Excitatory actions of homocysteic acid on hippocampal neurons.

The actions of D- and D,L-homocysteate (DH and DLH) on CA3 neurons were studied in thin sections of the guinea pig hippocampus. DH and DLH administered to the stratum radiatum induced large depolarizations in CA3 neurons. The responses to DH and DLH were accompanied by increases in membrane conductance. The amplitudes of the responses increased and decreased, respectively, during tonic hyperpolarizing and depolarizing currents. In neurons injected with Cs+, these responses were reversed in polarity at membrane potentials of -13 to -19 mV. These results indicate that receptors for homocysteate in the hippocampus have different properties from those found in the spinal cord and are quite similar to glutamate receptors.