Nobusada Ishiko

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.

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.

Local gustatory functions associated with segmental organization of the anterior portion of cat's tongue.

Abstract Neural basis for local taste specificity within the anterior two-thirds of the mammalian tongue remains obscure. The present electrophysiological study aimed to clarify the topographical organization of tongue receptive areas in the cat and monkey and, also, to evaluate taste responsiveness of different tongue regions within the field of the cats lingual nerve. The anterior portion of the cats tongue was found to consist of three receptive areas, each receiving somatic as well as gustatory fibers from one of three lingual nerve ramifications, namely the anterior, medial, and posterior branches. The organization of tongue receptive areas in the monkey was found to be similar to that in the cat except that the anterior portion of the tongue comprised at least five receptive zones which overlapped more extensively than in the cat. Summed responses of the chorda tympani nerve component of the three lingual nerve branches to gustatory and thermal stimulations of the cats tongue were expressed relative to the whole chorda tympani response to 1 m NaCl, whereas the response of the trigeminal nerve component to cooling was expressed relative to the whole trigeminal nerve response to a standard temperature. It was found that the anterior branch field responded poorly to all taste qualities but strongly to cooling of the tongue. The medial branch field was highly responsive to NaCl, water and warmed saline, whereas the responsiveness of the posterior branch field to HC1 was stronger than other areas. The findings show localization of specific sensory properties over different tongue regions.

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.

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).

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.

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

The origin of climbing fibers activated by electrical stimulation of the frogs 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.