Effects of electrical stimulation of the glossopharyngeal nerve on cells in the nucleus of the solitary tract of the rat

Electrophysiological responses to electrical stimulation of the lingual branch of the glossopharyngeal (GP) nerve (which innervates taste buds on the caudal 1/3 of the tongue) were recorded from single cells in the rostral nucleus of the solitary tract (NTS) of anesthetized rats. Electrical stimulation was delivered as single pulses (n=55), paired-pulses (n=15) and tetanic trains (n=11). NTS cells with GP-evoked responses were also tested for responsivity to taste stimuli (0.1 M NaCl, 0.5 M sucrose, 0.01 M HCl and 0.01 M quinine HCl). Fifty-five neurons were studied: 49 cells showed GP-evoked (mean latency+/-SEM=18.0+/-1.32 ms); seven of these were taste-responsive. Spontaneous rate of these cells was low (mean+/-SEM=1.4+/-0.3 spikes per second; median=0.21 spikes per second) and many cells showed no spontaneous activity. Paired-pulse stimulation of the GP nerve in 13 rats produced both paired-pulse suppression (n=11) and paired-pulse enhancement (n=4); tetanic stimulation (25 Hz, 1.0 s) produced sustained (>20 s) increases or decreases in firing rate in 7 of 11 cells tested. Histological data suggested that GP-evoked responses recorded in the most rostral NTS were likely the result of polysynaptic connections. Cells with GP-evoked responses formed a heterogeneous group in terms of their response properties and differed from cells with evoked responses to chorda tympani (CT; which innervates taste buds on the rostral 1/3 of the tongue) nerve stimulation. These differences may reflect the respective functional specializations of the GP and CT nerves.     

Convergence onto hamster medullary taste neurons

Research has shown that gustatory afferents innervating different areas of the oral cavity converge onto single neurons in the nucleus tractus solitarii (NTS). However, most studies of gustatory physiology have only stimulated the receptors on the anterior tongue. No information exists on the responses of hamster NTS neurons to stimulation of receptors located in other areas of the oral cavity. The present investigation compared responses of hamster NTS neurons to stimulation of receptors on the anterior tongue and posterior oral cavity, and to stimulation of both receptor populations together. Of the neurons, 64% responded to both anterior tongue and posterior oral cavity stimulation. The remaining neurons responded exclusively to stimulation of one area. Cells responsive to both fields of stimulation were found throughout the rostral NTS. Cells responding to stimulation of only one field were anatomically separate. Most neurons (69%) were more responsive to anterior tongue than posterior oral cavity stimulation. The neural responses to stimulation of both fields simultaneously were complex. Frequently, a cell's response was intermediate between those produced by stimulation of either receptor population alone. In other cases the response was the same as the larger of the two individual responses. The breadth of responsiveness to the 4 basic taste stimuli (sucrose, NaCl, HCl and quinine-HCl) was similar for both receptor populations, but the breadth of tuning of an individual cell for one field of stimulation was not correlated with its breadth of responsiveness for the other. In contrast, the breadth of tuning following stimulation of the entire oral cavity was correlated with that following stimulation of the anterior tongue.     

Convergence of lingual and palatal gustatory neural activity in the nucleus of the solitary tract

The responses of 54 neurons to independent sapid stimulation of 4 taste receptor subpopulations associated with: (1) anterior tongue; (2) nasoincisor ducts; (3) soft palate; and (4) foliate papillae were recorded from the nucleus of the solitary tract (NST) of the Rat. Neurons responding to stimulation of receptor subpopulations in the anterior oral cavity (anterior tongue or nasoincisor ducts) were located more rostrally in the NST than neurons responding to stimulation of receptor subpopulations in the posterior oral cavity (soft palate or foliate papillae). Half of the sampled neurons responded exclusively to stimulation of one receptor subpopulation with the remaining neurons responsive to stimulation of two or more receptor subpopulations. The most common pattern of convergence observed was between responses arising from stimulation of the taste buds on the anterior tongue and those associated with the nasoincisor ducts of the hard palate. The sensitivity of NST neurons to anterior tongue and nasoincisor duct stimulation with the 4 standard taste stimuli was determined. When stimulating the anterior tongue, the order of effectiveness was NaCl greater than HCl greater than sucrose greater than quinine hydrochloride (QHCl). When the nasoincisor ducts were tested, however, the order of stimulus effectiveness was strikingly different: sucrose was the best stimulus, followed by HCl, NaCl, and QHCl. If both the anterior tongue and nasoincisor ducts are included, stimulation of taste receptors in the anterior oral cavity of the rat produces good responses to stimuli representing 3 of the 4 classical taste qualities: sweet, salty, and sour.     

