Blocking effects of ethanol on stress-induced activation of rat mesoprefrontal dopamine neurons.

We investigated the effects of ethanol on stress-induced activation of the brain dopamine (DA) systems in rats. Ethanol (0.5 and 1.0 g/kg) was injected IP 25 min before sacrifice (5 min before 20-min immobilization stress). Ethanol treatment by itself did not affect the levels of either DA or its major metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), in the mesoprefrontal cortex, cingulate cortex, olfactory tubercle, or caudate putamen. Immobilization stress for 20 min caused increases in DOPAC levels in the prefrontal cortex (160% of control) and cingulate cortex (135% of control), but not in the olfactory tubercle or caudate putamen. The stress had no effects on DA levels in any of the four brain regions studied. Pretreatment with ethanol blocked, in a dose-dependent manner, the stress-induced increases in DOPAC levels in the mesoprefrontal cortex. The present data suggest that ethanol exhibits a blocking effect on stress-induced activation of the mesoprefrontal DA neurons. This blocking effect may be related to the anxiolytic action of ethanol.

Effects of acute and repeated alcohol ingestion on hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal functioning in normal males.

We investigated the effects of acute and repeated alcohol ingestion on plasma levels of hormones associated with the functioning of the hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-adrenal (HPA) systems in normal males. In the first experiment, 7 normal male subjects were given ethanol (1.3 g/kg) in the form of a 43% alcohol solution of whiskey and water over a 30-min period (from 19:00 h to 19:30 h); blood samples were collected 30 min and immediately before the beginning of alcohol ingestion and then at intervals of 30 min for 180 min. Blood ethanol levels rose sharply and reached their maximum at 60 min, remaining above 1.0 mg/ml until 180 min. Prolactin levels increased, reaching a peak at 60 min, gradually returning to the initial value at 180 min. Decreased testosterone levels were observed only at 30 min. Luteinizing hormone (LH), adrenocorticotrophic hormone (ACTH) and cortisol levels did not show any increases. In the second experiment, 9 normal males were given the same dose of alcohol, but this was given on 7 consecutive evenings and the hormonal changes were examined on the 1st and 7th days, only at 30 and 60 min after alcohol ingestion began (during the period that blood ethanol levels were ascending to their peak). The results on the 1st day reconfirmed the findings in the first experiment and on the 7th day, the last alcohol ingestion produced increases in prolactin levels and decreases in testosterone levels at 30 and 60 min, but did not change other hormone levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin B12 accelerates re-entrainment of activity rhythms in rats.

The effects of methyl vitamin B12 (5-6 mg/kg, p.o.) on the entrainment of circadian running wheel activity rhythm to a new lighting schedule were measured in rats. After the light-dark (LD) cycle was abruptly reversed, rats given vitamin B12 took less time to entrain their circadian locomotor activity rhythm to the new cycle than did controls. This result indicates that vitamin B12 accelerates the reentrainment of the mammalian circadian activity rhythm following an abrupt change in the environmental LD cycle.

Pentobarbital attenuates stress-induced increases in noradrenaline release in specific brain regions of rats.

To examine whether anxiolytic action of drugs acting at the GABA/BZD-chloride channel complex may be related to the brain noradrenergic system, we investigated the effect of pentobarbital, a typical barbiturate which has potent GABA modulating properties, on increased NA release in nine brain regions of stressed rats. Pentobarbital (10 and 25 mg/kg) was injected IP 65 min before sacrifice (5 min before one-hour immobilization stress). Levels of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), the major metabolite of brain noradrenaline (NA), and of plasma corticosterone, were fluorometrically determined. Pentobarbital treatment by itself increased MHPG-SO4 levels in the thalamus, locus coeruleus (LC) region, midbrain and basal ganglia of nonstressed rats. Stress produced increases in MHPG-SO4 levels in all brain regions examined and elevation of plasma corticosterone levels. Pentobarbital attenuated, in a dose-dependent manner, stress-induced increases in MHPG-SO4 levels in the hypothalamus, thalamus, anterior cerebral cortex, LC region and basal ganglia and also attenuated the stress-induced elevation of plasma corticosterone levels. These data suggest that pentobarbital can attenuate both stress-induced increases in NA release in specific brain regions as well as activation of the hypothalamo-pituitary-adrenocortical system. These attenuating effects may be related to the anxiolytic action of barbiturates.

