Research report Failure of g-hydroxybutyric acid both to increase neuroactive steroid concentrations in adrenalectomized–orchiectomized rats and to induce tolerance to its steroidogenic effect in intact animals Patrizia Porcu a , Cristiana Sogliano a,b , Cristina Ibba a , Massimo Piredda a , Silvia Tocco a , Carla Marra a , Robert H. Purdy c , Giovanni Biggio a,b , Alessandra Concas a,b, * a Department of Experimental Biology, Center of Excellence for Neurobiology of Dependence, University of Cagliari, Cagliari, Italy b CNR Institute for Neuroscience, Unit of Neuropsychopharmacology, Cagliari, Italy c Department of Psychiatry, University of California, San Diego, CA, USA Accepted 26 March 2004 Abstract g-Hydroxybutyric acid (GHB), a drug proposed in the treatment of alcohol withdrawal syndrome, increases the cerebrocortical and plasma concentrations of the neuroactive steroids allopregnanolone and allotetrahydrodeoxycorticosterone (THDOC). In the present study, we examined the role of hypothalamic –pituitary –adrenal (HPA) axis in the effect of GHB by measuring the concentrations of these steroids in the brain and plasma of adrenalectomized – orchiectomized (Adx – Orx) rats. The acute administration of GHB (500 mg/kg, i.p.) induced in 30 min an increase in the concentrations of allopregnanolone, THDOC and their precursors pregnenolone and progesterone in different brain areas (cerebral cortex, hypothalamus and cerebellum) and plasma of sham-operated rats but had no effect on the concentrations of these compounds in Adx– Orx rats, suggesting that activation of the HPA axis mediates the effect of GHB on brain and plasma concentrations of neuroactive steroids. Moreover, we evaluated whether repeated exposure of GHB induces tolerance to its steroidogenic effects. Chronic administration of GHB (500 mg/kg, i.p., twice a day for 10 days) to intact animals failed to affect the levels of progesterone, allopregnanolone, or THDOC measured 3 or 48 h after the last drug administration, whereas a challenge injection of GHB or ethanol was still able to increase the concentrations of these steroids in brain and plasma. These results indicate that repeated exposure to GHB fails to induce tolerance or cross-tolerance to the steroidogenic action of GHB or ethanol, respectively. D 2004 Elsevier B.V. All rights reserved. Theme: Neural basis of behavior Topic: Psychopharmacological agents Keywords: g-Hydroxybutyric acid; Ethanol; Neuroactive steroid; Adrenalectomy; Tolerance; Rat 1. Introduction g-Hydroxybutyric acid (GHB), a naturally occurring compound derived from g-aminobutyric acid (GABA), was first studied in the early 1960s because of its ability to cross the blood – brain barrier and to induce surgical anesthesia [29]. It subsequently became a drug abused for its sedative, euphoric, and anabolic properties [18]. Evidence suggests that GHB also might play a role in the brain as a neurotrans- mitter or neuromodulator. Indeed, the presence of specific and high-affinity neuronal receptors for GHB has been demonstrated in discrete brain regions [21,30,46]. Moreover, GHB may mimic the action of GABA by interacting at high concentrations (100 AM) with GABA B receptors; certain effects of GHB are thus inhibited by GABA B receptor antagonists and mimicked by the GABA B receptor agonist baclofen [3,7,31,36,38]. GHB has recently proved effective in the treatment of alcohol withdrawal syndrome and for the control of alcohol consumption and craving [16,17]. Consistent with this efficacy, the pharmacological profile of GHB appears 0006-8993/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2004.03.059 * Corresponding author. Department of Experimental Biology ‘‘B. Loddo,’’ University of Cagliari, Via Universita, 40 09100 Cagliari, Italy. Tel.: +39-70-675-4137; fax: +39-70-675-4166. E-mail address: aconcas@unica.it (A. Concas). www.elsevier.com/locate/brainres Brain Research 1012 (2004) 160 – 168