BRAIN RESEARCH ELSEVIER Brain Research 700 (1995) 289-294 Short communication NMDA receptors mediate heat shock protein induction in the mouse brain following administration of the ibotenic acid analogue AMAA Anna M. Planas a, *, Isidre Ferrer b, Eduard Rodrlguez-Farr6 a a Departament de Farmacologia i Toxicologia, CID, CSIC, Jordi Girona, 18-24, 08034 Barcelona, Spain b Unitat de Neuropatologia, Servei d'Anatomia Patolbgica, Hospital Princeps d'Espanya, Universitat de Barcelona, Barcelona, Spain Accepted 8 August 1995 Abstract Expression of inducible heat shock protein-70 (HSP-70) and hsp-70 mRNA were studied in the adult mouse brain following systemic administration of the ibotenic acid analogue (_)-2-amino-3-hydroxy-5-methyl-4-isoxazoleacetic acid (AMAA), which is a potent N-methyl-D-aspartate (NMDA) agonist. At the dose of 20 mg/kg, AMAA produced excitatory behaviours in adult mice but overt convulsions were not seen. This treatment did not result in any detectable morphological brain damage at 4 days following administration. At 2.5 h and 5 h following treatment induction of hsp-70 mRNA expression was found in the pyramidal cell layers of CA1 and, to a lesser extent, CA3 fields of hippocampal Ammon's horn, amygdala, olfactory lobes, tenia tecta, hypothalamic nuclei and a superficial layer of cingulate, frontal and retrosplenial cortices. The presence of HSP-70 was detected by immunohistochemistry at 24 h following drug administration in those regions previously showing hsp-70 mRNA induction. AMAA-induced hsp-70 mRNA expression was prevented by pre-treatment with the non-competitive NMDA antagonist MK-801. These results suggest that NMDA receptors are involved in the stress response induced by AMAA. Keywords: Heat shock protein; mRNA; In situ hybridization; lmmunohistochemistry;(+)-2-Amino-3-hydroxy-5-methyl-4-isoxazoleacetic acid; MK-80I The brain responds to a variety of insults by expressing inducible heat shock genes which are 'silent' under normal conditions. Evidence from in vitro experiments has shown that heat shock proteins (HSPs) are chaperones implicated in protein folding and assembly [4,13,28] that can be induced by the presence of denatured proteins in cells [2,10,30]. HSPs may have a protective function in cells under stress conditions [17,29,32], including neurons cul- tured in vitro which can be protected by HSPs from glutamate toxicity [35]. The molecular event triggering a heat shock response in vivo is not well understood. Several insults that induce intense HSP-70 (mRNA and protein) expression in certain regions of the rodent brain, such as exposure to excitotoxic agents [14,33,34] and ischemia [15,20,22,23,38,40,44], produce neuropathological changes which are putatively mediated through glutamate receptors [7,16]. Whether or not the mediation of glutamate receptors is involved in the * Corresponding author. Fax: (34) (3) 204 59 04. 0006-8993/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0006-8993(95)01055-6 heat shock response in vivo remains to be elucidated. This study examined the induction of HSP-70 and hsp-70 mRNA in the mouse brain following administration of the ibotenic acid analogue (±)-2-amino-3-hydroxy-5-methyl-4-iso- xazoleacetic acid (AMAA), which has a potent agonist action on the N-methyl-o-aspartate (NMDA) receptor [18,19,21]. In addition, the effect of NMDA receptor blockade on the HSP-70 stress response elicited by AMAA was studied. Adult male OF1 mice (30 g body weight) (n = 28) from Iffa-Credo (Lyon, France) were allowed free access to food and water and were kept in standard conditions of temperature, humidity and 12 h day-night light cycle. Mice received an i.p. injection of ( +)-2-amino-3-hydroxy- 5-methyl-4-isoxazoleacetic acid (AMAA) (RBI, USA) that was disolved in saline brought to slightly alkaline pH (< 8) with NaOH. AMAA was given at the dose of 20 mg/kg of body weight (n = 18) or 25 mg/kg (n = 3), although in preliminary experiments doses ranging from 2 to 20 mg/kg were tested and overt signs of excitatory behaviour were only seen with the dose of 20 mg/kg. Control mice (n = 7) received an i.p. injection of vehicle solution. AMAA or saline was administered between 09.00