Adrenergic stimulation of the paraventricular nucleus and its effects on ingestive behavior as a function of drug dose and time of injection in the light-dark cycle.

The paraventricular nucleus (PVN) has been identified as the most responsive site in the brain for eliciting feeding and preprandial drinking responses with local injection of norepinephrine (NE) in satiated rats. The present study examined these phenomena as a function of dose and time of injection in the light-dark cycle. The lowest effective doses for producing these ingestive responses with exogenous NE in the PVN are found to be between 5.6 and 16.9 ng for preprandial drinking and between 1.0 and 4.2 ng for feeding. Tests with NE injection into the PVN at different times in the light-dark cycle indicate that an increase in feeding effect can occur in the dark as well as in the light and at varying levels of food intake baseline and with solid and liquid food. Site of injection in the brain is believed to be a crucial factor in determining the nature of NE's effects on feeding behavior.