Michael J. Owens

Effects of 5-HT1A receptor agonists on hypothalamo-pituttary-adrenal axis activity and cortlcotropin-releasing factor containing neurons in the rat brain

Corticotropin-releasing factor (CRF) is the major physiological regulator of the hypothalamo-pituitary-adrenal axis. There is evidence that CRF release from the hypothalamus is under stimulatory serotonergic control. The specific 5-HT receptor subtypes that mediate this effect is unclear. Administration of the 5-HT1A agonists, 8-OH-DPAT (1 mg/kg) and ipsapirone (4 mg/kg), to rats resulted in activation of the HPA axis as evidenced by increased plasma ACTH and corticosterone concentrations in acutely treated rats and increased plasma corticosterone concentrations in both acutely and chronically treated rats. However, chronic administration of these compounds failed to alter CRF concentrations in the medium eminence or CRF receptor number of affinity in the anterior pituitary. Chronic administration of both compounds resulted in increased CRF concentrations in the piriform cortex and hippocampus, whereas 8-OH-DPAT alone increased CRF concentrations in the amygdala and entorhinal cortex. These results suggest that both hypothalamic and extrahypothalamic CRF neurons are influenced by activation of 5-HT1A receptors.

5a-Pregnane-3a,21-diol-20-one (THDOC) attenuates mild stress-induced increases in plasma corticosterone via a non-glucocorticoid mechanism: comparison with alprazolam

5 alpha-Pregnane-3 alpha,21-diol-20-one (THDOC; 5 mg/kg) and the triazolobenzodiazepine alprazolam (1 mg/kg) attenuated mild stress-induced increases in plasma corticosterone concentrations via GABAergic mechanisms. Unlike alprazolam, THDOC failed to decrease corticotropin-releasing factor (CRF) concentrations in the locus ceruleus. While THDOC may plausibly act via endogenous GABAergic mechanisms to reduce stress-induced endocrine and behavioral responses that are likely mediated in part by CRF neurons, these preliminary findings suggest that, at the dose and time point studied, THDOC does not identically mimic the actions of alprazolam, another drug which potentiates GABAergic activity.

Potential Corticotropin-Releasing Factor Pathways in the Rat Brain as Determined by Bilateral Electrolytic Lesions of the Central Amygdaloid Nucleus and the Paraventricular Nucleus of the Hypothalamus

The projection fields of corticotropin‐releasing factor (CRF)‐containing perikarya in the rat central nervous system were studied using a combination of electrolytic lesions, microdissection and radioimmunoassay. The effects of bilateral electrolytic lesions of the central nucleus of the amygdala (Ce) or the paraventricular nucleus (PVN) of the hypothalamus were measured by a sensitive and specific radioimmunoassay. Following lesions of the Ce, CRF concentrations in the locus ceruleus (LC) were significantly decreased. Following lesions of the PVN, CRF concentrations in the median eminence were markedly decreased (>85%), with smaller but consistent reductions of CRF in the hippocampus as well. In contrast to the Ce lesions, PVN lesions resulted in increases in CRF concentratixhtmlons in the LC.

SUBCELLULAR DISTRIBUTION OF CORTICOTROPIN-RELEASING-FACTOR-LIKE IMMUNOREACTIVITY IN RAT CENTRAL NERVOUS SYSTEM

Corticotropin-releasing-factor-like immunoreactivity (CRF-LI) was measured in a number of subcellular fractions from rat brain using a highly sensitive and specific radioimmunoassay. CRF-LI was highly enriched in the crude synaptosomal/mitochondrial fraction (P2) relative to the homogenate, P1, S1, and S2 fractions. Separation of the P2 fraction into synaptosomal, myelin, and mitochondria-enriched subfractions on a rapid one-step sucrose gradient revealed that CRF-LI was present at higher concentration in the synaptosomal fraction than in the mitochondrial and myelin fractions. The distribution of CRF-LI paralleled that of synapsin, a synaptic vesicle marker phosphoprotein, but not that of pyruvate dehydrogenase, a mitochondrial phosphoprotein. These results are consistent with a nerve terminal localization of CRF and a potential role for this peptide as a central nervous system neurotransmitter.

Preliminary studies of 6β-hydroxydexamethasone and its importance in the DST

Abstract The role of the metabolites of dexamethasone (DEX) in the dexamethasone suppression test (DST) has never been fully elucidated. We report here our preliminary studies of 6β-hydroxydexamethasone (6 OH-Dex), a known metabolite of DEX, on the hypothalamic-pituitary-adrenal (HPA) axis of the rat; its activity in the most commonly used radioimmunoassay for plasma DEX; and its plasma concentrations in a normal human subject during the standard 1.0 mg DST. Six OH-Dex administered subcutaneously to rats at a dose of 1 mg/kg was able to completely suppress corticosterone production for at least 3 hr. In the IgG Corp. radioimmunoassay for plasma DEX, 6 OH-Dex was moderately cross-reactive yielding a 50% cross-reactivity of 10%. Gas chromatographic coupled mass spectroscopic analysis of human plasma samples, obtained 12 to 20 hr after the oral ingestion of 1.0 mg DEX, demonstrated similar plasma concentrations for both the parent compound and the 6-hydroxyl metabolite. The relevance of these findings, particularly to pharmacokinetic studies of the DST, is discussed.

Preclinical and Clinical Investigations of Corticotropin-Releasing Factor: Assessment of Its Role in Depressive Disorders

Starting with nearly a half million hypothalami, Vale and his colleagues1 succeeded in determining the amino acid sequence of ovine corticotropin-releasing factor (CRF) in 1981. Shortly thereafter, human and rat CRF were sequenced and found to be identical; they differed from ovine CRF (oCRF) in only 7 of the 41 amino acid residues. The endocrine role of CRF as the major physiological regulator of ACTH and β-endorphin secretion from the anterior pituitary has now been well established. However, considerable data have accumulated from a variety of disciplines which indicate that this peptide plays an important neurobiological role apart from its neuroendocrine role. These findings have been comprehensively reviewed elsewhere.2