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.

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.

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.

Intraganglionic distribution of the primary afferent neurons in the frog glossopharyngeal nerve and its transganglionic projection to the rhombencephalon studied by HPR method.

Anterograde transport of horseradish peroxidase (HRP) along the bullfrog IXth nerve was studied 6-16 days after application of HRP to the cut end of either the IXth nerve trunk or its distal 2 branches. The jugular and IXth nerve ganglia attached to the rhombencephalon were removed after fixation and serial sections of 50 microns in thickness were stained by the Graham and Karnovsky method. Of all the primary afferent neurons in the IXth nerve, 62% of the cell bodies were distributed within the IXth nerve ganglion, the remaining 38%, within the jugular ganglion. Similar distribution was found with the cells belonging to each of the IXth nerve branches. A part of the transganglionic IXth nerve fibers entering the medulla oblongata ascended to the cerebellar peduncle while the majority descended along the fasciculus solitarius. Some of the descending fibers in the fasciculus extended to the dorsal field of the spinal cord at the third spinal nerve, while some others run to join the descending tract of trigeminal nerve.

Surface and intramedullary potentials evoked by stimulation of the glossopharyngeal nerve in frogs.

The bulbar potentials evoked by afferent volleys in the bullfrog glossopharyngeal nerve and in its 2 distal branches were studied. Following supramaximal electric stimulation of the peripheral nerve, the potential consisting of 2 triphasic deflections (S1 and S2) of presynaptic origin and 4 postsynaptic negative waves, N1, N2, N3 and N4, having the peak latency of 5, 8, 30 and 80 ms, respectively, was obtained along the nucleus fasciculus solitarius. By lowering the stimulus intensity to the threshold for exciting mechanosensitive fibers, only S1 followed by N1, N3 and N4 was produced, whereas, at higher intensities, S2 which accompanied by N2 became apparent. N1 and N2 waves were distributed over the bulbar dorsal surface with the maximal amplitude at 1-2 mm rostral to the obex and 0.5-1 mm lateral from the midline, the negativity being found maximal at the depth 0.5-1 mm from the surface. The surface-recorded N2 potential evoked by stimulation of the medial branch distributed caudal to that produced by stimulation of the lateral branch. Of intramedullary-recorded 4 negative waves, only N1 caused by volleys in the lateral branch distributed deeper layer than the one evoked by those in the other branch.

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.

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.

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.

Responses of cerebellar cortex to electrical stimulation of the glossopharyngeal nerve in the frog.

In the frog cerebellar cortex, electrical stimulation of the glossopharyngeal (IXth) nerve induced negative field potentials with a peak latency of 57 ms whose distribution was bilateral with ipsilateral predominance. The site where the maximum negativity was induced by IXth nerve stimulation was histologically located within the molecular layer near the Purkinje cell layer. In extracellular recording, electrical stimulation of the IXth nerve induced complex and/or simple spike discharges of Purkinje cells. Such evoked potentials and unitary spikes in the cerebellum were attributed to the excitation of the IXth nerve afferents of higher threshold which are mainly composed of fibers sensitive to taste stimulation. These results suggest that gustatory information projects to the cerebellum, as well as those of other kinds of senses, such as touch, visual and auditory sensation.

Origin of the climbing fibers activated by glossopharyngeal nerve stimulation in the frog.

The origin of climbing fibers activated by electrical stimulation of the frog's glossopharyngeal (IXth) nerve was investigated using histological and electrophysiological technique. At the molecular layer near the Purkinje cell layer, where the maximum negative cerebellar field potential could be recorded following electrical stimulation of the IXth nerve, horseradish peroxidase (HRP) was iontophoretically injected through the tip of the recording micropipette. The HRP labeled cells were seen in the contralateral inferior olive (IO). In some cases, a small number of HRP-labeled cells were seen in the ipsilateral IO. Labeled cells were not found in the other areas of the brain stem. After electrolytic lesion of the contralateral IO, the negative cerebellar field potential which would be recorded in the molecular layer following electrical stimulation of the IXth nerve had almost ceased. These results demonstrate that the climbing fibers activated by the IXth nerve stimulation have their origin in the contralateral IO.

Depression of lingual tactile sensation during chemical stimulation of the human tongue.

The subjectively estimated magnitude of human tactile sensation elicited by tapping the tongue was depressed during taste stimulation by 3 and 6% NaCl solution, 0.1% quinine and 0.5% acetic acid. No significant change in the tactile sensation occurred during flow of 2-20% sucrose solution. The result may be attributed to presynaptic inhibition exerted by gustatory onto lingual tactile afferents.

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.

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.

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.

Origin of cyclic adenosine monophosphate in saliva.

The level of cyclic adenosine monophosphate (AMP) in duct saliva from the dog submandibular gland was increased after cyclic AMP was administered intravenously in vivo. Isoproterenol increased the level of cyclic AMP in plasma and saliva in vivo and in salivary gland slices in vitro, but increased the level only slightly in saliva in a prefused dog submaxillary gland.

