Effects of various ion transport inhibitors on the water response in the superior laryngeal nerve in rats.

The effects of inhibitors [acetazolamide, an inhibitor of carbonic anhydrase; amiloride, an inhibitor of the Na channel; furosemide, an inhibitor of the Na/K/2Cl transporter; 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of the Cl channel] on the water response in the superior laryngeal nerve (SLN) were investigated using whole nerve recordings from the SLN of anesthetized and paralyzed rats. Changes in spontaneous activity in the SLN after i.v. injection of a hypo- or hypertonic solution were also investigated. The water response to higher concentration amiloride solutions (0.1, 1, 5 and 10 mM) were significantly smaller in comparison with the control, i.e. the water response to deionized water (88-59% of the control, Fisher's PLSD, P < 0.05). DIDS suppressed the water response significantly at concentrations of 0.5 and 2 mM by 18 and 33%, respectively (P < 0.05). Likewise, acetazolamide (2 mM) and furosemide (5 mM) significantly suppressed the water response by 9 and 40%, respectively (P < 0.05). An i.v. bolus injection of a hypertonic solution (1 ml of 1.5 M NaCl or 1.0 M mannitol) depressed spontaneous activity of the SLN. In contrast, an i.v. injection of a hypotonic solution (0.015 M NaCl) increased spontaneous activity. These results suggest that several ion transporters and ion channels, as well as carbonic anhydrase, that may exist in the dorsal surface in the epiglottis may regulate the water response in the SLN and that osmotic changes in the dorsal surface of the epiglottis and in the interstitial space can affect nerve activity in the SLN.

Participation of arterial baroreceptors input and peripheral vasopressin in the suppression of renal sympathetic nerve activity induced by central salt loading in conscious rats.

We examined whether renal sympathetic nerve activity (RSNA) is suppressed in response to intracerebroventricular (i.c.v.) administration of hypertonic saline (HS) in conscious rats. RSNA was suppressed by i.c.v. administration of HS (0.3 M, 0.67 M, and 1.0 M, 1 microl/min for 20 min) in a concentration-dependent manner, which was attenuated under pentobarbital anesthesia. To elucidate mechanisms responsible for central HS-induced decrease in RSNA, possible involvement of arterial baroreceptors and peripheral arginine vasopressin (AVP) secreted from the posterior pituitary gland was examined using sinoaortic denervated (SAD) rats and non-peptide vasopressin receptor antagonists. The maximum suppression of RSNA (-81.5 +/- 5.5%) in control rats was significantly attenuated to -32.5 +/- 6.7% in SAD rats and to -55.8 +/- 5.7% in rats pretreated with intravenous vasopressin V1 receptor antagonist, OPC-21268 (5 mg/kg, i.v.). However, in SAD rats, pretreatment with vasopressin V1 receptor antagonist did not further affect the RSNA inhibition induced by central salt loading. The results suggest that the suppression of RSNA during central salt loading is mainly dependent on the arterial baroreceptors input and the 'additive' role of peripheral vasopressin.

Cardiovascular and sympathetic effects of proadrenomedullin NH2-terminal 20 peptide in conscious rats.

Proadrenomedullin NH2-terminal 20 peptide (PAMP) and adrenomedullin (AM), which are derived from the same gene, are novel vasodilative peptides and have been shown to exhibit hypotensive action in anesthetized animals. To avoid the modification via anesthesia, we investigated the effects of intravenously administered PAMP on mean arterial pressure, heart rate (HR), and renal sympathetic nerve activity (RSNA) relative to those of AM in conscious unrestrained rats. We also examined whether the arterial baroreceptor reflex was altered with the two peptides. Intravenous injection of rat PAMP (rPAMP) (10, 20 and 50 nmol/kg) and rat AM (rAM) (0.3, 1.0 and 3.0 nmol/kg) similarly elicited dose-related hypotension accompanied by increases in HR and RSNA. However, the responses to rPAMP were less potent in magnitude and shorter in duration than those to rAM. Moreover, rAM facilitated baroreflex control, whereas rPAMP attenuated it. These findings indicate that although PAMP, as well as AM, may play an important role as a circulating hormone in the systemic circulation of conscious rats, the two peptides derived from an identical origin might have different mechanisms responsible for their cardiovascular and RSNA actions.

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.

Abdominal vagotomy attenuates interleukin-1 beta-induced nitric oxide release in the paraventricular nucleus region in conscious rats.

