Lamprey GABA

Cross references:  Lamprey Neurotransmitters    GABA    GABA Gate   
GABAA Receptor Evolution
  GABA Metabotropic Receptor
GABA/Glycine Inhibition            

Searching for "lamprey GABA" yielded:                
        PubMed = 138            
Google = 39,800   

Note:  There are a number of references which considered GABA but do not directly consider its role in behavioral inhibition.  They are filed here

Three types of GABA-immunoreactive cells in the lamprey spinal cord.  
Polyclonal antisera raised against conjugated GABA were used to study the distribution of GABAergic neurons in the spinal cords of lampreys (Lampetra fluviatilis and Ichtyomyzon unicuspis) using immunofluorescence and peroxidase-antiperoxidase techniques.  
    Three morphologically distinct types of GABA-immunoreactive (GABA-ir) cell bodies were observed, multipolar neurons in the lateral grey cell column, apparently bipolar cells in the ventral aspect of the dorsal horn, and small liquor-contacting cells surrounding the central canal.  
    A high density of immunoreactive fibers of spinal origin were present in the lateral and ventral funiculi, whereas the dorsal column had a relatively low density. Dense GABA-ir plexuses were situated in the lateral spinal margin, and in the dorsal part of the dorsal horn. A chronic lesion of the rostral spinal cord did not result in any observable loss of GABA-ir fibers below or above the lesion, suggesting that the 3 types of segmental GABA-ir neurons are the main sources of the GABAergic innervation of the lamprey spinal cord."  
    134 Related citations:   


Putative GABAergic input to axons of spinal interneurons and primary sensory neurons in the lamprey spinal cord as shown by intracellular Lucifer yellow and GABA immunohistochemistry.
    "GABAergic phasic modulation of the membrane potential occurs in spinal interneurons during fictive locomotion in lamprey presumably indicating a presynaptic inhibition. GABA also modulates synaptic transmission from primary sensory neurons (dorsal cells) at a presynaptic site. From these findings GABA terminals would be expected to be in close contact with phasically modulated axons of spinal interneurons and/or dorsal cells and their axons. To test this supposition intracellular injections of Lucifer yellow into spinal interneurons or dorsal cells were combined with GABA immunohistochemistry. GABA-immunoreactive (ir) varicosities were found to be in close contact (less than 1 micron distance) with axons modulated during fictive locomotion as well as dorsal cell axons. Small GABA-ir bipolar neurons form processes, which are in close contact with the axons of dorsal cells." 
141 Related citations:
and 2 Cited by's.

Ontogeny of gamma-aminobutyric acid-immunoreactive neuronal populations in the forebrain and midbrain of the sea lamprey.

Afferents of the lamprey optic tectum with special reference to the GABA input: combined tracing and immunohistochemical study.   
    "The optic tectum in the lamprey midbrain, homologue of the superior colliculus in mammals, is important for eye movement control and orienting responses. There is, however, only limited information regarding the afferent input to the optic tectum except for that from the eyes. The objective of this study was to define specifically the gamma-aminobutyric acid (GABA)-ergic projections to the optic tectum in the river lamprey (Lampetra fluviatilis) and also to describe the tectal afferent input in general.  
    The origin of afferents to the optic tectum was studied by using the neuronal tracer neurobiotin. Injection of neurobiotin into the optic tectum resulted in retrograde labelling of cell groups in all major subdivisions of the brain. The main areas shown to project to the optic tectum were the following: the caudoventral part of the medial pallium, the area of the ventral thalamus and dorsal thalamus, the nucleus of the posterior commissure, the torus semicircularis, the mesencephalic M5 nucleus of Schober, the mesencephalic reticular area, the ishtmic area, and the octavolateral nuclei.  
    GABAergic projections to the optic tectum were identified by combining neurobiotin tracing and GABA immunohistochemistry. On the basis of these double-labelling experiments, it was shown that the optic tectum receives a GABAergic input from the caudoventral part of the medial pallium, the dorsal and ventral thalamus, the nucleus of M5, and the torus semicircularis. The afferent input to the optic tectum in the lamprey brain is similar to that described for other vertebrate species, which is of particular interest considering its position in phylogeny."   
    7 Cited by's:  

19<143    2007
Descending GABAergic projections to the mesencephalic locomotor region in the lamprey Petromyzon marinus.  