Met-enkephalin, injected during the early phase of stress, attenuates stress-induced increases in noradrenaline release in rat brain regions.

By measuring levels of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), the major metabolite of noradrenaline (NA), we investigated the effects of Met-enkephalin (Met-ENK) ICV injected at three different stages of stress, i.e., 0 min, 5 min, or 10 min after exposure to immobilization stress. Immobilization stress caused significant increases in MHPG-SO4 levels in all brain regions examined, i.e., the hypothalamus, amygdala, thalamus, midbrain, hippocampus and locus coeruleus (LC), which suggests that stress increases NA release in these regions. Met-ENK at a dose of 50 micrograms, injected ICV immediately before stress exposure significantly attenuated stress-induced increases in MHPG-SO4 in the amygdala, thalamus and LC, but did not have such an effect when injected either 5 min or 10 min or 10 min after exposure to stress. Similarly, Met-ENK at 150 micrograms at 0 min significantly attenuated these increases in all brain regions examined, however, it did not do so when given at 5 min or 10 min after stress initiation. The amount of defecation and the weight loss caused by stress were also significantly attenuated by Met-ENK injected but only at 0 min. These results suggest that the attenuating effect of Met-ENK on stress-induced increases in NA release is greatly affected by the time of the peptide administration and that Met-ENK might inhibit stress-induced increases in NA release in these regions by affecting the initial changes induced by stress.

Effects of neurotropin on regional brain noradrenaline metabolism in rats.

By measuring levels of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in various rat brain regions, we investigated the effects of an extract isolated from vaccinia virus-inoculated and inflamed skin or tissue of rabbits (Neurotropin, NSP), administered acutely or chronically, on regional NA metabolism in stressed and nonstressed rats. An acute administration of NSP at 50 mg/kg significantly elevated MHPG-SO4 levels in the amygdala and cerebral cortex; and 100 mg/kg of the drug significantly increased the metabolite levels in the hypothalamus, amygdala, thalamus, midbrain, cerebral cortex and pons plus medulla oblongata without affecting NA levels. This suggests that acutely injected NSP slightly increases NA release in these brain regions. One hour immobilization stress caused significant increases in MHPG-SO4 levels, which were not affected by pretreatment with either 50 mg/kg or 100 mg/kg of NSP. Chronic injection with NSP daily at either 50 mg/kg or 100 mg/kg for 7 days was without effect on NA metabolism in all brain regions examined. However, increases in MHPG-SO4 levels caused by stress were significantly attenuated in some regions including the hypothalamus, amygdala and midbrain in chronic NSP-treated rats. This indicates that although an acute administration of NSP slightly increases brain NA release, a chronic treatment with NSP rather attenuates increases in NA release caused by immobilization stress in brain regions such as the hypothalamus, amygdala and midbrain. This suggests a possibility that these attenuating effects on stress-induced increases in brain NA release caused by chronic administration of NSP might be related to the stress-reducing or anti-stress properties of NSP.

Stressor predictability and rat brain noradrenaline metabolism.

This study examined the effects of stressor predictability on regional rat brain noradrenaline (NA) turnover, by measuring levels of a principal metabolite of NA (3-methoxy-4-hydroxyphenylethyleneglycol sulfate, MHPG-SO4). Male Wistar rats were exposed to one of three shock conditions for 19 hr: nonshock, signalled, and unsignalled shocks. Rats in the shock conditions received shock (1.2 mA intensity, 2 sec duration) on a 2.5 min variable time (VT) either preceded by a 12-sec, 10-W light signal (signal-shock interval of 10 sec) or not preceded by this signal. The tail electrodes for these rats were in series, so that the shock received by all rats was of exactly the same number and duration. After 19 hr in a VT-2.5 min shock session, the rats exposed to unsignalled shock (unpredictable group) showed significantly greater increases in MHPG-SO4 levels in the hypothalamus, amygdala, midbrain, cerebral cortex, thalamus and locus coeruleus, as well as in plasma corticosterone levels. Rats exposed to signalled shock (predictable group) showed significant increases in MHPG-SO4 levels in the first four of these regions, as compared to the nonshocked rats. Moreover, the unpredictably shocked rats exhibited greater elevations in MHPG-SO4 levels in the hypothalamus, amygdala, and thalamus, as well as in plasma corticosterone levels, when compared to the predictably shocked rats. These results are consistent with previous reports showing that unsignalled shock induced extensive somatic effects in comparison to signalled shock. The present study suggests that the presence of a signal attenuates the extent of NA release in some brain regions resulting from irregular inescapable shock stress.

