Role of GABA<Subscript>B</Subscript> receptor in the regulation of excitatory synaptic transmission in trigeminal motoneurons

The aim of the present study was to determine if excitatory synaptic transmission onto trigeminal motoneurons is subject to a presynaptic modulation by gamma-aminobutyric acid (GABA) via GABA(B) receptor in this system. Whole cell recordings were made from trigeminal motoneurons in longitudinal brain stem slices taken from 8-day-old rats. Monosynaptic excitatory postsynaptic potential (EPSP) activity was evoked by placing bipolar stainless steel electrodes dorsal-caudal to the trigeminal motor nucleus. Bath application of the GABA(B) receptor agonist, baclofen, produced a marked reduction in the mean amplitude and variance of evoked EPSPs and also increased the portion of transmission failures. It also produced a decrease in the frequency, but not in the mean amplitude, of spontaneous miniature EPSPs. Bath application of GABA(B) receptor antagonists 6-hydroxy-saclofen and CGP35348 increased both the amplitude and frequency of miniature EPSP activity. Taken together the above results suggest that the excitatory synaptic inputs onto trigeminal motoneurons are controlled by tonic presynaptic modulation by GABA(B) receptor.     

GABAB receptors in the NTS mediate the inhibitory effect of trigeminal nociceptive inputs on parasympathetic reflex vasodilation in the rat masseter muscle

The present study was designed to examine whether trigeminal nociceptive inputs are involved in the modulation of parasympathetic reflex vasodilation in the jaw muscles. This was accomplished by investigating the effects of noxious stimulation to the orofacial area with capsaicin, and by microinjecting GABA(A) and GABA(B) receptor agonists or antagonists into the nucleus of the solitary tract (NTS), on masseter hemodynamics in urethane-anesthetized rats. Electrical stimulation of the central cut end of the cervical vagus nerve (cVN) in sympathectomized animals bilaterally increased blood flow in the masseter muscle (MBF). Increases in MBF evoked by cVN stimulation were markedly reduced following injection of capsaicin into the anterior tongue in the distribution of the lingual nerve or lower lip, but not when injected into the skin of the dorsum of the foot. Intravenous administration of either phentolamine or propranolol had no effect on the inhibitory effects of capsaicin injection on the increases of MBF evoked by cVN stimulation, which were largely abolished by microinjecting the GABA(B) receptor agonist baclofen into the NTS. Microinjection of the GABA(B) receptor antagonist CGP-35348 into the NTS markedly attenuated the capsaicin-induced inhibition of MBF increase evoked by cVN stimulation, while microinjection of the GABA(A) receptor antagonist bicuculline did not. Our results indicate that trigeminal nociceptive inputs inhibit vagal-parasympathetic reflex vasodilation in the masseter muscle and suggest that the activation of GABA(B) rather than GABA(A) receptors underlies the observed inhibition in the NTS.     

Sensory discrimination between innocuous and noxious cold by TRPM8-expressing DRG neurons of rats

Background

In our present study, we studied the role of demyelination of the trigeminal nerve root in the development of prolonged nociceptive behavior in the trigeminal territory.

Results

Under anesthesia, the Sprague-Dawley rats were mounted onto a stereotaxic frame and 3 ??L of lysophosphatidic acid (LPA, 1 nmol) was injected into the trigeminal nerve root to produce demyelination. This treatment decreased the air-puff thresholds, persisted until postoperative day 130, and then returned to the preoperative levels 160 days after LPA injection. The LPA-treated rats also showed a significant hyper-responsiveness to pin-prick stimulation. We further investigated the antinociceptive and neuroprotective effects of progesterone in rats undergoing demyelination of the trigeminal nerve root. Progesterone (8, 16 mg/kg/day) was administered subcutaneously, beginning on the operative day, for five consecutive days in the LPA-treated rats. Treatment with progesterone produced significant early anti-allodynic effects and delayed prolonged anti-allodynic effects. The expression of protein zero (P0) and peripheral myelin protein 22 (PMP22) were significantly down-regulated in the trigeminal nerve root on postoperative day 5 following LPA injection. This down-regulation of the P0 and PMP22 levels was blocked by progesterone treatment.

