Comparison of chemoreceptions of terminal buds and pit organs of the carp, Cyprinus carpio L.

Neural responses to several chemicals of the pit organs and terminal buds on the facial skin of the carp were compared electrophysiologically. Nerve inpulses from the pit organs were larger than those from the terminal buds. The pit organs were more sensitive to salts and especially acids than the terminal buds. The former did not respond to sucrose, silk worm pupa extract, betaine and amino acids except acidic ones. The latter, however, responded well to them.     

Axonal projection patterns of neurons in the secondary gustatory nucleus of channel catfish

The secondary gustatory nucleus of teleost fishes receives ascending fibers from the primary gustatory center in the medulla and sends efferent fibers to several nuclei in the inferior lobe of the diencephalon. Similar to the corresponding parabrachial nucleus in birds and mammals, the secondary gustatory nucleus of catfish consists of several cytoarchitectonically distinct subnuclei which receive input from different portions of the primary gustatory nuclei. However, it is unclear how the subnuclear organization relates to the processing of gustatory information in the hindbrain and the subsequent transmission of that information to the forebrain. To determine whether cells within different subnuclei of the secondary gustatory nucleus of channel catfish project to different diencephalic targets, single cells were intracellularly labeled with biocytin. Three subnuclei have been identified in the secondary gustatory nucleus: a medial subnucleus spanning most of the rostrocaudal extent of the nucleus, a central subnucleus and a dorsal subnucleus, the latter two located in the rostrolateral portion of the complex. Cells throughout the secondary gustatory nucleus typically possessed similar collateral projections to several nuclei in the inferior lobe, although four of the six cells filled in the medial subnucleus projected only to nucleus centralis. The only apparent subnucleus-specific projection pattern involved cells at the rostral edge of the secondary gustatory nucleus and in the secondary visceral nucleus. Axons of these cells terminated only in restricted portions of nucleus lobobulbaris. These results suggest that efferents from different subnuclei of the secondary gustatory nucleus of catfish, like those of the parabrachial nucleus of birds and mammals, do not possess simple, topographical projections to target nuclei in the diencephalon. © 1996 Wiley-Liss, Inc.     

Mechanism of the water response in carp gustatory receptors: Independent generation of the water response from the salt response

The carp gustatory responses to various salts and those to distilled water after adaptation of the receptors to the salts were recorded from the palatine nerve under varying conditions. (a) As far as Na4Fe(CN)6 solution prepared freshly was used, any peak in the dose-response curve was not observed, while the solution stored overnight induced a large peak response at the low concentration region as Konishi reported. The magnitude of the water response after adaptation to the stored solution was practically equal to that after adaptation to the fresh solution, suggesting that the receptor site for the water response is different from that for the dilute salts. (b) The responses to salts depended largely on the species of both cations and anions of the salts. The responses were deceased with an increase in the lyotropic number of the anions and increased with an increase in the number above 11. The response to distilled water was practically independent of the species of both monovalent cations and anions of the salts used for the adaptation. The pH dependence of the response to 10 mM NaCl was largely different from that to distilled water after adaptation to 10 mM NaCl. (c) The water response was suppressed by the presence of electrolytes in stimulating solution; the data obtained with different species of salts were described by a single curve as a function of the ionic strength. (d) The mechanism to explain how distilled water leads to depolarization of the taste cell was discussed in terms of the electric double-layer potential.     

Anatomy of the gustatory system in the hamster: synaptology of facial afferent terminals in the solitary nucleus

