Do GABA(A) and GABA(B) inhibitory postsynaptic responses originate from distinct interneurons in the hippocampus?

GABAergic inhibition of hippocampal pyramidal cells is mediated by two distinct subtypes of postsynaptic receptors, GABA(A) and GABA(B). Electrical stimulation of inhibitory cells or fibres in the CA1 subfield of the hippocampus yields a biphasic inhibitory postsynaptic potential (IPSP) in pyramidal cells, consisting of an early GABA(A)- and a late GABA(B)-mediated component. CA1 interneurons are a heterogeneous population of cells, which differ on the basis of their morphology, physiological properties, target selectivity onto principal cells, and network connectivity, inhibitory synaptic circuitry appears to be specialized, since feedback inhibition may invoke only postsynaptic GABA(A) receptors, whereas feedforward inhibition may invoke both postsynaptic GABA(B) and GABA(B) receptors. In this review, we examine the evidence for and against the notion that distinct interneurons may be responsible for GABA(A)- and GABA(B)-mediated inhibition. Overall, the evidence suggests that (i) certain interneurons may generate solely GABA(A) inhibition, but the available data do not distinguish whether other interneurons mediate (ii) solely GABA(B) inhibition or (iii) a combination of both GABA(A) and GABA(B).