Does an initial phasic response exist in the receptor potential of taste cells?

The depolarizing receptor potentials to 0.5 M NaCl recorded from frog taste cells did not exhibit any phasic response, even when the rectangular waveform of stimulus onset was employed. The quickest depolarizations recorded reached the peak in 50 msec. On the other hand, the gustatory neural response showed initial overshoot of the impulse discharge even when 0.5 M NaCl was delivered at the slower rate of 0.06 ml/sec. It is concluded that the initial neural response may be associated with the rate of rise of the receptor potential before its plateau level is reached.     

Signaling in the Chemosensory Systems

Taste bud cells communicate with sensory afferent fibers and may also exchange information with adjacent cells. Indeed, communication between taste cells via conventional and/or novel synaptic interactions may occur prior to signal output to primary afferent fibers. This review discusses synaptic processing in taste buds and summarizes results showing that it is now possible to measure real-time release of synaptic transmitters during taste stimulation using cellular biosensors. There is strong evidence that serotonin and ATP play a role in cell-to-cell signaling and sensory output in the gustatory end organs.     

Reticular potentials evoked by electrical stimulation of individual semicircular canals.

Responses of pontine reticular formation neurons following single shock electrical stimulation of single semicircular canals were recorded with tungsten microelectrodes in 40 curarized guinea-pigs. The field and unitary potentials obtained from 62 reticular sites, exhibited latency values ranging from 0.3 to 2.5 msec. The early latencies (0.3-0.5 msec) have been interpreted as responses mediated by primary vestibular fibres projecting directly to the reticular substance.     

Molecular neurophysiology of taste in <Emphasis Type="Italic">Drosophila</Emphasis>

The recent identification of candidate receptor genes for sweet, umami and bitter taste in mammals has opened a door to elucidate the molecular and neuronal mechanisms of taste. Drosophila provides a suitable system to study the molecular, physiological and behavioral aspects of taste, as sophisticated molecular genetic techniques can be applied. A gene family for putative gustatory receptors has been found in the Drosophila genome. We discuss here current knowledge of the gustatory physiology of Drosophila. Taste cells in insects are primary sensory neurons whereupon each receptor neuron responds to either sugar, salt or water. We found that particular tarsal gustatory sensilla respond to bitter compounds. Electrophysiological studies indicate that gustatory sensilla on the labellum and tarsi are heterogeneous in terms of their taste sensitivity. Determination of the molecular bases for this heterogeneity could lead to an understanding of how the sensory information is processed in the brain and how this in turn is linked to behavior.Received 12 May 2003; received after revision 9 June 2003; accepted 13 June 2003     

Reticular potentials evoked by electrical stimulation of individual semicircular canals

Summary Responses of pontine reticular formation neurons following single shock electrical stimulation of single semicircular canals were recorded with tungsten microelectrodes in 40 curarized guinea-pigs. The field and unitary potentials obtained from 62 reticular sites, exhibited latency values ranging from 0.3 to 2.5 msec. The early latencies (0.3–0.5 msec) have been interpreted as responses mediated by primary vestibular fibres projecting directly to the reticular substance.This work was supported by a grant of CNR.     

Gustatory sensitivity of an anuran to cantharidin

Glossopharyngeal nerve stimulation of the bullfrog, Rana catesbeiana, revealed responsiveness to low levels of cantharidin (1.3 x 10(-6) M), providing a first demonstration of neural gustatory sensitivity of an animal to this defensive chemical from blister beetles (Meloidae).     

Substance P-like immunoreactive fibers in the frog taste organs

In the frog tongue, substance P(SP)-like immunoreactive fibers were consistently present in each fungiform papilla, which contained the gustatory apparatus. Numerous SP-like immunoreactive fibers were usually distributed in the periphery of the gustatory disc and formed a varicose meshwork among the ciliated cells encircling the gustatory disc. SP-like immunoreactive fibers were rarely evident inside the gustatory disc. The role of SP-containing fibers in the frog taste organ was discussed.     

Substance P-like immunoreactive fibers in the frog taste organs

Summary In the frog tongue, substance P(SP)-like immunoreactive fibers were consistently present in each fungiform papilla, which contained the gustatory apparatus. Numerous SP-like immunoreactive fibers were usually distributed in the periphery of the gustatory disc and formed a varicose meshwork among the ciliated cells encircling the gustatory disc. SP-like immunoreactive fibers were rarely evident inside the gustatory disc. The role of SP-containing fibers in the frog taste organ was discussed.     

Excitatory effect of the superior colliculus on the motor neurons of extra-ocular muscles of cats]

The synaptic actions which might underline the caccadic eye movements induced by stimulation of the superior colliculus have been studied in the unanesthetized cat "encéphale isolé". Intracellular recordings of extraocular muscle medial rectus motoneurons have revealed a minimally disynaptic excitatory projection from the superior colliculus to the ipsilateral medial rectus motoneurons (latency 1.3 to 2.6 msec).     

