Brain research
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Although noradrenergic neurons in the nucleus locus coeruleus are known to project to the spinal cord, these neurons appear to innervate different regions of the spinal cord in Sprague-Dawley rats obtained from two different vendors. Recent anatomical studies demonstrated that the noradrenergic neurons in the locus coeruleus in Sasco Sprague-Dawley rats primarily innervate the ventral horn, whereas Harlan Sprague-Dawley rats have coeruleospinal projections that terminate in the dorsal horn of the spinal cord. This report describes the results of behavioral experiments that were designed to determine the functional significance of these anatomical differences. ⋯ These observations indicate that coeruleospinal noradrenergic neurons in Harlan and Sasco Sprague-Dawley rats have different physiological functions. Thus, electrical stimulation of noradrenergic neurons in the locus coeruleus that innervate the spinal cord dorsal horn (Harlan rats) produces antinociception, but stimulation of coeruleospinal noradrenergic neurons that project to the ventral horn (Sasco rats) does not produce antinociception. It is likely that genetic differences between these outbred stocks of rats account for the fundamental differences in the projections of coeruleospinal neurons and their function in controlling nociception.
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Supraspinal opioid analgesia is mediated in part by connections between the midbrain periaqueductal gray (PAG) and rostral ventral medulla (RVM) which includes the nuclei raphe magnus and reticularis gigantocellularis. Serotonergic 5HT2 and 5HT3 receptor subtypes appear to participate in this pathway since general and selective serotonergic antagonists microinjected into the RVM significantly reduced morphine analgesia elicited from the PAG. ⋯ Naltrexone in the RVM failed to alter basal nociceptive thresholds and none of the opioid antagonists were effective in reducing mesencephalic morphine analgesia when they were microinjected into placements lateral or dorsal to the RVM. These data indicate that mu and delta 2 opioid receptors in the RVM modulate the transmission of opioid pain-inhibitory signals from the PAG.
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Neuron-specific enolase (NSE) is an isoform of the glycolytic enzyme, enolase, and is found in neurons and neuroendocrine cells. We evaluated cerebral immunohistologic and plasma changes in NSE in rats from 2 h to 15 days following permanent or transient middle cerebral artery occlusion (MCAO). At 1-2 days post-MCAO, loss of NSE immunofluorescence from within neurons to the extracellular space was observed in the infarcted areas of all MCAO animals. ⋯ Quantified contralateral forelimb and hindlimb neurological deficits in these animals were significant and persisted for at least 15 days following MCAO but were not observed following sham surgery. These data suggest that MCAO-induced cortical infarction and neurological dysfunction is associated with neuronal depletion and vascular redistribution of brain NSE resulting in a measurable increase in plasma NSE. Such diffusion of NSE into the cerebral vasculature and systemic circulation from ischemic tissue can be expected to serve as a marker for the incidence of cerebral damage in acute and chronic ischemic brain infarcts.
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Comparative Study
Nociceptive C fibre input to the primary somatosensory cortex (SI). A field potential study in the rat.
In the present study, noxious thermal stimulation of the skin with short pulses of CO2-laser radiation was used to identify a cutaneous nociceptive C fibre input to SI and investigate the organization of this input in halothane-nitrous oxide anaesthetized rats. Noxious CO2-laser stimulation of the glabrous skin of the hindpaw consistently evoked late surface positive field potentials in SI (average onset latency 226 ms, peak latency 296 ms). It was demonstrated that these late potentials were evoked by an input from nociceptive C fibres, using a combination of latency measurements, anodal block of A fibre conduction and graded intensities of stimulation. ⋯ The latter potential had a different time course as compared to the nociceptive C fibre potential evoked in laminae III-IV. In conclusion, an input from cutaneous nociceptive C fibres to SI was demonstrated for the first time in animal experiments. The input to SI from tactile receptors and cutaneous C nociceptors were differently organized.
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Comparative Study
Distribution of galanin-immunoreactive cells within sexually dimorphic components of the medial preoptic area of the male and female rat.
A high percentage of galanin-immunoreactive (GAL-I) cells within sexually dimorphic components of the medial preoptic area (MPOA) of the rat also concentrate estrogen and GAL microinjected within the medial preoptic nucleus (MPN) facilitates masculine sexual behavior after testosterone priming. Thus, we determined the distribution of GAL-I cells within the MPOA and their response to gonadal steroids. We report significantly greater numbers of GAL-I cells within the central division of the medial preoptic nucleus (MPNc) and fewer within the anteroventral periventricular nucleus (AVPv), of the gonadectomized male than the gonadectomized female; that GAL-I cell numbers and densities within the AVPv are increased significantly in the intact, testosterone- or estrogen-treated male compared to the gonadectomized male and that GAL-I cell numbers and densities within the MPNc and GAL-I cell densities within the medial division of the MPN (MPNm), are increased significantly by gonadal steroids in rats of both sexes. The results suggest an involvement of galaninergic cells within the MPOA in the regulation of sexually dimorphic, gonadal steroid-sensitive functions.