Uptake and transport of exogenous peroxidase in the masticatory muscles of cats. Localization of ganglionic neurons]

Retrograde axonal transport of Horseradish peroxydase (HRP) has been used to trace the cells of origin of proprioceptive fibers in jaw-closing and jaw-opening muscles. After injection of HRP in young cats' masticatory muscles (masseteric, temporal, pterygoid, mylohyoid and digastric) labelled neurons were found in the ipsilateral semi-lunar ganglion and trigeminal mesencephalic nucleus. It is concluded that sensory endings are present in jaw-opening as in jaw-closing muscles; possibly the afferent fibers from muscle endings of the opener muscles have their somata in the mesencephalic nucleus, afferent fibers from tendinous receptors in the semi-lunar ganglion.     

Electrical responses to taste chemicals across the dorsal epithelium of bullfrog tongue

Stimulation of the bullfrog tongue with taste chemicals produced a slow change in transepithelial potential difference across the dorsal epithelium. The potential profile was in many respects similar to that of the intracellularly recorded potential changes in taste cells and to the activity of taste fibers in frogs.     

Electrical responses to taste chemicals across the dorsal epithelium of bullfrog tongue

Summary Stimulation of the bullfrog tongue with taste chemicals produced a slow change in transepithelial potential difference across the dorsal epithelium. The potential profile was in many respects similar to that of the intracellularly recorded potential changes in taste cells and to the activity of taste fibers in frogs.     

Determination of the connectivity of newborn neurons in mammalian olfactory circuits

The mammalian olfactory bulb is a forebrain structure just one synapse downstream from the olfactory sensory neurons and performs the complex computations of sensory inputs. The formation of this sensory circuit is shaped through activity-dependent and cell-intrinsic mechanisms. Recent studies have revealed that cell-type specific connectivity and the organization of synapses in dendritic compartments are determined through cell-intrinsic programs already preset in progenitor cells. These progenitor programs give rise to subpopulations within a neuron type that have distinct synaptic organizations. The intrinsically determined formation of distinct synaptic organizations requires factors from contacting cells that match the cell-intrinsic programs. While certain genes control wiring within the newly generated neurons, other regulatory genes provide intercellular signals and are only expressed in neurons that will form contacts with the newly generated cells. Here, the olfactory system has provided a useful model circuit to reveal the factors regulating assembly of the highly structured connectivity in mammals.     

Information processing along the course of a visual interneuron.

Locust ocellar retinal cells are innervated by giant second order cells, 2 mm long, which show discrete zones of integration along their course, including a major zone in the axonal length of the neuron. The complex synaptic arrangements which exist between higher-order afferent and efferent cells and these second order cells along their course suggests that transmission takes place by the electrotonic spread of slow potentials. The size and accessibility of these visual interneurons offers a unique preparation for examining mechanisms of graded synaptic transmission.     

Information processing along the course of a visual interneuron

Summary Locust ocellar retinal cells are innervated by giant second order cells, 2 mm long, which show discrete zones of integration along their course, including a major zone in the axonal length of the neuron. The complex synaptic arrangements which exist between higher-order afferent and efferent cells and these second order cells along their course suggests that transmission takes place by the electrotonic spread of slow potentials. The size and accessibility of these visual interneurons offers a unique preparation for examining mechanisms of graded synaptic transmission.     

Espins and the actin cytoskeleton of hair cell stereocilia and sensory cell microvilli

The espins are novel actin-bundling proteins that are produced in multiple isoforms from a single gene. They are present at high concentration in the parallel actin bundle of hair cell stereocilia and are the target of deafness mutations in mice and humans. Espins are also enriched in the microvilli of taste receptor cells, solitary chemoreceptor cells, vomeronasal sensory neurons and Merkel cells, suggesting that espins play important roles in the microvillar projections of vertebrate sensory cells. Espins are potent actin-bundling proteins that are not inhibited by Ca2+. In cells, they efficiently elongate parallel actin bundles and, thereby, help determine the steadystate length of microvilli and stereocilia. Espins bind actin monomer via their WH2 domain and can assemble actin bundles in cells. Certain espin isoforms can also bind phosphatidylinositol 4,5-bisphosphate, profilins or SH3 proteins. These biological activities distinguish espins from other actin-bundling proteins and may make them well-suited to sensory cells.     

Destruction of afferent nerve terminals in the inner ear of frog by aminooxyactic acid.

The drug aminooxyacetic acid, which inhibits GABA-transaminase, destroys the afferent nerve ending in the inner ear of the frog. The efferent nerve endings and the sensory cells are not affected.     

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     

Destruction of afferent nerve terminals in the inner ear of frog by aminooxyacetic acid

Summary The drug aminooxyacetic acid, which inhibits GABA-transaminase, destroys the afferent nerve endings in the inner ear of the frog. The efferent nerve endings and the sensory cells are not affected.     

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.     

