Input specific neuronal circuitry in the ventrolateral periaqueductal gray area

Abstract

Play-like behavior exist in animals especially in young animals, that could be the mimicry and learning of useful survival skills as hunting behavior for an adult animal. Several recent publications have identified the associated brain regions i.e. Medial Preoptic Area (MPA), Central Amygdala (CeA) and Lateral Hypothalamus (LH). All these presumably redundant circuits for hunting are converging onto similar brain region with in the midbrain i.e. ventrolateral Periaquaductal Gray Area (vlPAG). But so far little is known about the specific vlPAG neuronal targets and the interaction of these circuits within the vlPAG region. In this study, combination of retrograde and anterograde tracing techniques, single unit fiber photometry and whole cell patch clamp has been used to understand the neuronal architecture within the vlPAG with respect to both MPA and CeA and to identify the neurons within vlPAG which are involved in object interaction and probably in hunting behavior. The results show that both MPA and CeA send projections throughout the length of the vlPAG, however, the neuronal architecture within the vlPAG differs for both. Moreover, it is likely that object interaction and hunting related CamkIIa neurons from MPA are connected to GABAergic neurons within the vlPAG region. There are two types of glutamergic neurons in the vlPAG

the CamKIIa and vGlut2 type. The results show that the vGlut2 neurons within the vlPAG depicts significant decrease in activity upon active manipulation of object. The study, therefore, signifies the role of vGlut2 neurons and local inhibitory neurons in object interaction and presumably in hunting behavior and suggests the probable model for the micro-circuitry connectivity within the vlPAG region with respect to macro-circuits converging from amygdala and hypothalamus.