Gustatory sensitivity of an anuran to cantharidin

Summary Glossopharyngeal nerve stimulation of the bullfrog,Rana catesbiana revealed responsiveness to low levels of cantharidin (1.3×10^–6M), providing a first demonstration of neural gustatory sensitivity of an animal to this defensive chemical from blister beetles, (Meloidae).Acknowledgments. Study supported in part by grant AI 02908 from NIH.     

Effects of deneravation and decentralization upon taste buds.

Denervation of vallate papillae results in failure of tactile and gustatory reception at a time when impulse conduction in the distal stump of the glossopharyngeal nerve is still unimpaired; delay of receptor deficit depends on axon length between receptor and axotomy sites; taste buds disappear by 10 days. Decentralization, through intracranial rhizotomy, does not modify lingual receptors structure or function.     

Receptor potential of rat taste cell to potassium benzoate.

Rat taste cells responded to relatively low concentrations of K-benzoate with a hyperpolarization and to the high concentrations with a depolarization. During both responses the membrane resistance of a taste cell decreased. Depolarization elicited by application of a combination of 0.25 M NaCl and 0.05 M K-benzoate was smaller than that by the NaCl alone, indicating a depressant action of K-benzoate.     

Receptor potential of rat taste cell to potassium benzoate

Summary Rat taste cells responded to relatively low concentrations of K-benzoate with a hyperpolarization and to the high concentrations with a depolarization. During both responses the membrane resistance of a taste cell decreased. Depolarization elicited by application of a combination of 0.25 M NaCl and 0.05 M K-benzoate was smaller than that by the NaCl alone, indicating a depressant action of K-benzoate.     

Deletion mapping of a new gustatory mutant inDrosophila melanogaster

Summary A gustatory mutant ofDrosophila melanogaster insensitive to the taste of salt has been isolated. Genetic crosses and a deletion mapping analysis show that this mutation, designatedgust-M ₁ is located in the 93C_3–6-93D_6–7 region of the third chromosome.gust-M ₁ is also insensitive to the taste of quinine sulfate. The behavior of this mutant may be explained by assuming thatgust-M ₁ could be a mutation perturbing functions in the central nervous system affecting the responses to both compounds.     

Speed and consistency of human decisions to swallow or spit sweet and sour solutions

Measurements of the frequency and speed of spitting or swallowing citric acid, sodium saccharin, or mixture solutions, using the taste of one of them as the definition of what was to be spit, revealed that ‘correct’ spits occurred on ≥70% of trials with equal reliability and latency among the liquids, indicating that recognition-based rejection decisions in adult humans are as rapid and consistent for an arbitrary sweet taste as for a sour or mixed taste.     

Speed and consistency of human decisions to swallow or spit sweet and sour solutions.

Measurements of the frequency and speed of spitting or swallowing citric acid, sodium saccharin, or mixture solutions, using the taste of one of them as the definition of what was to be spit, revealed that 'correct' spits occurred on > or = 70% of trials with equal reliability and latency among the liquids, indicating that recognition-based rejection decisions in adult humans are as rapid and consistent for an arbitrary sweet taste as for a sour or mixed taste.     

Criteria for the appearance of post-tetanic potentiation of transmission at central synapses in Helix aspersa.

Long-lasting potentiation of inhibitory post-synaptic potentials occurs at 2 identifiable synapses in Helix brain. It appears only after tetanic stimulation and after a minimum of 20 impulses. Its amplitude and duration depends on the number of stimuli.     

The role of the substantia nigra on the rage reaction elicited by hypothalamic stimulation, in the cat

The effects of substantia nigra stimulation on the rage reaction evoked by hypothalamic activation were studied. The reference value of the rage reaction was the latency of the hissing, which was constant in all animals when hypothalamic stimulation was performed with the same parameters. Simultaneous activation of substantia nigra and hypothalamus determined a significant decrease in hissing latency. The influence of the substantia nigra on the affective components of the aggressive behavior is underlined.     

Criteria for the appearance of post-tetanic potentiation of transmission at central synapses inHelix aspersa

Summary Long-lasting potentiation of inhibitory post-synaptic potentials occurs at 2 identifiable synapses inHelix brain. It appears only after tetanic stimulation and after a minimum of 20 impulses. Its amplitude and duration depend on the number of stimuli.     

Antidromic latency variations of nigral compacta neurones

Summary Variations in the antidromic latency of substantia nigra compacta neurones were commonly observed following striatal stimulation. These results provide electrophysiological evidence for a branched unmyelinated nigrostriatal pathway and demonstrate that the antidromic criterion of constant latency is not valid for this type of pathway.