Conclusions

These results suggest that progesterone produces antinociceptive effects through neuroprotective action in animals with LPA-induced trigeminal neuropathic pain. Moreover, progesterone has potential utility as a novel therapy for trigeminal neuropathic pain relief at an appropriate managed dose and is therefore a possible future treatment strategy for improving the recovery from injury.     

Ontogenetic changes in the distribution of the vesicular GABA transporter VGAT correlate with the excitation/inhibition shift of GABA action

GABA is the major inhibitory neurotransmitter in the adult CNS and is among others involved in the synchronization of large neuronal networks. During development, GABA acts as a morphogenetic factor and has transient excitatory actions in many brain regions. One distinct protein, the vesicular GABA transporter (VGAT), has been identified accumulating GABA into presynaptic vesicles prior to its exocytotic release. The function of VGAT and its distribution is well defined in the adult, but its contribution to the transient excitatory action at putative GABAergic nerve terminals in the immature brain and its potential roles in putative glutamatergic nerve terminals remain elusive. We have studied VGAT expression in the brain from late embryonic stages through several postnatal stages until adulthood. Quantitative immunoblotting and immunolabeling of tissue sections at the light microscope and the electron microscope levels show an abrupt augmentation in VGAT staining in the cerebral cortex during the first three postnatal weeks, resembling the increase in other proteins involved in GABA synthesis and recycling in the same time frame - such as GAD65, GAD67, GAT1 (Slc6a1) and SN1 (Slc38a3) - and coincides with the synaptogenetic spurt. Dynamic changes in the expression of VGAT are seen in many cellular populations and in several layers in different brain regions. However, mossy fiber terminals (MFT) elude staining for VGAT. We also demonstrate that VGAT(+) nerve terminals undergo a developmental reorganization so that from targeting primarily the dendrites of the principal neurons in several brain regions in the immature brain, they target the soma of the same cells in the adult. This shift in the targeted subcellular compartment coincides with the conversion of the chloride gradient across neuronal membranes and suggests that it may be important for the shift of GABA action from excitation to inhibition and for the establishment of the potent synchronization of neuronal networks.     

Nerve repulsion by the lens and cornea during cornea innervation is dependent on Robo-Slit signaling and diminishes with neuron age

The cornea, the most densely innervated tissue on the surface of the body, becomes innervated in a series of highly coordinated developmental events. During cornea development, chick trigeminal nerve growth cones reach the cornea margin at embryonic day (E)5, where they are initially repelled for days from E5 to E8, instead encircling the corneal periphery in a nerve ring prior to entering on E9. The molecular events coordinating growth cone guidance during cornea development are poorly understood. Here we evaluated a potential role for the Robo-Slit nerve guidance family. We found that Slits 1, 2 and 3 expression in the cornea and lens persisted during all stages of cornea innervation examined. Robo1 expression was developmentally regulated in trigeminal cell bodies, expressed robustly during nerve ring formation (E5-8), then later declining concurrent with projection of growth cones into the cornea. In this study we provide in vivo and in vitro evidence that Robo-Slit signaling guides trigeminal nerves during cornea innervation. Transient, localized inhibition of Robo-Slit signaling, by means of beads loaded with inhibitory Robo-Fc protein implanted into the developing eyefield in vivo, led to disorganized nerve ring formation and premature cornea innervation. Additionally, when trigeminal explants (source of neurons) were oriented adjacent to lens vesicles or corneas (source of repellant molecules) in organotypic tissue culture both lens and cornea tissues strongly repelled E7 trigeminal neurites, except in the presence of inhibitory Robo-Fc protein. In contrast, E10 trigeminal neurites were not as strongly repelled by cornea, and presence of Robo-Slit inhibitory protein had no effect. In full, these findings suggest that nerve repulsion from the lens and cornea during nerve ring formation is mediated by Robo-Slit signaling. Later, a shift in nerve guidance behavior occurs, in part due to molecular changes in trigeminal neurons, including Robo1 downregulation, thus allowing nerves to find the Slit-expressing cornea permissive for growth cones.     

