstract
    Tectoreticular (TR) cells along the diencephalic-mesencephalic border are the origin of prominent crossed and uncrossed pathways that project to the middle (MRRN) and posterior (PRRN) rhombencephalic reticular nuclei in juvenile and adult lampreys.  
    This study investigated the synaptic contacts between TR axons and the reticular cells. Intracellular recordings were carried out in reticular neurones (n=124) while microstimulating the TR regions.  
    Tectoreticular inputs were recorded in all reticular cells studied (248 PSPs); although stronger responses were evoked in the MRRN neurones. The majority of responses were excitatory, but increasingly mixed and inhibitory when recorded in the middle and caudal part of the reticular nuclei. The excitation had the shortest onset latencies and sharpest slopes measured in both reticular nuclei, while the inhibition was longer and smoother. The characteristics of TR inputs to different reticular cell types is also presented. The transmission of evoked responses was isolated to the crossed and uncrossed TR pathways by studying the effects of 1% Xylocaine ejections and surgical lesions.  
    The TR inputs were transmitted to reticular cells through monosynaptic and polysynaptic contacts. The synaptic transmission involved excitatory amino acids, acting through AMPA and NMDA receptors, while the inhibition was glycinergic. Comparisons with other sensory systems in lampreys are discussed."  
    178 Related citations
http://www.ncbi.nlm.nih.gov/pubmed?linkname=pubmed_pubmed&from_uid=9757053  


Tectum (Tec)  >  Mesencephalic Locomotor Region  (MLR)   >   Reticular Activating Sytem  (RAS)           


From:  Searching PubMed for "thalamus tectal connections" identified 60 references (above):   
http://www.ncbi.nlm.nih.gov/pubmed/?term=thalamus+tectal+connections     
    Some are considered in the Th > Tec section, above. 

1975
The connections and laminar organization of the optic tectum in a reptile (lguana iguana).   
http://www.ncbi.nlm.nih.gov/pubmed/1176645   
    "The total pattern of projections from the optic tectum in the Iguana and the turtle is similar to that reported for representatives of other vertebrate classes." 
    "Tectotectal connections and several descending pathways were also recognized in each species.  The descending pathways include ipsilateral tectobulbar and tecto-isthmi pathways and a contralateral predorsal bundle."  
    "A small lesion involving the deep periventricular layers as well as the superficial layers produced degeneration in the predorsal bundle and the ipsilateral tectobulbar tract as well as in the structures receiving input from the more superficial layers."  
    See also:  Tectum  for full Abstract .   


1981
Afferent and efferent connections of the optic tectum in the carp (Cyprinus carpio L.).
http://www.ncbi.nlm.nih.gov/pubmed/6168333  
from the Abstract:   
    "Following iontophoretic peroxidase injections in several parts of the tectum, anterograde transport of the enzyme revealed tectal projections to the ...  mesencephalic and bulbar reticular formations.   
    Tectal afferents were demonstrated by retrograde HRP transport in the ... dorsomedial and dorsolateral thalamic nuclei ..." 
    See also: Pretectum  for more connections and  Tectum  for full Abstract .   


1981
Efferent tectal pathways in two chondrichthyans, the shark Scyliorhinus canicula and the ray Raja clavata.
http://www.ncbi.nlm.nih.gov/pubmed/7204648 
    "... a descending projection to the rhombencephalic reticular formation. The last mentioned tract can be subdivided into  
    (a) the ipsilateral tractus tectobulbaris ventralis and intermedius, giving off fibers to the intercollicular nucleus, the nucleus reticularis isthmi, and the medial and median reticular formation of the rhombencephalon and  
    (b) the contralateral tractus tectobulbaris dorsalis, which connects the tectum with the contralateral medial reticular formation."  
    See also: Pretectum  for more connections and Tectum  for full Abstract .   


1988
Connections of the tectum opticum in two urodeles, Salamandra salamandra and Bolitoglossa subpalmata, with special reference to the nucleus isthmi.
http://www.ncbi.nlm.nih.gov/pubmed/3385198  
    "In both species retrogradely labelled cells were observed: ipsilaterally in the ... ventral and dorsal thalamus"     "Caudal efferents formed the bilaterally organized tecto-bulbar tracts innervating the rhombencephalon."   
"The tecto-isthmic projection was highly topographic forming a layered terminal field lateral to the nucleus isthmi."
    See also: Pretectum  for more connections and  Tectum  for full Abstract .   


