Naloxene enhances stress-induced increases in noradrenaline turnover in specific brain regions in rats

Male Wistar rats were injected subcutaneously with either saline or naloxone, 1 mg/kg or 5 mg/kg, 10 min before exposure to 1-hour immobilization-stress. Control animals were sacrificed 70 min after respective injections. Levels of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO₄) in seven discrete brain regions and plasma corticosterone levels were fluorometrically determined. Immobilization stress caused significant elevations of plasma corticosterone which were not affected by pretreatment with naloxone. In the hypothalamus, amygdala and thalamus, immobilization-stress caused significant elevations of MHPG-SO₄ levels, and naloxone at 5 mg/kg significantly enhanced these stress-induced elevations virtually without affecting the basal level of the metabolite. In contrast, in the hippocampus, cerebral cortex and pons plus medulla oblongata, MHPG-SO₄ levels were elevated by stress, but were not affected by naloxone pretreatment. The effect of naloxone on stress-induced reductions of NA levels was unclear, since naloxone by itself (5 mg/kg) significantly decreased the amine levels in 5 of 7 brain regions examined. These results indirectly suggest that endogenous opioid peptides in the hypothalamus, amygdala and thalamus are partly involved in the stress process and attenuate increases in NA turnover induced by stress.     

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.     

Brain histamine response to stress in 12 month old rats

The regional brain histamine regulation in response to stress was investigated in 12 month old Sprague-Dawley male rats. Air blast exposure (15 min) induced significant (26.5%) elevation in hypothalamic HA level; midbrain and cortical HA concentrations were not affected. Histamine methyltransferase activity was not altered by stress in any of the brain regions investigated. Plasma corticosterone levels of stressed rats were significantly elevated (6.5 fold). Hence, the response of hypothalamic HA to stress is still evident in 12 month old rats.     

Two-way avoidance and acute shock stress induced alterations of regional noradrenergic, dopaminergic and serotonergic activity in Roman high- and low-avoidance rats

Various brain regions of male RHA/Verh and RLA/Verh rats were dissected out and deep-frozen immediately after 30 min in a shuttle box involving a) no shock (control), b) 40 inescapable shocks or c) 40 avoidable shocks. The RHA/Verh rats used in the "c" category exhibited about 80-85% learned avoidance. 5-HT, 5-HIAA, NA, MHPG-SO4, DA, DOPAC and HVA levels were subsequently measured in selected regions. NA levels were considerably reduced in the hypothalamus and pons/medulla of both selected lines of rats after acute shock stress, supporting the results of numerous studies which have indicated that NA turnover is nonspecifically increased by all types of stress, at least in those regions. An increase in cortical MHPG-SO4 and a reduction in hypothalamic 5-HT seen after avoidance learning also occurred after shock stress in RHA/Verh rats. Whereas RLA/Verh rats showed an increased metabolism of 5-HT in the hypothalamus and pons/medulla after shock stress, RHA/Verh rats showed the opposite response in the hypothalamus after the same treatment. A reduction in 5-HT metabolism was also evident in RHA/Verh rats, after avoidance learning, in the cortex, hippocampus and hypothalamus. These results indicated, pending further studies regarding, for example, possible genetic differences in tryptophan uptake and utilization, that 5-HT probably plays at least a modulatory role in the reaction to stress, and in avoidance behavior. That role may be either active or passive, depending upon the emotional status of the subjects. In regard to the DA responses measured in striatum and hypothalamus of the two rat lines, some divergent inter-treatment tendencies, as well as some similarities, were seen in DA metabolism in both regions, but almost none of the differences were significant.     

Selective noradrenaline depletion markedly alters stress responses in rats

Rats were given FLA-63, followed by R04-1284 0.5 h later to relatively selectively deplete brain NA. After 8 h, some animals were examined for regional brain NA and MHPG-SO4, while some were subjected to 3 h of cold-restraint stress and then examined. All brain regions examined showed significant NA and MHPG reduction. Specific NA depletion markedly exacerbated restraint ulcer formation and plasma corticosterone levels. NA depletion without restraint stress did not induce ulcers or elevate corticosterone. Intact brain NA activity appears to be essential for coping with stress.     

