/ eh08 2483 Mp 215 Wednesday Jan 15 07:57 AM EL–PB (v. 61, No. 2) 2483 215 Physiology & Behavior, Vol. 61, No. 2, pp. 215–220, 1997 Copyright  1997 Elsevier Science Inc. Printed in the USA. All rights reserved 0031-9384/97 $17.00 / .00 PII S0031-9384( 96 ) 00362-9 Modulation of Plasma Glucose by the Medial Preoptic Area in Freely Moving Rats MAURICIO G. B. DE CASTRO, RODRIGO B. FOSCOLO, ADELINA M. REIS AND CANDIDO C. COIMBRA 1 Department of Physiology and Biophysics, Institute of Biological Science, Federal University of Minas Gerais, Av. Anto ˆnio Carlos 6627, 31270-901 Belo Horizonte, MG, Brazil Received 23 January 1996; Accepted 12 August 1996 DE CASTRO, M. G. B., R. B. FOSCOLO, A. M. REIS AND C. C. COIMBRA. Modulation of plasma glucose by the medial preoptic area in freely moving rats. PHYSIOL BEHAV 61 (2) 215–220, 1997.—The effect of norepinephrine (NE) injection into the medial preoptic area (MPOA) on plasma glucose was studied in freely moving male rats. The rats were implanted with chronic jugular catheters for blood sampling and with unilateral intracerebral cannulas placed just above the MPOA. Blood samples were taken immediately before and 5, 10, 15, and 30 min after NE injection. As early as 5 min after NE injection, plasma glucose levels rose rapidly, reaching a peak at 15 min poststimulus. The hyperglycemic response to NE injection into the MPOA was dose-related within the range of doses tested (10, 20, and 40 nmol). Previous administration of phentolamine (50 nmol), but not propranolol (100 nmol), into the MPOA blocked the hyperglycemic response to NE injection into the MPOA. The increase of plasma glucose induced by NE into the MPOA and the blockade of the hyperglycemic response to NE by phentolamine suggest the involvement of an a-adrenergic mechanism in MPOA-mediated hyperglycemia. On the basis of these and previous results, we propose that MPOA a-adrenergic synapses relay impulses activating the sympathetic outflow expressed by neurally mediated hyperglycemia. Copyright  1997 Elsevier Science Inc. Plasma glucose Preoptic area Norepinephrine Propranolol Phentolamine 1 To whom requests for reprints should be addressed. IN THE present study, we investigated the effect of chemical stim- ulation of the medial preoptic area (MPOA) on plasma glucose. It has been well established that the POA is a integrative area for the maintenance of internal homeostasis (2,12,20,21,30) that can strongly influence plasma free fatty acids and glucose levels, prob- ably by activation of sympathetic fibers of adipose tissue (5–7). In previous studies, we obtained evidence that the MPOA control of glycemia and lipolysis can be activated in situations that require rapid mobilization of metabolic reserves, such as exposure to cold (7,16 ) and neuroglucopenia (5,6). Although an increased release of norepinephrine (NE) into the MPOA has been shown to occur dur- ing neurocytoglycopenia (18), there are no experimental data show- ing that a direct stimulation of the adrenergic neurons in the preoptic area can interfere with hepatic glucose production or induce a change in plasma glucose levels. To study the influence of MPOA noradrenergic afferents on plasma glucose levels, we investigated the effect of NE injection into the MPOA of conscious unrestrained male rats. The results suggest the involvement of an a-adrenergic system in the MPOA that participates in the control of plasma glu- cose levels. METHODS Animals and General Conditions Adult male Wistar rats (12–14 weeks old) were used in the experiments. Animals were fed Purina rat chow and wa- ter ad lib and were housed in temperature-controlled quarters with 14 h of light (0500–1900 h) per day. At the age of 11 weeks, the rats were placed in individual cages and were fre- quently handled. One week later, they were anesthetized with thionembutal ( 30 mg / kg ) , and a silastic catheter was inserted through the jugular vein into the right atrium for blood sam- pling by the technique of Harms and Ojeda ( 13 ) . After inser- tion of the jugular catheter, the animals were placed in a ste- reotaxic apparatus (David Kopf 900, Tijunga, CA) and a unilateral guiding cannula (22 G) was implanted into the MPOA using the stereotaxic coordinates of DeGroot (9): an- teroposterior, 8.0 mm; lateral, 0.05 mm; vertical, 7.0 mm above the base of the skull. This cannula was provided with a mandril and a protective cap. Both cannulas were anchored firmly to the skull with jeweler’s screws and fixed with acrylic cement (15). The sampling catheter was rinsed every 2 days with 1 ml of saline containing 25 mU heparin (Liquemine, La Roche, Rio de Janeiro, Brazil). All animals were allowed to recover for 1 week before being utilized in the experiments. Experimental Design On the day of the experiments, the venous catether of the rats was rinsed regularly and connected to a peristaltic pump. An injection needle (27 G) exceeding the tip of the guiding cannula by 0.3 mm and connected to a Hamilton