Journal of neurophysiology
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1. Intravenous administration of 1.0 mg/kg of morphine produces inhibition of the nociceptive tail-flick (TF) reflex, hypotension, and bradycardia in the pentobarbital-anesthetized rat. The present experiments examined peripheral, spinal, and supraspinal relays for inhibition of the TF reflex and cardiovascular responses produced by morphine (1.0 mg/kg iv) in the pentobarbital-anesthetized rat using 1) bilateral cervical vagotomy, 2) spinal cold block or mechanical lesions of the dorsolateral funiculi (DLFs), or 3) nonselective local anesthesia or soma-selective lesions of specific CNS regions. ⋯ In all these cases, the microinjections failed to reveal a sustained pressor response as was observed with bilateral cervical vagotomy. Similar microinjections into the PAG failed to affect the depressor response produced by morphine. 6. The lidocaine and ibotenic acid microinjection treatments also showed that the bradycardic response produced by morphine depends on the integrity of the NTS, RMM, RVLM, and possibly the DLP, but not the PAG or VLPT.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. The activity of primary afferent axons was recorded in rats that had received a chronic constriction injury (CCI) to the common sciatic nerve. The CCI gives rise to a painful peripheral neuropathy that is characterized by allodynia, hyperalgesia, and, probably, spontaneous pain (or dysesthesia). ⋯ Both of the two spontaneously discharging C-fibers conducted through the injury. The frequency of the spontaneous discharge of the myelinated fibers ranged from 10 to 50 Hz and was usually regular or bursting. 5. Intravenous administration of gallamine triethiodide (Flaxedil), a K+ channel blocker, either induced activity in previously silent fibers or increased the frequency of spontaneous activity in 50% (21/42) of A beta fibers and 19% (3/16) of A delta fibers.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. The purpose of the present study was to compare the responsiveness unmyelinated cutaneous units in vivo and in vitro and to determine the proportion of primary afferents innervating the rat hairy skin that do not respond to transient mechanical or thermal stimuli. We have adopted electrical search strategies to locate the terminal arborization of unmyelinated fibers before testing the sensitivity to adequate stimuli. 2. ⋯ However, in vivo and in vitro, part of unmyelinated units are initially unresponsive even to noxious forms of stimulation. Because those unresponsive units were also encountered in sympathectomized preparations, and because some units can be recruited with repeated noxious stimuli or inflammatory agents, it is unlikely that all of them are sympathetic efferents. The same substances that cause sensitization of "normal" nociceptors are capable of recruiting initially unresponsive unmyelinated afferents.
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1. In the companion paper, we described a state of hypersensitivity that developed in dorsal horn wide dynamic range (WDR) neurons in rats after transient spinal cord ischemia. Thus the WDR neurons exhibited lower threshold and increased responses to low-intensity mechanical stimuli. ⋯ The GABAA receptor agonist muscimol (1 mg/kg ip) did not influence the response of WDR neurons in either normal or allodynic animals. 5. The present results demonstrated that the GABAB agonist baclofen is effective in reversing the hypersensitivity of dorsal horn WDR neurons to low-intensity mechanical stimulation after transient spinal cord ischemia, indicating that dysfunction of the GABAergic inhibitory system may be responsible for the development of neuronal hypersensitivity. 6. It is suggested that GABAergic interneurons exert a tonic presynaptic inhibitory control, through baclofen-sensitive B-type GABA receptors, on input from low-threshold mechanical afferents, and that disruption of this control may result in painful reaction to innocuous stimuli (allodynia).
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1. Selective ablations of the hand representations in postcentral cortical areas 3a, 3b, 1, and 2 were made in different combinations to determine each area's contribution to the responsivity and modality properties of neurons in the hand representation in SII. 2. Ablations that left intact only the postcentral areas that process predominantly cutaneous inputs (i.e., areas 3b and 1) yielded SII recording sites responsive to cutaneous stimulation and none driven exclusively by high-intensity or "deep" stimulation. ⋯ Further, area 3b provides the major source of cutaneous input to SII, directly and perhaps also via area 1. 7. The results are in line with accumulating anatomic and electrophysiologic evidence pointing to an evolutionary shift in the organization of the somatosensory system from the general mammalian plan, in which tactile information is processed in parallel in SI and SII, to a new organization in higher primates in which the processing of tactile information proceeds serially from SI to SII. The presumed functional advantages of this evolutionary shift are unknown.