Abstract
The effects of hypercarbia on afferent inputs and synaptic transmission in the cuneate nucleus were studied in decerebrate cats. Stimulation with microelectrodes placed in the cuneate nucleus and/or dorsal column evoked antidromic potentials in the superficial radial nerve; stimulation of afferent fibres in the forelimb, dorsal column, or cuneate nucleus evoked orthodromic responses in the medial lemniscus. Small increases of inspired C02 ( ≦ 5% ) often increased synaptic transmission and the excitability of afferent fibres. Further increases of Pco2 depressed transmission and terminal excitability, while producing considerably smaller changes in postsynaptic excitability. CO2 had no obvious effect on the inhibition of orthodromic transmission produced by afferent nerve interaction, but markedly depressed the dorsal column reflexes. The efficiency of synaptic transmission, as estimated from the input-output relation of the cuneate, was maintained at individual active synapses. It is suggested that C02 does not depress release of transmitter at this synapse, and that the changes in transmission are effected mainly by presynaptic events, possibly by block of conduction in the intraspinal afferent fibres and/or their terminals.
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