Synaptic potentials of motoneurons of the masseter muscle

Postsynaptic potentials of 93 motoneurons of the masseter muscle evoked by stimulation of different branches of the trigeminal nerve were studied. Stimulation of the most excitable afferent fibers of the motor nerve of the masseter muscle evoked monosynaptic EPSPs with a latent period of 1.2–2.0 msec, changing into action potentials when the strength of stimulation was increased. A further increase in the strength of stimulation produced an antidromic action potential in the motoneurons with a latent period of 0.9 msec. In some motoneurons polysynaptic EPSPs and action potentials developed following stimulation of the motor nerve to the masseter muscle. The ascending phase of synaptic and antidromic action potentials was subdivided into IS and SD components, while the descending phase ended with definite depolarization and hyperpolarization after-potentials. Stimulation of cutaneous branches of the trigeminal nerve, and also of the motor nerve of the antagonist muscle (digastric) evoked IPSPs with a latent period of 2.7–3.5 msec in motoneurons of the masseter muscle. These results indicate the existence of functional connections between motoneurons of the masseter muscle and its proprioceptive afferent fibers, and also with proprioceptive afferent fibers of the antagonist muscle and cutaneous afferent fibers.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 262–268, November–December, 1969.     

Effects of GABA, THIP, and potassium on excitability of myelinated axons of isolated amphibian spinal roots

The effects of direct applications of GABA (gamma-aminobutyric acid) and the GABAA agonist, THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) on the excitability of myelinated axons of individual dorsal and ventral spinal roots (lumbar VI and (or) VII) of the isolated bullfrog peripheral nerve are reported. Increases evoked by the GABA agonists (0.01-10 mM) in the amplitude of half-maximal A-fiber compound action potentials indicate the presence of depolarizing responses with apparently greater localization to the dorsal roots, and a sensitivity to GABA twofold greater than that for THIP. The changes evoked by GABA and THIP, as well as potassium have components that closely resemble those of sensory and motor fibers in the more distal, desheathed nerve bundle but are smaller and delayed, differences attributable to a closely attached root sheath that acts as a diffusion barrier. These results confirm the likely existence of GABAA receptors on both dorsal and ventral spinal roots.     

Epileptiform activity in the somatosensory cortex of rats with trigeminal neuralgia]

It was shown in experiments on rats that penicillin 1 microliter microinjection (100 U) into the caudal nucleus of the spinal tract of the trigeminal nerve, accounting for formation of a generator of pathologically enhanced excitation (GREE), brings about in rats the pain syndrome with characteristic for trigeminal neuralgia behavioural manifestations and the emergence of epileptiform activity in the somatosensory cortex, especially pronounced in the contralateral hemisphere. The emergence of this activity reflects, on the one hand, the action of the GREE in the caudal nucleus of the trigeminal nerve and, on the other hand, the involvement of the somatosensory cortex taking over stimulation from the hyperactive caudal nucleus, into formation of a pathological algic system of this form of trigeminal neuralgia.     

Pharmacologic and therapeutic aspects of the developmentally regulated expression of GABA(A) and GABA(B) receptors: cerebellar granule cells as a model system.

Cerebellar granule neurons can be conveniently kept in culture. They constitute a useful model to study regulation of glutamatergic activity, in particular the inhibitory action of GABA (7-aminobutyrate). GABA exerts an inhibitory action on evoked transmitter release acting on both GABA(A) and GABA(B) receptors. The functional properties of these receptors are dependent upon the environment of the neurons during early development in culture as the expression of both receptor subtypes is enhanced by exposure of the neurons to GABA(A) receptor agonists. Thus, the inducible GABA(A) receptors are of low affinity and lack benzodiazepine sensitivity, and the G-protein coupling differs among the native and the inducible GABA(B) receptors. Moreover, the GABA(A) and the GABA(B) receptors are functionally coupled, leading to a disinhibitory action of GABA. Therefore drugs exhibiting selective agonist or antagonist action on subclasses of GABA(A) and GABA(B) may be of potential use as regulators of glutamatergic excitatory activity.     

