Intracellular recordings from neurons in dorsolateral thalamic reticular nucleus during capsular, basal ganglia and midline thalamic stimulation

Abstract

Intracellular recordings from neurons in the dorsolateral segment of thalamic reticular nucleus have permitted interpretation of input-output functions of these elements during low-frequency (8/sec) stimulation of internal capsule, head of caudate nucleus, midline thalamus and substantia nigra. The tonic background activity of dorsolateral thalamic reticular neurons influences the background excitability of dorsal thalamic VA-VL neurons and therefore the capacity of the latter to respond to afferent volleys. Activities which arise in the motor cortex, basal ganglia or substantia nigra and which generate relatively short latency excitation of VA-VL neurons also gain access to dorsolateral thalamic reticular neurons. Motor cortex, basal ganglia, substantia nigra and midline thalamus synaptic pathways, through temporally dispersed presynaptic action, induce repetitive discharges in dorsolateral thalamic reticular neurons which project back to VA-VL. Low-frequency induced burst discharges in dorsolateral thalamic reticular neurons result in temporally dispersed release of inhibitory transmitters on VA-VL neurons and, thereby, in the production of prolonged IPSPs in these elements. Neurons in dorsolateral thalamic reticular nucleus are also linked to the motor cortex through relatively simple synaptic pathways: low-frequency activation of these pathways results in the generation of surface negative incrementing-decrementing, recruiting or augmenting responses. These parallel processes to single input volleys to dorsolateral thalamic reticular neurons form, in part, the basis of intrathalamic gaiting of cerebellofugal impulses as well as synchronization of rhythmic activities in the reciprocal thalamocortical circuit during low-frequency stimulation of internal capsule, head of caudate nucleus, midline thalamus and substantia nigra. This mechanism readily accounts for not only the present demonstration of various parallelisms between evoked bursts in dorsolateral thalamic reticular neurons and IPSPs in VA-VL neurons evoked by the same stimuli but also for previous extracellular observations which have revealed that unitary firings in dorsolateral thalamic reticular nucleus are associated with neuronal silence in VL.