NEUROPHYSIOLOGY AND NEUROPHARMACOLOGY OF PROJECTIONS FROM ENTORHINAL CORTEX TO STRIATUM IN THE RAT

We studied projections from the entorhinal cortex (Ent) to the striatu m in anesthetized rats using extra- and intracellular recording and mu ltibarrel iontophoresis. The majority of recordings were from the caud ate-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 n eurons, 61% of these tests proved to be excitatory and were often foll owed by inhibitory phases. In contrast to this, only 18% of tests from CPu neurons were excitatory. Intracellular HRP labeling showed that r esponsive cells were medium spiny neurons. During iontophoretic experi ments, application of the glutamatergic AMPA antagonist DNQX could sel ectively decrease or block excitatory responses. The GABA, antagonist bicuculline methiodide increased cellular firing rates and could revea l excitatory responses, suggesting block of a short-latency, short-dur ation inhibitory component. Ejection of the GABA, antagonist CGP-35348 could attenuate a later, longer-duration component of inhibition, The results indicate that the Ent excites striatal neurons at least in pa rt by glutamatergic receptors and suggest that this excitation is foll owed by secondary prolonged GABAergic inhibition.