Nitric oxide (NO) has recently been shown to modulate the hypothalamic-pituitary-adrenal axis response to interleukin-1 beta (IL-1 beta). We measured levels of nitrite (NO2-) and nitrate (NO3-) in the hypothalamic paraventricular nucleus (PVN) region using an in vivo brain microdialysis technique in conscious rats. Intraperitoneally administered IL-1 beta produced a significant increase in both NO2- and NO3- levels in the PVN region. We also examined the possible involvement of the abdominal vagal afferent nerves in this effect. In abdominal-vagotomized rats, the increase was significantly attenuated compared to that in sham-operated rats. Our results suggest that the abdominal vagal afferent nerves are involved in intraperitoneally administered IL-1 beta-induced NO release in the PVN region.

Responses of neurons in the insular cortex to gustatory, visceral, and nociceptive stimuli in rats.

Extracellular unit responses to baroreceptor and chemoreceptor stimulation, gustatory stimulation of the posterior tongue, electrical stimulation of the superior laryngeal (SL) nerve, and tail pinch were recorded from the insular cortex of anesthetized and paralyzed rats. Forty-three neurons identified responded to stimulation by at least one of the stimuli used in the present study. Of the 43 neurons, 33 responded to tail pinch, and the remaining 10 had no response; 18 showed an excitatory response, and 15 showed an inhibitory response. Of the 43 neurons, 35 responded to electrical stimulation of the SL nerve; 27 showed an excitatory response, and 8 showed an inhibitory response. Of the 20 neurons that responded to baroreceptor stimulation by an intravenous injection of methoxamine hydrochloride (Mex), 11 were excitatory and 9 were inhibitory. Twenty-seven neurons were responsive to an intravenous injection of sodium nitroprusside (SNP); 10 were excitatory and 17 were inhibitory. Ten neurons were excited and 16 neurons were inhibited by arterial chemoreceptor stimulation by an intravenous injection of sodium cyanide (NaCN). Twenty-six neurons were responsive to at least one of the gustatory stimuli (1.0 M NaCl, 30 mM HCl, 30 mM quinine HCl, and 1.0 M sucrose): four to six excitatory neurons and three to nine inhibitory neurons for each stimulus. A large number of the neurons (42/43) received convergent inputs from more than one stimulus among the nine stimuli used in the present study. Most neurons (38/43) were responsive to two or more stimulus groups when the natural stimuli used in the present study are grouped into three, gustatory, visceral, and nociceptive stimuli. The neurons recorded were located in the insular cortex between 2.8 mm anterior and 1.1 mm posterior to the anterior edge of the joining of the anterior commissure (AC); the mean location was 1.0 mm (n = 43) anterior to the AC. This indicates that most of the neurons identified in the present study were 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 baroreceptor, chemoreceptor, gustatory, and nociceptive organs and may have roles in taste aversion or in regulation of visceral responses.

Central actions of adrenomedullin on cardiovascular parameters and sympathetic outflow in conscious rats.

Adrenomedullin (ADM) is reported to be a peripherally acting hypotensive peptide, but its central actions are unclear. We investigated the effects of centrally administered ADM on blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA) in conscious rats and sinoaortic-denervated (SAD) rats. We also investigated the receptors interacting with ADM using two putative antagonists. Intracerebroventricular administration of ADM in doses of 0.1 and 0.5 nmol/kg caused tachycardia and early inhibition of RSNA. Central ADM (1.0 nmol/kg) induced hypertension, tachycardia, and a decrease followed by an increase in RSNA. In SAD rats, increases in BP, HR, and RSNA at the late phase were enhanced by central ADM (1.0 nmol/kg), whereas the early decrease in RSNA remained. Thus the inhibition of RSNA via central ADM may be unrelated to the arterial baroreceptor reflex. Pretreatment with antagonists human calcitonin gene-related peptide-(8-37) and human ADM-(22-52) significantly suppressed the central actions of ADM. The findings suggest that ADM is involved as a neuropeptide in the receptor-mediated central regulation of the cardiovascular system and RSNA.

Difference in water intake but not in renal sympathetic nerve activity in response to central salt-loading or angiotensin II in awake Dahl salt-sensitive and -resistant rats.

