Nervous system

About: Nervous system is a research topic. Over the lifetime, 16729 publications have been published within this topic receiving 847181 citations.

The shapes of sensory and motor neurones and the distribution of their synapses in ganglia of the leech: a study using intracellular injection of horseradish peroxidase.

Abstract: Three types of sensory neurones and two kinds of motor neurones in the segmental ganglion of the leech were examined with the light and electron microscope after intracellular injection of horseradish peroxidase (HRP) for a histological marker. The aim was to develop a method for identifying the synapses of specific cells in the ganglion’s complex neuropil and to form a picture of their distribution and structure. Reaction of HRP with different benzidine derivatives produces opaque and electron dense deposits. For light microscopy a blue stain is formed that makes processes visible in whole mounts millimeters away from the injection site at the soma. The reaction product for electron microscopy is distributed throughout the cytoplasm, yet ultrastructural details are preserved. The sensory neurones that respond specifically to touch or pressure or noxious mechanical stimuli to the skin share in their branching pattern a number of common features. A single process arising from each cell body forms large primary branches that pass through the neuropil and leave the ganglion by the ipsilateral connectives and roots. Within the neuropil these branches give rise to numerous smaller secondary processes. In contrast, the annulus erector and large longitudinal motoneurones send their main process across the ganglion to bifurcate and enter the contralateral roots. Secondary processes of the motoneurones are highly branched and more numerous than those of the sensory cells. Each type of sensory and motor cell is distinguished by the shape, length and distribution of its secondary processes. Secondary processes of sensory neurones exhibit numerous swellings and irregularly shaped fingers. Electron micrographs show that the sensory neurones make synapses at these specializations, each of which contacts several postsynaptic processes. The sensory neurones receive inputs at the same fingers and swellings, an arrangement suggesting that regions within a cell’s arborization may function semi-autonomously. The main process and large branches of the two motor neurones are studded with spines a few micrometres long and a fraction of a micrometre in diameter. Vesicle-containing varicosities from other cells make synaptic contact primarily with the spines, which themselves have few vesicles. These two motor neurones are largely, if not entirely, postsynaptic to other neurones within the leech nervous system.

Neuronal and nonneuronal expression of neurotrophins and their receptors in sensory and sympathetic ganglia suggest new intercellular trophic interactions

Abstract: Nerve growth factor promotes the survival of populations of sensory and sympathetic neurons. Although ganglia have been used for classical assays of neurotrophin action, knowledge is incomplete regarding the spatial arrangements through which neurotrophins are delivered to responsive cells within the ganglia and their attached nerve trunks. Whereas populations of ganglionic neurons may be capable of responding to a particular neurotrophin in vitro, the spectrum of receptor components and neurotrophins expressed by the various neuronal and nonneuronal cells comprising the ganglia in adult rats remains to be elucidated in vivo. Brain-derived neurotrophic factor (BDNF) mRNA was expressed by a population of small to medium sized neurons in all sensory ganglia except in the mesencephalic nucleus of the trigeminal nerve. Interestingly, BDNF immunoreactivity was detected in a more widespread population of neurons of these ganglia, as well as in scattered satellite cells of both sensory and sympathetic ganglia. These nonneuronal cells also expressed mRNA encoding a truncated form of the BDNF receptor, trkBtrunc, and full-length transcripts of trkB appeared to be confined to neuronal populations. Several other components of neurotrophin receptors (low-affinity neurotrophin receptor, trk, and trkC) were prominently expressed by different populations of neuronal cells in sympathetic and sensory ganglia, but they were not detected in nonneuronal cells. Neither nerve growth factor nor neurotrophin-3 mRNAs were detected in these ganglia. Unexpectedly, BDNF and trkBtrunc expression was detected in oligodendrocytes myelinating the central processes of sensory neurons. Schwann cells did not express detectable quantities of either entity, thereby establishing a dramatic boundary delineated by neurotrophin/neurotrophin receptor expression that coincided with the interface between the oligodendroglia of the central nervous system (CNS) and Schwann cells of the peripheral nervous system (PNS). Localization of BDNF expression to an additional population of nonneuronal cells--satellite cells within sensory and sympathetic ganglia--suggest a more extensive role for neurotrophic factors than originally encompassed by the target-derived neurotrophic-factor-concept paradigm. These data support the hypothesis of a possible autocrine or paracrine trophic interaction between populations of neuronal and nonneuronal cells in the peripheral nervous system. BDNF expression in oligodendrocytes but not in Schwann cells at the CNS/PNS junction may provide an additional means of maintaining cell-appropriate connections in the nervous system.