Effect of acute ethanol administration on noradrenaline metabolism in brain regions of stressed and nonstressed rats.

The effects of ethanol on noradrenaline (NA) metabolism of brain regions in stressed and nonstressed rats were investigated. Male Wistar rats were injected IP with either saline, or ethanol at 0.5 g/kg or 2 g/kg, 5 min before exposure to 1-hr immobilization stress. Levels of NA and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) in various brain regions and plasma corticosterone levels were fluorometrically determined. Immobilization stress caused significant increases in MHPG-SO4 levels in all brain regions examined, i.e., the hypothalamus, amygdala, hippocampus, cerebral cortex and locus coeruleus (LC) region. In nonstressed rats, ethanol significantly increased MHPG-SO4 levels in the hypothalamus, hippocampus and cerebral cortex, but not in the amygdala or in the LC region. In stressed rats, ethanol attenuated stress-induced increases in MHPG-SO4 levels preferentially in the amygdala and LC region, but not in the remaining three regions. Although ethanol per se dose-dependently elevated plasma corticosterone levels in nonstressed rats, ethanol at 2 g/kg attenuated the stress-induced elevation of corticosterone. These results suggest that the attenuating effect of ethanol on stress-induced increases in NA turnover in the amygdala and LC region might be related to the stress-relieving properties of this drug.

[Stressor controllability and brain noradrenaline turnover in rats].

A series of experiments examined the effects of a purely psychological factor in a stressful situation (i.e., the ability to manage a stressor or inability to do so) on noradrenergic metabolism in regional rat brains. In Experiment 1, uncontrollable rats which could not escape and avoid electric shock developed more gastric ulceration than did controllable rats which had exactly the same shock but could exert control over the shock. In Experiment 2, the uncontrollable rats displayed sustained increases in noradrenaline (NA) turnover in various brain regions regardless of stress durations. After the controllable rats had firmly mastered the coping response, excess NA utilization at the earlier stage of stress was reduced in many brain regions. These findings suggested that noradrenergic neuronal activity in some specific brain regions, such as the hypothalamus and limbic areas, might be involved in the coping processes under a stressful situation. This hypothesis was supported by the results of Experiment 3 showing that the effects of stressor controllability on regional brain NA turnover were covaried with the complexity of coping task required. Taken together, it is concluded that the degree of behavioral control (the ability to alter the termination or duration) that an organism has over a stressor modulates the physiological and neurochemical impact of that stressor, and that brain NA is implicated in the learning process where an organism copes with a stressor.

Effects of shock controllability on rat brain noradrenaline turnover under FR-1 and FR-3 Sidman avoidance schedules.

We examined changes in brain noradrenaline (NA) turnover as a function of shock controllability and the task complexity (fixed ratio, FR-1 and FR-3) under a 21-hr continuous discriminated Sidman avoidance schedule with shock intensity of 0.7-1.0 mA, shock duration of 1.0 sec, shock-shock interval of 1.5 sec, response-shock interval of 100 sec and signal-shock interval of 10 sec, by measuring levels of a principal metabolite of NA, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in discrete brain regions of male Wistar rats. In an FR-1 operant schedule, experimental rats which could avoid or escape shock by pulling a disk manipulandum only once showed significantly lower levels of MHPG-SO4 in the hypothalamus, amygdala, thalamus, locus coeruleus (LC) region and cerebral cortex than did yoked rats which received the same amount of shock but could not perform any effective avoidance and/or escape responses. The MHPG-SO4 levels for the experimental rats did not differ significantly from "non-shock" control rats in most regions. In an FR-3 operant schedule, however, the experimental rats which could control shock by emitting three disk-pulling responses showed significantly higher levels of MHPG-SO4 in most brain regions, as compared to FR-1 experimental rats. The FR-3-experimental rats exhibited levels of MHPG-SO4 similar to those seen in the FR-3 yoked rats in all brain regions. These two groups of shocked rats showed significantly higher levels of MHPG-SO4 in all brain regions with the exception of the basal ganglia, as compared to the FR-3 control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of preshock experience on enhancement of rat brain noradrenaline turnover induced by psychological stress.

