Chronic administration of the triazolobenzodiazepine alprazolam produces opposite effects on corticotropin-releasing factor and urocortin neuronal systems.

In view of the substantial preclinical evidence that supports a seminal role of central corticotropin-releasing factor (CRF) neuronal systems in the physiology and pathophysiology of stress and anxiety, it is reasonable to suggest that the anxiolytic properties of benzodiazepines are mediated, at least in part, via regulation of CRFergic function. To begin to test this complex hypothesis, we examined the effects of acute and chronic administration of the triazolobenzodiazepine agonist alprazolam on CRF peptide concentrations, receptor-binding density, and mRNA expression in the CNS. Additionally, we measured mRNA expression for urocortin, a recently discovered neuropeptide that is generally considered to be a second endogenous ligand for CRF receptors. Both acute and chronic alprazolam administration was found to decrease CRF concentrations within the locus coeruleus. Furthermore, chronic alprazolam decreased basal activity of the hypothalamic-pituitary-adrenal axis, CRF mRNA expression in the central nucleus of the amygdala, and CRF(1) mRNA expression and receptor binding in the basolateral amygdala. In marked contrast, urocortin mRNA expression in the Edinger-Westphal nucleus and CRF(2A) receptor binding in the lateral septum and ventromedial hypothalamus were increased. Similar findings of an inverse relationship between the CRF(1) and CRF(2A) receptor systems have been reported in an anxiety model based on adverse early-life experience, suggesting the intriguing possibility that CRF neuronal systems may be comprised of two separate, but interrelated, subdivisions that can be coordinately and inversely regulated by stress, anxiety, or anxiolytic drugs.

A comparison of plasma alprazolam concentrations following different routes of chronic administration in the Sprague-Dawley rat: implications for psychotropic drug research.

RATIONALE: Benzodiazepines are effective in the treatment of anxiety disorders over a prolonged period of time. This results in relatively stable plasma concentrations over the course of a day. However, due to differences in drug clearance in rats, which generally metabolize and clear drugs much more rapidly than humans, it is difficult to model this steady level in rats. OBJECTIVES: Several methods of chronic alprazolam administration were compared to determine which would best result in reproducible, therapeutically relevant levels of the drug. METHODS: Male Sprague-Dawley rats were administered alprazolam via two subcutaneous routes, Alzet 2ML2 osmotic minipumps and commercially produced slow-release pellets, for 1 week and 2 weeks, respectively. Additionally, alprazolam was orally administered for 2 weeks by mixing the compound into a commercially available liquid, fat emulsion-based diet. The use of silastic implants to deliver several different benzodiazepines was also evaluated in vitro. RESULTS: Following 7 days of alprazolam administration at 2 mg/kg per day via osmotic minipump, plasma concentrations in ten identically treated rats ranged from <1 ng/ml to 97 ng/ml. Slow-release pellets produced more consistent plasma concentrations, but were only minimally effective at raising plasma concentrations. In vitro studies utilizing silastic implants containing 90 mg drug in 6 cm of tubing revealed stable release of only 45-55 microg/day alprazolam versus 625-650 microg/day diazepam. In contrast to these methodologies, incorporation of alprazolam into a commercially available liquid diet (approximately 25-150 mg/kg per day) provided consistent, dose-dependent increases in plasma concentrations of alprazolam and its metabolites in a range appropriate for mimicking clinical exposure. CONCLUSIONS: These findings indicate that the most effective technique to produce plasma concentrations of alprazolam that are reproducible, clinically pertinent, and consistent between rats is to incorporate the drug into a liquid diet. These findings may also be of value in determining dosing routes for other benzodiazepines or psychotropic drugs.

The neurobiology of urocortin.

Urocortin (UCN) is a recently isolated 40 amino acid-containing neuropeptide that is the second endogenous mammalian ligand for the corticotropin-releasing factor (CRF) receptors. While UCN and CRF both display a similar high affinity for the CRF(1) receptor, the affinity of UCN for the CRF(2) receptor is more than 10-fold higher than that of rat/human CRF. UCN mRNA expression is highest in the Edinger-Westphal nucleus and lateral superior olive, with the most prominent terminal fields found in the lateral septum. Because of the higher relative affinity of UCN for the CRF(2) receptor and the corresponding neuroanatomical distribution of the highest density of UCN expression and innervation to brain regions preferentially expressing the CRF(2) receptor subtype, it has been hypothesized that UCN is the preferred endogenous ligand for the CRF(2) receptor. Following central administration, UCN has been demonstrated to produce behavioral and physiological effects that are qualitatively similar to CRF. Quantitatively, however, UCN appears to be a more potent suppressor of ingestive behavior (food and water intake) and a less potent inducer of anxiogenic behavior than CRF.

Chronic administration of the selective corticotropin-releasing factor 1 receptor antagonist CP-154,526: behavioral, endocrine and neurochemical effects in the rat.

Corticotropin-releasing factor 1 (CRF(1)) receptor antagonists may represent a novel group of drugs for the pharmacotherapy of depression and/or anxiety disorders. We have investigated the behavioral, endocrine, and neurochemical effects of chronic administration of a selective CRF(1) receptor antagonist, CP-154,526. After 9 to 10 days of treatment with CP-154,526 (3.2 mg/kg/day), defensive withdrawal behavior was significantly decreased suggesting anxiolytic activity. In animals treated for 14 days with the low dose of CP-154,526, serum corticosterone concentrations returned to baseline levels faster after application of an airpuff startle. Using in situ hybridization, no changes in CRF(1) receptor mRNA expression were detected in parietal cortex, basolateral amygdala, or cerebellum after chronic treatment with CP-154,526. A dose-dependent decrease in CRF mRNA expression was observed in the hypothalamic paraventricular nucleus (PVN) and the Barrington's nucleus, an effect that was significant at the high but not the low dose of CP-154,526. CP-154,526 did not alter central CRF(2A) receptor binding or mRNA expression, or urocortin mRNA expression. The present findings suggest that chronic administration of CP-154, 526 produces anxiolytic-like effects but no evidence of adrenal insufficiency. Previous postmortem studies revealed increased CRF peptide and mRNA levels in the PVN of depressed patients, which may mediate the hyperactivity of the hypothalamic-pituitary-adrenal axis observed in such patients. In view of a possible use for CRF(1) receptor antagonists in the treatment of depression, the present finding that CP-154,526 decreases CRF synthesis in the PVN is of considerable interest.