Regional changes in brain 14C-2-deoxyglucose uptake after feeding-inducing intrahypothalamic norepinephrine...

Although norepinephrine (NE) injections into the paraventricular hypothalamus (PVN) have been extensively documented to induce feeding in satiated rats, there have been few systematic attempts to elucidate the neural circuitry subserving this response. In this study quantitative 14C-2-deoxyglucose (14C-2DG) autoradiography was used to map regional brain changes induced by PVN NE injections. Male Wistar rats, bearing PVN cannulae and previously shown to be positive responders for NE-induced feeding, were given 125 microCi/kg 14C-2DG IV immediately following a PVN injection of either 40 nmol NE or vehicle, then killed 45 min later. 14C-2DG uptake was examined in 97 brain structures using computerized densitometry. PVN NE injections resulted in small, localized changes in brain 14C-2DG uptake. Forebrain structures affected included the somatosensory parietal cortex (+15%), the CA3 hippocampal field (-8%), and the reticular thalamic nucleus (+14%). Midbrain changes involved the anterior pretectal area (+8%) and the central gray area (-11%). At the hindbrain level, the lateral reticular nucleus showed the most pronounced changes of all brain regions examined (-24%), followed by the nucleus of the solitary tract (-16%) and the laterodorsal tegmental nucleus (+16%). No changes were seen in the median eminence or in other hypothalamic areas. This pattern of results largely agrees with recent proposals for the circuitry of a PVN-hindbrain system subserving NE-induced as well as hypothalamic lesion-induced feeding effects. In addition, however, they suggest the possibility that altered activity in some forebrain structures may also be involved in the NE response.