Neuropeptides in pelvic afferent pathways

Neurochemical and pharmacological experiments have raised the possibility that several neuropeptides including, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), substance P, calcitonin gene-related peptide (CGRP), neurokinin A, cholecystokinin (CCK) and opioid peptides may be transmitters in afferent pathways to the pelvic viscera. These substances are widely distributed in: 1) nerve fibers in the pelvic organs, 2) visceral afferent neurons in the lumbosacral dorsal root ganglia and 3) at sites of afferent termination in the spinal cord. Double staining immunocytochemical techniques have shown that more than one peptide can be localized in individual visceral afferent neurons and that neuronal excitatory (VIP, substance P, CCK) and inhibitory peptides (leucine enkephalin) can coexist in the same afferent cell. Studies with the neurotoxin, capsaicin, indicate that peptidergic afferent pathways are involved in the initiation of central autonomic reflexes as well as peripheral axon reflexes which modulate smooth muscle activity, facilitate transmission in automatic ganglia and trigger local inflammatory responses.     

Neuropeptides in pelvic afferent pathways

Summary Neurochemical and pharmacological experiments have raised the possibility that several neuropeptides including, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), substance P, calcitonin gene-related peptide (CGRP), neurokinin A, cholecystokinin (CCK) and opioid peptides may be transmitters in afferent pathways to the pelvic viscera. These substances are widely distributed in: 1) nerve fibers in the pelvic organs, 2) visceral afferent neurons in the lumbosacral dorsal root ganglia and 3) at sites of afferent termination in the spinal cord. Double, staining immunocytochemical techniques have shown that more than one peptide can be localized in individual visceral afferent neurons and that neuronal excitatory (VIP, substance P, CCK) and inhibitory peptides (leucine enkephalin) can coexist in the same afferent cell. Studies with the neurotoxin, capsaicin, indicate that peptidergic afferent pathways are, involved in the initiation of central autonomic reflexes as well as peripheral axon reflexes which modulate smooth muscle activity, facilitate transmission in automatic ganglia and trigger local inflammatory responses.     

Mechanisms of glial-guided neuronal migration in vitro and in vivo

Summary Our laboratory has developed an in vitro model system in which glial-guided neuronal migration can be observed in real time. Cerebellar granule neurons migrate on astroglial fibers by apposing their cell soma against the glial arm, forming a specialized migration junction, and extending a motile leading process in the direction of migration. In vitro assays indicate that the neuronal antigen astrotactin functions as a neuron-glia ligand, and is likely to play a role in the movement of neurons along glial fibers. In heterotypic recombinations of neurons and glia from mouse cerebellum and rat hippocampus, neurons migrate on heterotypic glial processes with a cytology, speed and mode of movement identical to that of neuronal migration on homotypic glial fibers, suggesting that glial fibers provide a permissive pathway for neuronal migration in developing brain. In vivo analyses of developing cerebellum demonstrate a close coordination of afferent axon ingrowth relative to target cell migration. These studies indicate that climbing fibers contact immature Purkinje neurons during the migration and settling of Purkinje cells, implicating a role for afferents in the termination of migration.     

Chemoelectrical signal transduction in olfactory sensory neurons of air-breathing vertebrates

When odorants bind to the sensory cilia of olfactory sensory neurons, the cells respond with an electrical output signal, typically a short train of action potentials. This review describes the present state of knowledge about the olfactory signal transduction process. In the last decade, a set of transduction molecules has been identified which help to explain many aspects of the sensory response. Odor-induced second-messenger production, activation of transduction channels, the central role of the ciliary Ca²⁺ concentration, as well as mechanisms that mediate adaptation, are all qualitatively understood on the basis of a consistent scheme for chemoelectrical transduction. This scheme, although necessarily incomplete, can serve as a working model for further experimentation which may reveal kinetical aspects of signal transduction processes in olfactory sensory neurons.     

Mechanisms of glial-guided neuronal migration in vitro and in vivo

Our laboratory has developed an in vitro model system in which glial-guided neuronal migration can be observed in real time. Cerebellar granule neurons migrate on astroglial fibers by apposing their cell soma against the glial arm, forming a specialized migration junction, and extending a motile leading process in the direction of migration. In vitro assays indicate that the neuronal antigen astrotactin functions as a neuron-glia ligand, and is likely to play a role in the movement of neurons along glial fibers. In heterotypic recombinations of neurons and glia from mouse cerebellum and rat hippocampus, neurons migrate on heterotypic glial processes with a cytology, speed and mode of movement identical to that of neuronal migration on homotypic glial fibers, suggesting that glial fibers provide a permissive pathway for neuronal migration in developing brain. In vivo analyses of developing cerebellum demonstrate a close coordination of afferent axon ingrowth relative to target cell migration. These studies indicate that climbing fibers contact immature Purkinje neurons during the migration and settling of Purkinje cells, implicating a role for afferents in the termination of migration.     

An initial phasic depolarization exists in the receptor potential of taste cells.

When frog taste cells were stimulated by varying salts after adaptation to water, quinine or acetic acid, a phasic depolarization appeared initially in the receptor potential of taste cells. The initial transient depolarization may be related to the enhancement of an initial phasic response in the taste nerve.     

Peptidergic innervation of the temporomandibular disk in the rat

Summary The peptidergic innervation of the temporomandibular disk was investigated in the postnatal young rat by using an indirect immunofluorescence method. Calcitonin gene-related peptide-containing nerve fibers were located around the blood vessels and terminated as free nerve endings in the disk. These nerve fibers may be of a sensory nature.