Morphological changes in different taste bud cells of the tongue

Bulletin of Experimental Biology and Medicine -     

Morphohistochemical changes of the blood cells in the hibernating frog (Rana esculenta L.)

Some morphological features (degree of nuclear segmentation in neutrophils and eosinophils), histochemical patterns (DHFR, LDH, G6PDH) and, in addition, the nucleic acid distribution (DNA, RNA with acridine orange) in the peripheral blood cells of Rana esculenta, during the hibernation phase were investigated. All the observed parameters varied significantly in the frog during hibernation in comparison with the active period. The most evident changes were an increase in the nuclear segmentation of the neutrophils and a lower activity of the histochemically demonstrable DHFR and LDH, probably due to cell ageing. These findings suggest that, in hibernating frogs, there is an increase in the life span of the peripheral blood cells as a consequence of a reduced metabolic activity and a slowing of haematopoiesis.     

Fever and Behavioural Temperature Regulation in the Frog Rana esculenta

The skin and colonic temperatures were recorded in frogs (Rana esculenta) which had selected a suitable microenvironment in a box filled with 2–3 cm water. The water temperatures ranged from 0°C to + 40°C. Such measurements were performed before and after intraperitoneal injections of killed pathogenic bacteria (M. xenopi and M. ranae), killed non-pathogenic bacteria (M. aquae II) and 0.9% sterile saline, intraperitoneal injections of blood plasma from frogs pre-injected with killed M. ranae, injections of PGE, into the brain. The injections of pathogenic bacterial endotoxin caused, after latencies of 5–120 min, higher preferred water temperatures, which produced an average maximum colonic temperature increase of 6.5°C ± 1.0°C (S.E.) (p< 0.001). The non-pathogenic bacteria and sterile saline caused no temperature change. Monophasic hyperthermia of shorter latency was caused by injections of blood plasma from frogs pre-injected with M. ranae. Monophasic hyperthermia of the shortest latency was observed after diencephalic injections of PGE₁. Based on their similarity we suggest that ectothermic and endothermic fever have a common phylogenetic origin.     

NADPH-diaphorase-positive neurons and pathways in the brain of the frog Rana esculenta

We described the NADPH-diaphorase-containing neurons and fibres in the brain of the frog Rana esculenta. In the telencephalon stained cells occurred in the olfactory bulb, all subdivisions of the pallium, the diagonal band, the medial septum and the striatum. The olfactory glomeruli showed the most intense enzyme reaction. The neuropil of the accessory olfactory bulb was also heavily stained and this staining extended to the rostral diencephalon through the ventral lateral pallium. Fibre staining was less intense in the medial pallium and the medial septum. In the diencephalon, NADPH-diaphorase staining was concentrated in the middle third of this part of the brain. The stained cells were embedded in a dense network of thin, stained fibres and terminals in the lateral anterior and central thalamic nuclei. Faintly stained cells were present also in the posterior preoptic nucleus, anterior thalamic nucleus, nucleus of Bellonci, corpus geniculatum thalamicum and the suprachismatic nucleus. In the mesencephalon, heavily stained cells occurred in the nucleus profundus mesencephali, anterodorsal, anteroventral and especially in the posterodorsal tegmental nuclei. Neuronal staining was less intense in the optic tectum and the torus semicircularis. Thick, intensely stained fibres occupied the lateral part of the tegmentum and the 7th layer of the tectum. A loose network of thin fibres occupied the periventricular area and all tegmental nuclei. In the rhombencephalon, the reticular nuclei and the inferior raphe nucleus showed the most intense staining, while some cells in the nucleus of the solitary tract and the dorsal column nuclei were less intensely stained. Heavy staining of fibres was characteristic of the spinal trigeminal tract, the solitary tract and the reticulospinal pathway.     

Relation between translingual potential changes induced by NaCl in the bullfrog tongue and taste nerve activity

NaCl at various concentrations applied to the dorsal surface of the bullfrog tongue induced slow potential changes across the tongue. They were almost in parallel with changes in impulse discharges simultaneously recorded from the glossopharyngeal nerve.     

Fever and behavioural temperature regulation in the frog Rana esculenta.