Influence of nucleus tractus solitarius stimulation and baroreceptor activation on rat parabrachial neurons.

The parabrachial nucleus (PBN) within the dorsolateral pons is a major recipient of autonomic-related inputs from more caudal levels of the brainstem and, in particular, the nucleus of the solitary tract (NTS). Although the anatomical projections from the NTS to the PBN are well characterized, less is known concerning the influence of activating NTS efferents on PBN neurons and the response of the latter to cardiovascular-related inputs. The present study examined the response of PBN neurons to electrical stimulation of the depressor area within the NTS in urethane anesthetized rats, and subsequently, the influence of arterial baroreceptor activation and systemic angiotensin II (ANG II) on these cells. Extracellular single-unit PBN recordings indicated that 92 of 227 (40.5%) cells were orthodromically excited and 35 of 227 (15.4%) inhibited consequent to NTS stimulation. Ten (4.5%) PBN cells displayed antidromic activation from the NTS. Of 41 of 119 neurons responding to both NTS stimulation and baroreceptor activation, 29.3% revealed a excitatory and 31.7% an inhibitory response to the two stimuli. Fifteen PBN cells responded to NTS stimulation, baroreceptor activation, and the administration of systemic ANG II, with six cells displaying either an excitatory or inhibitory response to all three stimuli. These observations provide electrophysiological support for reciprocal connections between the NTS and PBN and indicate the presence of both excitatory and inhibitory projections to the pontine nucleus. A population of neurons influenced by activation of NTS efferents also reveal a similarity of responses to inputs originating from peripheral arterial baroreceptors and systemic ANG II.     

Quinine suppression of single facial taste fiber responses in the channel catfish

Two groups of single facial taste fibers that were responsive to quinine hydrochloride (QHCl) and amino acids were identified in the channel catfish, Ictalurus punctatus. Group I fibers were significantly more excited by quinine hydrochloride (QHCl) than were group II fibers. QHCl (10⁻³ M), as one component in a binary mixture, suppressed taste responses of group II fibers to 10⁻⁴ M amino acids (other component) by 61%, but did not inhibit significantly the responses to

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-alanine of group I fibers. QHCl (10⁻² M) suppressed the response to 10⁻⁴ M

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-alanine of group I fibers by 58% and group II fibers to 10⁻⁴ M

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-alanine,

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-arginine and

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-proline by 89–100%. The suppression of amino acid responses of both groups of fibers by QHCl was reversible in subsequent testing of stimuli in the absence of QHCl. QHCl also suppressed the taste responses to other bitter stimuli [10⁻³ M caffeine and 10⁻² M denatonium benzoate(DB)]; however, neither caffeine nor DB suppressed amino acid taste responses. Possible mechanisms for the suppressive effect of QHCl on taste nerve activity are discussed.     