Response properties of cerebellar neurons to stimulation of the frog glossopharyngeal nerve and tongue.

The cerebellum receives information from many kinds of sensory organs (muscle, somatosensory, auditory, vestibular, visual) as well as from the autonomic system. The cerebellum presumably has a role in the control of tongue movement and salivary secretion. However, the relationship between cerebellar neuron activity and tongue sensation has not been investigated previously. In the present study, negative cerebellar field potentials in the molecular layer and single unit responses of Purkinje cells induced by electrical stimulation of the bullfrog glossopharyngeal (IXth) nerve or tongue surface were investigated. The interaction between IXth nerve stimulation and natural (taste and touch) stimulation of the tongue in their effects on cerebellar neuron activity were investigated. The negative field potentials were potentiated by a brief train of electrical pulses to the tongue or IXth nerve. With electrical stimulation of the tongue surface, several fungiform papillae were needed to elicit cerebellar field potentials. The latency of Purkinje cells following IXth nerve stimulation was 44.4-53.6 msec for complex spikes, whereas for simple spikes two maxima were seen, with mean values at 33.9-36 msec and 96.8 msec. A preceding electrical stimulation of the IXth nerve depressed the negative field potentials or Purkinje cell complex spike responses induced by test stimulation of the IXth nerve. These depressive effects were also seen following a preceding natural stimulation of the tongue and were dependent upon the type of preceding stimulation. The depressive effects were produced by preceding stimulation with NaCl, CaCl2, water, and touch, but not with quinine and acetic acid stimulation. These results clearly demonstrate that gustatory and tactile signals from the tongue can influence cerebellar neuron activity.

Central projections of the hamster superior laryngeal nerve.

The superior laryngeal nerve (SLN) is known to innervate taste buds on the epiglottis of several mammalian species. Because of an increasing interest in the physiology of the gustatory system of hamsters, the brainstem projections of the SLN were investigated in this species. Crystallized HRP was applied to the proximal portion of the cut SLN or to one of its five distal branches. Anterograde transganglionic transport of HRP revealed afferent fibers of the SLN projecting into the ipsilateral solitary tract (ST) from 0.3 to 3.0 mm caudal to the dorsal cochlear nucleus (DCN), with the major area of termination in the nucleus of the solitary tract (NST) between 0.6 and 1.6 mm caudal to DCN. Some afferent fibers crossed the midline approximately 2.0 mm caudal to DCN to terminate contralaterally within the NST. Efferent cell bodies were retrogradely labeled within the nucleus ambiguus (NA) and in and around the more rostral portions of NST. There were five identifiable distal branches of SLN, termed A1, A2, M1, M2 and P, from anterior to posterior. Afferent fibers were carried in A2 and P, whereas efferent fibers were evident in all five branches. The heaviest projection from the NA occurred in the two middle branches (M1 and M2) and that from the NST in the posterior branch (P). Afferent projections of the Xth cranial nerve, along with those from the VIIth and IXth, into the NST provide a neural substrate for the integration of sensory inputs related to a number of oral and respiratory reflexes.

Multimodal responses of taste neurons in the frog nucleus tractus solitarius.

The responses of 216 neurons in the nucleus tractus solitarius (NTS) of the American bullfrog were recorded following taste, temperature, and tactile stimulation. Cells were classified on the basis of their responses to 5 taste stimuli: 0.5 M NaCl, 0.0005 M quinine-HCl (QHCl), 0.01 M acetic acid, 0.5 M sucrose, and deionized water (water). Neurons showing excitatory responses to 1, 2, 3, or 4 of the 5 kinds of taste stimuli were named Type I, II, III, or IV, respectively. Cells whose spontaneous rate was inhibited by taste and/or tactile stimulation of the tongue were termed Type V. Type VI neurons were excited by tactile stimulation alone. Of the 216 cells, 115 were excited or inhibited by taste stimuli (Types I-V), with 35 being Type I, 34 Type II, 40 Type III, 2 Type IV and 4 Type V. The remaining 101 cells were responsive only to tactile stimulation (Type VI). Of those 111 cells excited by taste stimulation (Types I-IV), 106 (95%) responded to NaCl, 66 (59%) to acetic acid, 44 (40%) to QHCl, 10 (9%) to water, and 9 (8%) to warming. No cells responded to sucrose. Of the 111 cells of Types I-IV, 76 (68%) were also sensitive to mechanical stimulation of the tongue. There was some differential distribution of these neuron types within the NTS, with more narrowly tuned cells (Type I) being located more dorsally in the nucleus than the more broadly tuned (Type III) neurons. Cells responding exclusively to touch (Type VI) were also more dorsally situated than those responding to two or more taste stimuli (Types II and III).