Brain research
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The ability of heterotopic noxious stimuli to inhibit the activity of dorsal horn convergent neurones was investigated in both intact anesthetized, and spinal unanesthetized rats. Forty-four convergent neurones in lumbar dorsal horn were recognized by their ability to respond to both noxious and non-noxious natural stimuli and by their characteristic responses corresponding to A- and C-fibre activity following electrical stimulation of their cutaneous excitatory receptive fields on the ipsilateral hindpaw. The application of a sustained pinch to the excitatory receptive field resulted in an initial phasic activation of the neurone, which adapted to a stable tonic level of activity (mean 31.8 +/- 2.2 spikes/s). ⋯ The differences between the inhibitions found in the intact and spinal preparations were subsequently confirmed in a series of experiments in which single convergent neurones were studied before and after the pharmacological blocking of the cervical spinal cord in anaesthetized rats. The results in the spinal preparations provide evidence for the existence of some propriospinal modulatory processes, triggered by the onset of noxious stimulation and acting on convergent neurones. These processes appear to be different from those mediating DNIC, which have been shown to involve supraspinal structures, to concern all convergent neurones, to be very potent and associated with long-lasting post-effects whether the conditioning noxious stimuli are applied to parts of the body proximal or distal to the excitatory receptive field.
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Intracellular recordings were made from neurons of the red nucleus (RN) in cats where the cerebellar cortical effects were removed by chronic ablation of the intermediate part of the anterior lobe of the cerebellum. A prolonged depolarization could be elicited by stimulating the nucleus interpositus (IP) of the cerebellum, nucleus reticularis tegmenti pontis (NRTP) and the nucleus reticularis paramedianus (PMRN). This prolonged depolarization was abolished after cooling the inferior and middle cerebellar peduncles and persisted after ablation of the cerebral sensorimotor cortex. ⋯ The possible constituent neurons of the reverberating circuits were investigated in light of previous physiological investigations of stimulating the NRTP, PMRN, nucleus reticularis lateralis (LRN), nucleus olivaris inferior (IO) and recording EPSPs in RN cells. The RN cells receive axon reflex activation from NRTP and PMRN, and disynaptic excitation from NRTP, PMRN, LRN and IO. Based on these and other available data, the components of the cerebello-precerebellar reverberating circuits are discussed.