    "The mesencephalic locomotor region (MLR) plays a significant role in the control of locomotion in all vertebrate species investigated. Forebrain neurons are likely to modulate MLR activity, but little is known about their inputs.   
    Descending GABAergic projections to the MLR were identified by double-labeling neurons using Neurobiotin injected into the MLR combined with immunofluorescence against GABA. Several GABAergic projections to the MLR were identified in the telencephalon and diencephalon.  
    The most abundant GABAergic projection to the MLR came from the caudal portion of the medial pallium, a region that may have similarities with the amygdala of higher vertebrates.  
    A small population of GABAergic cells projecting to the MLR was found in the striatum and the ventral portion of the lateral pallium, which could respectively correspond to the input and output components of the basal ganglia thought to be involved in the selection of motor programs.  
    Other GABAergic projections were found to come from the thalamus and the hypothalamus, which could take part in the motivational aspect of motor behavior in lampreys. Electrophysiological experiments were also carried out to examine the effects of GABA agonists and antagonists injected into the MLR in a semi-intact lamprey preparation. The GABA agonist inhibited locomotion, whereas the GABA antagonist initiated it. These results suggest that the GABAergic projections to the MLR modulate the activity of MLR neurons, which would be inhibited by GABA at rest."
My comments:   
1.  This paper provides strong support to my impression that release of GABAergic inhibition is an important, and perhaps even necessary, part of behavior. 
2.  "...
double-labeling neurons ..." provides clear evidence that, in this case at least, GABA is functioning as a neurotransmitter rather than a neuromodulator. 
3.  "...
agonists and antagonists injected ..." are clearly neuromodulators rather than neurotransmitters.  Please see:  Neuromodulators vs Neurotransmitters  .  
4.  I need a clearer understanding of the  Mesencephalic Locomotor Region (MLR) .  In particular, does it supply input to the  Reticular Activating Sytem (RAS) , or the other way around?   How about the  Spinal Locomotor Generator (SLG)?   Just off hand, I would guess that the causal sequence is MLR > RAS > SLG, but I need to pin this down.  Also, which neurotransmitters and which neuromodulators are used?  Where does GABA fit in?  Does it function as a neurotransmitter or as a neuromodulator or both?   
5.  This reference considered only GABA.  Does glycine also inhibit locomotion at the level of the MLR, or does glycine inhibit locomotion only at the spinal level? 
    149 Related citations
See:   Tonic Inhibition  and   GABA/Glycine Inhibition  .     

GABA distribution in lamprey is phylogenetically conserved.  
The localization of gamma-aminobutyric acid (GABA) has been well described in most classes of vertebrates but not in adult lampreys. The question if the GABA distribution is similar throughout the vertebrate subphylum is therefore still to be addressed. We here investigate two lamprey species, the sea lamprey, Petromyzon marinus, and the river lamprey, Lampetra fluviatilis, and compare the GABA pattern with that of other vertebrates. The present immunohistochemical study provides an anatomical basis for the general distribution and precise localization of GABAergic neurons in the adult lamprey forebrain and brainstem. GABA-immunoreactive cells were organized in a virtually identical manner in the two species. They were found throughout the brain, with the following regions being of particular interest: the granular cell layer of the olfactory bulb, the nucleus of the anterior commissure, the septum, the lateral and medial pallia, the striatum, the nucleus of the postoptic commissure, the thalamus, the hypothalamus, and pretectal areas, the optic tectum, the torus semicircularis, the mesencephalic tegmentum, restricted regions of the rhombencephalic tegmentum, the octavolateral area, and the dorsal column nucleus. The GABA distribution found in cyclostomes is very similar to that of other classes of vertebrates, including mammals. Since the lamprey diverged from the main vertebrate line around 450 million years ago, this implies that already at that time the basic vertebrate plan for the GABA innervation in different parts of the brain had been developed. 
See:   Tonic Inhibition


Distribution of glycine immunoreactivity in the brain of adult sea lamprey (Petromyzon marinus). Comparison with gamma-aminobutyric acid.

Development and organization of the lamprey telencephalon with special reference to the GABAergic system.