Opioid peptide-like immunoreactivity localized in GABAErgic neurons of rat neostriatum and central amygdaloid nucleus.

Opioid peptide-like (OPL)-immunoreactivity and (the GABA-biosynthetic enzyme) glutamic acid decarboxylase-like (GAD)-immunoreactivity were localized in rat neostriatum and central amygdaloid nucleus (ACE) using a polyclonal sheep antiserum to rat brain GAD and a monoclonal mouse antibody to the N-terminus of beta-endorphin (3-E7) as primary antisera. PAP-immunohistochemistry revealed GAD-immunoreactivity in the majority of neurons in neostriatum and ACE. OPL-immunoreactivity was observed in numerous neurons in ACE, but only in few neostriatal nerve cells. In double immunofluorescence in the same section OPL- and GAD-immunoreactivity colocalized in few medium size cells in the neostriatum, but in numerous neurons in ACE. The existence of opioid peptide containing GABAergic neurons in ACE and neostriatum is demonstrated.