The solitary nucleus is the first level of the central nervous system where processing of taste information can occur. A structural basis for that processing was investigated. Facial taste afferent axons were labelled by application of horseradish peroxidase to either the chorda tympani or the geniculate ganglion. The labelled afferent fibers in the rostral solitary nucleus were studied with light and electron microscopy. Preterminal facial taste afferent axons enter the nucleus from the solitary tract with a pronounced lateral to medial trajectory. The axons bear numerous preterminal and terminal swellings that, with the electron microscope, were identified as synaptic endings located in glomeruli. The endings are ovoid or scalloped, indented by structures that surround them. The primary afferent endings contain large, round vesicles and synapse, by means of slightly asymmetrical junctional complexes, on small dendrites and spines. Two types of unlabelled endings, surrounding the labelled ones, contact the dendrites receiving taste afferent input or contact the endings of taste afferent axons themselves. One type is variable in size and contains scattered large round vesicles. It resembles a presynaptic dendrite. The other is a small axonal ending packed with small, pleomorphic vesicles, that engages in symmetrical junctions. The synaptic milieu of the taste endings allows for the possibility of modulation of taste-elicited activity in afferent endings or second-order neurons by other, possibly interneuronal, inputs.     

Experimental study of the connections of the gustatory system in the rainbow trout,Oncorhynchus mykiss

Salmonids are a group of teleosts with a nonspecialized gustatory system. With the aim of describing the gustatory connections in a member of this group, we carried out tract-tracing experiments using the lipophilic carbocyanine dye 1,1'-dioctadecyl 3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) in fixed brains of the rainbow trout (Oncorhynchus mykiss). The neural tracer was applied to the primary viscerosensory column, secondary gustatory visceral nucleus (SGN), torus lateralis (TL), and tertiary gustatory nucleus (TGN), the dorsal part of the ventral area of the telencephalon (dorsal-Vv), and the medial area of the dorsal telencephalon (Dm). The primary viscerosensory column projects mainly to the SGN. DiI application to the SGN showed a bilateral and reciprocal connection with the TGN and a rostral portion of the nucleus of the lateral hypothalamic recess. The application of DiI in the dorsal-Vv and Dm at levels rostral to the anterior commissure led to labeling of a restricted group of diencephalic neurons in the TGN and sending dendrites to the TL. DiI application to the TL/TGN anterogradely labeled fibers that coursed in the medial forebrain bundle innervating the precommissural portion of the dorsal-Vv and Dm. Caudally, this type of application led to labeling of fibers in the viscerosensory column and perikarya in the SGN. Tract-tracing results showed direct projections from the diencephalic and rhombencephalic gustatory nuclei to the telencephalon. There was a direct and reciprocal connection between the SGN and the ventral telencephalon. The results showed that the gustatory connections of the trout are similar to those of teleosts, with highly specialized gustatory centers as in cyprinids and ictalurids, and to that observed in the percomorph tilapia, thus demonstrating a basic organization that is shared by most teleosts.     

电刺激大鼠杏仁中央核对脑桥臂旁核味觉神经元的影响(英文)

利用电生理学方法观察了电刺激杏仁中央核对脑桥臂旁核味觉神经元的影响。结果表明 :电刺激杏仁中央核抑制大部分臂旁核味觉神经元的活动 ,并且提高臂旁核味觉神经元对五种基本味觉刺激反应的特异性。电刺激杏仁中央核对臂旁核的抑制作用以对盐酸和奎宁刺激的反应尤为明显 (P <0 .0 1) ,并且对这两种厌味刺激反应的抑制作用是基本一致的。本研究的结果提示 ,杏仁中央核可能通过抑制脑干味觉神经元对厌味刺激的反应 ,从而参与对摄食行为的调控     

电刺激大鼠杏仁中央核对脑桥臂旁核味觉神经元的影响

利用电生理学方法观察了电刺激杏仁中央核对脑桥臂旁核味觉神经元的影响.结果表明:电刺激杏仁中央核抑制大部分臂旁核味觉神经元的活动,并且提高臂旁核味觉神经元对五种基本味觉刺激反应的特异性.电刺激杏仁中央核对臂旁核的抑制作用以对盐酸和奎宁刺激的反应尤为明显(P＜0.01),并且对这两种厌味刺激反应的抑制作用是基本一致的.本研究的结果提示,杏仁中央核可能通过抑制脑干味觉神经元对厌味刺激的反应,从而参与对摄食行为的调控.     

