Neurophysiology and neuropharmacology of projections from entorhinal cortex to striatum in the rat.

We studied projections from the entorhinal cortex (Ent) to the striatum in anesthetized rats using extra- and intracellular recording and multibarrel iontophoresis. The majority of recording were from the caudate-putamen (CPu) and core of the nucleus accumbens (AcbC). Electrical stimulation of the Ent evoked synaptic responses in 77% of tests with AcbC neurons and 48% of tests with CPu neurons. In the case of AcbC neurons, 61% of these tests proved to be excitatory and were often followed by inhibitory phases. In contrast to this, only 18% of tests from CPu neurons were excitatory. Intracellular HRP labeling showed that responsive cells were medium spiny neurons. During iontophoretic experiments, application of the glutamatergic AMPA antagonist DNQX could selectively decrease or block excitatory responses. The GABAA antagonist bicuculline methiodide increased cellular firing rates and could reveal excitatory responses, suggesting block of a short-latency, short-duration inhibitory component. Ejection of the GABAB antagonist CGP-35348 could attenuate a later, longer-duration component of inhibition. The results indicate that the Ent excites striatal neurons at least in part by glutamatergic receptors and suggest that this excitation is followed by secondary prolonged GABAergic inhibition.