ELSEVIER Neuroscience Letters 168 (1994) 147 150 NHROSCIfNCE LETTERS Drugs acting at the strychnine-insensitive glycine receptor do not induce HSP-70 protein in the cingulate cortex Paul Berger a'*, Kevin Farrel", Frank Sharp a, Phil Skolnick b "Laboratory of Po'chiatry and Neurology, SFVAMCIUCSE Psychiatry l16m, 4150 Clement St., San Francisco, CA 94121, USA hLahoratory of Neuroscienee, NIDDK. N1H, 9000 Rockville Pike, Bethesda, MD 20892, USA Received 12 July 1993; Revised version received 5 December 1993: Accepted 15 December 1993 Abstract The potential for compounds acting at the strychnine-insensitive glycine receptor to injure neurons was examined using induction of a 70 kDa heat shock protein (HSP-70) as a marker. HSP-70 was consistently detected in retrosplenial and cingulate cortices after MK-801 but not glycine drug treatment. Elsewhere in the cortex, mild diffuse HSP-70 immunoreactivity was detected following 7-chlorokynurenic acid. Following HA-966, intense hippocampal HSP-70 immunoreactivity was observed. These findings indicate that even after very high doses, drugs acting at the strychnine-insensitive glycine receptor are less likely to injure cingulate cortical neurons than other classes of NMDA antagonists. Key words: Glycine; NMDA: ACPC; HA-966; 7-Chlorokynurenic acid; d-Cycloserine Competitive N-methyl-D-aspartate (NMDA) antago- nists (e.g. 3-[(+)-2-carboxypiperazin-4-yl]-propyl] 1]- phosphonic acid; CPP) and use-dependent channel blockers (e.g. MK-801) reduce neuronal injury in animal models of cerebral ischemia and other neuropathologies associated with excessive activation of NMDA receptors [2]. However, the clinical potential of these agents may be limited by the recent observations that neuroprotec- tive doses of these NMDA antagonists may damage vulnerable neurons. This damage was manifest as a vac- uolization in neurons of the cingulate and retrosplenial cortices [9,10] as well as an induction of the 70 kDa heat shock protein (HSP-70) in neurons manifesting vacuoli- zation [14,15]. HSP-70 was used as a marker for neuronal injury by Sharp and colleagues since this protein is induced in brain regions subject to severe neuronal insults such as seizures or ischemia [6,18]. Neither HSP-70 protein nor HSP-70 mRNA can be detected by immunohistochemis- try and polymerase chain reaction assay, respectively, in * Corresponding author. 0304-3940/94/$7.00 cO 1994 Elsevier Science Ireland Ltd. All rights reserved SSDI 0304-3940(93)E0895-3 uninjured brain [15,22]. Using this marker, we have ex- amined drugs acting at the strychnine-insensitive glycine receptor for their ability to injure the cingulate cortex. Both partial agonists and competitive antagonists at the strychnine-insensitive glycine receptor function as NMDA antagonists in a variety of measures including neuroprotection paradigms (ref. 11, reviewed in refs. 12 and 19). It is not known whether the NMDA antagonism produced by drugs acting at the strychnine-insensitive glycine receptor results in the same neuronal injury to the cingulate and retrosplenial cortex as is observed follow- ing competitive or non-competitive NMDA receptor blockade. If the hypothesis of Olney et al. [9,10] relating psychotomimetic actions to neuronal injury is correct, then drugs acting at strychnine-insensitive glycine recep- tors may not have the same intrinsic ability to damage vulnerable neurons as other NMDA antagonist since their behavioral profiles in animals are markedly differ- ent than either competitive NMDA antagonists or use- dependent channel blockers. This hypothesis was tested by examining the neurotoxic potential of drugs acting at strychnine-insensitive glycine receptors using the induc- tion of HSP-70 as a marker of neuronal damage.