Metallothionein-I induction by stress in specific brain areas

The distribution of metallothionein-I (MT) in several areas of the brain and its induction by immobilization stress has been studied in the rat. MT content was highest in hippocampus and midbrain and lowest in frontal cortex and pons plus medulla oblongata. Immobilization stress for 18 hours (which was accompanied by food and water deprivation) significantly increased MT levels in the frontal cortex, pons plus medulla oblongata and hypothalamus, but not in midbrain and hippocampus. The effect of stress on MT levels was specific as food and water deprivation along had no significant effect on MT levels in any of the brain areas studied. The effect of stress on MT levels was independent of changes in cytosolic Zn content; this was generally unaffected by stress or food and water deprivation but decreased in pons plus medulla oblongata from stressed rats. The results suggest that MT is induced more significantly in the brain areas that are usually involved in the response of animals to stress.     

Twenty-four hour daily rhythms of glycine in the rodent brain

Male Sprague Dawley rats weighing 200–250 grams each were adapted for a minimum period of three weeks to a 12-hour light: 12-hour dark programmed illumination cycle with a temperature of 23 ± 1°C before used in this study. Every four hours for a twenty-four hour period glycine levels were measured in specific brain areas. Glycine levels were determined in the caudate nucleus, cerebellum, cortex, midbrain and pons by the method of Aprison and Shank (16). The highest level of glycine was observed in the pons. Through concentrations appeared in the cerebellum, cortex, midbrain and pons at D-0400 hours and the peak concentrations occurred at L-1600 hours. The glycine levels were significantly lower during the dark period of the light-dark cycle for all brains except the caudate nucleus.     

Characteristics of central binding sites for [3H] DAMGO in spontaneously hypertensive rats

The binding of [3H] DAMGO, a highly selective ligand for mu-opiate receptors, to membranes of discrete brain regions and spinal cord of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. The brain regions examined were hypothalamus, amygdala, hippocampus, corpus striatum, pons and medulla, midbrain and cortex. [3H] DAMGO bound to membranes of brain regions and spinal cord at a single high affinity site. The receptor density (Bmax value) and apparent dissociation constant (Kd value) of [3H] DAMGO to bind to membranes of hippocampus, corpus striatum, pons and medulla, cortex and spinal cord of WKY and SHR rats did not differ. The Bmax value of [3H] DAMGO in membranes of hypothalamus and midbrain of SHR rats was significantly higher than in WKY rats but the Kd values in the two strains did not differ. On the other hand, the Bmax value of [3H] DAMGO in membranes of amygdala of SHR rats was lower than that of WKY rats but the Kd values in the two strains were similar. It is concluded that SHR rats have higher density of mu-opiate receptors in hypothalamus and midbrain but lower density in amygdala in comparison with WKY rats, and that such differences in the distribution of mu-opiate receptors may be related to the elevated blood pressure in SHR rats.     

Cerebral serotonin and the hypothalamo-hypophyseal-adrenal system of the rat during aging]

The role of brain serotonin (5HT) on the hypothalamus-pituitary-adrenal system (HPAs) under basal condition and after injections of p-chlorophenylalanine (pCPA) and L-5-hydroxytryptophan (L-5HTP) has been studied in 6, 12 and 28 month old male Wistar rats. Four experimental groups were made for each age: control, saline, injected with pCPA (250 mg/kg i.p.) and L-5HTP (200 mg/kg i.p.), the effects being valued 2 hours after L-5HTP administration and 24 hours after pCPA injection. In all groups the plasmatic ACTH, the corticosterone levels as well as the simultaneous changes of the 5TH content tryptophan hydroxylase activity in whole brain were estimated two hours after the L-5HTP injection and 24 hours after that of pCPA. Significant changes are not found in the plasmatic ACTH and corticosterone values with respect to age under basal condition. Nevertheless, the response of HPAs differs with the age after pCPA or L-5HTP injection. The ACTH and corticosterone levels augment by L-5HTP and decrease by pCPA in all age groups, but this corresponding increase or decrease was less marked in the older rats. The 5HT content as tryptophan hydroxylase activity in brain decreased in old animals. pCPA and L-5HTP determine, respectively, high falls and rise of 5TH values, these changes being more intense for pCPA in old rats and for L-5HTP in young and mature animals. The tryptophan hydroxylase activity is decreased by pCPA as L-5HTP injections.(ABSTRACT TRUNCATED AT 250 WORDS)     

