Hyperpolarization-activated current (Ih): A characterization of subicular neurons in brain slices from socially and individually housed rats

The hyperpolarization and cyclic nucleotide activated current Ih is thought to have a role in rhythmic brain activity that is important in complex behaviors and might be perturbed in some neuropsychiatric diseases. We have used whole-cell voltage and current clamp techniques to characterize Ih in neurons from the subiculum-the major output region of the hippocampal formation. Subicular projection neurons are themselves classifiable as intrinsically bursting (IB) or regular spiking (RS) and Ih is present in both. Given the possible involvement of Ih in neuropsychiatric diseases, we have also characterized Ih in subicular neurons from rats that have been housed in individual cages (though still able to see, smell, and hear other rats) as these rats can display behavioral changes similar to those seen in schizophrenia. Individual housing is associated with a 4.4-mV depolarization of the Ih activation curve (P = 0.0027) and an increase in mean firing rate measured in response to current injection (P = 0.037) specifically in RS neurons and a change in the relative amplitude of Ih between IB and RS neurons. Thus, we have shown significant changes in a current thought to be relevant to psychiatric disease in a partial model of schizophrenia. Its further investigation might reveal chemical targets for novel antipsychotic drugs.