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 (A(i) 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 A(i) 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] fur. 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. (C) 1996 Wiley-Liss, Inc.

Regulation of early embryonic expression of sodium current in cultured Xenopus laevis myocytes was investigated. In myocytes isolated before innervation and cultured for about 1 day, only 51% expressed sodium current at a mean density of 74 +/- 20 pA/pF (mean +/- SEM; n = 26), inadequately reflecting the functional development of skeletal muscle in vivo at this time. This cell-autonomous expression pattern could be modulated. First, co-culture of myocytes and dissociated neural tissue induced additional sodium current expression (82%; 172 +/- 31 pA/pF, n = 14) and, secondly, removal of calcium from the culture medium reduced sodium current density (13 +/- 6 pA/pF; n = 5). The former results suggest that a diffusible factor released from differentiating neurons is able to initiate the expression of sodium channels in myocytes.

1. Intracellular recordings of action potentials (APs) and after‐hyperpolarizations (AHPs) were made from the L3, L4 and L5 dorsal root ganglia (DRGs) of 6‐ to 8‐week‐old anaesthetized female Wistar rats in vitro at 36.5 +/‐ 1 degree C. Neurones were classified by their conduction velocities (CVs) as A alpha/beta (> 12 m s‐1), A delta (1.3‐12 m s‐1) or C fibre neurones (< 1.3 m s‐1). 2. Following the recording, fluorescent dye was injected intracellularly. Sections of injected neurones were tested for carbonic anhydrase (CA) activity histochemically. Reaction product intensity and cell size were measured. Control experiments showed that intracellular dye, time in vitro, axotomy and electrical stimulation did not affect proportions of CA‐positive neurones or their size distributions. 3. Approximately 28‐30% of DRG neurones were CA positive. Their sizes were approximately normally distributed and covered the entire size range of DRG neurones with no correlation between size and CA intensity. A greater proportion of A alpha/beta cells (62%) than of A delta (32%) or C cells (38%) were CA positive, but CA intensity was not correlated with CV. 4. In A neurones mean AP duration was significantly shorter in CA‐positive cells; for CA‐positive and CA‐negative cells, respectively, these values were 1.6 and 2.8 ms for A delta cells; 1.1 and 1.7 ms for A alpha/beta cells; and were 1.2 and 2.3 ms for all A cells. CA intensity was negatively correlated with AP duration at base in all these groups. 5. Again in A neurones, the mean AHP durations were significantly shorter in the CA‐positive cells; the mean AHP durations to 80% recovery for positive and negative cells were 8.8 and 36 ms, respectively, for A alpha/beta cells and were 8.6 and 26 ms, respectively, for all A cells. CA intensity was negatively correlated with AHP duration in A alpha/beta cells and all A cells together. 6. A fibre cells with the longer AP and AHP durations were all CA negative, while cells with the shorter durations included both CA‐positive and CA‐negative cells. 7. CA‐positive and CA‐negative A fibre neurones therefore have different electrophysiological characteristics. It is suggested that CA‐negative A fibre neurones may have slower somatic firing rates and different sensory functions from the CA‐positive neurones.

Intracellular voltage recordings were made in vitro at 36.5 +/- 1 degrees C from 35 rat lumbar dorsal root ganglion (DRG) neurones with a peripheral conduction velocity (CV) in the C-fibre range (0.3-2.2 m/s). The peripheral nerve (PN) was stimulated in one of three different ways, each delivering single stimuli (0.1-1 ms duration, 2-3-times threshold; maximum 50 V) at a low frequency (0.3 Hz). With each of the three stimulation methods used here a similar proportion of cells (approximately 30%) showed changes, either an abrupt latency change or a soma invasion by two action potentials (APs). Both of these changes were consistent with branching of primary afferent C-fibres in the PN.

This paper reviews and provides new data on the relationship of the peptide content in rat dorsal root ganglion (DRG) neurones to a) the neurofilament content of the soma and b) the conduction velocities of the fibres. The latter involved intracellular recordings made in vitro followed by dye injection and immunocytochemistry. Because neurofilament-poor DRG neurones have C-fibres and A-fibre neurones are neurofilament rich, the soma neurofilament content of peptide containing neurones allowed predictions to be made about their conduction velocity ranges. Substance P-like immunoreactive (SP-LI) neurones were mostly small, neurofilament poor, but a few (15%) were neurofilament rich. From conduction velocity measurements, about half the C-fibre neurones studied and 10% of Aδ-neurones but no Aαδ- neurones showed SP-LI. CGRP-LI neurones were also mainly neurofilament poor neurones, but 32% were neurofilament rich, including small, medium and large neurones. Fibres of CGRP-LI neurones conducted in the C, Aδ or Aαβ ranges. Neurones with somatostatin-LI (SOM-LI) were all neurofilament poor; preliminary data is consistent with SOM-LI neurones having C-fibres.