Plus-maze following the microinjection of muscimol into the dorsal periaqueductal gray of the rat.

Plus-maze following the microinjection of muscimol into the dorsal periaqueductal gray of the rat Performance no labirinto em cruz elevado após microinjeção de muscimol na substância cinzenta periaquedutal dorsal do rato Dear Editor, Some experimental findings have indicated that the rat dorsal periaqueductal gray (DPAG) is part of a longitudinally organized neural system responsible for behavioral and vegetative manifestations of anxiety-like and aversive/defensive behaviors as well as active and passive emotional coping strategies towards threatening stimuli. 1 DPAG-evoked defense reactions might also provide some insights about panic attacks in humans. Systemically injected diazepam or intra-DPAG injection of midazolam promoted anxiolytic effects when animals were tested in the elevated plus-maze (EPM), 2 a behaviorally and pharmacologically validated animal model for the study of anxiety. 3 The inhibitor y neurotransmitter γ-aminobutyric acid (GABA) and both GABA A and GABA B receptors are found in the DPAG. Here we report discrepant results found when we looked for the behavioral effects of microinjections of different doses of muscimol, a GABA A receptor agonist, into the DPAG of rats tested in the EPM compared to the reported anxiolytic effects of midazolam. We studied 3-month old male Wistar rats locally bred under standard laboratory conditions and according to international laws for ethical care. The EPM and its use were identical to previous descriptions. 2 Rats were submitted to unilateral stereotaxic surgery (Figure 1) and were microinjected into the DPAG with saline (0.3 µl, n = 10), muscimol at the doses of 20 pg (n = 8), 50 pg (n = 12) and 150 pg (n = 8) or midazolam at the doses of 0.1µg (n = 5) or 35.3 µg (n = 7). Other experimental groups served for testing the experimental procedure itself and we studied rats injected i.p. with saline and midazolam and tested in the EPM (n = 5-8, respectively) and a 'non-target' group (n = 15), i.e., rats that received saline or muscimol microinjections in the vicinity of the DPAG.