The Ganglionic Origins and Central Projections of Primary Sensory Neurons Innervating the Upper and Lower Lips in the Rat

Retrograde and transganglionic transport of horseradish peroxidase (HRP) was used to investigate the neurons innervating the upper and the lower lips and their central projections in the rat. Both the upper and the lower lips were observed to be innervated by a very large number of trigeminal sensory neurons, with their cell bodies located in the maxillary and the mandibular parts of the trigeminal ganglion, respectively. The central projections of neurons innervating the upper lip formed a long continuous column starting rostrally at midlevels of the trigeminal main sensory nucleus (5P) and extending caudally through the CI dorsal horn, with occasional fibers reaching the C3 segment. The heaviest projections appeared in the middle portions of 5P and nucleus interpolaris (51), as well as in the rostral part of nucleus caudalis (5C). A small but consistent projection to the solitary tract nucleus, originating from cells in the inferior vagal ganglion, was observed in the upper-lip experiments. The central projections from neurons innervating the lower lip also appeared as a long column located dorsally or dorsomedially to the projections from the upper lip. The most prominent projections from the lower lip were located in the caudal part of 5P, the middle part of 5I, and the caudal two-thirds of 5C. Sparse projections could be traced as far caudally as C4. At 5C and cervical levels, some labeling appeared contralaterally in the same location as on the ipsilateral side.     

Differences in the distribution and chemical coding between neurons in the inferior mesenteric ganglion supplying the colon and rectum in the pig

The distribution and chemical coding of neurons in the porcine left and right inferior mesenteric ganglion projecting to the ascending colon and rectum have been investigated by using combined retrograde tracing and double-labelling immunohistochemistry. The ganglion contained many neurons supplying both gut regions. The colon-projecting neurons (CPN) occurred exclusively in the cranial part of the ganglia where they formed a large cluster distributed along the dorso-lateral ganglionic border and a smaller cluster located close to the caudal colonic nerve output. The rectum-projecting neurons (RPN) formed a long stripe along the entire length of the lateral ganglionic border and, within the right ganglion only, a small cluster located close to the caudal colonic nerve output. Immunohistochemistry revealed that the vast majority of the CPN and RPN were noradrenergic (tyrosine-hydroxylase-positive). Many noradrenergic neurons supplying the colon contained somatostatin or, less frequently, neuropeptide Y. In contrast, a significant subpopulation of the noradrenergic RPN expressed neuropeptide Y, whereas only a small proportion contained somatostatin. A small number of the non-adrenergic RPN were cholinergic (choline-acetyltransferase-positive) and a much larger subpopulation of the nerve cells supplying both the colon and rectum were non-adrenergic and non-cholinergic. Many cholinergic neurons contained neuropeptide Y. The non-adrenergic non-cholinergic neurons expressed mostly somatostatin or neuropeptide Y and some of those projecting to the rectum contained nitric oxide synthase, galanin or vasoactive intestinal polypeptide. Many of both the CPN and RPN were supplied with varicose nerve fibres exhibiting immunoreactivity against Leu5-enkephalin, somatostatin, choline-acetyltransferase, vasoactive intestinal polypeptide or nitric oxide synthase The somatotopic and neurochemical organization of this relatively large population of differently coded inferior mesenteric ganglion neurons projecting to the large bowel indicates that these cells are probably involved in intestino-intestinal reflexes controlling peristaltic and secretory activities.     

The motor nuclei of the glossopharyngeal-vagal and the accessorius nerves in the rat