Three-dimensional reconstructions of mouse circumvallate taste buds using serial blockface scanning electron microscopy: I. Cell types and the apical region of the taste bud

Taste buds comprise four types of taste cells: three mature, elongate types, Types I–III; and basally situated, immature postmitotic type, Type IV cells. We employed serial blockface scanning electron microscopy to delineate the characteristics and interrelationships of the taste cells in the circumvallate papillae of adult mice. Type I cells have an indented, elongate nucleus with invaginations, folded plasma membrane, and multiple apical microvilli in the taste pore. Type I microvilli may be either restricted to the bottom of the pore or extend outward reaching midway up into the taste pore. Type II cells (aka receptor cells) possess a large round or oval nucleus, a single apical microvillus extending through the taste pore, and specialized “atypical” mitochondria at functional points of contact with nerve fibers. Type III cells (aka “synaptic cells”) are elongate with an indented nucleus, possess a single, apical microvillus extending through the taste pore, and are characterized by a small accumulation of synaptic vesicles at points of contact with nerve fibers. About one-quarter of Type III cells also exhibit an atypical mitochondrion near the presynaptic vesicle clusters at the synapse. Type IV cells (nonproliferative “basal cells”) have a nucleus in the lower quarter of the taste bud and a foot process extending to the basement membrane often contacting nerve processes along the way. In murine circumvallate taste buds, Type I cells represent just over 50% of the population, whereas Types II, III, and IV (basal cells) represent 19, 15, and 14%, respectively.     

Role of the central amygdaloid nucleus in shaping the discharge of gustatory neurons in the rat parabrachial nucleus

The central amygdaloid nucleus (CeA) receives projection from the parabrachial nucleus (PBN) gustatory neurons and descendingly projects to the PBN. To assess if the CeA is involved in modulating the activity of gustatory neurons in the PBN, the effects of electrical stimulation and electrolytic lesion of CeA on PBN gustatory neurons were observed. Of 60 neurons observed, 30 were classified as NaCl-best, 18 as HCl-best, 5 as Quinine HCl (QHCl)-best, and 7 as sucrose-best. During CeA stimulation, the responses to at least one effective stimulus were inhibited in most PBN neurons, with the response magnitudes to HCl and QHCl significantly decreased (P<0.01). In contrast, bilateral lesions of CeA facilitated the responses to HCl and QHCl (P<0.01). According to the best-stimulus category, the effects on the responses to HCl and QHCl were similarly subjected to these modulations either during electrical stimulation or after electrolytic lesions of CeA. Analyses of across-unit patterns indicated that the CeA stimulation increased the chemical selection of PBN taste neurons while the CeA lesions depressed the effect on the chemical selection between NaCl and QHCl. These findings suggest that the CeA may be involved in mediating feeding behavior via modulating the activity of gustatory neurons of PBN.     

Evidence for two populations of rat spinal dorsal horn neurons excited by urinary bladder distension

Spinal L6-S2 dorsal horn neurons of cervical spinal cord-transected, decerebrate female rats were characterized using urinary bladder distension (UBD) as a visceral stimulus. Constant pressure, phasic, graded (20-80 mm Hg, 20 s) air UBD was delivered via a transurethral catether and extracellular single-unit recordings obtained from all neurons excited by UBD. Responses to graded UBD and noxious/non-noxious cutaneous stimuli were determined in 258 neurons which could be stratified into two groups based on their effect of a counterirritation stimulus: Type I neurons (n=112) were inhibited by noxious pinch presented in a non-segmental field; Type II neurons (n=146) were not similarly inhibited. Both Types of neurons were identified in both superficial and deep recording sites and demonstrated graded responses to graded UBD. All UBD-excited neurons had convergent cutaneous receptive fields (RFs) excited by non-noxious and/or noxious stimuli. As a group, Type I neurons had a period of decreased activity following termination of the distending stimulus whereas Type II neurons typically had a sustained afterdischarge. UBD-evoked activity in Type II neurons was inhibited more than similar activity in Type I neurons by both intravenous morphine and lidocaine. These results support the assertion that at least two different populations of spinal dorsal horn neurons exist which encode for a stimulus of urinary bladder distension. These populations are an analogue to previously characterized, similar neuronal populations excited by colorectal distension and suggest that they are representative of the overall phenomenon of visceral sensory processing, a component of which is nociception.     

