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J Comp Neurol. 2004 Mar 29;471(2):219-40.

Somatotopic organization and functional properties of mechanosensory neurons expressing sensorin-A mRNA in Aplysia californica.

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1
Department of Integrative Biology and Pharmacology, University of Texas-Houston Medical School, Houston, Texas 77030, USA. edgar.t.walters@uth.tmc.edu

Abstract

A previous study reported that a peptide, sensorin-A, is expressed exclusively in mechanosensory neurons having somata in central ganglia of Aplysia. The present study utilized in situ hybridization, staining by nerve back-fill and soma injection, and electrophysiological methods to characterize the locations, numbers, and functions of sensorin-A-expressing neurons and to define the relationships between soma locations and the locations of peripheral axons and receptive fields. Approximately 1,000 cells express sensorin-A mRNA in young adult animals (10-30 g) and 1,200 cells in larger adults (100-300 g). All of the labeled somata are in the CNS, primarily in the abdominal LE, rLE, RE and RF, pleural VC, cerebral J and K, and buccal S clusters. Expression also occurs in a few sparsely distributed cells in most ganglia. Together, receptive fields of all these mechanosensory clusters cover the entire body surface. Each VC cluster forms a somatotopic map of the ipsilateral body, a "sensory aplunculus." Cells in the pleural and cerebral clusters have partially overlapping sensory fields and synaptic targets. Buccal S cells have receptive fields on the buccal mass and lips and display notable differences in electrophysiological properties from other sensorin-A-expressing neurons. Neurons in all of the clusters have relatively high mechanosensory thresholds, responding preferentially to threatening or noxious stimuli. Synaptic outputs to target cells having defensive functions support a nociceptive role, as does peripheral sensitization following noxious stimulation, although additional functions are likely in some clusters. Interesting questions arise from observations that mRNA for sensorin-A is present not only in the somata but also in synaptic regions, connectives, and peripheral fibers.

PMID:
14986314
DOI:
10.1002/cne.20042
[Indexed for MEDLINE]
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