Experiments were conducted to examine whether renal sympathetic nerve activity (RSNA) and water intake in response to central salt-loading or angiotensin II (A II) differ between freely-moving Dahl salt-sensitive (DS) and -resistant (DR) rats maintained on a low-salt diet. Intracerebroventricular (i.c.v.) administration of hypertonic saline (0.3 M, 1 microl/min, 20 min) or A II (100 ng/1 microl) evoked water intake, pressor response and suppression of RSNA in both strains. The cumulative water intake in DS rats over a 60-min period after i.c.v. infusion of hypertonic saline or A II was significantly attenuated compared with that in DR rats. The RSNA response did not show a significant difference between the strains. These results demonstrate that water intake, but not RSNA response to acute central salt-loading or A II differ between awake DR and DS rats.

Convergence of oropharyngolaryngeal, baroreceptor and chemoreceptor afferents onto insular cortex neurons in rats.

Forty-two neurons that responded to electrical stimulation of at least one of four nerves, the chorda tympani (CT), the lingual-tonsillar branch of the glossopharyngeal (LT-IXth) nerve, the pharyngeal branch of the glossopharyngeal (PH-IXth) nerve and the superior laryngeal (SL) nerve, were identified from the insular cortex by using glass microelectrodes in paralysed and anesthetized rats. Four, 42, 41 and 40 neurons responded to the CT, LT-IXth, PH-IXth and SL nerve stimulation respectively. Of these 42 neurons, most (37/42, 88.1%) responded to three nerves (the LT-IXth, PH-IXth and SL), two (4.8%) responded to two nerves and the remaining three (7.1%) responded to all four nerves. No neurons responded to one specific stimulus. The responsiveness of these 42 neurons to baroreceptor and chemoreceptor stimulation by an i.v. injection of three drugs was investigated. For baroreceptor stimulation, methoxamine hydrochloride (Mex) and sodium nitroprusside (SNP) were used; for chemoreceptor stimulation, sodium cyanide (NaCN) was used. Of the 42 neurons, 31 (73.8%) showed an excitatory or inhibitory response to baroreceptor and chemoreceptor stimulation with at least one of the three drugs, and the remaining 11 (26.2%) showed no response. Of these 31 baroreceptor and chemoreceptor-sensitive neurons, 19 (61.3%) responded to two or all three drugs, and the rest (12; 38.7%) responded to one. Most neurons recorded were distributed in the posterior insular cortex. These results indicate that the neurons in the posterior insular cortex receive convergent inputs from the oropharyngolaryngeal region, the baroreceptors and the chemoreceptors, suggesting that the posterior insular cortex may integrate various sensory information.

Convergence of afferent inputs from the chorda tympani, lingual-tonsillar and pharyngeal branches of the glossopharyngeal nerve, and superior laryngeal nerve on the neurons in the insular cortex in rats.

The responses of single neurons in the insular cortex to electrical stimulation of the chorda tympani (CT), lingual-tonsillar branch of the glossopharyngeal (LT-IXth) nerve, pharyngeal branch of the glossopharyngeal (PH-IXth) nerve, and superior laryngeal (SL) nerve were recorded in anaesthetized and paralyzed rats. Ninety-four neurons responding to stimulation of at least one of the four nerves were identified from the insular cortex. Most of the neurons were located in the posterior portion of the insular cortex; the mean location was 0.8 mm anterior to the anterior edge of the joining of the anterior commissure (AC) and was 1.4 mm dorsal to the rhinal fissure (RF). Of the 94 neurons, 84 (89%) received convergent inputs from two or more nerves, and the remaining 10 (11%) received inputs from one nerve. The neurons responding to the CT stimulation were distributed more anteriorly than those responding to other three nerves in the anterior-posterior dimension. Our results indicate that the neurons recorded mainly from the posterior portion of the insular cortex receive convergent inputs from the oropharyngolaryngeal regions.

Effects of systemic interleukin-1beta administration on daily drinking and renal excretory function in conscious rats.