“Tripartite Synapses” in Taste Buds: A Role for Type I Glial-like Taste Cells

In mammalian taste buds, Type I cells comprise half of all cells. These are termed “glial-like” based on morphologic and molecular features, but there are limited studies describing their function. We tested whether Type I cells sense chemosensory activation of adjacent chemosensory (i.e., Types II and III) taste bud cells, similar to synaptic glia. Using Gad2;;GCaMP3 mice of both sexes, we confirmed by immunostaining that, within taste buds, GCaMP expression is predominantly in Type I cells (with no Type II and ≈28% Type III cells expressing weakly). In dissociated taste buds, GCaMP+ Type I cells responded to bath-applied ATP (10-100 μm) but not to 5-HT (transmitters released by Type II or III cells, respectively). Type I cells also did not respond to taste stimuli (5 μm cycloheximide, 1 mm denatonium). In lingual slice preparations also, Type I cells responded to bath-applied ATP (10-100 μm). However, when taste buds in the slice were stimulated with bitter tastants (cycloheximide, denatonium, quinine), Type I cells responded robustly. Taste-evoked responses of Type I cells in the slice preparation were significantly reduced by desensitizing purinoceptors or by purinoceptor antagonists (suramin, PPADS), and were essentially eliminated by blocking synaptic ATP release (carbenoxolone) or degrading extracellular ATP (apyrase). Thus, taste-evoked release of afferent ATP from type II chemosensory cells, in addition to exciting gustatory afferent fibers, also activates glial-like Type I taste cells. We speculate that Type I cells sense chemosensory activation and that they participate in synaptic signaling, similarly to glial cells at CNS tripartite synapses.SIGNIFICANCE STATEMENT Most studies of taste buds view the chemosensitive excitable cells that express taste receptors as the sole mediators of taste detection and transmission to the CNS. Type I “glial-like” cells, with their ensheathing morphology, are mostly viewed as responsible for clearing neurotransmitters and as the “glue” holding the taste bud together. In the present study, we demonstrate that, when intact taste buds respond to their natural stimuli, Type I cells sense the activation of the chemosensory cells by detecting the afferent transmitter. Because Type I cells synthesize GABA, a known gliotransmitter, and cognate receptors are present on both presynaptic and postsynaptic elements, Type I cells may participate in GABAergic synaptic transmission in the manner of astrocytes at tripartite synapses.     

Noxious and non-noxious responses in the medial thalamus of the rat

Single-cell experiments were undertaken to localize and characterize the medial thalamic (MT) neurons which respond to noxious and non-noxious input in the rat. The observations demonstrated that: (1) 61 and 42% of MT neurons respond to noxious (Nox) and non-noxious (NN) stimulation, respectively; (2) MT neurons exhibit 4 cell types according to their pattern of response; Type A units were excited exclusively by Nox stimulation; Type B units were excited exclusively by NN stimulation; Type C units were excited by both (Nox and NN) stimulation, and Type D units exhibited decreases in firing rate following both stimulation modalities; (3) neurons of the parafascicularis nucleus exhibit more noxious responses (Type A units) than other medial thalamic areas.     

Cardiovascular responses to gustatory and mechanical stimulation of the nasopharynx in rats

The effects of natural (mechanical and gustatory) stimulation of the nasopharynx or electrical stimulation of the pharyngeal branch of the glossopharyngeal (PH-IXth) nerve on the changes in heart rate (HR) and arterial blood pressure (BP) were investigated in paralyzed and anesthetized rats. Afferent responses in the PH-IXth nerve were also investigated. Electrical stimulation of the PH-IXth nerve elicited a tachycardia and an increase in BP. Among the gustatory (1.0 M NaCl, 0.03 M HCl, 0.03 M QHCl, 1.0 M sucrose, H₂O, and 0.9% NaCl) and mechanical stimuli applied to the nasopharynx, 1.0 M sucrose and 0.9% NaCl were ineffective in changing HR and BP; the rest of the stimuli were strongly effective as was the case with electrical stimulation of the PH-IXth nerve. Responses were evoked in the PH-IXth nerve by nasopharyngeal stimulation with the stimuli which were effective in producing cardiovascular responses. On the other hand, 1.0 M sucrose and 0.9% NaCl, which were ineffective stimuli for cardiovascular responses, did not produce any response in the PH-IXth nerve. There was a high correlation between the magnitude of the responses in the PH-IXth nerve and those of the cardiovascular system. These results indicate that gustatory and mechanical information carried in the PH-IXth nerve innervating the nasopharynx plays an important role in cardiovascular regulation as well as the sense of taste.     

