Behavioral effects of ''vehicle'' microinjected into the dorsal periaqueductal grey of rats tested in the elevated plus maze

To investigate the behavioral effects of different vehicles microinjected into the dorsal periaqueductal grey (DPAG) of male Wistar rats, weighing 200-250 g, tested in the elevated plus maze, animals were implanted with cannulas aimed at this structure. One week after surgery the animals received microinjections into the DPAG of 0.9% (w/v) saline, 10% (v/v) dimethyl sulfoxide (DMSO), 2% (v/v) Tween-80, 10% (v/v) propylene glycol, or synthetic cerebrospinal fluid (CSF). Ten min after the injection (0.5 mu l) the animals (N = 8-13/ group) were submitted to the elevated plus maze test. DMSO significantly increased the number of entries into both the open and enclosed arms when compared to 0.9% saline (2.7 +/- 0.8 and 8.7 +/- 1.3 vs 0.8 +/- 0.3 and 5.1 +/- 0.9, respectively, Duncan test, P<0.05), and tended to increase enclosed arm entries as compared to 2% Tween-80 (8.7 +/- 1.3 vs 5.7 +/- 0.9, Duncan test, P<0.10). In a second experiment no difference in plus maze exploration was found between 0.9% saline- or sham-injected animals (N = 11-13/group). These results indicate that intra-DPAG injection of some commonly used vehicles such as DMSO, saline or Tween-80 affects the exploratory activity of rats exposed to the elevated plus maze in statistically different manners.