To elucidate the roles of interleukin-1beta (IL-1beta), a cytokine with several diverse actions, in the control of body fluid balance, its effects on daily drinking behavior and renal excretory function were examined in conscious rats. Administration of IL-1beta (4 microg/kg, I.P.) resulted in the suppression of both daily drinking and food intake and a decrease in daily urinary sodium and potassium excretion, but had no effect on urine volume. The IL-1beta-induced decrease in sodium excretion was abolished in renal-denervated rats. Kainic acid was then injected into the anteroventral third ventricle region, including the organum vasculosum of the lamina terminalis, to examine whether neurons in this region are involved in the IL-1beta-induced responses; the effects on daily drinking and urinary sodium and potassium excretion were abolished, whereas the effects on food intake, although attenuated, were still present. In contrast, electrical lesion of the subfomical organ did not affect the IL-1beta-induced responses. Thus, IL-1beta seems exert its effects on body fluid balance at several distinct sites in the central nervous system.

Effects of area postrema lesion and abdominal vagotomy on interleukin-1 beta-induced norepinephrine release in the hypothalamic paraventricular nucleus region in the rat.

Peripherally administered interleukin-1 beta (IL-1 beta) has been shown to increase extracellular norepinephrine (NE) concentration in the paraventricular nucleus (PVN) of the hypothalamus. The present study was carried out using an in vivo microdialysis technique in conscious rats in order to examine the possible involvement of the area postrema (AP) and the abdominal vagal afferent nerves in this effect. Extracellular NE concentrations in the PVN region were measured by high performance liquid chromatography with electrochemical detection. In AP-lesioned or abdominal-vagotomized rats, the NE increase was significantly attenuated compared to that in sham-operated rats; this reduction was greater in abdominal-vagotomized rats than in AP-lesioned rats. The results suggest that the AP as well as the abdominal vagal afferent nerves is involved in intraperitoneal (i.p.) administered IL-1 beta-induced NE release in the PVN region.

Fiber types of the lingual branch of the trigeminal nerve, chorda tympani, lingual-tonsillar and pharyngeal branches of the glossopharyngeal nerve, and superior laryngeal nerve and their relation to the cardiovascular responses in rats.

The effect of repetitive electrical stimulation at 50 Hz for 20 s of the lingual branch of the trigeminal nerve (LN), chorda tympani (CT), lingual-tonsillar (LT-IXth) and pharyngeal (PH-IXth) branches of the glossopharyngeal nerve, and superior laryngeal nerve (SLN) on the changes in arterial blood pressure (BP) and heart rate (HR) were investigated in anesthetized and paralyzed rats. The compound action potentials in these nerves were simultaneously recorded to know the relationships between the fiber types and the cardiovascular responses. In all nerves except the CT, repetitive electrical stimulation of the nerve elicited a tachycardia and an increase in BP. These cardiovascular responses were mainly related to the component-2 in the compound action potentials in respective nerves. The conduction velocities of the component-2 in the five nerves examined in the present experiment were between 9.5 and 17.0 m/s (mean, n = 4-7). Other components which have faster (component-1) or slower conduction velocities (component-3 and -4) than the component-2 were not likely to elicit the cardiovascular responses. These results suggest that nociceptive and taste fibers of A-delta fibers innervating the oral cavity and pharyngolaryngeal region largely contribute to the cardiovascular responses.

Inhibition of nitric oxide synthase attenuates osmotic thirst in the rat.

Changes in water intake after intraperitoneal injection of a nitric oxide synthase (NOS) inhibitor was studied in the rat. Administration of NW-nitro-L arginine methyl ester (L-NAME) at a dose of 50 mg/kg attenuated osmotic thirst induced by intraperitoneal injection of hypertonic saline, but did not affect spontaneous intake of water and thirst induced by subcutaneous injection of angiotension II. Pretreatment with L-arginine significantly attenuated the inhibition of osmotic thirst evoked with subsequent L-NAME. Administration of NW-nitro-D-arginine methyl ester (D-NAME) altered neither the spontaneous nor the osmotic drinking behavior. These findings suggest that NO may affect the osmotically induced drinking.

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.

Organization of gustatory sensitivities in hamster superior laryngeal nerve fibers.

