Activation of meiotic maturation in rat oocytes after treatment with follicular fluid meiosis-activating sterol in vitro and ex vivo.

Meiosis-activating sterols (MAS) have been found to induce meiotic maturation in mouse oocytes in vitro. In the present study we have extended these observations by investigating the effects of follicular fluid MAS (FF-MAS) on rat oocyte maturation in vitro and ex vivo. Rat oocytes freed from their follicles were cultured with FF-MAS (0 microM, 1 microM, 3 microM, 10 microM, 30 microM) for 22 h in a medium containing the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX; 250 microM). A dose-dependent significant increase in germinal vesicle breakdown (GVB) was observed after adding FF-MAS to the culture medium in both cumulus-enclosed (CEO) and denuded (DO) oocytes. A time course study (0, 3, 8, 14, and 22 h) showed a significant increase in GVB after 14 h when DO and CEO were cultured in the presence of 10 microM FF-MAS + 250 microM IBMX. Furthermore immature rats were primed with eCG (20 IU) and 48 h later perfused ex vivo for 12 h in a recirculating system with either FF-MAS (0 microM, 10 microM, 30 microM, 60 microM), cholesterol (60 microM), or LH (0.2 microg/ml) in the presence of 200 microM IBMX, respectively. In addition, ovarian perfusion was carried out with FF-MAS (30 microM, 60 microM) or 0.2 microg/ml LH in the absence of IBMX. After 12 h, oocytes were freed from the ovaries and checked for GVB. By using the ex vivo perfused rat ovary, we found that FF-MAS, starting at 30 microM, was dose-dependently able to overcome IBMX-induced meiotic arrest leading to a comparable increase in GVB as was observed for LH. Furthermore, it was found that FF-MAS in the absence of IBMX was also able to induce meiotic maturation. Our data are consistent with the notion that the maturation-inducing effects of FF-MAS are mediated by different mechanisms compared to spontaneous maturation.

The effects of ibotenic acid lesions of the basal forebrain on visual discrimination performance in rats.

Rats were trained to stable performance in a conditional brightness discrimination task and then received infusions of ibotenic acid or vehicle into the basal forebrain. Following 2 weeks of recovery, animals were retested in the original discrimination. Lesioned rats tended to performed badly on the first day of testing as measured by all parameters (percent correct responding, latency to respond, and missed trials) but thereafter, most rats recovered quickly to prelesion levels. In keeping with previous reports, an approximately 30% reduction in choline acetyltransferase activity was observed in the lesioned animals. Four rats showed no recovery over a period of several months; however, an analysis of the choline acetyltransferase in several brain regions revealed no obvious differences to those animals in which performance recovered. Postlesion testing with the putative nootropic beta-carboline ZK 93426 showed no major differences to the effects observed in control animals. Scopolamine had similar negative effects in both groups tested. These data indicate that deficits induced by lesions of the basal forebrain do not correlate with reductions in cholinergic activity.

Effects of cholinergic and non-cholinergic drugs on visual discrimination and delayed visual discrimination performance in rats.

The effects of several centrally active drugs were investigated using two visual discrimination tasks: a two-lever food-rewarded conditional brightness discrimination, and a similar conditional brightness discrimination where a delay was introduced between the disappearance of the stimulus and the opportunity to respond on the levers for food. The substances tested (amphetamine, scopolamine, methylscopolamine, physostigmine, diazepam and beta-carboline benzodiazepine receptor antagonist, ZK 93426), all produced differing profiles of action on the performance parameters recorded. In the simple conditional visual discrimination, amphetamine increased omissions without significant effects on accuracy or response latency. Physostigmine enhanced response latencies and failures to respond without significant effects on accuracy. ZK 93426 had no consistent effects on accuracy although at higher doses, some increase in response latency was seen in the delayed responding version of the visual discrimination task. Diazepam had negative effects on all parameters in both discrimination procedures. Scopolamine disrupted responding, but not accuracy in the simple discrimination, whereas accuracy was reduced in a dose, but not delay dependent manner in the delayed discrimination. A similar effect to that observed with scopolamine was observed following methylscopolamine in the delayed discrimination procedure. In the simple visual discrimination small increases in accuracy were recorded, accompanied by increased response latencies.

Does the excitatory amino acid receptor antagonist 2-APH exhibit anxiolytic activity?

The activity of 2-amino-7-phosphonoheptanoic acid (2-APH), an antagonist of the NMDA subtype of glutamate receptor, was tested in several animal models of anxiolytic activity in rats and mice and compared with the activity of the standard benzodiazepine anxiolytic, diazepam. 2-APH was effective, but about 100 times less potent than diazepam in antagonising the suppressive effects of punishment on locomotor activity in the four-plate test in mice. 2-APH was also effective in enhancing exploration of the open, exposed arms of a plus maze, without altering exploration of the enclosed arms. Again 2-APH was about 100 times less effective than diazepam. In contrast to diazepam, 2-APH was ineffective in antagonising the pro-punishment properties of the anxiogenic beta-carboline DMCM in a modified four-plate test, and in antagonising the discriminative stimulus provided by pentylenetetrazol. These results are discussed in the context of the equivalence of the antagonism of excitatory mechanisms and the enhancement of inhibitory systems as anxiolytic treatments.