Corticotropin releasing factor-like immunoreactivity in sensory ganglia and capsaicin sensitive neurons of the rat central nervous system: colocalization with other neuropeptides

Immunohistochemistry and radioimmunoassay (RIA) revealed that corticotropin releasing factor (CRF)-like immunoreactivity was found to be colocalized with substance P (SP)-, somatostatin (SST)- and leu-enkephalin (LENK)-like immunoreactivity in the dorsal root- and trigeminal ganglia, the dorsal horn of the spinal cord (laminae I and II), the substantia gelatinosa, and at the lateral border of the spinal nucleus and in the tractus spinalis of the trigeminal nerve. These peptides were also located in fast blue labeled cells of the trigeminal ganglion following injection of the dye into the spinal trigeminal area. This indicates that there are possible sensory projections of these peptides into the spinal trigeminal area. Capsaicin treatment of neonatal rats resulted in a marked decrease in the density of CRF-, SP-, VIP- and CCK-containing neurons in the above mentioned hindbrain areas, whereas SST- and LENK-immunoreactivity were not changed. RIA revealed that, compared to controls, CRF, SP and VIP concentrations in these areas were decreased in rats pretreated with capsaicin, while SST levels were increased; CCK and LENK levels were unchanged. It is concluded that the primary afferent neurons of the nucleus and tractus spinalis of the trigeminal nerve are richly endowed with a number of peptides some of which are sensitive to capsaicin action. The close anatomical proximity of these peptide containing neurons suggests the possibility of a coexistance of one or more of these substances.     

The GABA postsynaptic membrane receptor-ionophore complex

Summary The function of the inhibitory neurotransmitter, -aminobutyric acid (GABA), has been implicated in the mode of action of many drugs which excite or depress the central nervous system. Many convulsant agents appear to block GABA action whereas anticonvulsants enhance GABA action. Some of these drug effects involve altered GABA-mediated synaptic transmission at the level of GABA biosynthesis, release from nerve endings, uptake into cells, and metabolic degradation. A greater number of agents of diverse classes appear to affect GABA action at the postsynaptic membrane, as determined from both electrophysiological and biochemical studies. The recently developedin vitro radioactive receptor binding assays have led to a wealth of new information about GABA action and its alteration by drugs. GABA inhibitory transmission involves the regulation, by GABA binding to its receptor site, of chloride ion channels. In this GABA receptor-ionophore system, other drug receptor sites, one for benzodiazepines and one for barbiturates/picrotoxinin (and related agents) appear to form a multicomponent complex. In this complex, the drugs binding to any of the three receptor categories are visualized to have an effect on GABA-associated chloride channel regulation. Available evidence suggests that the complex mediates many of the actions of numerous excitatory and depressant drugs showing a variety of pharmacological effects.     

Disruption of KCC2 reveals an essential role of K-Cl cotransport already in early synaptic inhibition

Synaptic inhibition by GABA(A) and glycine receptors, which are ligand-gated anion channels, depends on the electrochemical potential for chloride. Several potassium-chloride cotransporters can lower the intracellular chloride concentration [Cl(-)](i), including the neuronal isoform KCC2. We show that KCC2 knockout mice died immediately after birth due to severe motor deficits that also abolished respiration. Sciatic nerve recordings revealed abnormal spontaneous electrical activity and altered spinal cord responses to peripheral electrical stimuli. In the spinal cord of wild-type animals, the KCC2 protein was found at inhibitory synapses. Patch-clamp measurements of embryonic day 18.5 spinal cord motoneurons demonstrated an excitatory GABA and glycine action in the absence, but not in the presence, of KCC2, revealing a crucial role of KCC2 for synaptic inhibition.     

Evaluation of the mechanisms by which gamma-amino-butyric acid in association with phosphatidylserine exerts an antiepileptic effect in the rat

The i.p. injection in rats of GABA (740 mg/Kg) after sonication with an equal amount of phosphatidylserine (PS) has an antiepileptic effect. The injection of plain GABA has no such an effect. Blood, brain and synaptosomal accumulation of exogenous labeled GABA under the two circumstances are evaluated. In the case of GABA/PS injection there is a higher passage of the exogenous labeled neurotransmitter into the blood and brain nerve endings (synaptosomes). A higher synaptosomal accumulation of the exogenous labeled neurotransmitter is found even when GABA and PS are injected separately. Since these accumulation increases occur at a time when there is the antiepileptic effect, they seem relevant to it. Our interpretation of the chain of the events resulting in the antiepileptic action is that the phospholipid facilitates from the beginning the first passage of the exogenous neurotransmitter form the peritoneum to the blood. Then a higher passage to the brain tissue and eventually to the GABA-ergic nerve endings ensues. The brisker accumulation of the exogenous neurotransmitter in the nerve endings could be at the basis of a more efficient GABA-ergic inhibitory control in the brain.     

