Sexually diergic hypothalamic-pituitary-adrenal axis responses to selective and non-selective muscarinic antagonists prior to cholinergic stimulation by physostigmine in rats.

Central cholinergic systems regulate the hypothalamic-pituitary-adrenal (HPA) axis differentially in males and females (sexual diergism). We previously investigated the role of muscarinic receptors in this regulation by administering physostigmine (PHYSO), an acetylcholinesterase inhibitor, to male and female rats pretreated with scopolamine (SCOP), a nonselective muscarinic antagonist. SCOP pretreatment enhanced adrenocorticotropic hormone (ACTH) and corticosterone (CORT) responses in both sexes, but males had greater ACTH responses while females had greater CORT responses.

Influence of environmental enrichment on hypothalamic-pituitary-adrenal (HPA) responses to single-dose nicotine, continuous nicotine by osmotic mini-pumps, and nicotine withdrawal by mecamylamine in male and female rats.

In the present study, we determined the effects of environmental enrichment (EE; Kong Toys and Nestlets) on sexually diergic HPA axis responses to single-dose nicotine (NIC), single-dose NIC following continuous NIC administration for two weeks, and NIC withdrawal by single-dose mecamylamine (MEC) in male and female rats. Blood sampling occurred before and after MEC and NIC administrations for the determination of adrenocorticotropic hormone (ACTH) and corticosterone (CORT). Supporting and extending our previous findings, EE appeared to produce anxiolytic effects by reducing hormone responses: Male and female rats housed with EE had lower baseline ACTH and significantly lower HPA axis responses to the mild stress of saline (SAL) injection than did those housed without EE.

Sexually diergic hypothalamic-pituitary-adrenal (HPA) responses to single-dose nicotine, continuous nicotine infusion, and nicotine withdrawal by mecamylamine in rats.

Hypothalamic-pituitary-adrenal (HPA) responses to single-dose nicotine (NIC) are sexually diergic: Female rats have higher adrenocorticotropic hormone (ACTH) and corticosterone (CORT) responses than do males. In the present study we determined HPA responses in male and female rats following single doses of NIC, a single-dose of NIC immediately following continuous NIC for two weeks, and NIC withdrawal by single-dose mecamylamine (MEC) following continuous NIC infusion for two weeks. Blood sampling occurred before and after MEC and NIC administrations for the determination of ACTH and CORT.

Sexually diergic, dose-dependent hypothalamic-pituitary-adrenal axis responses to nicotine in a dynamic in vitro perfusion system.

Introduction: The hypothalamic-pituitary-adrenal cortical (HPA) axis modulates physiological responses to stress. We previously reported sexually diergic, dose-dependent HPA responses in vivo following nicotine administration: Male rats had greater arginine vasopressin (AVP) responses than females, and female rats had greater adrenocorticotropic hormone (ACTH) and corticosterone (CORT) responses than males. The goal of the present study was to further investigate sexually diergic, dose-dependent HPA responses following nicotine addition to an in vitro model of the HPA axis, so that hormone output could be determined at each level of the axis.

Sequence of pituitary-adrenal cortical hormone responses to low-dose physostigmine administration in young adult women and men.

We previously demonstrated greater HPA axis activation in adult men compared to adult women following low-dose administration of the anticholinesterase inhibitor, physostigmine (PHYSO). Because blood sampling was done infrequently following PHYSO, the rise times of AVP, ACTH1-39, and cortisol could not be determined. In the present study, we determined the sequence of hormone increases by frequent blood sampling following PHYSO.

Adrenal cortical responses to low- and high-dose ACTH(1-24) administration in major depressives vs. matched controls.

Increased hypothalamo-pituitary-adrenocortical (HPA) axis activity occurs in 30-50% of patients with major depression. This includes normal-to-increased adrenal cortical hormone (cortisol) secretion in spite of reduced corticotropin (ACTH) stimulation. A possible explanation is increased adrenal responsiveness to ACTH.

Growth hormone responses to low-dose physostigmine in elderly vs. young women and men.

