VICIA-VILLOSA AGGLUTININ LABELS A SUBSET OF NEURONS COEXPRESSING BOTHTHE MU-OPIOID RECEPTOR AND PARVALBUMIN IN THE DEVELOPING RAT SUBICULUM

Vicia villosa agglutinin (VVA), anti-parvalbumin antiserum and an affi nity-purified anti-mu opioid receptor antibody were used to triple-lab el neurons in the postnatal rat subiculum. VVA labeled a subset of mu opioid receptor-positive neurons that were also immunoreactive for par valbumin. The morphology of the triple-labeled neurons was heterogeneo us, and included multipolar, ovoid and pyramidal-shaped neurons. Neuro ns single-labeled for the mu opioid receptor, VVA or parvalbumin were also morphologically heterogeneous. The postnatal development of mu op ioid receptor immunoreactivity (IR), parvalbumin-IR and WA binding was investigated using triple-labeling immunocytochemistry. Mu opioid rec eptor-IR appeared first and was present at postnatal day 1 (P1). Parva lbumin-IR was first observed in somata at P10, followed by proximal an d distal dendrites at P15 and P20 respectively. Faint VVA labeling was seen first at P10 and surrounded a Limited number of neurons. The int ensity of labeling and the number of neurons labeled with VVA increase d between P10 and P20; however, both measures remained below adult lev els at P20. This study further illustrates the neurochemical heterogen eity of interneurons in the hippocampal formation and shows the develo pmentally early appearance of mu opioid receptor-IR compared to the la te appearance of VVA binding and parvalbumin-IR.