Retrograde cobalt labeling was performed by incubating the rootlets of cranial nerves IX, X and XI, or the central stumps of the same nerves, in a cobaltic lysine complex solution, and the distribution of efferent neurons sending their axons into these nerves was investigated in serial sections of the medulla and the cervical spinal cord in young rats. The following neuron groups were identified. The inferior salivatory nucleus lies in the dorsal part of the tegmentum at the rostral part of facial nucleus. It consists of a group of medium-sized and a group of small neurons. Their axons make a hair-pin loop at the midline and join the glossopharyngeal nerve. The dorsal motor nucleus of the vagus situates in the dorsomedial part of the tegmentum. Its rostral tip coincides with the first appearance of sensory fibres of the glossopharyngeal nerve, the caudal end extends into the pyramidal decussation. The constituting cells have globular or fusiform perikarya and they are the smallest known efferent neurons. The ambiguous nucleus is in the ventrolateral part of the tegmentum. The rostral tip lies dorsal to the facial nucleus, and the caudal tip extends to the level of the pyramidal decussation. The rostral one third of the ambiguous nucleus is composed of tightly-packed medium sized neurons, while larger neurons are arranged more diffusely in the caudal two thirds. The long dendrites are predominantly oriented in the dorsoventral direction. The dorsally-oriented axons take a ventral bend anywhere between the ambiguous nucleus and dorsal motor nucleus of the vagus. The motoneurons of the accessorius nerve are arranged in a medial, a lateral and a weak ventral cell column. The medial column begins at the caudal aspect of the pyramidal decussation and terminates in C2 spinal cord segment. The lateral and ventral columns begin in C2 segment and extend into C6 segment. The neurons have large polygonal perikarya and characteristic cross-shaped dendritic arborizations. The axons follow a dorsally-arched pathway between the ventral and dorsal horns. The accessorius motoneurons have no positional relation to any of the vagal efferent neurons. It is concluded that the topography and neuronal morphology of accessorius motoneurons do not warrant the designation of a bulbar accessorius nucleus and a bulbar accessorius nerve.     

Horseradish peroxidase localization of sympathetic postganglionic and parasympathetic preganglionic neurons innervating the monkey heart

The localization of the sympathetic postganglionic and parasympathetic preganglionic neurons innervating the monkey heart were investigated through retrograde axonal transport with horseradish peroxidase (HRP). HRP (4 mg or 30 mg) was injected into the subepicardial and myocardial layers in four different cardiac regions. The animals were euthanized 84-96 hours later and fixed by paraformaldehyde perfusion via the left ventricle. The brain stem and the paravertebral sympathetic ganglia from the superior cervical, middle cervical, and stellate ganglia down to the T9 ganglia were removed and processed for HRP identification. Following injection of HRP into the apex of the heart, the sinoatrial nodal region, or the right ventricle, HRP-labeled sympathetic neurons were found exclusively in the right superior cervical ganglion (64.8%) or in the left superior cervical ganglion (35%). Fewer labeled cells were found in the right stellate ganglia. After HRP injection into the left ventricle, labeled sympathetic cells were found chiefly in the left superior cervical ganglion (51%) or in the right superior cervical ganglion (38.6%); a few labeled cells were seen in the stellate ganglion bilaterally and in the left middle cervical ganglion. Also, in response to administration of HRP into the anterior part of the apex, anterior middle part of the right ventricle, posterior upper part of the left ventricle, or sinoatrial nodal region, HRP-labeled parasympathetic neurons were found in the nucleus ambiguus on both the right (74.8%) and left (25.2%) sides. No HRP-labeled cells were found in the dorsal motor nucleus of the vagus on either side.     

Neural control of heartbeat in the pteropod mollusk Clione limacina

The heart of the pteropod molluskClione limacina is innervated by the median nerve arising from the left abdominal ganglion. Five neurons sending axons to the heart have been identified in theClione central nervous system with retrograde cobalt or Lucifer yellow staining. Neuron H1 located in the left pedal ganglion produced an excitatory effect on heart beat. Stimulation of three neurons, H2–H4, situated in a compact group in the medial region of the left abdominal ganglion, led to inhibition of cardiac contraction, while H5, located in the caudal region of the left abdominal ganglion, did not affect heart beat. The activity of efferent cardiac neurons (ECN) was found to be related to the operation of the locomotor rhythm generator. Spontaneous or reflex depression of the latter was found to inhibit neuron H1 and activate units H2–H4. The behavior of these ECN accounts for the positive correlation between heart operation and locomotor activity inClione limacina.Institute of Research on Information Transmission, Academy of Sciences of the USSR, Moscow, M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 185–192, March–April, 1989.     