1996  
A mesencephalic relay for visual inputs to reticulospinal neurones in lampreys.
http://www.ncbi.nlm.nih.gov/pubmed/8773792    
    "Visual stimuli elicit motor responses in lampreys. These responses rely, in part, on the activation of reticulospinal (RS) neurones which constitute the main descending pathway in these early vertebrates.  
    Please see:  Mesencephalic Locomotor Region  for full Abstract and Related citations . 


1996       75<144   
    A mesencephalic relay for visual inputs to reticulospinal neurones in lampreys.   
    in  Rhombencephalon  and  Initiation of Locomotion in Lampreys .
http://www.ncbi.nlm.nih.gov/pubmed/8773792          
    See:   Initiation of Locomotion in Lampreys  for full Abstract and Related citations .    
My comment
    This is an example of behavior which was initiated not by the  Substantia Nigra pars Compacta  (SNc) and not by the rhombocephalon but by sensory input.  This may turn out to be what is actually happening in most cases.   


Mesencephalic Locomotor Region  (MLR)  >  Reticular Activating Sytem  (RAS)  >  
Spinal Locomotor Generator   (SLG)    


Searching PubMed for "mesencephalic locomotor region reticular activating system" yielded only three references: 
http://www.ncbi.nlm.nih.gov/pubmed/?term=mesencephalic+locomotor+region+reticular+activating+system   


1988 
Cholinergic vs. noncholinergic efferents from the mesopontine tegmentum to the extrapyramidal motor system nuclei.
http://www.ncbi.nlm.nih.gov/pubmed/2461392 
from the Abstract:
    "Previous studies have suggested that the pedunculopontine tegmental nucleus (PPTn) is reciprocally connected with extrapyramidal motor system nuclei (EPMS) whereas other studies have implicated the PPTn in behavioral state control phenomena such as sleep-wakefulness cycles. Many of these studies define the nonprimate PPTn as an area of mesopontine tegmentum which is labeled from injections of anterograde tracers into the basal ganglia." 
    "This body of evidence suggests that the noncholinergic MEA represents an additional component of the EPMS and may correspond to the "mesencephalic locomotor region." The cholinergic PPTn may play a role in more global thalamic functions such as the "reticular activating system" rather than a primary role in motor function."       See:  Mesencephalic Locomotor Region for full Abstract, Related citations and Cited by's.   

 
2014
Identification of a brainstem circuit regulating visual cortical state in parallel with locomotion.
http://www.ncbi.nlm.nih.gov/pubmed/25033185  
    "In mice, locomotion is accompanied by changes in cortical state and enhanced visual responses."  
"The mesencephalic locomotor region (MLR) has been shown to be capable of initiating running and is associated with the ascending reticular activating system."  
    "These studies demonstrate that the MLR regulates cortical state in parallel with locomotion."  
See:  Mesencephalic Locomotor Region for full Abstract and Related citations. 


2015
The physiology of the pedunculopontine nucleus: implications for deep brain stimulation. http://www.ncbi.nlm.nih.gov/pubmed/24880787  
    "This brief review resolves a number of persistent conflicts regarding the location and characteristics of the mesencephalic locomotor region, which has in the past been described as not locomotion-specific and is more likely the pedunculopontine nucleus (PPN). The parameters of stimulation used to elicit changes in posture and locomotion we now know are ideally suited to match the intrinsic membrane properties of PPN neurons. The physiology of these cells is important not only because it is a major element of the reticular activating system, but also because it is a novel target for the treatment of gait and postural deficits in Parkinson's disease (PD)."  
    See:  Mesencephalic Locomotor Region for full Abstract and Related citations. 


Reticular Activating Sytem (RAS)  > Spinal Locomotor Generator (SLG)  

Please see: Reticulospinal Transmission .  


Medium Spiny Neurons   
    Medium spiny neurons have dopamine receptors, where dopamine has a dual action on MSNs; it inhibits the (D2-type) MSNs in the indirect pathway and excites (D1-type) MSNs in the direct pathway. Consequently, when dopamine is lost from the striatum, the indirect pathway becomes overactive and the direct pathway becomes underactive.

from  Basal Ganglia
    Once excited by glutamate, the cells in the striatum project in two different directions giving rise to two major pathways: the "direct" and the "indirect" pathways.  

     It's beginning to look like the Th > Ptc > Tec section is misleading.  Although the sequence does exist, the Pretectum  (Ptc) seems to have very little to do with locomotion.  So I've eliminated the Ptc  from the  Locomotion Sequence  and the section has become just Th > Tec



SubC:  Locomotion Sequence 
170715 - 2253 

 





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