1. Mammalian taste receptors are distributed within several distinct subpopulations, innervated by branches of cranial nerves VII, IX, and X. Most gustatory electrophysiology has focused on input from the fungiform papillae on the anterior portion of the tongue, carried by the chorda tympani branch of the VIIth nerve. However, laryngeal taste buds in the hamster are as numerous as those in the fungiform papillae. Gustatory fibers in the hamster's chorda tympani and glossopharyngeal nerves have been well characterized. In comparison with these taste fibers, much less is known about the chemical sensitivities of fibers innervating laryngeal taste buds. 2. Action potentials were recorded from 65 individual fibers in the superior laryngeal nerve (SLN) of the hamster. Stimuli were distilled H2O and five concentrations each of sucrose, NaCl, HCl, and quinine hydrochloride (QHCl). All stimuli except the NaCl series were made in physiological saline (0.154 M NaCl) and were delivered from the laryngeal side of the epiglottis via a tracheal cannula. Responses were quantified as the number of impulses in 10 s minus the responses in the preceding 10 s of baseline activity during a rinse with physiological saline. 3. Distilled H2O, HCl, and NaCl were by far the most excitatory stimuli, with mean responses across all cells 5-10 times greater than those evoked by sucrose or QHCl. The order of effectiveness of the strongest concentrations of the stimuli was H2O greater than 0.03 M HCl greater than 1.0 M NaCl much greater than 0.03 M QHCl greater than 1.0 M sucrose. 4. The mean concentration-response function for NaCl was U shaped, with the greatest number of impulses to distilled H2O and 1.0 M NaCl. The responses diminished as the concentrations approached physiological levels (0.154 M NaCl), where there was no response, and increased as NaCl concentration rose above this level. Increasing concentrations of HCl above 0.0003 M elicited increasing responses in these fibers. 5. The mean time course of the responses to distilled H2O and to hypotonic NaCl solutions (0.01 and 0.03 M) peaked in the first few seconds and then declined slowly. This was distinct from the time course of the responses to hypertonic NaCl concentrations (0.3 and 1.0 M), which increased gradually throughout the 10-s response period. Responses to HCl peaked in the initial second and then decayed rapidly to a slowly declining plateau. These distinctively different time courses suggest different receptor mechanisms for water, salt, and acid stimuli. 6. The across-fiber pattern of the responses to hypotonic NaCl solutions correlated strongly to that elicited by distilled H2O.(ABSTRACT TRUNCATED AT 400 WORDS)

Receptive fields and gustatory responsiveness of frog glossopharyngeal nerve. A single fiber analysis.

Receptive fields and responsiveness of single fibers of the glossopharyngeal (IXth) nerve were investigated using electrical, gustatory (NaCl, quinine HCl, acetic acid, water, sucrose, and CaCl2), thermal, and mechanical stimulation of the single fungiform papillae distributed on the dorsal tongue surface in frogs. 172 single fibers were isolated. 58% of these fibers (99/172) were responsive to at least one of the gustatory stimuli (taste fibers), and the remaining 42% (73/172) were responsive only to touch (touch fibers). The number of papillae innervated by a single fiber (receptive field) was between 1 and 17 for taste fibers and between 1 and 10 for touch fibers. The mean receptive field of taste fibers (X = 6.6, n = 99) was significantly larger than that of touch fibers (X = 3.6, n = 73) (two-tailed t test, P less than 0.001). In experiments with natural stimulation of single fungiform papillae, it was found that every branch of a single fiber has a similar responsiveness. Taste fibers were classified into 14 types (Type N, Q, A, NA, NCa, NCaA, NCaW, NCaAW, NCaWS, NQ, NQA, NQAS, NQWarm, Multiple) on the basis of their responses to gustatory and thermal stimuli. The time course of the response in taste fibers was found to be characteristic of their types. For example, the fibers belonging to Type NQA showed phasic responses, those in Type NCa showed tonic responses, etc. These results indicate that there are several groups of fibers in the frog IXth nerve and that every branch of an individual fiber has a similar responsiveness to the parent fiber.

Gustatory innervation in the rabbit: central distribution of sensory and motor components of the chorda tympani, glossopharyngeal, and superior laryngeal nerves.