The skin and colonic temperatures were recorded in frogs (Rana esculenta) which had selected a suitable microenvironment in a box filled with 2-3 cm water. The water temperatures ranged from 0 degrees C to + 40 degrees C. Such measurements were performed before and after intraperitoneal injections of killed pathogenic bacteria (M. xenopi and M. range), killed non-pathogenic bacteria (M. aquae II) and 0.9% sterile saline, intraperitoneal injections of blood plasma from frogs pre-injected with killed M. ranae, injections of PGE1 into the brain. The injections of pathogenic bacterial endotoxin caused, after latencies of 5-120 min, higher preferred water temperatures, which produced an average maximum colonic temperature increase of 6.5 degrees C +/- 1.0 degrees C (S.E.) (p less than 0.001). The non-pathogenic bacteria and sterile saline caused no temperature change. Monophasic hyperthermia of shorter latency was caused by injections of blood plasma from frog preinjected with M. ranae. Monophasic hyperthermia of the shortest latency was observed after diencephalic injections of PGE1. Based on their similarity we suggest that ectothermic and endothermic fever have a common phylogenetic origin.     

Distribution of calretinin-like immunoreactivity in the brain of Rana esculenta.

The distribution of calretinin-like immunoreactivity has been analyzed in the brain of Rana esculenta. Several neurons of nuclei belonging to sensory pathways, subhabenular area and left habenula were immunopositive. Immunoreactivity was present in fibers of motor and sensory pathways, thalamus, tegmentum and isthmus. The immunolabeling pattern partially overlapped that previously described in the rat. However, in comparison with the rat, fewer cells and fibers were immunoreactive and there were less positive brain nuclei, especially in the pallium, septum and striatum, that were totally negative. Taking into consideration that these regions are rather simple in the frog, the presence of calretinin seems to be consistent with the degree of complexity of brain areas and segregation of different nuclei.     

The sweet taste in the calf. II. Glossopharyngeal nerve responses to taste stimulation of the tongue

Recordings were obtained from the glossopharyngeal nerve in 1-5-week-old calves during stimulation of the circumvallate tongue area with NaCl, quinine hydrochloride, citric acid, and the sweet compounds: acesulfam-K, aspartame, fructose, galactose, glucose, glycine, lactose, maltose, monellin, Na-saccharin, sucrose, thaumatin, and xylitol. All compounds except aspartame, monellin and thaumatin gave a nerve response. Glycine, followed by Na-saccharin, elicited the largest responses. Sucrose gave the largest response among the disaccharides, while there was no significant difference between the monosaccharides. Expressed as percent of the NaCl responses, the responses to glycine, sucrose, xylitol, fructose, galactose, glucose, lactose and maltose were considerably larger in the glossopharyngeal nerve than in the chorda tympani nerve. This can be taken as an indication that the posterior region of the tongue serves as the major receptive area for sweet in cattle.     

Interactions between taste receptors in the frog tongue

Summary Receptors sensitive to stimulation with dilute CaCl₂ solutions and located in different fungiform papillae of the frog tongue are cross-connected via branches of the glossopharyngeal nerve fibers to form chemical sensory units comprising on average about 3 papillae; often one or more papillae were found to be common to different units.The receptor response observed when single papillae were individually stimulated increased, when the strength of the stimulus was raised, at a much lower rate than that obtained by stimulating the whole tongue surface. This proves that the antidromic impulses travelling in the cross-connections linking different papillae result in an evident depression of the receptor response to CaCl₂.The possible functional significance of mutual interaction between the receptors in the frog tongue is discussed.This study was supported by grants from the Consiglio Nazionale delle Ricerche (Impresa di Elettrofisiologia) of Rome, Italy.     

The vomeronasal organ in the frog, Rana esculenta. An electron microscopy study

The ultrastructure of the vomeronasal organ (Jacobson's VNO) of the frog, Rana esculenta, was studied under the transmission and scanning electron microscope. Four cell types were identified: ciliated, bipolar, glial-like, and basal. Ciliated cells are unique to the frog VNO and show morphological evidence of secretion; bipolar (neuronal) cells are arranged in columns and reach the free surface of the epithelium with knobs bearing microvilli. The latter are in contact with amorphous material not described previously. Glial-like cells wrap bipolar cells in the epithelium and poorly differentiated basal cells are found just over the basal lamina. The vascular pump described in mammal VNO is not present at all in the frog VNO. We conclude that in the frog the VNO is closer to the reptilian than the mammalian VNO, although the frog VNO shows some unique morphological characteristics.     