Background: Growth hormone (GH) secretion is a sensitive measure of CNS cholinergic neurotransmission, and GH decreases considerably with age. Cholinesterase inhibitors, which increase acetylcholine concentrations, have been used in elderly subjects to investigate the neuroendocrine effects of aging and Alzheimer's disease. However, there have been only a few studies of a potential sex difference in GH responses to cholinesterase inhibitors in elderly subjects, with mixed results.

Novel in vitro perfusion system for the determination of hypothalamic-pituitary-adrenal axis responses.

Introduction: The hypothalamic-pituitary-adrenal (HPA) axis is a three-gland component of the endocrine system and a key modulator of the stress response. We have developed a novel in vitro perfusion system to enable the study of pharmacological and hormonal challenges to tissue components of the HPA axis. In vivo studies have shown functional sex differences (sexual diergism) in HPA responses to cholinergic drugs, and in the present in vitro study, we examine these differences at several levels of the HPA axis.

Rat estrous cycle influences the sexual diergism of HPA axis stimulation by nicotine.

We previously reported that female rats had significantly greater hypothalamic-pituitary-adrenal (HPA) axis responses to cholinergic stimulation by nicotine (NIC) than did male rats. Females in defined estrous cycle stages, however, were not studied because of sample size limitations. We further explored this finding by determining HPA axis responses to two doses of NIC in female rats (N = 101) during different estrous cycle stages, and in males (N = 69).

Environmental enrichment lowers stress-responsive hormones in singly housed male and female rats.

Structural and social aspects of an environmental system can influence the physiology and behavior of animals occupying that system. This study examined the physiological effects of environmental enrichment (EE) with Kong Toys and Nestlets on stress-responsive hormones of the hypothalamic-pituitary-adrenal (HPA) axis under basal and mild stress conditions in singly housed, jugular vein-cannulated, male and female rats. Animals of both sexes housed with EE had significantly lower baseline adrenocorticotropic hormone (ACTH) and corticosterone (CORT) concentrations compared to those housed without EE.

Plasma leptin suppression by arginine vasopressin in normal women and men.

Leptin inhibits appetite by activating several neuroendocrine systems, including the hypothalamo-pituitary-adrenal cortical (HPA) axis. In turn, elevated glucocorticoids can increase circulating leptin. We therefore measured plasma leptin in 12 normal women and eight normal men administered low-dose physostigmine (PHYSO) and arginine vasopressin (AVP) to stimulate the HPA axis.

Sexual diergism of baseline plasma leptin and leptin suppression by arginine vasopressin in major depressives and matched controls.

Leptin inhibits appetite by activating several neuroendocrine systems, including the hypothalamo-pituitary-adrenal cortical (HPA) axis. In turn, chronically elevated glucocorticoids increase circulating leptin. HPA axis hyperactivity occurs in 30-50% of patients with major depression, but the few prior reports of leptin measurements in this illness have shown inconsistent results.

Estrous cycle influences on sexual diergism of HPA axis responses to cholinergic stimulation in rats.

Central cholinergic systems differentially modulate hypothalamic-pituitary-adrenal (HPA) axis activity in female and male animals (sexual diergism). We previously reported that male rats had significantly greater HPA axis responses to stimulation by physostigmine (PHYSO), an acetylcholinesterase (AChE) inhibitor, compared to females. Females in defined estrous cycle stages, however, were not studied because of sample size limitations.

Sexual diergism of hypothalamo-pituitary-adrenal cortical responses to low-dose physotigmine in elderly vs. young women and men.

We previously demonstrated that the reversible cholinesterase inhibitor, physostigmine (PHYSO), administered to normal young adult women and men (average age 35 years) at a dose that produced few or no side effects, resulted in a sex difference (sexual diergism) in hypothalamo-pituitary-adrenal cortical (HPA) axis responses: Plasma ACTH(1-39), cortisol, and arginine vasopressin (AVP) concentrations increased to a significantly greater extent in the men than in the women. To explore the effect of age on these sexually diergic hormone responses, in the present study we used the same dose of PHYSO (8 microg/kg IV) to stimulate ACTH(1-39), cortisol, and AVP secretion in normal elderly, non-estrogen-replaced women and elderly men (average ages 73 years and 70 years, respectively). The subjects underwent three test sessions 5-7 days apart: PHYSO, saline control, and a second session of PHYSO.