Discriminative-stimulus effects of azaspirodecanedione anxiolytics in baboons trained to discriminate beta-carboline-3-carboxylic acid ethyl ester or pentylenetetrazole.

Abstract

Baboons were trained to discriminate either pentylenetetrazole (PTZ) or beta-carboline-3-carboxylic acid ethyl ester (beta-CCE) from the no-drug condition. Both drugs specifically bind sites in the gamma-aminobutyric acid A (GABA(A)) receptor complex and decrease GABAergic transmission. beta-CCE occasioned drug-lever responding in baboons trained to discriminate PTZ and vice versa. Flumazenil, the benzodiazephine receptor antagonist, blocked beta-CCE, consistent with beta-CCE's receptor binding activity. The azaspirodecanedione anxiolytics buspirone and ipsapirone produced full generalization in all baboons; gepirone and tandospirone yielded full generalization in some baboons and partial in others. These anxiolytics are inactive in the GABA(A) complex and potently bind 5-HT(1A) sites. A specific 5-HT(1A) ligand, 8-hydroxy-2-(di-n-propylamino)tetralin, produced generalization similar to gepirone and tandospirone, which show the most specific 5-HT(1A) binding. The major azaspirodecanedione metabolite, 1-(2-pyrimidinyl)piperazine (an alpha(2)-adrenergic antagonist), occasioned the least drug-appropriate responding. Full generalization to buspirone and ipsapirone may have resulted from dopaminergic or alpha(1)-adrenergic activity combined with 5-HT(1A) activity. The molecular mechanism of the generalization profile for PTZ and beta-CCE shown by the present results is unclear. The data may reflect altered relationships between GABAergic and serotonergic transmission, and altered stimulus effects of the training drugs, in the context of chronically decreased GABAergic transmission.