Anxiolytic-like effect of neuropeptide Y (NPY), but not other peptides in an operant conflict test.

The peptide messengers neuropeptide Y (NPY), growth hormone-releasing hormone (GHRH), atrial natriuretic peptide (ANP) and beta-endorphin (BEND) were tested in an animal model of anxiety, the Geller-Seifter conflict test. Rats were subjected to a multiple schedule consisting of three components: in the first component, lever-pressing produced food-reward ('unpunished responding'). The second component was a time-out period, during which lever-pressing had no consequences. During the third component, lever-pressing produced food-reward, but was also punished by an incremental foot-shock ('punished responding'). After establishing a stable baseline of both unpunished and punished responding, animals were injected with various doses of NPY, GHRH, ANP, BEND, or with saline into the lateral cerebral ventricle, and testing was repeated. While changes in unpunished responding can reflect alterations in performance factors or motivational strength, increases in punished responding have previously been shown to be highly specific for anxiety-reducing drugs, such as the benzodiazepines. NPY markedly and dose-dependently increased punished responding. A smaller increase of unpunished responding was also seen. These results add further support to the hypothesis that NPY may be an endogenous anxiolytic. GHRH, ANP and END did not affect punished responding.