Location of efferent sympathetic neurons and afferent neurons in spinal ganglia innervating the heart

Location and numbers of neurons associated with sympathetic innervation of the heart within the right stellate and accessory cervical ganglia, the spinal cord, and spinal ganglia were investigated using horseradish peroxidase retrograde axonal transport techniques in cats. The enzyme was applied to central sections of the anastomosis of the stellate ganglion with the vagus nerve, the inferior cardiac nerve, and the vagosympathetic trunk caudal to the anastomosis. Labeled neurons within the stellate ganglion were located close to the point of departure of the nerves and more thinly distributed in the accessory cervical ganglion. A group of labeled cells was found in the anastomosis itself. Preganglionic neurons associated with sympathetic innervation of the heat were detected at segmental levels T₁–T₅ in the spinal cord. Labeled neurons were diffusely located in the spinal ganglia, concentrated mainly at levels T₂–T₄.Medical Institute, Ministry of Public Health of the RSFSR, Yaroslavl'. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 106–111, January–February, 1989.     

Localization and Central Projections of Primary Afferent Neurons That Innervate the Temporomandibular Joint in Cats

Primary afferent neurons that innervate the temporomandibular joint (TMJ) in cats were labeled by injecting a 2-5% solution of wheatgerm agglutinin bound to horseradish peroxidase into the joint capsule and capsular tissues in 14 cats and processing the brain stem and trigeminal ganglia using the tetramethylbenzidine method described by Mesulam (1978). The perikarya of ganglion cells that innervate the TMJ ranged in diameter from 15 to 109 μm and were primarily located in the posterolateral portion of the trigeminal ganglion. The central processes of these neurons entered the brain stem in middle pons and were distributed to all portions of the sensory trigeminal nuclei. However, the majority of labeled fibers and greatest density of terminal labeling were observed in the dorsal part of the main sensory nucleus and the subnucleus oralis of the spinal trigeminal nucleus. Very few labeled fibers were observed in the spinal tract of the trigeminal nerve below the obex. However, evidence for axon terminals was consistently observed in laminae I, II, and III of the medullary dorsal horn. These findings concur with physiological evidence showing that information from the TMJ influences neurons in rostral (Kawamura et al, 1967) and in caudal (Broton et al, 1985) portions of the trigeminal sensory nuclei.     

Characterization of cardiac innervation in the nudibranch, Archidoris montereyensis

The heart of the nudibranch mollusc Archidoris montereyensis is regulated by a small number of powerful effector neurons located in the right pleural and visceral ganglia. Two identifiable neurons in the pleural ganglion, a heart excitor (PlHE) and a heart inhibitor (PlHI), are especially important regulators of cardiac function in that low levels of spontaneous activity in either cell significantly alters the amplitude and rate of heart contractions. These neurons have extensive dendritic arbors within the right pleural ganglion and branching axonal processes within the visceral ganglion. The visceral ganglion also contains a heart excitor neuron (VHE) and at least two heart inhibitor neurons (VHI cells), but their influence on cardiac activity is weaker than that of the pleural ganglion cells. All of these heart effector cells appear to be motor neurons with axons that terminate predominantly in the atrio-ventricular valve region of the heart via the pericardial nerve. The simplicity and strength of these neuronal connections to the heart of Archidoris make this a favorable preparation for studies of cardiac regulation.     

Structures with GABA-like and GAD-like immunoreactivity in the cervical sympathetic ganglion complex of adult rats

Summary The distribution of gamma-aminobutyric acid (GABA)-like and glutamate decarboxylase (GAD)-like immunoreactivity was studied in the cervical sympathetic ganglion complex of rats, including the intermediate and inferior cervical ganglia and the uppermost thoracic ganglion. GABA-positive axons may enter the ganglion complex via its caudal end. Others apparently arise from small GABA-positive cell bodies which are scattered among principal neurons, within clusters of SIF cells and in bundles of GABA-negative axons. The majority of these cells is located in the lower half of the ganglion complex. Principal neurons did not react with antibodies against GABA or GAD. An unevenly distributed meshwork of GABA-immunoreactive axons was seen in each of the ganglia. Immunoreactive axons formed numerous varicosities. Some of them were aggregated in a basket-like form around a subpopulation of GABA-negative principal ganglion cell bodies. Electron-microscopic immunocytochemistry revealed that GABA-positive nerve fibers establish asymmetric synaptic junctions with dendritic and somatic spines of principal neurons, whereas postsynaptic densities are inconspicous or absent on dendritic shafts and somata. The results suggest that in the cervical sympathetic ganglion complex principal neurons are not GABAergic, but are innervated by axons which react with both antibodies against GAD and/ or GABA antibodies and originate from a subpopulation of small neurons.     