Changes in the Amino Acid Content of Nerve Endings (Synaptosomes) Induced by Drugs that Alter the Metabolism of Glutamate and γ-Aminobutyric Acid

The study was centered on the changes in the amino acid content of nerve endings (synaptosomes) induced by drugs that alter the metabolism of glutamate or gamma-aminobutyric acid (GABA), and that possess convulsant or anticonvulsant properties. The onset of seizures induced by various convulsant agents was associated with a decreased content of GABA and an increased content of glutamate in synaptosomes. The concurrent administration of pyridoxine prevented both the biochemical changes and the convulsions. The administration of gabaculine to mice resulted in large increases in the GABA content of synaptosomes that were counteracted by decreases in glutamate, glutamine, and aspartate levels such that the total content of the four amino acids remained unchanged. The administration of aminooxyacetic acid (0.91 mmol/kg) resulted initially in seizure activity, but subsequently in an anticonvulsant action. No simple relationship existed between the excitable state of the brain induced by aminooxyacetic acid and the changes in the synaptosomal levels of any of the amino acid transmitters. A hypothesis was, however, formulated that explained the convulsant-cum-anticonvulsant action of aminooxyacetic acid on the basis of compartmentation of GABA within the nerve endings.     

Synaptic potentials of digastric-muscle motoneurons

We studied the antidromic and synaptic potentials evoked from 32 digastric-muscle motoneurons by stimulation of the motor nerve to this muscle, different branches of the trigeminal nerve, and the mesencephalic trigeminal nucleus. Antidromic potentials appeared after 1.1 msec and lasted about 2.0 msec. Stimulation of the infraorbital, lingual, and inferior alveolar nerves led to development of excitatory postsynaptic potentials (EPSP) and action potentials in the motoneurons. The antidromically and synaptically evoked action potentials of the digastric-nerve motoneurons were characterized by weak after-effects. We were able to record EPSP and action potentials in two of the motoneurons investigated in response to stimulation of the mesencephalic trigeminal nucleus, the latent period being 1.3 msec. This indicates the existence of a polysynaptic connection between the mesencephalic-nucleus neurons and the digastric-muscle motoneurons. Eight digastric-muscle motoneurons exhibited inhibitory postsynaptic potentials (IPSP), which were evoked by activation of the afferent fibers of the antagonistic muscle (m. masseter). The data obtained indicate the presence of reciprocal relationships between the motoneurons of the antagonistic muscles that participate in the act of mastication.A. A. Bogomol'ts Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 52–57, January–February, 1971.     

GABA-mediated synaptic inhibition of projection neurons in the antennal lobes of the sphinx moth,Manduca sexta

Responses of neurons in the antennal lobe (AL) of the moth Manduca sexta to stimulation of the ipsilateral antenna by odors consist of excitatory and inhibitory synaptic potentials. Stimulation of primary afferent fibers by electrical shock of the antennal nerve causes a characteristic IPSP-EPSP synaptic response in AL projection neurons. The IPSP in projection neurons reverses below the resting potential, is sensitive to changes in external and internal chloride concentration, and thus is apparently mediated by an increase in chloride conductance. The IPSP is reversibly blocked by 100 microM picrotoxin or bicuculline. Many AL neurons respond to application of GABA with a strong hyperpolarization and an inhibition of spontaneous spiking activity. GABA responses are associated with an increase in neuronal input conductance and a reversal potential below the resting potential. Application of GABA blocks inhibitory synaptic inputs and reduces or blocks excitatory inputs. EPSPs can be protected from depression by application of GABA. Muscimol, a GABA analog that mimics GABA responses at GABAA receptors but not at GABAB receptors in the vertebrate CNS, inhibits many AL neurons in the moth.     

