Much attention has been given to the pelvic nerve afferent innervation of the urinary bladder; however, reports differ considerably in descriptions of afferent receptor types, their conduction velocities, and their potential roles in bladder reflexes and sensation. The present study was undertaken to do a relatively unbiased sampling of bladder afferent fibers of the pelvic nerve in adult female rats. The search stimulus for units to be studied was electrical stimulation of both the bladder nerves and the pelvic nerve. Single-unit activity of 100 L(6) dorsal root fibers, activated by both pelvic and bladder nerve stimulation, was analyzed. Sixty-five units had C-fiber and 35 units had Adelta-fiber conduction velocities. Receptive characteristics were established by direct mechanical stimulation, filling of the bladder with 0.9% NaCl at a physiological speed and by filling the bladder with solutions containing capsaicin, potassium, or turpentine oil. The majority (61) of these fibers were unambiguously excited by bladder filling with 0.9% NaCl and were classified as mechanoreceptors. All mechanoreceptors with receptive fields on the body of the bladder had low pressure thresholds (

The cutaneous receptive properties of unmyelinated (C) fibers of the rabbit's great auricular nerve were determined by single-unit recordings. The majority of C-fiber units could be excited by cutaneous stimulation, and such sensory units fell into three major categories on the basis of responses to mechanical and thermal stimulation of their cutaneous receptive fields: low-threshold mechanoreceptors, nociceptors, or specific thermoreceptors. The majority of afferent elements were nociceptive, and all nociceptors responded to strong mechanical stimulation. Three types of nociceptors could be distinguished by their responses to thermal stimuli. Polymodal nociceptors responded to heat with thresholds of 40-55 degrees C and typically displayed enhanced responses or sensitization after noxious heating of their receptive fields. High-threshold mechanoreceptors failed to respond promptly to heat before noxious cutaneous stimulation which, however, elicited subsequent back-ground activity or sensitivity to heat. A third type of nociceptor responded to cold but not to heat. Low-threshold mechanoreceptors were identified by their brisk responses to very gentle, slowly moving mechanical stimulation of their receptive fields, and were readily distinguished from any element classified as nociceptive by their lower mechanical thresholds. Rapid innocuous warming or cooling excited some of the low-threshold mechanoreceptors. Specific thermoreceptors, both warming and cooling types, were rare, insensitive to mechanical stimulation, and responded to very slight changes in temperature. In contrast to the sensitization to heat, which was characteristic of most nociceptors, specific warming receptors displayed depressed thermal responses after noxious heating of their receptive fields. These results provide further evidence of the similarity of C-fiber receptors innervating hairy skin of different species. Some differences from past reports and additional features are described.

1. The effects of ipsilateral removal of the superior cervical ganglion on the subsequent responsiveness of C-fiber polymodal nociceptors (CPMs) of the ear to close-arterial injections of norepinephrine (NE) were evaluated in adult, anesthetized rabbits. 2. In normal unanesthetized rabbits, the two ears were usually at the same temperature. Immediately after the ganglionectomy, the ipsilateral ear was warmer; however, at the time of electrophysiological recordings (4-23 days) the majority of animals had the ipsilateral ear cooler by > or = 1 degree C, suggestive of denervation supersensitivity. 3. NE (50 ng) did not activate any CPMs (n = 28) from intact animals. 4. Seven of 22 CPMs recorded from sympathectomized ears were activated by NE (50 ng). The responses varied considerably but typically consisted of 2-4 impulses in the 60 s after the NE injection. In some instances, repetitive activity continued for many minutes. Such prolonged discharge differs from the adrenergic responses seen after partial nerve damage. 5. The induction of adrenergic excitability in CPMs by sympathectomy is suggested to be a counterpart to postsympathectomy neuralgia in human beings and a possible part of the mechanism leading to sympathetically related pain states.

The responses of polymodal nociceptors with unmyelinated (C) fibers of the rabbit's great auricular nerve were examined with and without intermittent stimulation of the ipsilateral cervical sympathetic trunk. The receptive field of each polymodal nociceptor was heated twice in a stepwise manner from 30 to 50 or 55 degrees C in 5 degree C steps. For each unit, one heating trial was a control trial and the other was accompanied by sympathetic stimulation. The order of the control and sympathetic stimulation trials and the maximum testing temperature were varied systematically among the units examined. The initial responses of polymodal nociceptors in the first heating trial in the presence of sympathetic stimulation were similar to the responses of units whose first heating was a control trial. Units whose receptive fields were tested to a maximum temperature of 50 degrees C in the first trial displayed enhanced responses to heat in their second trial (sensitization), while units tested initially to 55 degrees C responded less briskly during their second heating trial (depression). However, the occurrence of sympathetic stimulation in the second heating trials had no apparent effect on the responses to heat of sensitized or depressed elements. Alterations in the numbers of impulses, instantaneous frequency, or pattern of impulse activity of individual units could not be attributed to sympathetic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

The cutaneous receptive properties of C-fiber units were studied 1-8 mo after transection and repair of the rabbit's great auricular nerve. The proportions of C-fiber units that could be excited by the cutaneous stimuli known to excite normal C-fiber afferent elements of the same nerve increased with time of recovery and approached the normal range within 5 mo after transection. No evidence was obtained that suggests that any specific receptor type regenerated more rapidly than others. No differences were established between the cutaneous receptive properties of normal and regenerated low-threshold mechanoreceptors or specific thermoreceptors. However, the properties of regenerated polymodal nociceptors were different from those of normal polymodal nociceptors. Mechanical thresholds for regenerated polymodal nociceptors were greater than normal at 2 mo after transection but not later, and nearly 20% of regenerated polymodal units had heat thresholds lower than normal. It is argued that the abnormal properties of some regenerated polymodal nociceptors could explain, in part, the elevated thresholds to noxious mechanical stimulation and the thermal hyperalgesia reported during recovery from nerve transection in man.