Synaptic and neurochemical features of calcitonin gene-related peptide containing neurons in the rat accessory optic nuclei

Prenatal expression of purinergic receptor P2X3 in human dorsal root ganglion

The dorsal root ganglion (DRG) is consisted of neurons that relay multiple types of spinal sensory stimuli to the central nervous system. Several neuroactive molecules may be involved in sensory modulation especially pain processing at the DRG, including the purinergic receptor P2X3 and calcitonin-gene-related peptide (CGRP). P2X3 receptor has been considered a promising pharmaceutical target for the development of new pain medicine. Currently, litter is known about the expression of P2X3 in the human DRG. The present study characterized the localization of P2X3 in prenatal human DRG obtained from fetuses at 4-8 gestational months, by comparing to CGRP expression as well as binding pattern of isolectin-B4 (IB4), a marker of small DRG neurons presumably relevant to nociception. P2X3 immunoreactivity (IR) appeared in most neuron-like perikarya, with their numerical density reduced during the gestational period studied. P2X3 IR was co-labeled very commonly with IB4 binding and infrequently with CGRP IR and was not colocalized with IR for the gliocyte marker glutamine synthetase. Together, the data show an early and broad expression of P2X3 in prenatal human DRG neurons, pointing to a biological role of purinergic signaling during the development of spinal sensory system.

Abnormal response of dopaminergic neurons to nicotine without perturbation of nicotinic receptors in alphaCGRP knock-out mice

Alpha-calcitonin gene-related peptide (alphaCGRP) is a neuropeptide with multiple biological properties, including the regulation of nicotinic acetylcholine receptors (nAChRs). We have previously reported a reduction of somatic withdrawal symptoms in alphaCGRP knock-out mice exposed to chronic nicotine, leading us to investigate the contribution of alphaCGRP to the regulations of ventral tegmental area (VTA) neurons and their response to nicotine. The electrophysiological activity of VTA dopaminergic (DA) neurons was recorded in vivo, under anesthesia. These neurons displayed identical spontaneous electrophysiogical activities in wild-type and alphaCGRP-/- mice. However, we found that intravenous administration of nicotine (30 microg/kg) had no significant effect on the activity of DA neurons in alphaCGRP-/- mice, whereas it induced a doubling of the firing rate in wild-type animals. A higher dose (90 microg/kg) produced a significant excitation in both strains, but this effect remained smaller in the mutants. To investigate this difference, we have studied the functional state of nAChRs in wild-type and alphaCGRP-/- mice. Both strains exhibited identical expression of alpha(7) and alpha(4)beta(2) nAChRs as revealed by autoradiographical studies in the VTA. In addition, focal application of acetylcholine on DA neurons recorded by patch-clamp revealed identical currents mediated by nAChRs in mutant animals, as compared to wild-type mice. These data outline the possibility of a contribution of alphaCGRP to the effects of nicotine on DA neurons, by a physiological pathway independent of VTA nicotinic receptors.

The accessory optic system: basic organization with an update on connectivity, neurochemistry, and function

The accessory optic system (AOS) is formed by a series of terminal nuclei receiving direct visual information from the retina via one or more accessory optic tracts. In addition to the retinal input, derived from ganglion cells that characteristically have large receptive fields, are direction-selective, and have a preference for slow moving stimuli, there are now well-characterized afferent connections with a key pretectal nucleus (nucleus of the optic tract) and the ventral lateral geniculate nucleus. The efferent connections of the AOS are robust, targeting brainstem and other structures in support of visual-oculomotor events such as optokinetic nystagmus and visual-vestibular interaction. This chapter reviews the newer experimental findings while including older data concerning the structural and functional organization of the AOS. We then consider the ontogeny and phylogeny of the AOS and include a discussion of similarities and differences in the anatomical organization of the AOS in nonmammalian and mammalian species. This is followed by sections dealing with retinal and cerebral cortical afferents to the AOS nuclei, interneuronal connections of AOS neurons, and the efferents of the AOS nuclei. We conclude with a section on Functional Considerations dealing with the issues of the response properties of AOS neurons, lesion and metabolic studies, and the AOS and spatial cognition.

A review on electron microscopy and neurotransmitter systems

The purpose of this article is to review the contributions of transmission electron microscopy studies to the understanding of brain circuits and neurotransmitter systems. Our views on the microstructure of connections between neurons have gradually changed, and now we recognize that the classical mental image we had on a chemical synapse is no longer applicable to every neuronal connection. We highlight studies that converge to point out that, while the most prevalent fast transmitters in the brain, glutamate and GABA, are stored in small, clear synaptic vesicles (SSV) and released at synapses, neuropeptides are exclusively stored in large dense core vesicles (LDCV) and released extrasynaptically. Amine transmitters are preferentially, but not exclusively, accumulated in LDCV and may be released at synaptic or extrasynaptic sites. We discuss evidence suggesting that axon terminals from pyramidal cortical neurons and dorsal thalamic neurons lack LDCV and therefore could not use neuropeptides as transmitters. This idea fits with the fast, high temporal resolution information processing that characterizes cortical and thalamic function.

Parcellation of the human pretectal complex: a chemoarchitectonic reappraisal

The pretectum is composed of numerous small nuclei that control various oculomotor functions. In all the non-human mammals investigated, the different pretectal nuclei have been named uniformly according to their structural and functional homology. However, the human pretectal nuclei still bear their traditional, in most cases misleading, nomenclature.In order to reveal the presumed chemoarchitectonic similarities between human and non-human pretectal nuclei, neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-immunohistochemistry was performed in the human pretectum, after being utilised successfully for the identification of different pretectal nuclei in the cat. No VIP neurones were observed in the human pretectal area, but numerous NPY cells were found in the 'nucleus lentiformis', and in the anterior bulge of the pretectum, while the 'nucleus sublentiformis' contained an abundant NPY fibre network. Some NPY neurones were present in the 'principal pretectal nucleus' as well. The olivary pretectal nucleus possessed NPY fibres, too. In the accessory optic system, the lateral terminal nucleus contained both NPY and VIP neurones, while in the dorsal terminal nucleus only NPY neurones were found. Our chemoanatomical findings were compared to the standard cytoarchitecture as well. Based on the homotopies in the spatial distribution pattern of NPY neurones in the cat and human pretectum, the current, widely accepted non-human anatomical nomenclature was applied to the morphologically homologous nuclei of the human pretectum. Accordingly, the 'nucleus lentiformis' (which contains numerous NPY cells) corresponds to the nucleus of the optic tract, the 'nucleus sublentiformis' (containing a dense network of NPY fibres) to the posterior pretectal nucleus, and the 'nucleus of the pretectal area' corresponds to the medial pretectal nucleus. We identified the anterior part of the pretectum as the human equivalent of the anterior pretectal nucleus in non-humans, including its two compact and reticular subdivisions. In addition, two accessory optic nuclei were verified chemoarchitectonically in the human brain.