Locus coeruleus-induced potentiation of the perforant path evoked potential in the dentate gyrus of the awake and behaving animal

Abstract

The effects of glutaminergic activation of the pontine nucleus locus coeruleus on the perforant path evoked potential in the dentate gyrus of the awake and behaving animal were investigated. Twenty-two male Long Evans rats received 150-450 nanolitre intracranial injections of .25-.5 M 1-glutamate in the vicinity of the locus coeruleus. Injection sites localized to within 300 μm of the locus coeruleus reliably produced an enhancement (167% of control) of the population spike of the evoked potential. In 50% of these animals, a long-lasting (i.e. greater than 20 minutes) enhancement of the population spike amplitude was observed. Changes in the excitatory postsynaptic potential and population spike onset latency were variable. Injection sites in lobule centralis of the rostral vermis of the cerebellum also produced both short and long-lasting potentiation of the population spike. Behaviors recorded following glutamate application were not correlated with the production of an enhancement. Behaviors were sufficiently heterogeneous that a behavioral profile for locus coeruleus-activated animals could not be ascertained. Norepinephrine-mediated potentiation of granule cell responsivity may represent a neural substrate for the processing and storage of information.