Axon collaterals of pontine taste area neurons project to the posterior ventromedial thalamic nucleus and to the gustatory neocortex

Retrograde axonal transport of fluorescent dyes was used to demonstrate collateral projections from neurons of the pontine taste area (PTA) to gustatory-responsive areas of the posterior ventromedial thalamic nucleus (VPM), and to the gustatory neocortex (GN) of the rat. Dual-labeled PTA neurons were reliably observed following application of two different fluorescent dyes to the GN and to VPM thalamus. Dye injections into the GN and into thalamic regions surrounding the VPM nucleus, the bed nucleus of stria terminalis or the infralimbic neocortex, did not result in dual-labeled cells within the PTA. This finding suggests that gustatory information may be relayed simultaneously and specifically to VPM thalamus and to the GN via collateral axons of PTA neurons.     

Tactile input to the facial lobe of the carp,Cyprinus carpio L.

Single unitary discharges in the facial lobe and trigeminofacial nerve trunks of the carp,Cyprinus carpio L., were studied electrophysiologically in response to electrical stimulation of the trigeminofacial nerve complex and the facial skin, and to chemical and tactile stimulation of the facial skin. Recording bimodal responses to chemical and tactile stimulation after sectioning the cranial Vth or VIIth (communis) nerves, and microelectrode recordings of trigeminal and facial (communis) nerve trunks revealed that taste messages are transmitted to the brain by the communis fibers and tactile ones by the trigeminus.Latencies measured in the facial lobe by electrical stimulation of the trigeminofacial nerve complex or the facial skin surface ranged from 6 to 59 msec, most firing between 10 and 29 msec in both cases. The receptive field sizes of the lobe neurons were larger than those of the primary ones.Of 84 neurons recorded from the facial lobe, 96.5% were facilitated by press and gliding movements with a glass rod on the facial skin and 3.5% by changing barbel's position. The glide group was classified into three types which were tonically firing (52.4% of total neurons), adaptive firing (39.3%) and after firing (4.8%) types. Twelve out of 84 tactile neurons responded to chemical solution, as well. The latencies of taste neurons were not centered at a certain range.The facial lobe of the carp is not only a primary gustatory center, but also a tactile one, and might play an important role for the purpose of effecting a correlation of the two diverse modalities.     

A field-potential study of centripetal and centrifugal connections of the olfactory bulb in the carp, Cyprinus carpio (L.)

The projection areas of mitral cell axons in the lateral (LOT) and medial (MOT) olfactory tracts and the pathways of two groups of centrifugal fibers (with fast and slow conduction velocities) to the olfactory bulb were studied in the carp using the field potential method. Mitral cell axons of the LOT and those of the MOT projected to the overlapping areas in the bilateral telencephalon and preoptic area (POA), the contralateral MOT, and the nucleus posterior tuberis (NPT) in the diencephalon. However, the precommissural, ventromedial part of the ipsilateral telencephalon received the projection only from mitral cell axons of the MOT, not from those of the LOT. No projection was detected in the contralateral LOT and the contralateral olfactory bulb. The distribution of the fast and slow centrifugal fibers and/or their cells of origin were similar to each other. They were distributed bilaterally in the telencephalon and POA, in the NPT, and contralateral LOT and MOT. These areas overlapped with the projection areas of the mitral cell axons considerably. The results support and extend those obtained from anatomical studies.     

Structure and function of gustatory neurons in the nucleus of the solitary tract: II. Relationships between neuronal morphology and physiology

This study employed intracellular recording and labeling techniques to examine potential relationships between the physiology and morphology of brainstem gustatory neurons. When we considered the neuronal response to the four “prototypic” tastants, we were able to demonstrate a positive correlation between breadth of responsiveness and the number of dendritic branch points. An analysis of the response to eight tastants also revealed an association between dendritic spine density and the breadth of responsiveness, with more narrowly tuned neurons exhibiting more spines. Interestingly, a neuron's “best response” was a relatively poor predictor of neuronal morphology. When we focused on those neurons that responded to only one tastant, however, a number of potentially important relationships became apparent. We found that the cells that only responded to quinine were smaller than the neurons that only responded to NaCl, HCl, or sucrose. The HCl-only neurons, however, were more widespread in the rostrocaudal dimension than the neurons that only responded to NaCl. A number of additional structure-function relationships were identified when we examined the neuronal response to selected tastants. We found that neurons that responded to sucrose but not quinine, as well as neurons that responded to quinine but not sucrose, were more widespread in the mediolateral dimension than neurons that responded to both sucrose and quinine. We also discovered that the neurons that responded to NaCl, but not to NH₄Cl or KCl, were larger than neurons that responded to all three salts. We believe that these results support the hypothesis that there are relationships between the structure and function of gustatory neurons in the nucleus of the solitary tract, with the data highlighting the importance of three themes: 1) the relationship between dendritic specializations and tuning, 2) the relationship between dendritic arbor orientation and response properties, and 3) the potential importance of stimulus-specific neurons. © 1996 Wiley-Liss, Inc.     

