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Physiology Neonatal rat spinal cord slice preparation: postsynaptic effects of neuropeptides on dorsal horn neurons
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followed high frequency stimulation (20-100 Hz) of the nerves. The axons were unmyelinated (conduction velocity 1.02 C 1 S.D., n = 14), had no ongoing discharges and could not be excited by afferent stimuli via a spinal or supraspinal reflex pathway. Therefore, it is likely that these fibers are afferent. The findings support the hypothesis that referred pain may be produced by dichotomizing sensory fibers, one branch passing to visceral organs and the other branch to the site of reference in muscle or skin.
PHYSIOLOGY Neonatal rat spinal cord slice preparation: postsynaptic effects of neuropeptides on dorsal horn neurons. - V. MiletiE and M. RandiE, Develop. Brain Res., 2 (1982) 432-438. The in vitro rat spinal cord slice preparation was utilized for the study on the cellular mechanisms of actions of neuropeptides. In the neonatal rat spinal cord slice preparation responses of the dorsal horn interneurons to iontophoretic or bath application of methionine-enkephalin (ME), substance P (SP) and somatostatin (SS) were found similar to those obtained in intact spinal cord. SP powerfully excited almost all neurons tested, while ME and SS depressed neuronal discharges. Angiotensin II had no effect on dorsal horn units. In the slices perfused with a Ca2+ -free, Mg2+-high Krebs solution the extracellularly recorded effects of ME, SP and SS were not significantly modified, suggesting that the peptides were acting directly on postsynaptic sites. Effects of naloxone upon diffuse noxious inhibitory controls (DNIC) in the rat. - D. De Bars, D. Chitour, E. Kraus, A.H. Dickenson and J.M. Besson, Brain Res., 204 (198 1) 387-402. Neurons, responding to both noxious and innocuous stimuli applied to their cutaneous receptive fields were recorded at the lumbar level in anesthetized intact rats. These cells received Aa and C fiber inputs a shown by electrical stimulation of their receptive fields, and were located in the medial part of the dorsal horn. For 15 units, DNIC were investigated by applying noxious thermal stimuli (52°C) to the distal two-thirds of the tail. This conditioning stimulus induced strong inhibition of the responses to both Aa and C fibers. Post-effects of long duration were commonly observed after cessation of the conditioning stimulus. The systemic injection of naloxone (0.3 mg/kg, i.v.) resulted in a partial reduction in these inhibitory effects for both Aa and C fiber response. 28 convergent units, including the 15 reported above, were recorded to investigate the effect of naloxone upon the unconditioned response. Responses to Aa fiber were unaffected, whereas the responses to C fiber were slightly increased by naloxone. It is suggested that pain transmission is dependent on at least two complementary systems, both involving endogenous opiates. The opposite functional actions of these two systems might explain the bidirectional effects of naloxone upon nociception reported in the literature.
followed high frequency stimulation (20-100 Hz) of the nerves. The axons were unmyelinated (conduction velocity 1.02 C 1 S.D., n = 14), had no ongoing discharges and could not be excited by afferent stimuli via a spinal or supraspinal reflex pathway. Therefore, it is likely that these fibers are afferent. The findings support the hypothesis that referred pain may be produced by dichotomizing sensory fibers, one branch passing to visceral organs and the other branch to the site of reference in muscle or skin.
PHYSIOLOGY Neonatal rat spinal cord slice preparation: postsynaptic effects of neuropeptides on dorsal horn neurons. - V. MiletiE and M. RandiE, Develop. Brain Res., 2 (1982) 432-438. The in vitro rat spinal cord slice preparation was utilized for the study on the cellular mechanisms of actions of neuropeptides. In the neonatal rat spinal cord slice preparation responses of the dorsal horn interneurons to iontophoretic or bath application of methionine-enkephalin (ME), substance P (SP) and somatostatin (SS) were found similar to those obtained in intact spinal cord. SP powerfully excited almost all neurons tested, while ME and SS depressed neuronal discharges. Angiotensin II had no effect on dorsal horn units. In the slices perfused with a Ca2+ -free, Mg2+-high Krebs solution the extracellularly recorded effects of ME, SP and SS were not significantly modified, suggesting that the peptides were acting directly on postsynaptic sites. Effects of naloxone upon diffuse noxious inhibitory controls (DNIC) in the rat. - D. De Bars, D. Chitour, E. Kraus, A.H. Dickenson and J.M. Besson, Brain Res., 204 (198 1) 387-402. Neurons, responding to both noxious and innocuous stimuli applied to their cutaneous receptive fields were recorded at the lumbar level in anesthetized intact rats. These cells received Aa and C fiber inputs a shown by electrical stimulation of their receptive fields, and were located in the medial part of the dorsal horn. For 15 units, DNIC were investigated by applying noxious thermal stimuli (52°C) to the distal two-thirds of the tail. This conditioning stimulus induced strong inhibition of the responses to both Aa and C fibers. Post-effects of long duration were commonly observed after cessation of the conditioning stimulus. The systemic injection of naloxone (0.3 mg/kg, i.v.) resulted in a partial reduction in these inhibitory effects for both Aa and C fiber response. 28 convergent units, including the 15 reported above, were recorded to investigate the effect of naloxone upon the unconditioned response. Responses to Aa fiber were unaffected, whereas the responses to C fiber were slightly increased by naloxone. It is suggested that pain transmission is dependent on at least two complementary systems, both involving endogenous opiates. The opposite functional actions of these two systems might explain the bidirectional effects of naloxone upon nociception reported in the literature.