Localization of heart-innervating sympathetic neurons

Localization, amount, form of the bodies and maximal diameter of horseradish peroxidase (HP)-labelled neurons in the right stellate ganglion (SG) in the cat spinal cord have been investigated. HP application has been performed on the central parts of the SG connective branch with vagus nerve, or with the caudal cardiac nerve. In the neurons HP has been revealed after Straus or Mesulam method. In the SG, regardless the HP application place, the labelled neurons arrange in the zone, adjoining the place, where the caudal cardiac nerve and the connective branch get to the vagus nerve. In the spinal cord, when HP is applied on the connective branch, the labelled neurons are revealed in the lateral horns of the TI-TVI segments. The amount of the labelled neurons decreases in the rostro-caudal direction. Their greatest amount is revealed in the TI-TIII segments. When HP is applied on the central part of the caudal cardiac nerve, a small amount of the labelled neurons has been found in TI-TIII segments of the spinal cord only in one experiment. Thus, in the connective branch of the SG with the vagus nerve much more amount of the preganglionar fibers run than in the caudal cardiac nerve.     

Organization of the sensory and motor nuclei of the glossopharyngeal and vagal nerves in lampreys

Anterograde and retrograde transport of horseradish peroxidase was used to examine the afferent and efferent projections of the glossopharyngeal and vagal nerves in the lamprey, Lampetra japonica. Except for the ganglion cells and motoneurons, the distribution patterns of HRP-positive elements differed little between the two nerves. Afferent fibers mainly terminated in the ipsilateral cerebellar area, medial octavolateralis nucleus, and between the ventral octavolateralis nucleus and descending tract and nucleus of the trigeminal nerve (dV). In the cerebellar area, most of the labeled fibers were located in the molecular zone, but some penetrated into the granular zone. In the rostral part of the medial octavolateralis nucleus, labeled fibers coursed from the middle to the lateral area, and in the caudal part, they were localized in the dorsal area of the nucleus. In the area between the dV and ventral octavolateralis nucleus, labeled fibers coursed near the dorsal margin of the rostral part of the dV, and in the caudal part, they shifted dorsally. Ganglion cells and motoneurons of each nerve were also labeled.     

Mechanisms of the inhibitory effect of the stellate ganglion on cardiac activity

The mechanisms of cardiac activity inhibition caused by stimulation of the stellate ganglion were studied in acute experiments on 28 dogs and 37 cats and chronic experiments on 12 cats. It was shown that inhibition of cardiac activity is caused by stimulation of the parasympathetic fibers of the vagus, anastomozing with stellate ganglion branches and ingoing as part of these fibers to the heart. The hypothesis of change over of the sympathetic nerve fibers to the intracardial cholinergic neurons and the hypothesis of the cholinergic component in the mechanism of catecholamine release by the sympathetic nerve terminals was not confirmed. Therefore, the known Dale's principle as to that one neuron exerts its efferent effect with the aid of one transmitter is quite just. alpha-Adrenoreceptors does not produce any noticeable effect on cardiac activity.     

Comparative anatomical study of the autonomic cardiac nervous system in macaque monkeys

The main aim of this study was to clarify the general morphology of the autonomic cardiac nervous system in macaque monkeys. A submacroscopic comparative anatomical study of the autonomic cardiac nervous system was performed by examining 22 sides of 11 bodies of four species of macaque monkeys, including some previously unreported species (pig-tailed and stump-tailed monkeys), under a surgical stereomicroscope. The following results were obtained. 1) The basic arrangement of the autonomic cardiac nervous system is constant in all examined macaques. 2) A superior cardiac nerve originating from the superior cervical ganglion was not observed, whereas the thoracic cardiac nerve originating from the sympathetic trunk/ganglia under the cervicothoracic ganglion was rarely observed in all the examined macaques. 3) The main cardiac nerve is the middle cardiac nerve originating from the middle cervical ganglion, similar to the situation in humans. 4) Although the superior, inferior, and thoracic cardiac branches of the vagus nerve were consistently observed, the left thoracic cardiac branch is rarely absent because of its lower origin to the heart. 5) The cranial autonomic nerves tend to distribute into the heart medially (arterial porta), and the caudal autonomic nerves tend to distribute into the heart laterally (venous porta). To comprehend the comparative morphological and evolutionary changes more completely, these results were compared with our previous studies and some references. Consequently, differences in the sympathetic cardiac nerves of macaques and humans are recognized, in spite of the similar morphologies of the vagal cardiac branches. These differences include the composition of the cervicothoracic ganglion, the lower positions of the middle cervical and cervicothoracic ganglia, and the narrow range for the origin of the cardiac nerves in macaques compared to that in humans.     

