title: Using drug combinations to assess potential contributions of non-GABAA receptors in the discriminative stimulus effects of the neuroactive steroid pregnanolone in rats.
abstract: Neuroactive steroids are increasingly implicated in the development of depression and anxiety and have been suggested as possible treatments for these disorders. While neuroactive steroids, such as pregnanolone, act primarily at γ-aminobutyric acidA (GABAA) receptors, other mechanisms might contribute to their behavioral effects and could increase their clinical effectiveness, as compared with drugs acting exclusively at GABAA receptors (e.g., benzodiazepines). The current study examined the role of non-GABAA receptors, including N-methyl-d-aspartate (NMDA) and serotonin3 (5-HT3) receptors, in the discriminative stimulus effects of pregnanolone. Separate groups of rats discriminated either 3.2mg/kg pregnanolone from vehicle or 0.32mg/kg of the benzodiazepine midazolam from vehicle while responding under a fixed-ratio 10 schedule for food pellets. When administered alone in both groups, pregnanolone and midazolam produced ≥80% drug-lever responding, the NMDA receptor antagonists dizocilpine and phencyclidine produced ≥60 and ≥30% drug-lever responding, respectively, and the 5-HT3 receptor agonist 1-(m-chlorophenyl)-biguanide (CPBG) and morphine produced <20% drug-lever responding up to doses that markedly decreased response rates. When studied together, neither dizocilpine, phencyclidine, CPBG nor morphine significantly altered the midazolam dose-effect curve in either group. Given that CPBG is without effect, it is unlikely that 5-HT3 receptors contribute substantially to the discriminative stimulus effects of pregnanolone. Similarities across groups in effects of dizocilpine and phencyclidine suggest that NMDA receptors do not differentially contribute to the effects of pregnanolone. Thus, NMDA and 5-HT3 receptors are not involved in the discriminative stimulus effects of pregnanolone.
authors: Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr.-mail code 7764, San Antonio, TX 78229-3900, USA.
authors: Amy K
authors: AK
authors: Eppolito
authors: Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr.-mail code 7764, San Antonio, TX 78229-3900, USA.
authors: Hanna R
authors: HR
authors: Kodeih
authors: Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr.-mail code 7764, San Antonio, TX 78229-3900, USA. Electronic address: gerak@uthscsa.edu.
authors: Lisa R
authors: LR
authors: Gerak
mesh_terms: D000818:Animals; D001645:Biguanides / Q000494:pharmacology; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D004192:Discrimination, Psychological / Q000187:drug effects / Q000502:physiology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018757:GABA Modulators / Q000494:pharmacology; D008297:Male; D008874:Midazolam / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology; D010622:Phencyclidine / Q000494:pharmacology; D011280:Pregnanolone / Q000494:pharmacology*; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism; D044406:Receptors, Serotonin, 5-HT3 / Q000378:metabolism; D058827:Serotonin 5-HT3 Receptor Agonists / Q000494:pharmacology
chemical_list: D001645:Biguanides; D002492:Central Nervous System Depressants; D018691:Excitatory Amino Acid Antagonists; D018757:GABA Modulators; D009294:Narcotics; D016194:Receptors, N-Methyl-D-Aspartate; D044406:Receptors, Serotonin, 5-HT3; D058827:Serotonin 5-HT3 Receptor Agonists; D016291:Dizocilpine Maleate; D009020:Morphine; C065734:1-(3-chlorophenyl)biguanide; D011280:Pregnanolone; D010622:Phencyclidine; D008874:Midazolam
keywords: Drug discrimination; Midazolam; Neuroactive steroids; Pregnanolone; Rats