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The Journal of Neuroscience, June 28, 2006, 26(26):7093-7104; doi:10.1523/JNEUROSCI.0408-06.2006

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Behavioral/Systems/Cognitive
Panic-Prone State Induced in Rats with GABA Dysfunction in the Dorsomedial Hypothalamus Is Mediated by NMDA Receptors

Philip L. Johnson and Anantha Shekhar

Department of Psychiatry, Indiana University School of Medicine, Indianapolis, Indiana 46202

Correspondence should be addressed to Dr. Anantha Shekhar, Indiana University School of Medicine, 1111 West 10th Street, Indianapolis, IN 46202. Email: ashekhar{at}IUPUI.edu

Rats with chronic inhibition of GABA synthesis and consequently enhanced glutamatergic excitation in the dorsomedial hypothalamus (DMH) develop panic-like responses, defined as tachycardia, tachypnea, hypertension, and increased anxiety as measured by a social interaction (SI) test, after intravenous sodium lactate infusions, a phenomenon similar to patients with panic disorder. Therefore, the present studies tested the role of the postsynaptic NMDA and AMPA type glutamatergic receptors in the lactate-induced panic-like responses in these rats. Rats were fit with femoral arterial and venous catheters and Alzet pumps [filled with the GABA synthesis inhibitor L-allylglycine (L-AG; 3.5 nmol/0.5 µl per hour) or its inactive isomer D-AG] into the DMH. After 4–5 d of recovery only those rats with L-AG pumps exhibited panic-like responses to lactate infusions. Using double immunocytochemistry, we found that rats exhibiting panic-like responses (e.g., L-AG plus lactate) had increased c-Fos immunoreactivity in DMH neurons expressing the NMDA receptor 1 (NR1) subunit, but not those expressing the glutamate receptor 2 and 3 subunits of the AMPA receptors. To confirm this pharmacologically, we tested another group of rats implanted with L-AG pumps with intravenous lactate infusions preceded by injections of either NMDA [aminophosphonopentanoic acid (AP-5) or (+)-5-methyl-10,11-dihydro-⁵H-dibenzo [a,d]cyclohepten-5,10-imine maleate (MK-801)] or non-NMDA [CNQX or 4-(8-methyl-⁹H-1,3-dioxolo[4,5-h][2,3]benzodazepin-5-yl)-benzenamine dihydrochloride (GYKI52466)] antagonists into the DMH. Injections of NMDA, but not non-NMDA, antagonists into the DMH resulted in dose-dependent blockade of the tachycardia, tachypnea, hypertension, and SI responses after lactate infusions. These results suggest that NMDA, and not non-NMDA, type glutamate receptors regulate lactate-induced panic-like responses in rats with GABA dysfunction in the DMH.

Key words: anxiety; subfornical; glutamate decarboxylase; circumventricular; hypothalamus; glutamate; GABA; GAD; immunoreactivity; hypotension; lactate; panic

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Received Jan. 28, 2006; revised May 8, 2006; accepted May 29, 2006.

Correspondence should be addressed to Dr. Anantha Shekhar, Indiana University School of Medicine, 1111 West 10th Street, Indianapolis, IN 46202. Email: ashekhar{at}IUPUI.edu

This article has been cited by other articles:

				T. Sajdyk, P. Johnson, S. Fitz, and A. Shekhar Chronic inhibition of GABA synthesis in the bed nucleus of the stria terminalis elicits anxiety-like behavior J Psychopharmacol, August 1, 2008; 22(6): 633 - 641. [Abstract] [PDF]

				P. Johnson, C. Lowry, W. Truitt, and A. Shekhar Disruption of GABAergic tone in the dorsomedial hypothalamus attenuates responses in a subset of serotonergic neurons in the dorsal raphe nucleus following lactate-induced panic J Psychopharmacol, August 1, 2008; 22(6): 642 - 652. [Abstract] [PDF]

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