On the anatomical organization of the vagal nuclei

The neurons of origin of the right vagus and its components in both the monkey (Macaca fascicularis) and albino rats were localized by the retrograde transport of horseradish peroxidase (HRP) applied to the stomach wall, the vagal trunk and its recurrent laryngeal branch. An attempt was also made to localize the neurons forming the superior laryngeal nerve and those supplying the thoracic organs by a combination of operative procedures. The results showed that the stomach was innervated by neurons distributed throughout the entire rostrocaudal extent of the dorsal motor nucleus (DMN) on both sides of the brain stem. Neurons scattered throughout the entire extent of the DMN and nucleus ambiguus (NA) supplied the thoracic viscera. There did not appear to be any topographic arrangement in the DMN neurons supplying the abdominal and thoracic viscera as reported by other workers, and there was no clear evidence of crossing of vagal fibers in the monkey brain stem, though such crossing was seen in the rat brain stem. Both the superior and inferior ganglia of the vagus nerve were labeled following application of HRP to the vagal trunk. Neurons in the caudal part of the NA gave rise to fibers in the ipsilateral recurrent laryngeal nerve, at least on the right side. The neurons giving rise to the superior laryngeal nerve could not be delineated in this study. In all the experimental procedures described, the hypoglossal nucleus was labeled only after applying HRP to the hypoglossal nerve.     

Origin and the functional role of adrenergic fibers of the vagus nerve in cats

Origin of adrenergic fibres of vagus is studied. They are shown to appear in the thoracic vagus through caudal anastomosis introduction. The observations indicated that axons of spinal neurons and neurons of the ganglion stellate passed through caudal anastomosis and entered a thoracic vagus nerve. Stimulation of the thoracic vagus in cats after atropine sulphate injection increases the heart rate.     

Ganglionic circulation and its effects on neurons controlling cardiovascular functions in Aplysia californica

The abdominal ganglion of the mollusk Aplysia californica receives most of its blood supply through a small caudal artery that branches off the anterior aorta near its junction with the heart. Injection of an ink/gelatin mixture into the caudal artery revealed a consistent pattern of arterial branching within the ganglion and a general proximity of larger vessels to identified neurons controlling circulation in this animal. This morphological arrangement was particularly evident for the heart excitor interneuron, cell L10, which lies next to the caudal artery near its entry into the ganglion. In electrophysiological experiments, L10 was excited when blood flow or oxygen tension within the ganglion was reduced. This effect was expressed as a gradual increase in impulse frequency of L10 and conversion from tonic to bursting mode of spike discharge. L10 follower cells in the RB and LD neuron clusters were affected synaptically by the changes in L10 activity, while other follower cells (L3 and RD neurons) responded independently of L10's synaptic influence. The neurosecretory white cells (R3 to R14) that innervate the major arteries and pericardial tissues were also excited when ganglionic circulation was interrupted. In innervated preparations of the heart and respiratory organs, decreased circulation through the abdominal ganglion stimulated a transient increase in the rate and amplitude of respiratory (gill) pumping and pericardial contractions and caused a sustained increase in activity of the heart. Both responses increase cardiac output and both appear to involve a direct influence of ganglionic circulation on interneurons controlling the gill and heart. These results indicate that the cell-specific patterns of excitation and inhibition caused by fluctuations in ganglionic circulation may be important factors for maintaining circulatory homeostasis in this animal.     

Origin of autonomic nerve fibers innervating the parathyroid gland in the rabbit

The cells of origin of nerve fibers innervating the parathyroid gland were studied in the rabbit using the HRP-retrograde transport method. Numerous labeled neurons were observed in the caudal half of the ipsilateral superior cervical ganglion following HRP injection into the parathyroid gland. Furthermore, in the medulla oblongata, labeled neurons were found in the dorsal nucleus of the vagus and many of them were distributed caudal to the level of the obex.     

