Interactions of isolated dorsal column and ventral spinal ascending volleys on single neurons in the postcruciate cortex (Sml) of the cat (original) (raw)

Three ascending spinal cord pathways conduct somatic sensory inputs towards the cat somatic sensory cortex: (1) the dorsal column medial lemmscal (DCML) system; (2) the ventral tracts which include spinothalamic, spinobulbar and spinotectal components; and (3) the spinocervical tract (reviewed in refs. 18 and 23). No anatomical or well-controlled physiological data are available on whether the dorsal column and ventral tracts can interact on single neurons m the somatic sensory cortex. Physiological approaches have been hampered by the difficulty of restricting electrical stimulation to one of the three pathways due to their mtraspinal connections z,5,6,o,11,13,2z. A technique combining spinal surgical lesions and localized electrical stimuh was devised for studying interactions between spmally disconnected dorsal column and ventral inputs on single postcruclate cortical (SmI) neurons in cats. Experiments were performed on 18 adult cats, 12 of which were m~tlally anesthetized with chloralose (70 mg/kg, 1.p.) and 6 with Nembutal (36 mg/kg, l.p.) Supplementary doses of Nembutal (10 mg/kg, i.v.) were given as required. All animals were subsequently paralyzed with Flaxedil and artificially respired. In some animals, bilateral pneumothorax was performed to reduce brain pulsations due to respiratory movements. Body temperature, end-t~dal CO2 and blood pressure were monitored and maintained within the physiological range. The pencruciate region of one hemisphere and the first 4 cervical segments were exposed. Additional surgery was necessary to expose the ventral tracts on one side. The usual precautions to keep the exposed cerebral and spinal tissues warm were taken. Extracellular unit recordings were made from the forepaw focus of the postcruciate cortex with glass (3 M NaC1 filled) microelectrodes using conventional electrophysiological equipment. At least 10 photographed observahons were made of each stimulus condition. The size, locus, and nature of the receptive field, as well as unit depth within the cortex, were noted. Electrical stimuli from the output of a Grass ($88