Neuronal and Glial Release of [3H]GABA from the Rat Olfactory Bulb

Abstract: GABA uptake and release mechanisms have been shown for neuronal as well as glial cells. To explore further neuronal versus glial components of the [³H]-γ-aminobutyric acid ([³H]GABA) release studies were performed with two different microdissected layers of the olfactory bulb of the rat: the olfactory nerve layer (ONL), consisting mainly of glial cells, and the external plexiform layer (EPL) with a high density of GABAergic dendritic terminals. In some experiments substantia nigra was used as a GABAergic axonal system and the trigeminal ganglia as a peripheral glial model. Spontaneous release of [³H]GABA was always lower in neuronal elements as compared with glial cells. A veratridine-evoked release was observed from the ONL but not from the trigeminal ganglia. Tetrodotoxin (TTX) abolished the veratridine-evoked release from the ONL, which also showed a partial inhibition when high magnesium concentrations were used in a Ca²⁺-free solution. β-Alanine was strongly exchanged with [³H]GABA from the ONL of animals with the olfactory nerve lesioned and from animals with no lesion; but only a small heteroexchange was found from the external plexiform layer. The β-alanine heteroexchange was able to deplete the releasable GABA store from the ONL of lesioned animals. In nonlesioned animals and the external plexiform layer, the veratridine-stimulated release of [³H]GABA was not significantly reduced after the β-alanine heteroexchange. Stimulation of the [³H]GABA release by high concentrations of potassium elicited a higher release rate from axonal terminals than from dendrites or glia. Neurones and glia showed a similar inhibition of [³H]GABA release when a high magnesium concentration was added to a calcium-free solution. When D-600 was used as a calcium-flux blocker no inhibition of the release was observed in glial cells, whereas an almost complete blockage was found in both neuronal preparations (substantia nigra and EPL). These results provide further evidence for differential release mechanisms of GABA from CNS neurones and glial cells.     

Effect of gamma-aminobutyric acid and phenibut on the central links of the vascular reflexes with chemo- and mechanoreceptors of the aorto-carotid zone]

Experiments were conducted on decerebrated cats. A depressive effect of gamma-aminobutyruc acid (GABA)--100--200 mg/kg and its phenyl derivative phenibut--20 mg/kg--on depressive reactions of the systemic arterial pressure and on the inhibition of spontaneous bioelectrical activity in the renal nerve occurring in stimulation of the mechanoreceptors of the carotid sinus and of the sinus and depressor nerve afferents (having a mechanoreceptor modality) was demonstrated. Pressor reactions of the systemic arterial pressure and evoked bioelectrical activity were enhanced in the renal nerve in stimulation of chemoreceptors of the carotid sinus following administration of the same GABA and phenibut doses. The data obtained are interpreted from the aspect of a deprimating action of GABA and phenibut in the area of the paramedian reticular nuclei of the medulla oblongata.     

昆虫γ-氨基丁酸受体研究现状

γ-氨基丁酸(gamma-aminobutyric acid,GABA)是脊椎动物和无脊椎动物体内重要的抑制性神经递质,其作用是引起神经传递的抑制,造成突触后膜的超极化,因而抑制动作电位的产生。占领GABA受体或破坏GABA受体的作用即能影响动物(昆虫)正常的突触传递,造成神经功能失常,从而引起死亡。基于此开发的杀虫剂主要有环戊二烯类,阿维菌素类等。近年GABA受体基因及其表达的研究,已为不同的种属GABA受体的亚基组成、生理功能及其对很多杀虫剂药物反应的多样性提供了令人信服的依据。     

Coexistence of GABA- and choline acetyltransferase (ChAT)-like immunoreactivity in the hypoglossal nucleus of the rat

Single and sequential double immunocytochemical techniques were applied to localize gamma-aminobutyric acid (GABA)- and choline acetyltransferase (ChAT)- like immunoreactivity (-LI) in the hypoglossal nucleus of the rat. After subsequential double staining a relatively high number of hypoglossal motor neurons showed the coexistence of both ChAT- and GABA-LI. Coexistence of both substances was also revealed in the axons of the hypoglossal nerve situated within the medulla oblongata. Cells showing only ChAT- or GABA-LI were also observed. Differences in immunostaining between the different cell groups of the hypoglossal nucleus were established. Following axotomy of the right hypoglossal nerve, a decrease or loss of the immunoreactivity for both ChAT and GABA in the motor neurons was established until the 3rd week after the operation. The results obtained do not give evidence on the origin of the GABA-like immunoreactive material and its functional significance in the cholinergic neurons. It can be only speculated that the GABA-like material is either taken up from the intercellular space or is synthesized by the ChAT-LI nerve cells. Functionally, the importance of GABA for the synthesis of gamma-hydroxybutyrate (a novel neurotransmitter candidate) and its postsynaptic transmitter action or presynaptic regulatory action (through autoreceptors in the membrane of the nerve endings) on the release of acetylcholine (ACh) should be taken into consideration.