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.
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.
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
"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
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:
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
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."
1. This paper provides strong support to my impression that release of
GABAergic inhibition is an important, and perhaps even necessary, part
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
, 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?
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?
2007 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.
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.