Discharge patterns evoked by depolarizing current injection in basal optic nucleus neurons of the pigeon

The nucleus of the basal optic root of the accessory optic system in birds is involved in optokinetic nystagmus, which stabilizes images on the retina by compensatory movements of the eyes. The present paper studies the physiological and morphological properties of basal optic neurons in the pigeon by using a brain slice preparation and intracellular recordings. Sixty-one cells examined could be categorized into six types based on their firing patterns in response to depolarizing current injection. Type I cells (54%) fire spontaneously and more spikes as current intensity is increased. Type II cells (15%) discharge regular spikes with similar interspike intervals. Type III cells (5%) show an early burst followed by tonic firing. Type IV cells (5%) fire regular bursts with similar interburst intervals. Type V cells (16%) fire a few spikes in a cluster only at onset of current application. Type VI cells (5%) produce a hump-like depolarization or a single spike depending on current intensities. Seventeen cells stained with Lucifer yellow have multipolar or piriform perikarya (15-28 microm) with two to eight primary dendrites. In some cases, an axon is observed to originate from the cell body, traveling dorsolaterally or dorsally. The physiological significance of these findings is discussed.     

Electrophysiological characterization of reciprocal connections between the parabrachial nucleus and the area postrema in the rat

Neuroanatomical studies have demonstrated reciprocal connections between the parabrachial nucleus (PBN) and both the area postrema (AP) and the nucleus tractus solitarius (NTS). To functionally characterize these projections, antidromic identification of AP and NTS neurons projecting to the PBN was attempted. Orthodromic influences on these cells, resulting from PBN stimulation, were also examined. Four percent of AP neurons tested (n = 74) were antidromically identified as projecting to the PBN [latency (L) = 26 +/- 4 msec, threshold current (T) = 79 +/- 11 microA]. Parabrachial stimulation orthodromically influenced 24% of AP cells. Equal numbers of these neurons (12%) were excited [L = 25 +/- 9 msec, duration (D) = 29 +/- 14 msec] and inhibited (L = 28 +/- 8 msec, D = 107 +/- 40 msec). Of 46 NTS neurons tested, 11% were antidromically identified as projecting to the PBN (L = 12 +/- 4 msec, T = 61 +/- 18 microA), while orthodromic influences were seen in 41% of these neurons. Initial responses of 30% of the cells were excitatory (L = 34 +/- 14 msec, D = 63 +/- 24 msec), PBN stimulation inhibited the remaining 11% of NTS neurons (L = 30 +/- 10 msec, D = 108 +/- 32 msec). These findings suggest that a functional heterogeneity exists in the PBN efferents to the AP and NTS. However, the small proportion of antidromically identified AP and NTS efferents to the PBN disagrees with neuroanatomical studies suggesting a denser projection.     

Responses of T2-T4 spinal neurons to stimulation of the greater splanchnic nerves of the cat

Effects of electrical stimulation of the greater splanchnic nerves on T2-T4 spinal neurons were determined in 16 cats anesthetized with alpha-chloralose. Of 77 neurons responding to somatic stimuli, 65 (84%) were excited, inhibited, or both excited and inhibited by splanchnic input. Each of the splanchnic responsive cells also was responsive to electrical stimulation of cardiopulmonary sympathetic afferent fibers. All but one neuron with left splanchnic input also received input from the right splanchnic nerve. Short- and long-latency excitatory responses were observed after splanchnic stimulation. The cell response to splanchnic stimulation was greatly inhibited by a conditioning stimulus applied to the other splanchnic nerve. A similar, although weaker, interaction occurred between splanchnic and cardiopulmonary sympathetic afferent fibers. The activity of 17 cells was inhibited by repetitive stimuli applied to one or both splanchnic nerves. Cells were found in laminae I, IV, V, VII, and VIII. These data provide the first evidence for splanchnic modulation of upper thoracic dorsal horn neurons.     

