Journal of neurophysiology
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1. We examined the contribution of voltage-gated conductances to inhibitory postsynaptic potential (IPSP) effects under current clamp in silent and spiking slowly adapting stretch receptor neurons (SN1s) in the slow receptor muscle of the crayfish Procambarus. The receptor exemplifies the simplest inhibitory neural circuit, with one presynaptic and one postsynaptic neuron. ⋯ In conclusion, IPSP and hyperpolarizing pulse effects were essentially identical, implying that extrasynaptic membrane properties were decisive. Interestingly, net excitatory consequences were usual, effectively increasing sensitivity and reducing the sensory threshold. Pharmacological evidence is provided suggesting that the hyperpolarization-activated current, IQ, and also probably the K+ M-current, the A-current, and the low-threshold, persistent Na+ conductances participate in sag and rebound genesis.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. We studied the degree and source of response variability in different classes of cell in the dorsal lateral geniculate nucleus (dLGN). The response of single cells to a series of contrasts of a stationary flashing light spot was measured. ⋯ No difference of Cv was seen between lagged and nonlagged cells at a given level of response. The difference found at a given level of contrast reflected differences in firing rate of the two cell classes. During PBR stimulation, there was no clear difference between the Cvs of the dLGN cell and its retinal input at a given level of response.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. Noxious stimuli have been shown to produce a diffuse inhibition of nociresponsive neurons in the spinal and trigeminal dorsal horns. The present study sought to extend these electrophysiological studies of diffuse noxious inhibitory controls (DNIC) by determining the effect of a spatially remote noxious stimulus on behavioral measures of nociception. ⋯ Both the hindpaw reflex facilitation and the tail flick reflex inhibition produced by a noxious conditioning stimulus were attenuated in spinally transected rats indicating supraspinal modulation of both reflexes. 3. In addition, and consistent with the work of others, placing the tail in hot water reduced the evoked activity of convergent neurons in both the trigeminal and lumbar spinal dorsal horns. Thus inhibition of the activity of nociresponsive neurons in the dorsal horn is consistent with inhibition of the tail flick reflex, but not with facilitation of the hindpaw withdrawal reflex.(ABSTRACT TRUNCATED AT 250 WORDS)
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1. Brain regions that inhibit nociception can be activated by various environmental stimuli, including prolonged noxious stimuli. The present study tested the effect of such a prolonged noxious stimulus on the activity of nociceptive modulatory neurons in the rostral ventromedial medulla (RVM). ⋯ In contrast, lidocaine inactivation of the RVM completely reversed the hindpaw reflex facilitation produced by tail heat, indicating the involvement of RVM ON-cells in facilitation of this reflex. 4. These data demonstrate that RVM neurons respond in a consistent manner to noxious stimuli whether applied for a brief or prolonged time: ON-cell activity increases and OFF-cell activity decreases. Moreover, the activation of RVM ON-cells produced by a noxious stimulus is sufficient to enhance some nocifensor reflexes, whereas neural structures other than the RVM appear to mediate the antinociceptive effects produced by a prolonged noxious stimulus.