Discharge pattern and corticofugal control of OFF/ON-OFF neurons in the guinea pig auditory thalamus: an in-vivo intracellular study

Abstract

Neuronal responses to noise bursts/pure tones in medial geniculate body (MGB) were examined intracellularly while the auditory cortex of the pentobarbital-sodium-anesthetized guinea pig was activated through electrical current. 24 OFF and 7 ON-OFF neurons were recorded in the MGB. The OFF response ranged from 1 to 15 spikes. 9 neurons showed an inhibition during the presence of the acoustic stimulus and followed by a low-threshold-calcium spike burst after the offset of the stimulus. The buildup and decay of the low-threshold spike/burst of OFF responses were different from those of the ON responses, suggesting that different neural mechanisms are involved in generating the responses. Of two neurons tested with the duration selectivity, both were long-duration-selective. Cortical activation elicited either an elevation or a depression in the membrane potential of the thalamic OFF/ON-OFF neurons with long time constants up to 1 s. Cortical activation could cause facilitations/inhibitions in both the ON and OFF components, or either ON or OFF components depending on the resting membrane potential. Supported by Research Grants Council of Hong Kong: PolyU5211/99M