Sustained increase in adrenergic activity in gerbil striatum following transient ischemia

Pivotal roles of alpha-melanocyte-stimulating hormone and the melanocortin 4 receptor in leptin stimulation of prolactin secretion in rats

Leptin, the obese gene product, was reported to stimulate prolactin (PRL) secretion, but the neuroendocrine mechanism underlying this hormonal response is largely unknown. Thus, in this study we examined the involvement of several important PRL regulators in the leptin-induced PRL secretion in male rats. Compared with the values in normally fed rats, food deprivation for 3 days significantly decreased both PRL and leptin levels in the plasma. These changes were reverted to normal by a 3-day constant infusion of 75 microg/kg/day of leptin to the fasted rats, while 225 microg/kg/day of leptin further elevated both PRL and leptin levels. These four groups of animals were used for the following experiments. Results of dopamine and serotonin turnover studies in the brain and the pituitary indicated that neither of these biogenic amines plays a primary role in mediating leptin's effects on PRL. Repeated intracerebroventricular injections over 72 h of neutralizing antibodies against vasoactive intestinal peptide, PRL-releasing peptide, or beta-endorphin, did not significantly suppress the leptin actions. However, both the blockade of the melanocortin (MC) 4 receptor (R) and the immunoquenching of brain alpha-melanocyte-stimulating hormone (alpha-MSH) completely abolished the leptin-induced PRL release, and the stimulation of the MC4-R, but not the MC3-R, significantly elevated PRL levels in the fasted rats. These results suggest that alpha-MSH, a cleaved peptide from pro-opiomelanocortin of which synthesis is stimulated by leptin, may be the pivotal neuropeptide in the brain mediating the leptin's stimulatory influence on PRL secretion. It was also suggested that the MC4-R may be the primary subtype of the MC-Rs mediating this action of alpha-MSH.

Relationship between locomotor activity and monoamines following single and double transient forebrain ischemia in gerbils

The relationship between locomotor activity and monoamine levels in gerbils after single and/or double forebrain ischemic insult was studied. Locomotor hyperactivity was observed after the first ischemic episode, but the gerbils failed to show hyperactivity after the second ischemic episode induced one week later. The monoamine levels were determined in order to clarify the biochemical basis of post-ischemic locomotor hyperactivity. Norepinephrine increased in response to first ischemic episode but remained at normal levels after the second episode of ischemia. Metabolites of dopamine and serotonin increased after both the first and second ischemic insults, which indicates that these monoamines do not play significant roles in post-ischemic locomotor activity. Therefore, increases in norepinephrine after first ischemic insult may play a role in increasing locomotor activity during the period following such an episode.

A dual-probe microdialysis study in simultaneously monitoring extracellular pyruvate, lactate, and biogenic amines in gerbil striata during unilateral cerebral ischemia

A dual-probe microdialysis technique coupled with liquid chromatographic assays was developed for the simultaneous monitoring of neurochemicals in gerbil striata during cerebral ischemia. Isocratic separation of lactate and pyruvate was achieved within 5 min whereas the separation of biogenic amines was completed within 30 min. An unilateral ligation was produced by occlusion of the right common carotid artery for 30 mins in anesthetized gerbils to perform a typical focal cerebral ischemia. Microdialysis probes were inserted in both sides of the striata to simultaneously monitor biogenic amines, lactate and pyruvate during cerebral ischemia. Dynamic and comparative changes of these analytes in ipsilateral and contralateral sides of the brain can be simultaneously measured by the assay. The present assay can be used as a research tool to explore neurochemical substances and their relationships during cerebral ischemia.

Concentration of catecholamines and indoleamines in the cerebrospinal fluid of patients with vascular parkinsonism compared to Parkinson's disease patients

The concentration of catecholamines and indoleamines in the cerebrospinal fluid of patients with vascular parkinsonism (VP) was compared to that in patients with Parkinson's disease (PD) and controls. Compared to the controls, the concentration of tyrosine was significantly higher, and the concentration of L-dopa and 3-O-methyldopa (3-OMD) was significantly lower in both VP and PD patients. The balance between the 3-OMD/L-dopa and dopamine (DA)/L-dopa ratios was changed in favor of 3-OMD/L-dopa in both VP patients and PD patients suggesting the preservation of a compensatory mechanism. All these changes were less marked in VP patients than in PD patients. A remarkable finding was that in contrast to PD patients the concentration of DA and norepinephrine (NE) was significantly higher in VP patients than in the controls. The decrease in the concentration of 5-hydroxytryptamine (5-HT) was significantly greater in VP patients than in PD patients. In PD patients, the concentration of DA, NE, and 5-HT showed significant correlation with the severity of motor symptoms. In VP patients, the concentration of 5-HT alone showed significant correlation with the severity of motor symptoms and cognitive dysfunction. These findings suggest that VP patients may have similar disturbances in the DA synthesis pathway as PD patients, but differ from PD patients in that the concentrations of DA and NE are elevated and the decrease in the 5-HT concentration is greater in VP patients.

An attenuated alpha-1 potentiation of beta adrenoceptor-stimulated cyclic AMP formation after repeated saline injections in Fischer 344 strain rats

We investigated the behavioral and neurochemical features of Fischer 344 strain rats in which a depressive state was induced by repeated handling and saline injections as a mild stressor. The repeated intraperitoneal injections of saline (2 ml/kg, twice a day for 14 days) elicited a moderate suppression of body weight gain, a decrease in their open field activity and a prolonged immobility in the tail suspension test. In the stress-exposed rats, the tissue content of norepinephrine (NE) was increased in the cerebral cortex and hypothalamus, whereas that of dopamine or serotonin was not affected. Although the stress exposure did not affect the binding properties of either the alpha-1 or beta adrenoceptors, it suppressed cAMP formation stimulated by NE, but not by isoproterenol or forskolin, in the cerebral cortical slices. In the presence of prazosin or phorbol ester, the difference in NE-stimulated cAMP formation between the control and the stress groups was totally abolished. Phenylephrine enhanced isoproterenol-stimulated cAMP formation in the control but not in the stress group. From these results, it is postulated that the alpha-1 potentiation of beta adrenoceptor- stimulated cAMP formation was attenuated in the stress group. These findings suggest that the manipulation of mild stressor with repeated handling and saline injections to Fischer 344 rats elicits a depressive state characterized by the behavioral changes and the attenuated alpha-1 potentiation in the cerebral cortex, and that this manipulation might be available for the study of the stress-induced depressive state as a generally acceptable mild stress model.