Laminar distribution of neurons with different types of receptive fields in the visual cortex of the rabbit

232 neurons of rabbit visual cortex were classified as cells with simple (34.1%), complex (16.4%), hypercomplex (18.5%), non-oriented (21.1%) receptive fields and other (9.9%). Some quantitative characteristics of cellular responses (background activity, velocity and tuning of orientation selectivity) correlated with these receptive field properties. Cells with non-oriented receptive fields were predominant in layer IV and occurred very rarely in layer VI. Cells with simple receptive fields were found in all layers, but were predominant in layer VI. Cells with complex receptive fields occurred with greater frequency in layer V and VI and less commonly in layer IV. Cells with hypercomplex receptive fields occurred frequently in layers II + III and IV but very rarely in layers V and VI. The rate of the background activity of layer II + III cells was the lowest and that of layer V cells--the highest. Tuning of orientation selectivity of simple and complex cells was narrower in layers II + III and V than in layers IV and VI.     

The role of cardiovascular and muscle afferent systems in control of body water balance

Influences of afferent inputs from cardiovascular and muscle receptors on the activities of neurosecretory neurons in the hypothalamus, which secrete vasopressin (ADH) were studied. Recordings were made from identified neurosecretory neurons in the supraoptic (SON) and paraventricular nuclei (PVN) of cats and rats. Activation of baroreceptors in the carotid sinus and aortic arch and atrial receptors inhibited SON and PVN neuron activities, while activation of chemoreceptors in the carotid sinus excited them. Repetitive electrical stimulation of the carotid sinus and aortic nerves showed that weak stimulation produced excitation and stronger stimulation produced inhibition of SON and PVN neurons. Electrical stimulation of these nerves and the nucleus tractus solitarius (NTS) by a single or short train of pulses showed that 'fast' and 'slow' pathways between the NTS and the SON existed, while these two types of pathways were not observed between the NTS and the PVN. Evidence of direct connections from the NTS to the PVN was found by means of antidromic stimulation of the PVN. Electrical stimulations of group I afferent fibers from the gastrocnemius muscle did not change SON neuron discharges, while activation of group III and IV afferent fibers excited them. Injection of chemicals (NaCl, KCl, bradykinin) into arteries supplying the muscle excited SON neurons. The excitation disappeared after section of the muscle nerves. The results indicated that activation of small afferents from the muscle excites the SON neurons, leading to an increase in vasopressin secretion. All these studies show that afferent inputs from receptors in the cardiovascular system and in the muscle have modulatory effects on neurosecretory neurons, and participate in control of body water balance by regulating vasopressin secretion from the neurohypophysis.     

Stimulation of area postrema by vasopressin and angiotensin II modulates neuronal activity in the nucleus tractus solitarius

There is an abundance of evidence suggesting that the area postrema (AP) is involved in the central actions of argininevasopressin (AVP) and angiotensin II (Ang II) on cardiovascular regulation. Furthermore, recent studies have shown that activation of the AP facililates the response of nucleus tractus solitarius (NTS) neurons to tractus stimulation. In the present study, using the perfused rabbit brain slice preparation, we examined the response of NTS neurons when AVP and Ang II were microinjected onto the AP. Spontaneous or solitary tract stimulation-induced neuronal activity was recorded extracellularly from the medial NTS before, during and after AVP or Ang II application. An increase or decrease in activity by more than 30% of the baseline value was considered excitatory or inhibitory. The effects of AVP were studied in 57 NTS cells, 14 of which were spontaneously active and 43 were driven by tract stimulation. Of the cells with evoked activity, 49% were excited, 19% were inhibited, and 32% did not respond. The percentage of cells responding to AVP was similar in spontaneously active cells. The effects of Ang II were tested in 85 cells including 54 with evoked activity and 31 with spontaneous activity. In NTS cells with evoked activity, AP application of Ang II caused inhibition in 37%, excitation in 7%, while 56% did not respond. The proportion of cells responding to Ang II was similar in spontaneously active cells. These results suggest that AVP may act on the AP to increase the excitatory response of NTS neurons while the actions of Ang II result in an inhibitory influence.     