Ultrastructural study of the semicircular canal cells of the frog Rana esculenta

The ultrastructure of the nonsensory cells (dark cells, transitional cells, and undifferentiated cells) of the frog semicircular canal was studied by using transmission electron microscopy in an attempt to correlate the structure with the functions of these epithelial cells. All the nonsensory cells were linked by tight junctions and desmosomes; this suggested that there is little paracellular ionic transport from perilymph to endolymph. In the dark cell epithelium, the apical intercellular spaces were dilated; in the basal part, numerous basolateral plasma membrane infoldings, containing mitochondria, delimited electron-lucent spaces. The undifferentiated cells and the transitional cells were devoid of any basal membrane infolding. Surrounding the semicircular canal, very flattened and interdigitated mesothelial cells constituted a thin multilayer tissue which limited the perilymphatic space. The morphological aspect of the dark cells suggests that they may play a role in the secretion and/or in the reabsorption of endolymph, which bathes the apical pole of these cells. The undifferentiated and transitional cells can play a role in the maintenance of the endolymphatic ionic composition because of their apical tight junctions and desmosomes.     

The sweet taste in the calf. I. Chorda tympani proper nerve responses to taste stimulation of the tongue

Electrophysiological recordings were obtained from the chorda tympani nerve in calves during stimulation with NaCl, quinine hydrochloride, citric acid, acesulfan-K, aspartame, fructose, galactose, glucose, glycine, lactose, maltose, monellin, Na-saccharin, sucrose, thaumatin, and xylitol. In cattle the chorda tympani innervates the posterior third of the tongue as well as the anterior part. It was found that the posterior receptive field generally responded better to sweet substances than the anterior. Glycine and Na-saccharin followed by xylitol were the most effective sweet stimuli. The monosaccharides elicited larger responses than the disaccharides. Aspartame gave a weak nerve response in 5 of 13 calves. Monellin and thaumatin elicited no change in chorda tympani nerve activity and did not crossadapt with any sweetener. No effects on citric acid responses were observed after application of miraculin.     

Two populations of serotonin-immunoreactive neurons in the frog (Rana esculenta) retina

Serotonin immunocytochemical staining in retina whole-mounts of Rana esculenta revealed two differently stained amacrine cell populations. Statistical investigations using nearest neighbor analysis and comparison with different theoretical cell distributions suggested that the two serotonin-immunoreactive cell populations are related to functionally different types. The analysis of type A (intensely stained somata, less numerous) revealed a good coincidence with the normal Gaussian distribution indicating a functionally homogeneous population. The distribution of the neurons of type B (weakly stained somata, more numerous) reflects rather a random dot pattern than a regular arrangement. Thus there is evidence that this last type is a heterogeneous cell population consisting of several functionally different types.     

The morphological changes in the pulmonary resistive vessels in the development of high-altitude pulmonary arterial hypertension

The structural alterations of pulmonary resistance vessels in rabbits during short-term adaptation to the high altitude were studied. As an example of ecological adaptation the structural alterations of pulmonary vessels in yaks living at altitudes above 3000 m were analyzed. Considerable structural alterations of endotheliocytes and blood cells were found that promote the appearance and development of high-altitude pulmonary hypertension. In yaks the adaptive alterations of pulmonary resistance vessels take place in the process of evolution. These alterations ensure, first, low resistance of pulmonary vessels when the volume of the vessel bed increases and, second, high functional activity of endotheliocytes. The changes are considered as a structural basis of ecological adaptation of pulmonary vessels providing a new level of homeostasis in pulmonary circulation.     

The nature of the substance P-containing nerve fibres in taste papillae of the rat tongue

The nature of the association of substance P (SP) with taste buds in the rat tongue was investigated by immunohistochemical and radioimmunoassay techniques. Both the circumvallate and fungiform papillae were found to receive a rich innervation by substance P-containing fibres. Although these fibres were closely associated with the taste buds in these structures, they assumed a perigemmal rather than an intragemmal location. Bilateral lesions of the glossopharyngeal nerve resulted in the depletion of taste buds from the vallate papilla and a large reduction in substance P immunoreactive fibres in this area. Lesions of the chorda tympani, which led to the degeneration of taste buds in fungiform papillae, had no effect on the immunohistochemical appearance of substance P in these papilla or on the substance P levels in the anterior part of the tongue. Lesions of the mandibular division of the trigeminal nerve or neonatal capsaicin treatment had no effect on the structural integrity of taste buds in fungiform papillae but led to the depletion of substance P-immunoreactive fibres from these papillae. Both of these procedures caused a 71% reduction in the substance P content of the anterior tongue, ipsilaterally after the nerve lesion and bilaterally after capsaicin treatment. The results are discussed in relation to the possible functional role of substance P-containing fibres within nerves supplying taste structures of the tongue.