Distribution of NADPH-diaphorase and nitric oxide synthase in the trigeminal ganglion and mesencephalic trigeminal nucleus of the cat. A histochemical and immunohistochemical study

The trigeminal ganglion (TrG) and mesencephalic trigeminal nucleus (MTN) neurons are involved in the transmission of orofacial sensory information. The presence of nitric oxide (NO), a putative neurotransmitter substance in the nervous system, was examined in the cat TrG and MTN using nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and nitric oxide synthase (NOS) immunohistochemistry. In the TrG, where the majority of the trigeminal primary afferent perikarya are located, most of the intensely NADPH-d/ NOS-stained cells were small in size and distributed randomly throughout the ganglion. The medium-sized neurons were moderately stained. A plexus of pericellular varicose arborizations around large unstained ganglion cells and densely stained fibers in-between could also be observed. In the caudal part of the MTN, both NADPH-d activity and NOS immunoreactivity was present in MTN neurons. In addition, a few scattered NADPH-d/NOS-containing neurons were found in the mesencephalic-pontine junction part of the nucleus. In contrast, only nerve fibers and their terminals were present at a more rostral level in the mid- and rostral MTN. MTN neuronal perikarya were enveloped in fine basket-like NADPH-d/ NOS-positive networks. Differential expression patterns of NOS and its marker NADPH-d suggest that trigeminal sensory information processing in the cat MTN is controlled by nitrergic input through different mechanisms. We introduce the concept that NO can act as a neurotransmitter in mediating nociceptive and proprioceptive information from periodontal mechanoreceptors but may also participate in modulating the activity of jaw-closing muscle afferent MTN neurons.     

Activity of in situ stellate ganglion neurons of dogs recorded extracellularly

Activity was recorded from 145 neurons in the in situ stellate ganglia of 36 dogs. The activity of 28 of these neurons, most of them located in the ganglia's cranial medial region, was related to the cardiac cycle primarily during systole. The activity of 16 of these cardiovascular-related neurons was modified by gentle mechanical distortion of the superior vena cava (1), heart (4), or thoracic aorta (11). Forty-one of the neurons were modified by respiration, with 17 being phase-locked to the respiratory cycle. Other neurons were activated by gentle mechanical distortion of localized regions of the thoracic wall (21% of all neurons), neck (18%), skin of the left foreleg (10%), or the mediastinum adjacent to the stellate ganglion (3%). Acutely decentralizing the stellate ganglion abolished the spontaneous activity of some, but not all, of these neurons including the respiratory or cardiovascular-related neurons. In the intact or acutely decentralized stellate ganglion, few neurons were activated by single short duration (1-4 ms) stimuli delivered to nerves attached directly or indirectly to the ganglion; however, most were activated by brief high frequency stimuli delivered in trains of 20-200 ms, or by single stimuli lasting 20-200 ms. As most cardiovascular, respiratory, or neck-related neurons in the stellate ganglion were not activated by single brief stimuli delivered to the cardiopulmonary nerves or vagosympathetic trunks, presumably they did not project their axons into the neck or thoracic organs. Thus, they were considered to be interneurons. It is postulated that interneurons in stellate ganglia can be modified by afferent receptors located in tissues of the neck, lungs, heart, or great thoracic vessels, whether the ganglion is intact or acutely decentralized. In addition, neurons in the stellate ganglion can be modified by mechanoreceptors located in the thoracic wall, abdominal wall, foreleg, or adjacent mediastinum. The majority of these neurons are activated by trains of impulses rather than single short duration impulses.     

Gaba-ergic mechanisms in the caudal ventrolateral region of the cat medulla regulating vascular tonus and cardiac activity

In acute experiments on anesthetized cats data are obtained attesting to the fact that injections of GABA (0.5–50 µmoles/liter) into neuronal structures of the caudal ventrolateral medulla (CVLM) are accompanied by the development of hypertensive reactions caused by an increase in spontaneous activity in the sympathetic fibers of the renal and inferior cardiac nerves. An asymmetry is discovered in the realization of the inhibitory chrono- and inotropic influences on the heart emanating from the region investigated. Blocking of the GABA receptors with bicuculline (0.2–5.0 µmoles/liter) causes a sharp drop in the level of the systemic arterial pressure, a decrease in the strength and frequency of cardiac contractions, and a falling-off of the background activity in the peripheral symphathetic nerves. The findings suggest that the sympathoinhibitory CVLM neurons are under the constant inhibitory control of the GABA-ergic neurons.A. A. Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 698–703, November–December, 1991.