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In Experiment I, rabbits received training to establish a clicker as a conditioned inhibitor. In a subsequent test phase this stimulus was used as a signal for shock either to the eye reinforced during initial training or to the opposite eye. Learning to the clicker was slower in both conditions than in the appropriate control groups. The second experiment replicated the results of those subjects trained and tested with opposite eyes and ruled out the possibility that the slower learning was due to the effects of latent inhibition. Experiment III demonstrated that excitatory conditioning to a clicker to one eye facilitated future excitatory conditioning to that stimulus to the opposite eye. These results are consistent with the view that inhibitory and excitatory conditioning both involve the acquisition of a general, motivational conditioned response which is capable of mediating the transfer of conditioning across different response systems.

The effects of the nitric oxide synthase inhibitor, Nw-nitro-L-arginine methyl ester (L-NAME) were investigated in two animal models of anxiety: the elevated plus-maze and the social interaction test. In the elevated plus-maze, L-NAME (12.5-50 mg/kg) had an anxiogenic-like profile as indicated by dose-dependent reductions in the time spent on the open arms, open arm entries, the percentage of open arm entries and head dips, but there was no significant effect on the number of stretch attend postures. In contrast, L-NAME (12.5-50 mg/kg) failed to modify time spent in social interaction but did reduce a measure of vertical activity. The differential effects of L-NAME in the two anxiety paradigms are discussed.

Two specific 5-HT1A agonists, 8-OH-DPAT (0-300 micrograms/kg), and buspirone (0-3.0 mg/kg), were tested on variable-interval, threshold-current self-stimulation of rat lateral hypothalamus. Buspirone produced a prolonged monotonic depression of responding, whereas the effects of 8-OH-DPAT were biphasic: 3.0 micrograms/kg produced a sustained enhancement of responding while higher doses (100-300 micrograms/kg) produced a relatively short-lasting depression. This biphasic pattern parallels previously reported effects of 8-OH-DPAT on food intake and on various other behaviours. Threshold-current self-stimulation is highly sensitive to alterations in dopaminergic transmission but relatively insensitive to changes in 5-HT. Thus the facilitatory effect of low-dose 8-OH-DPAT seems most plausibly interpreted in terms of enhanced dopaminergic transmission. This could be brought about by 5HT1A autoreceptor-mediated inhibiton of 5-HT release and consequent disinhibition of dopaminergic transmission. Depression of self-stimulation by higher doses of 8-OH-DPAT may reflect the activity of 8-OH-DPAT at postsynaptic 5-HT receptors, with consequent inhibition of DA transmission. Suppression of responding after buspirone at all doses tested may reflect the action of this compound as a partial agonist at postsynaptic 5-HT receptors, and/or its effects on other systems.