Effect of peripheral cholinergic activation on the adrenal cortex function

Peripheral involvement in nicotine-induced enhancement of ethanol intake

It is a well-known fact that a large percentage of alcoholics smoke, and in the experimental rat, intermittent nicotine administration enhances ethanol intake and ethanol preference in a free-choice situation between 6% (v/v) ethanol and water. The present study focuses on the possible involvement of central and/or peripheral nicotine acetylcholine receptors (nAChR) in nicotine-induced sensitization to dopamine-related behavioral effects of ethanol. Wistar rats drinking less than 60% of their total daily fluid from a 6% ethanol solution were used in the study. Nicotine, vehicle, mecamylamine, hexamethonium, mecamylamine+nicotine, and hexamethonium+nicotine were administered subchronically for 15 days. All groups, except the vehicle pre-treated group, markedly increased their ethanol preference to approximately 80%, as well as their ethanol intake. NMRI mice received the same treatments for 10 days, after which ethanol (2.5 g/kg, intraperitoneal (i.p.)) was given acutely and locomotor activity was recorded. Ethanol-induced locomotor stimulation was enhanced in most groups, as compared to the vehicle pre-treated group. Administration of quarternary autonomic drugs to ethanol high-preferring rats (hexamethonium, methscopolamine, sotalol and phentolamine) according to different acute and chronic treatment protocols indicated that the enhanced ethanol intake may involve increased ganglionic and/or peripheral muscarinic neurotransmission. Taken together, the above results indicate that peripheral mechanisms may be involved in the enhancement of dopamine-related behavioral effects of ethanol observed after subchronic intermittent treatment with nicotinic drugs.

Biochemical evidence for peripheral neural regulation of adrenocortical regeneration in response to bilateral adrenal enucleation

Male Sprague-Dawley rats (130-150 g) with bilateral adrenal enucleation were used in this study. Animals were sacrificed at 2, 7, and 11 days post enucleation and plasma corticosterone and adrenal gland acetylcholine-esterase (AChE), choline acetyltransferase (ChAT), corticosterone, epinephrine (EP) and norepinephrine (NE) were assayed. The results show a progressive and gradual increase in plasma and adrenal corticosterone levels, AChE, ChAT, EP, and NE levels in the regenerating adrenal cortex from day 2 to day 11 post bilateral adrenal enucleation. At day 11 post surgery, the activities of ChAT and AChE were 60% and 25%, respectively when compared to sham operated control. The EP and NE levels returned to normal levels after 11 days post surgery in the regenerating gland when compared to the sham control. The presence of both cholinergic enzymes and the availability of high levels of catecholamine strongly suggest a progressive development of sympathetic innervation in the regenerating adrenal cortex.

Antagonism of physostigmine induced hypothermia and neuroendocrine changes following exposure to different environmental temperatures

1. The magnitude of physostigmine-induced hypothermia increased with decreasing environmental temperature. 2. The hypothermic response was accompanied by significant changes in plasma levels of corticosterone, glucose and fatty acids. 3. Central cholinergic mediation appears to be a significant component of physostigmine-induced hypothermia and neuroendocrine changes at moderate temperature. 4. At lower ambient temperatures cholinergic blockers produced less antagonism of physostigmine-induced effects. 5. The decreased effectiveness of cholinergic blockers at low environmental temperatures and the increased plasma fatty acid levels under almost all conditions studied may be of importance in considering long term therapy with cholinergic agonists.

Plasma corticosterone is increased and correlated with brain acetylcholine in physostigmine- but not in neostigmine-treated rats

Rats were given intraperitoneal injections of physostigmine (PHYSO), neostigmine (NEO) or saline (SAL). Either 15 or 30 min later the number and intensity of observable cholinomimetic effects (OCE) was determined, plasma was collected for corticosterone (Cst) measurement, and the cerebral cortex, striatum, hippocampus and hypothalamus were removed after microwave treatment for the measurement of tissue acetylcholine (ACh) and choline (Ch) concentrations. Plasma Cst correlated with the number of OCEs at both 15 and 30 min in both NEO- and PHYSO-treated animals. Although the number and intensity of OCE were the same in NEO- and PHYSO-treated animals 15 min after injection, plasma Cst was significantly higher in the PHYSO-treated group. ACh levels in the cortex were also increased in PHYSO- compared with NEO-treated animals 15 min after injection. Ch levels remained unchanged. Plasma Cst correlated positively with ACh levels in the cortex and striatum in PHYSO-treated rats both 15 and 30 min after injection. These data support the involvement of central cholinergic mechanisms in the regulation of the HPA axis.

Time course of physostigmine effects on neuroendocrine responding at varying environmental temperatures

1. Hypothermia was found to be related to both the dose of physostigmine and the environmental temperature. 2. Plasma corticosterone levels were elevated above controls regardless of dose of physostigmine or environmental temperature. 3. Plasma free fatty acid levels appeared to be inversely related to physostigmine-induced hypothermia. 4. A hyperglycemic response was observed under all experimental conditions at 0.5 hours and 1.0 hour post injection. 5. Significant inhibition of brain acetylcholinesterase was observed, whereas, plasma and erythrocyte acetylcholinesterase activity was inconsistent.

Effects of muscarinic receptor antagonism upon two forms of stress-induced analgesia

The present study assessed in rats the effects of muscarinic receptor antagonism upon analgesia induced by cold-water swims (CWS: 2 degrees C for 3.5 min) and 2-deoxy-D-glucose (2DG: 600 mg/kg). First, CWS analgesia was significantly reduced 30 min after the swim by scopolamine (0.01 and 0.1 mg/kg) and methylscopolamine (10 mg/kg) pretreatment, and was eliminated 60 min after the swim by scopolamine (0.01-10 mg/kg) and methylscopolamine (1,10 mg/kg) pretreatment. In contrast, scopolamine potentiated CWS hypothermia. Second, while scopolamine (1 mg/kg) and methylscopolamine (1,10 mg/kg) pretreatment prolonged 2DG analgesia, both antagonists dose-dependently reduced 2DG hyperphagia. Third, the changes in analgesic and hypothermic stress responses were not due to baseline shifts in jump thresholds or body temperatures. However the dose-dependent reductions by scopolamine and methylscopolamine in baseline food intake and 2DG hyperphagia were significantly correlated. Fourth, the dose-dependent reduction by scopolamine and methylscopolamine of pilocarpine analgesia differed in pattern from the other analgesic effects, suggesting heterogeneity in muscarinic receptor modulation of different analgesic responses.

The effect of adrenalectomy and dexamethasone on the antinociceptive effects of physostigmine

The tail-flick procedure was used to study the antinociceptive effects of physostigmine in adrenalectomized and sham-operated rats. At 5 days after surgery, they were tested 30 min after either 0.32 or 0.45 mg/kg IP physostigmine. Adrenalectomized animals showed significantly greater elevation of TF scores from predrug latencies than the sham controls at both doses of physostigmine. Following 3 days of dexamethasone replacement therapy on days 18, 19, and 20 post-surgery the antinociceptive effects of physostigmine were uniformly attenuated across doses or surgical groups. On the other hand, animals receiving saline injection instead of dexamethasone did not manifest any reduction of the physostigmine antinociceptive effect. The potentiation by adrenalectomy and the reduction following dexamethasone of the antinociceptive effects of physostigmine suggest that these effects may be mediated through hypothalamic-pituitary-adrenal mechanisms and are consistent with beta-endorphin-induced sensitization of opiate or cholinergic receptors.