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.     

Tonotopic organization of the superior olivary nucleus in the chicken auditory brainstem

Topographic maps are salient features of neuronal organization in sensory systems. Inhibitory components of neuronal circuitry are often embedded within this organization, making them difficult to isolate experimentally. The auditory system provides opportunities to study the topographic organization of inhibitory long-range projection nuclei, such as the superior olivary nucleus (SON). We analyzed the topographic organization of response features of neurons in the SON of chickens. Quantitative methods were developed to assess and communicate this organization. These analyses led to three main conclusions: 1) sound frequency is linearly arranged from dorsal (low frequencies) to ventral (high frequencies) in SON; 2) this tonotopic organization is less precise than the organization of the excitatory nuclei in the chicken auditory brainstem; and 3) neurons with different response patterns to pure tone stimuli are interspersed throughout the SON and show similar tonotopic organizations. This work provides a predictive model to determine the optimal stimulus frequency for a neuron from its spatial location in the SON.     

Satiety does not affect gustatory activity in the nucleus of the solitary tract of the alert monkey

Feeding to satiety decreases the acceptability of the taste of food. In order to determine whether the responsiveness of gustatory neurons in the nucleus tractus solitarius (NTS) is influenced by hunger, neural activity in the NTS was analyzed while monkeys were fed to satiety. Gustatory neural activity to glucose, fruit juice, NaCl, HCl and quinine HCl was measured before, while and after the monkey was fed to satiety with glucose, fruit juice or sucrose. While behavior turned from avid acceptance to active rejection upon repletion, the responsiveness of NTS neurons to the stimulus array, including the satiating solution, was unmodified. It is concluded that at the first central synapse of the taste system of the primate, neural responsiveness is not influenced by the normal transition from hunger to satiety. This is in contrast to the responses of a population of neurons recorded in the hypothalamus, which only occur to the taste of food when the monkey is hungry. Thus, NTS gustatory activity appears to occur independently of normal hunger and satiety, whereas hypothalamic neuronal activity is more closely related to the influence of motivational state on behavioral responsiveness to gustatory stimuli.     

Convergence of oral and extraoral information in the superior secondary gustatory nucleus of the channel catfish.

Neurons within the superior secondary gustatory nucleus (nGS) of the channel catfish were examined electrophysiologically for responses to mechanical and chemical stimulation of neural peripheral receptive fields (RFs). Of the 28 single units sampled, 18 had mechanosensory RFs on the extraoral epithelium, two had RFs within the oropharyngeal cavity, and eight had RFs that included both oral and extraoral surfaces. RF sizes varied from approximately 2 cm2 on the ipsilateral lips and barbels to the whole body surface, bilaterally. No obvious correlation existed between RF pattern and recording location within the nGS. Eight of the mechanosensory nGS units also responded to amino acid taste stimuli with thresholds from micromolar to millimolar concentrations. The convergence of oral and extraoral information within the nGS determined electrophysiologically was corroborated anatomically by HRP labeling experiments. Restricted HRP injections into each of the primary gustatory nuclei of the medulla, the vagal (VL) and facial (FL) lobes, labeled fibers that appeared to terminate diffusely throughout the nGS, and injections into different portions of the nGS retrogradely labeled cells in both the FL and VL. The present electrophysiological and neuroanatomical data distinguish the convergent gustatory representation within the nGS of the catfish from the highly specific somatotopic and viscerotopic sensory maps previously identified in the FL and VL, respectively.     

