Intrinsic connections of caudate neurons. Locally evoked intracellular responses

Abstract

The intracellular responses of caudate neurons to local single shocks delivered at a distance of 1.5 mm were investigated in anesthetized, paralyzed cats. The majority of cells did not fire spontaneously either when recorded extracellularly or after impalement. Intrinsic stimulation yielded results which are in general agreement with previous extra- and intracellular responses to extrinsic stimulation in the sense that the usual early response was excitatory after about a 10 msec latency and the later effect was inhibition (IPSP) after a latency of 12–22 msec. In many units extracellular spike responses were suppressed following impalement of the neuron but EPSP remained for several minutes thereafter, even in cells which were damaged irreversibly. We suggested that this finding may partly explain the frequent occurence, in this and previous studies, of large EPSP incapable of generating spikes. We did not rule out the existence of IPSP of earlier onset capable of prematurely curtailing the excitatory component of responses, thus possibley accounting for failure of spike response in many neurons. The low degree of spontaneous activity and the apparent ready accommodation to intracellularly delivered pulses would support previous impressions suggesting that caudate neurons are maintained under conditions of marked quiescence by relatively high resting membrane potentials. Further investigation of the effects of intracellularly applied currents are required however to reinforce this contention.