Layer-specific immunocytochemical localization of GABABR1a and GABABR1b receptors in the rat piriform cortex

A peculiar, layer-segregated immunoreactive distribution of GABA(B)R1a and GABA(B)R1b receptor antibodies is present in the piriform cortex of adult rats. The GABA(B)R1a antibody selectively marked the neuropile in layer la, where afferent olfactory fibres and intrinsic GABAergic (gamma-aminobutyric acid) axons terminate on the distal apical dendrites of pyramidal neurons. The GABA(B)R1b antibody was detected in the soma and the large basal dendrites of layer II and III neurons. The pattern of distribution observed supports the hypothesis that (presynaptic) GABA(B)R1a receptors in the superficial molecular layer modulate neurotransmitter release in a feedforward synaptic circuit, whereas GABA(B)R1b (postsynaptic) receptors mediate feedback inhibitory potentials on principal cells.