The modulator role of the hypothalamic paraventricular nucleus on immune responsiveness.

Role of the paraventricular nucleus of the hypothalamus (PVH) upon immune modulation was studied by either mechanically destroying the PVH (PVHL) or by isolating the PVH (PVHI) with a knife-cut. PVHL or PVHI manipulations induced significant leukopenia characterized by a decrease in the number of neutrophils and lymphocytes two weeks post surgery. The numbers of circulating monocytes and eosinophils were not affected by PVH interventions. In addition, PVHL and PVHI were also associated with a reduction, relative to controls, in the phagocytosis by neutrophils and an increase in blastic transformation of T lymphocytes induced by phytohemagglutinin-M (PHA-M). Antibody titers rose against sheep red blood cells (SRBC) after either PVHL or PVHI were reduced. The magnitude of the SRBC antibody reduction after PVH manipulations was similar to that observed in rats that received a peripheral chemical sympathectomy two hrs prior immunization. Comparison of thyroid hormones blood levels two weeks after PVHL or PVHI revealed significant reductions in comparison with sham-operated group (SO), whereas blood corticosterone was not significantly altered. In summary, we provide evidence that lesion or isolation of the PVH selectively reduces circulating white blood cells and the primary immune response, while it enhances the cell-mediated immune function. Taken together our data showed that PVH modulates immune functions by altering both the peripheral sympathetic tone and thyroid hormone secretion.

The interaction between the cholinergic and dopaminergic system in learning and memory process in rats.

In normal rats, muscarinic acetylcholine receptors (mAChRs) have a facilitating role on both short-term and long-term memory tested by Y-maze task and multi-trial passive avoidance test, respectively, since scopolamine, a specific mAChRs antagonist, impairs both types of memory. A low dose of nicotine (0.3 mg/kg b.w., i.p.), a specific nicotinic acetylcholine receptors (nAChRs) agonist, administered once caused a significant facilitating effect on short-term memory. A higher dose of nicotine (3 mg/kg b.w., i.p.) administered 5 consecutively days had about the same facilitating effect on short- and long-term memory without affecting information acquisition. In rats, having mAChRs and nAChRs blocked by means of scopolamine and chlorisondamine respectively, a low dose of nicotine administered once caused a significant improvement of long-term memory deficits without affecting significantly short-term memory. A higher dose of nicotine administered 5 consecutive days in rats with a double blockade of cholinergic receptors had the same ameliorating effect on long-term memory deficits as low dose. Our data suggest that the antiamnesic effect of nicotine can result from an action at nicotinic receptors subtypes not blocked by chlorisondamine or at nonnicotinic receptors.

Role of the mesotelencephalic dopamine system in learning and memory processes in the rat.

The effects of lesioning the ventral tegmental area or substantia nigra pars reticulata by means of bilateral microinjections of two doses of kainic acid (50 ng/250 nl and 100 ng/500 nl) or 6-hydroxydopamine (8 microg/4 microl) were investigated to clarify the role of the mesotelencephalic dopamine system in learning and memory processes. Our findings suggest that ventral tegmental area and substantia nigra dopaminergic neurons play an important role in retention of both short-term memory, tested in the Y-maze task and long-term memory evaluated with the multi-trial passive avoidance test, without affecting memory acquisition. As compared to short-term memory, long-term memory is more susceptible to the decreased dopamine level in nervous structures involved in processing and storage of information.

Effects of nicotine on memory impairment induced by blockade of muscarinic, nicotinic and dopamine D2 receptors in rats.

Scopolamine dose-dependently inhibits passive avoidance latency and decreases spontaneous alternation in the Y-maze, suggesting effects on long-term and short-term memory, respectively. Chlorisondamine (10 mg/kg), a compound which produces a long-lasting central nicotinic receptor blockade, did not affect short-term and long-term memory performance. In normal rats, nicotine at the doses of 0.3, 1.0, and 3.0 mg/kg administered once had a facilitating effect on short-term memory; a higher dose (3.0 mg/kg) did not show a more pronounced effect than a lower one (0.3 mg/kg). Nicotine, by activating the nicotinic acetylcholine receptors, attenuated the impairment of short-term memory induced by muscarinic or dopamine D2 receptor blockade. On long-term memory, a single dose of nicotine (0.3, 1.0, 3.0 mg/kg) did not affect memory performance, but improved it after chronic (10 consecutive days, 0.3 mg/kg) administration. The antiamnesic effect of nicotine administered once was observed in scopolamine-, scopolamine+chlorisondamine- or sulpiride-treated rats. These results suggest that the antiamnesic effect of nicotine can result from an action at nicotinic receptors subtypes not blocked by chlorisondamine or at nonnicotinic receptors.