Although rabbits have been used extensively in neurophysiological studies of the gustatory system, there is little information about the anatomical organization of taste in this species. Afferent and efferent central connections of three nerves innervating oral or laryngeal taste buds in the rabbit, including the chorda tympani (CT), the lingual-tonsillar branch of the glossopharyngeal (IX), and the superior laryngeal nerve (SLN), were traced by means of horseradish peroxidase neurohistochemistry. After entering the brainstem, most afferent fibers of CT, IX, and SLN turned caudally in the solitary tract, with fibers of the CT terminating in the nucleus of the solitary tract from 1.0 mm rostral to 3.8 mm caudal to the caudal border of the dorsal cochlear nucleus. There was terminal label from the CT also in the principal trigeminal nucleus. There was terminal label from the CT also in the principal trigeminal nucleus and the oral and intermediate divisions of the spinal trigeminal nucleus. Preganglionic parasympathetic cell bodies of the superior salivatory nucleus were labeled retrogradely in the reticular formation ventral to the rostral pole of the solitary nucleus. Afferent fibers of the IXth nerve terminated in the solitary nucleus from 0.6 mm rostral to 5.0 mm caudal to the caudal border of the dorsal cochlear nucleus. There were also labeled terminals in the principal trigeminal nucleus and in all three divisions of the spinal trigeminal nucleus. Cell bodies composing the inferior salivatory nucleus were labeled in and around the solitary nucleus and subadjacent reticular formation just rostral to the caudal border of the dorsal cochlear nucleus. There were also a few lightly labeled cells within the nucleus ambiguus at its most rostral extent. Afferent fibers of the SLN terminated in the solitary nucleus from 1.2 to 6.8 mm caudal to the dorsal cochlear nucleus. There was also some terminal label in the intermediate and caudal divisions of the spinal trigeminal nucleus. Many cells were retrogradely labeled in the nucleus ambiguus following application of HRP to the SLN and a few cells were labeled in and around the solitary nucleus just caudal to the dorsal cochlear nucleus. These three nerves show an overlapping rostral to caudal distribution of afferent input within the nucleus of the solitary tract that may be related to their gustatory and visceral functions.

Gustatory responsiveness of fibers in the hamster glossopharyngeal nerve.

1. Mammalian taste receptors are distributed within separate subpopulations, innervated by branches of cranial nerves VII, IX, and X. Most gustatory electrophysiology has focused on input from the fungiform papillae on the anterior portion of the tongue, carried by the chorda tympani branch of the VIIth nerve. However, only a small percentage of the taste buds are located in the fungiform papillae (approximately 18% in the hamster). There have been no studies on the hamster's IXth nerve, which innervates greater than 50% of its taste buds, and most other studies of IXth nerve function have employed only whole-nerve recording. 2. Action potentials were recorded from 83 individual fibers in the IXth nerve of the hamster. Stimuli were five concentrations each of sucrose, NaCl, HCl, and quinine hydrochloride (QHCl), all presented to every fiber at 37 degrees C. Responses were quantified as the number of impulses in 10 s minus the preceding 10 s of spontaneous activity. 3. Across these concentration series, HCl and QHCl were by far the most excitatory stimuli, with mean responses across all cells three to four times greater than those evoked by sucrose or NaCl. The order of effectiveness of the stimuli was H greater than Q much greater than N greater than S. 4. Of the 83 fibers, 56 were stimulated via the foliate papillae and 27 via the single vallate papilla. No fibers responded to both of these fields. There were generally no differences in the sensitivity of these two subpopulations of taste buds, except that QHCl was more effective when applied to the foliates. 5. A "total" response measure was derived by summing the excitatory responses to each stimulus across the entire concentration series. The fibers were then classified according to the best total response, resulting in 52 HCl-, 19 QHCl-, 8 sucrose- and 4 NaCl-best cells. Considering the slope of the concentration-response functions as a criterion for classification produced very similar results. The fiber classification varied somewhat with concentration, with more fibers categorized as HCl- and QHCl-best at the higher concentration levels. 6. Breadth of responsiveness was measured using the equation developed by Smith and Travers. At the concentrations used to examine hamster chorda tympani fibers, IXth nerve fibers were not very responsive and were quite narrowly tuned to the four taste qualities. At higher concentrations the fibers became more broadly responsive across the four stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Taste responses of Purkinje cells in the frog cerebellum.

Fifty-nine Purkinje cells that responded to electrical stimulation of the glossopharyngeal (IXth) nerve with complex and/or simple spikes were isolated in the frog cerebellum. For these 59 Purkinje cells, changes in the complex and simple spike activity during taste stimulation of the tongue (42 cells for NaCl and 17 for quinine) were investigated. Of 42 Purkinje cells, 23 (54.8%) showed excitatory changes in simple and/or complex spike discharge rate during NaCl stimulation, and the remaining 19 (45.2%) showed no response. On the contrary, only a few Purkinje cells (2 of 17 cells, 11.8%) showed an excitatory change in simple or complex spike discharge rate during quinine stimulation. These results demonstrate that gustatory information influences cerebellar Purkinje cell activity.