Patterns of responses of neurons in cuneate nucleus to controlled mechanical stimulation of cutaneous velocity receptors in the cat

Abstract

The responses of single cuneate neurons to controlled mechanical stimulation of skin were recorded in cats lightly anesthetized with a nitrous oxide-halothane mixture. The discharge patterns and peripheral receptive-field characteristics were studied in neurons driven by sensitive cutaneous mechanoreceptors, including slowly adapting skin mechanoreceptors. Among cuneate neurons encountered, approximately 46% were driven by guard hair mechanoreceptors, 15% were driven by field receptors and 13% were driven by slowly adapting skin receptors. The rest of the neurons were driven by Pacinian corpuscules, received afferent inputs from several different 1st-order afferents, or were not definitely identified. The discharge pattern in response to a constant-velocity stimulus proved most valuable in describing submodality classes of neurons driven by hair and field receptors since sensitivity of these neurons to dynamic and to static phases of stimulation constitute respective continua and thus preclude sharp separation into distinct groups. The majority of neurons displayed response properties and receptive fields similar to those of 1st-order afferents. A minority of cells had receptive fields that were larger than those of primary afferents, with nearly identical modality and velocity characteristics throughout the receptive field. Inhibition of neuronal firing generated from outside the receptive field was rarely seen, possibly due to anesthetic conditions. In a small number of neurons, irregularities in the discharge were observed that might indicate inhibitory influences originating from within the receptive field.