The present study examined alterations of brain noradrenaline (NA) turnover as a function of preshock and psychological stress treatments, by measuring contents of NA metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in discrete brain regions of male Wistar rats. Psychological stress induced by exposing to the sight, sound and odor of other rats being shocked produced higher levels of MHPG-SO4 in the hypothalamus, amygdala and locus coeruleus (LC) region, as well as higher levels of plasma corticosterone. Preshock experienced rats also showed marked increases of MHPG-SO4 levels in the same regions described above and elevated plasma corticosterone levels when placed but not shocked in the same environment in which the rats had previously received shocks. The effects of psychological stress on brain NA turnover were affected by the animal's shock history preferentially in the hypothalamus and amygdala. These results suggest that: a purely psychological stressor caused acutely enhanced NA turnover in specific brain regions; regional NA activity appeared to be reinstated simply by reexposure to the environment previously associated with shock; preshock experience further intensified the enhancement of amygdaloid NA turnover evoked by psychological stress. An additional experiment, studying the aftereffects of preshock experience, clearly showed that these findings result from sensitization or conditioning to the environment previously paired with shock, and not merely from the aftereffects of the shock per se.

Attenuating effect of diazepam on stress-induced increases in noradrenaline turnover in specific brain regions of rats: antagonism by Ro 15-1788.

One-hour immobilization stress increased levels of the major metabolite of brain noradrenaline (NA), 3-methoxy-4-hydroxyphenyl-ethyleneglycol sulfate (MHPG-SO4), in nine brain regions of rats. Diazepam at 5 mg/kg attenuated the stress-induced increases in MHPG-SO4 levels in the hypothalamus, amygdala, hippocampus, cerebral cortex and locus coeruleus (LC) region, but not in the thalamus, pons plus medulla oblongata excluding the LC region and basal ganglia. The attenuating effects of the drug on stress-induced increases in metabolite levels in the above regions were completely antagonized by pretreatment with Ro 15-1788 at 5 or 10 mg/kg, a potent and specific benzodiazepine (BDZ) receptor antagonist. When given alone, Ro 15-1788 did not affect the increases in MHPG-SO4 levels. Behavioral changes observed during immobilization stress such as vocalization and defecation, were also attenuated by diazepam at 5 mg/kg and this action of diazepam was antagonized by Ro 15-1788 at 10 mg/kg, which by itself had no effects on these behavioral measurements. These findings suggest: (1) that diazepam acts via BDZ receptors to attenuate stress-induced increases in NA turnover selectively in the hypothalamus, amygdala, hippocampus, cerebral cortex and LC region and (2) that this decreased noradrenergic activity might be closely related to relief of distress-evoked hyperemotionality, i.e., fear and/or anxiety in animals.

State-dependent effects of beta-endorphin on core temperature in stressed and non-stressed rats.

beta-Endorphin, gamma-endorphin, delta-endorphin and morphine injected i.c.v. caused hyperthermia in non-stressed rats; however, the same dose of beta-endorphin and morphine caused hypothermia in stressed animals. These effects of beta-endorphin were antagonized by naloxone. The results suggest that effects of beta-endorphin are different depending on the animal's state and that these effects are mediated via opioid receptors.

Methionine-enkephalin inhibits stress-induced increases in noradrenaline turnover in brain regions of rats.

Met-Enkephalin injected i.c.v. attenuated stress-induced increases in levels of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate, the major metabolite of brain noradrenaline, in the hypothalamus, amygdala, hippocampus, thalamus, midbrain and LC region in rats. The data suggest that Met-enkephalin acts to attenuate stress-induced increases in noradrenaline turnover in these brain regions in rats.