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 l evels of norepinephrine (NE) were measured in the lateral hypothalamus (LH) . Wistar male rats, housed in standard operant boxes, were fed either norma l or nonprotein diet for 3 days. Beside a daily bar-mediated drinking sessi on (75 min), animals were without access to fluids. Microdialysates, collec ted from the LH during the 75 min of drinking, were analyzed using high-pre ssure liquid chromatography. No significant responses of the LH NE to the d rinking 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 rel ease 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. (C) 2000 Elsevier Science Inc. All rights reserved.