Projections from the rat cuneiform nucleus to the A7, A6 (locus coeruleus), and A5 pontine noradrenergic cell groups.

Stimulation of neurons in the cuneiform nucleus (CnF) produces antinociception and cardiovascular responses that could be mediated, in part, by noradrenergic neurons that innervate the spinal cord dorsal horn. The present study determined the projections of neurons in the CnF to the pontine noradrenergic neurons in the A5, A6 (locus coeruleus), and A7 cell groups that are known to project to the spinal cord. Injections of the anterograde tracer, biotinylated dextran amine in the CnF of Sasco Sprague-Dawley rats labeled axons located near noradrenergic neurons that were visualized by processing tissue sections for tyrosine hydroxylase-immunoreactivity.

Substance P induces the reversible formation of varicosities in the dendrites of rat brainstem neurons.

This study investigated the ability of substance P (Sub P) to induce dendritic varicosities (DVs) or beads in neurons of the rostral ventromedial medulla (RVM) of the rat. Microinjection of 5-200 pmol Sub P in the RVM produced a concentration-dependent increase in the number of DVs in distal dendrites of RVM neurons that were immunoreactive for the neurokinin-1 receptor, but not serotonin. The effect was reversible, as DVs were essentially absent 2 and 4h after microinjection.

Nociceptive responses to high and low rates of noxious cutaneous heating are mediated by different nociceptors in the rat: electrophysiological evidence.

Behavioral nociceptive responses evoked by relatively high rates of noxious radiant skin heating appear to be mediated by A delta nociceptor activation, whereas responses evoked by low rates of skin heating appear to be mediated by the activation of C-fiber nociceptors. This hypothesis was confirmed by the results of single unit recordings of A delta and C nociceptive afferent fibers isolated from the saphenous nerves of pentobarbital anesthetized rats. Heating the hind paw skin of the rat at a relatively high rate of 6.

Nociceptive responses to high and low rates of noxious cutaneous heating are mediated by different nociceptors in the rat: behavioral evidence.

Several lines of evidence suggest that different classes of nociceptive afferents mediate the responses produced by different rates of noxious skin heating. More specifically, low skin heating rates evoke nociceptive responses that appear to be mediated by the activation of capsaicin-sensitive C-fiber nociceptors, whereas high skin heating rates appear to produce responses mediated by the activation of other nociceptors. This hypothesis was examined by both electrophysiological and behavioral experiments.

Characterization of the foot withdrawal response to noxious radiant heat in the rat.

The rat foot withdrawal response to noxious radiant heat has been used as a model of nociception that is particularly useful for measurements of unilateral changes in nociceptive responses. The purpose of these studies was to characterize the foot withdrawal response to graded rates of noxious skin heating. Response latencies and both surface and subsurface temperatures produced by 6 different intensities of radiant heat were measured to determine whether response latency is an appropriate measure of nociceptive threshold.

Antinociception induced by electrical stimulation of spinally projecting noradrenergic neurons in the A7 catecholamine cell group of the rat.

Recent anatomical evidence indicates that the pontine A7 catecholamine cell group provides the major noradrenergic innervation of the spinal cord dorsal horn (laminae I-IV). The experiments described in this report were designed to determine if these neurons modulate nociception at the level of the spinal cord. To this end, the antinociceptive effect of electrical stimulation applied at various sites along several tracks through the dorsolateral pontine tegmentum was determined in lightly anesthetized rats.

Hypoalgesia following microinjection of noradrenergic antagonists in the nucleus raphe magnus.

The influence of the noradrenergic input to the nucleus raphe magnus (NRM) on the capacity of this nucleus to modulate nociceptive threshold was investigated in rat by microinjection of noradrenergic (NA) antagonists in the NRM. The distribution of NA terminals associated with the NRM was visualized histochemically using a glyoxylic acid-induced fluorescence technique. Microinjection of 5.