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Nervous tissue consisting of a fibrous network of nonmyelinated nerve fibers; gray matter with few nerve cell bodies; usually a region of synapses between axons and dendrites.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(1) An obsolete term designating a fibrous nerve tissue structure that is found predominantly in invertebrates. The supposedly interconnected nerve fibers form a continuous cytoplasmic network that resembles a syncytium. This use of the term “neuropil” does not accurately reflect the microstructure of the nervous system. (See.)

(2) The fibrous nerve tissue structure in which synaptic contacts between neuronal outgrowths are concentrated.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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In addition, only a small number of DA-ir nerve fibers were detected throughout the neuropils in the ventral horn of the pleuropedal ganglion (Fig.
While the immunoreactive 5-HT and FMRF-amide neurons were observed in all three ganglia, the immunoreactive nerve fibers containing 5-HT were found concentrated in the neuropils of the ganglia, as well as in musculature of the head, buccal, and foot regions, whereas FMRF-amide fibers were only found in the neuropils and around the hemolymph sacs.
To explore further histological structure of the central neuropil region, we utilized transmission electron microscopic analyses of the cell body regions.
Abbreviations: AGB, antennular grooming behavior; ASW, artificial seawater; DW, distilled water; LAN, lateral antennular neuropil; L-glu, L-glutamate; OL, olfactory lobe; SE, squid extract.
All projections from the precerebral ganglia and some nerves from the head-part converge into these neuropils. We name these distinct regions the first to fourth neuropil compartments of the anterior lobe (np1-4).
In contrast, no cellular elements displaying GLU-L immunoreactivity could be found during embryogenesis, apart from a few sensory elements localized in the tail and a strong but partly undifferentiated immunoreactivity in the ganglion neuropils. An especially intriguing observation is the sudden appearance of numerous GLUergic sensory cells by the time of hatching (P1 juvenile stage) at certain rostral and caudal regions of the periphery, such as the lips, tentacle, lateral foot, and tail.
This region of glomerular neuropil has proved to be enigmatic in both its functional significance and its capricious appearance across taxa (Sandeman and Sandeman, 1994; Sandeman et al., 1995; Sullivan and Beltz, 2004, 2005).
In electron microscopy studies (Morganelli and Sherman, 1987, Homarus; Mirolli et al., 1987, Portunus), synapses that were found extensively in neuropils throughout the CG had terminals with vesicles similar to those associated with inhibitory synapses on crustacean muscle (Atwood, 1976).
There is evidence that mechanoreceptor neurons and chemoreceptor neurons from bimodal sensilla on the antennules project to the same central neuropils (Schmidt et al., 1992; Schmidt and Ache, 1996a), but it is not known if their maps are overlapping as in some insects (Newland et al., 2000), or what is the spatial relationship between projections from mechanoreceptor neurons and chemoreceptor neurons from the same sensillum.
We find that the central nervous system is made up of about 2000 neurons and that it contains regionalized neuropils, many of which are linked to peripheral sense organs.
In decapods, as in insects, this pathway is composed of two elements: bilateral glomerular neuropils of the deutocerebrum, where olfactory afferents transmit information onto local interneurons and projection neurons (antennal lobes in insects; olfactory lobes in decapods); and bilateral second-order neuropils of the protocerebrum, to which the projection neurons ascend (mushroom bodies in insects; hemiellipsoid bodies in decapods) (e.g., Boeckh et al., 1984; Blaustein et al., 1988; Mellon et al., 1992).
We suggest that the motor program for AGB resides in these neuropils. Although the tuning of these chemosensory neurons has not been studied in P.