Somatotopic organization and functional properties of mechanosensory neurons expressing sensorin-A mRNA in Aplysia californica.
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.
Department of Integrative Biology and Pharmacology, University of Texas-Houston Medical School, Houston, Texas 77030, USA. edgar.t.walters@uth.tmc.edu
Edgar T
ET
Walters
Michaela
M
Bodnarova
Allen J
AJ
Billy
Michael F
MF
Dulin
Manuel
M
Díaz-Ríos
Mark W
MW
Miller
Leonid L
LL
Moroz
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001048:Aplysia / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D008465:Mechanoreceptors / Q000166:cytology / Q000378:metabolism*; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D009479:Neuropeptides / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis*
D009479:Neuropeptides; D012333:RNA, Messenger; C419310:sensorin A protein, Aplysia