Connections of neurons in the region of the nucleus tractus solitarius with the hypothalamic paraventricular nucleus: Their possible involvement in neural control of the cardiovascular system in rats

Extracellular recordings were made from 607 spontaneously firing neurons within the nucleus tractus solitarius (NTS) and its vicinity in urethane-anesthetized male rats. Following electrical stimulation of the hypothalamic paraventricular nucleus (PVN) area, 21% of the neurons were orthodromically excited, 6% were inhibited and 2.5% were antidromically activated. The antidromic spike latencies were 22-64 ms. Among those orthodromically responding neurons, 81 neurons were tested by pressure pulse stimulation of the isolated carotid sinus. The pressure stimulation produced excitation in 7 and inhibition in 13 neurons. Of the 8 tested neurons which were antidromically activated, one neuron was excited and another neuron inhibited by the pressure pulse stimulation. These results provide electrophysiological evidence for reciprocal connections between neurons in the NTS region and the PVN, and give support to the hypothesis that the PVN is involved in the neural control of the cardiovascular system.     

Neurons in the posterior insular cortex are responsive to gustatory stimulation of the pharyngolarynx, baroreceptor and chemoreceptor stimulation, and tail pinch in rats

Extracellular unit responses to gustatory stimulation of the pharyngolaryngeal region, baroreceptor and chemoreceptor stimulation, and tail pinch were recorded from the insular cortex of anesthetized and paralyzed rats. Of the 32 neurons identified, 28 responded to at least one of the nine stimuli used in the present study. Of the 32 neurons, 11 showed an excitatory response to tail pinch, 13 showed an inhibitory response, and the remaining eight had no response. Of the 32 neurons, eight responded to baroreceptor stimulation by an intravenous (i.v.) injection of methoxamine hydrochloride (Mex), four were excitatory and four were inhibitory. Thirteen neurons were excited and six neurons were inhibited by an arterial chemoreceptor stimulation by an i.v. injection of sodium cyanide (NaCN). Twenty-two neurons were responsive to at least one of the gustatory stimuli (deionized water, 1.0 M NaCl, 30 mM HCl, 30 mM quinine HCl, and 1.0 M sucrose); five to 11 excitatory neurons and three to seven inhibitory neurons for each stimulus. A large number of the neurons (25/32) received converging inputs from more than one stimulus among the nine stimuli used in the present study. Most neurons (23/32) received converging inputs from different modalities (gustatory, visceral, and tail pinch). The neurons responded were located in the insular cortex between 2.0 mm anterior and 0.2 mm posterior to the anterior edge of the joining of the anterior commissure (AC); the mean location was 1.2 mm (n=28) anterior to the AC. This indicates that most of the neurons identified in the present study seem to be located in the region posterior to the taste area and anterior to the visceral area in the insular cortex. These results indicate that the insular cortex neurons distributing between the taste area and the visceral area receive convergent inputs from gustatory, baroreceptor, chemoreceptor, and nociceptive organs.     

Neurons with visual receptive fields independent of eye position in the caudal portion of the ventral wall of the cruciate sulcus of the cat cerebral cortex

Neurons responding to tactile and visual stimulation have been found in alert behaving cats in the caudal part of the ventral bank of cruciate sulcus. Tactile receptive fields were located on the cat face mainly around the mouth. Visual stimuli (especially alimentary ones) were effective being presented near the tactile receptive field. It was found that these bimodal neurons (visual and somatosensory) are located in layer VI of the cortex and their visual responses demonstrate space constancy. The position of the visual receptive field of these neurons did not change after saccadic eyes displacements, but remained in-register with the tactile receptive field.