Release of hypothalamic norepinephrine during MSG intake in rats fed normal and nonprotein diet.

Effects of monosodium L-glutamate (MSG) solution (0.06 M) on interstitial levels of norepinephrine (NE) were measured in the lateral hypothalamus (LH). Wistar male rats, housed in standard operant boxes, were fed either normal or nonprotein diet for 3 days. Beside a daily bar-mediated drinking session (75 min), animals were without access to fluids. Microdialysates, collected from the LH during the 75 min of drinking, were analyzed using high-pressure liquid chromatography. No significant responses of the LH NE to the drinking of distilled water, MSG, NaCl (0.06 M), and glucose solution (0.6 M) were found in normally fed rats. However, a specific decline in LH NE release was detected during MSG solution-drinking in rats fed nonprotein diet. As MSG preference indicates protein intake, it is possible that LH NE is, at least partially, one of the brain signals that relate MSG preference to dietary protein intake.