Reflex connections of the facial and vagal gustatory systems in the brainstem of the bullhead catfish, Ictalurus nebulosus

The primary gustatory sensory nuclei in catfish are grossly divisible into a vagal lobe and a facial lobe. In this study, the reflex connections of each gustatory lobe were determined with horseradish peroxidase (HRP) tracing methods. In addition, in order to determine the loci and morphology of the other brainstem cranial nerve nuclei, HRP was applied to the trigeminal, facial, glossopharyngeal, or vagus nerve. The sensory fibers of the facial nerve terminate in the facial lobe. The facial lobe projects bilaterally to the posterior thalamic nucleus, superior secondary gustatory nucleus, and medial reticular formation of the rostral medulla. The facial lobe has reciprocal connections with the n. lobobulbaris, medial reticular formation of the rostral medulla, descending trigeminal nucleus, medial and lateral funicular nuclei, and the vagal lobe, ipsilaterally; and with the facial lobe contralaterally. In addition, the facial lobe receives inputs from the raphe nuclei, from a pretectal nucleus, and from perilemniscal neurons located immediately adjacent to the ascending gustatory lemniscal tract at the level of the trigeminal motor nucleus. The gustatory fibers of the vagus nerve terminate in the vagal lobe, while the general visceral sensory fibers terminate in a distinct general visceral nucleus. The vagal lobe projects ipsilaterally to the superior secondary gustatory nucleus, lateral reticular formation, and n. ambiguus; and bilaterally to the commissural nucleus of Cajal. The vagal lobe has reciprocal connections with the ipsilateral lobobulbar nucleus and facial lobe. In addition, the vagal lobe receives input from neurons of the medullary reticular formation and perilemniscal neurons of the pontine tegmentum. In summary, the facial gustatory system has connections consonant with its role as an exteroceptive system which works in correlation with trigeminal and spinal afferent systems. In contrast, the vagal gustatory system has connections (e.g., with the n. ambiguus) more appropriate to a system involved in control of swallowing. These differences in central connectivity mirror the reports on behavioral dissociation of the facial and vagal gustatory systems.     

Laminar distribution of tectal, parabigeminal and pretectal inputs to the primate dorsal lateral geniculate nucleus: Connectional studies in Galago crassicaudatus

We have studied the distribution of 3 extraretinal, subcortical inputs to the dorsal lateral geniculate nucleus of the prosimian primate Galago. Our connectional findings reveal that axons arising from the superior colliculus and the parabigeminal nucleus influence the W-cell system via their innervation of the two small-celled geniculate laminae (internal and external koniocellular) and the interlaminar zones; parabigeminal axons also innervate each of the 4 non-tectally innervated layers. Pretectal axons, on the other hand, distribute mainly to the parvocellular laminae and thus influence primarily the X-cell system.     

Afferent and efferent connections of the optic tectum in the carp (Cyprinus carpio L.)

The afferent and efferent connections of the tectum opticum in the carp (Cyprinus carpio L.) were studied with the HRP method. Following iontophoretic peroxidase injections in several parts of the tectum anterograde transport of the enzyme revealed tectal projections to the lateral geniculate nucleus, dorsal tegmentum, pretectal nuclei, nucleus rotundus, torus longitudinalis, torus semicircularis, nucleus isthmi, contralateral tectum and to the mesencephalic and bulbar reticular formations.Tectal afferents were demonstrated by retrograde HRP transport in the area dorsalis pars centralis of the telencephalon, torus longitudinalis, torus semicircularis, nucleus isthmi, nucleus profundus mesencephali, several pretectal nuclei, dorsomedial and dorsolateral thalamic nuclei, nucleus of the posterior commissure, mesencephalic and bulbar reticular nuclei and nucleus ruber. Visuo-cerebellar circuitry was investigated by means of peroxidase injections in the various parts of the cerebellum. These experiments revealed indirect retino- and tecto-cerebellar pathways via the pretectal nuclei and the nucleus isthmi.