Input-output relation of transmission through cuneate nucleus

Abstract

1. In decerebrate cats, micro-electrodes were inserted into the cuneate nucleus to stimulate afferent terminals with single shocks of varying intensities. Estimates of the input and output of the nucleus were obtained by integrating antidromic responses in forelimb cutaneous nerves and orthodromic responses in the medial lemniscus. 2. Input-output curves were normally very non-linear, reflecting the high synaptic potency of small inputs. They were fitted readily by power functions, with exponents averaging 0-50. 3. The normal input-output relation rapidly disappeared after interruption of the blood supply. A loss of synaptic efficiency of small inputs was indicated by curves with exponents of greater than or equal to 1; this was associated with a sharp increase in terminal excitability. 4. Within the range of surface temperature 30-40 degrees C, warming made the input-output curves steeper but reduced terminal excitability, whereas cooling had the opposite effect. The efficiency of transmission was thus inversely correlated with terminal excitability. 5. The non-linear shape of cuneate input-output curves is probably not determined by inhibitory control, since picrotoxin depressed rather than enhanced outputs. 6. On the other hand, pentobarbitone made the input-output curves markedly steeper and tended to lower terminal excitability.