Electrophysiological properties of neurones with CGRP-like immunoreactivity in rat dorsal root ganglia.
Intracellular voltage recordings and fluorescent dye injections were made in vitro in 107 neurons in lumbar dorsal root ganglia (DRGs) of 6- to 8-week-old rats. Calcitonin gene-related, peptide-like immunoreactivity (CGRP-LI) was examined in these neurones, which were divided into C-, A delta-, and A alpha/beta-fibre neurones on the basis of their conduction velocities (CVs). A-fibre neurones with CGRP-LI had significantly longer mean action potential (AP) and afterhyperpolarisation (AHP) durations than those without CGRP-LI. A delta neurones with CGRP-LI had significantly longer AHP durations, slower CVs and slower maximal fibre following frequencies than those without CGRP-LI. They also had longer AP durations (not significant). The largest A delta neurones were CGRP-LI negative, whereas the smaller cells were either positive or negative. A alpha/beta neurones with CGRP-LI also had longer mean APs (not significant) and AHPs (significant) than those without CGRP-LI, and the cell size distributions were similar for positive and negative neurones. Most A-fibre neurones with CGRP-LI had inflections on the falling phase of the somatic AP. Of the A-fibre neurones with such inflections (Ai neurones), those with CGRP-LI had longer AP durations (not significant) and longer AHP durations (significant) than Ai neurones without CGRP-LI, pointing to a functionally distinct subgroup of Ai neurones. There were no significant differences in electrophysiological properties or cell size measurements between C-fibre neurones with and without detectable CGRP-LI. The patterns of electrophysiological properties of A delta neuronal somata with CGRP-LI and of most, but not all, A alpha/beta neuronal somata with CGRP-LI are similar to those reported for cutaneous nociceptors with A fibres in rat (Ritter and Mendell [1992] J. Neurophysiol. 68:2033-2041). Because rat DRG neurones that express CGRP normally also express trkA (Averill et al. [1995] Eur. J. Neurosci. 7:1484-1494), the properties described here of neurones with CGRP-LI are probably the same as those of DRG neurones with trkA.
Lawson
S N
SN
Department of Physiology, University of Bristol, United Kingdom.
McCarthy
P W
PW
Prabhakar
E
E
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis*; D048429:Cell Size; D004996:Ethidium; D005260:Female; D005456:Fluorescent Dyes; D005727:Ganglia, Spinal / Q000737:chemistry* / Q000166:cytology; D007150:Immunohistochemistry; D007546:Isoquinolines; D009412:Nerve Fibers / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
D005456:Fluorescent Dyes; D007546:Isoquinolines; C017475:lucifer yellow; D004996:Ethidium; D015740:Calcitonin Gene-Related Peptide