Opiate antagonist binding sites in discrete brain regions of spontaneously hypertensive and normotensive Wistar-Kyoto rats

The binding of 3H-naltrexone, an opiate receptor antagonist, to membranes of discrete brain regions and spinal cord of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. The brain regions examined were hypothalamus, amygdala, hippocampus, corpus striatum, pons and medulla, midbrain and cortex. 3H-Naltrexone bound to membranes of brain regions and spinal cord at a single high affinity site with an apparent dissociation constant value of 3 nM. The highest density of 3H-naltrexone binding sites were in hippocampus and lowest in the cerebral cortex. The receptor density (Bmax value) and apparent dissociation constant (Kd value) values of 3H-naltrexone to bind to opiate receptors on the membranes of amygdala, hippocampus, corpus striatum, pons and medulla, midbrain, cortex and spinal cord of WKY and SHR rats did not differ. The Bmax value of 3H-naltrexone binding to membranes of hypothalamus of SHR rats was 518% higher than WKY rats but the Kd values in the two strains did not differ. It is concluded that SHR rats have higher density of opiate receptors labeled with 3H-naltrexone in the hypothalamus only, in comparison with WKY rats, and that such a difference in the density of opiate receptors may be related to the elevated blood pressure in SHR rats.     

Changes in hypothalamic noradrenaline and 5-hydroxytryptamine levels during the development of warm- and cold-adaptation in the rat

Hypothalamic 5-hydroxytryptamine (5-HT) and noradrenaline (NA) as well as plasma corticosterone levels were studied in male rats after 1, 2, 4 and 6 weeks of exposure to 4--7 or 30--31 degrees C. An increase of the NA concentration and a decrease of the 5-HT level was observed after the first week in both cold and warm environment together with an increase of plasma corticosterone levels in both groups. NA, 5-HT and plasma corticosterone levels returned to normal in cold-exposed animals by the 6th week whereas in warm-acclimated rats NA and corticosterone levels regained their initial values and 5-HT concentrations remained low. Changes by the end of the first week of exposure may result from the thermal stress. The low 5-HT levels of warm-adapted animals at the end of the 6th week were probably secondary to the process of adaptation.     

The influence of alpha-fluoromethylhistidine on the regional brain histamine and plasma corticosterone levels in aging

alpha-Fluoromethylhistidine, a histidine decarboxylase inhibitor, induced a significant depletion in the hypothalamic, midbrain, and cortical brain histamine amounts in 12- and 3-month-old rats. In all three brain regions the most evident depletion occurred 2 h after treatment. In both groups of rats midbrain histamine levels returned to control values 6 h after treatment; however, hypothalamic histamine depletion was still significant and more evident in the old than in the young animals. Cortical brain histamine also remained significantly depleted in old rats, but returned to control values in young animals 6 h after alpha-fluoromethylhistidine treatment. These results suggest that old rats show a slower rate of new histamine synthesis in the cortex and hypothalamus. Regional brain histamine depletion was associated with a very significant decrease in plasma corticosterone levels, which indicates that brain histamine-corticosterone interactions do occur.     

Circadian variation in the acetylcholinesterase activity of specific rat brain areas

Abstract

Acetylcholinesterase (AChE) activity of the adenohypophysis, cerebellum, cerebral cortex, hypothalamus, amygdala, hippocampus, midbrain, pons, medulla oblongata and caudate nucleus was determined by a spectro‐photometric method in adult, male rats adapted toan LD 12:12cycle. Results of the study show that AChE activity is highest during the light phase and lowest during the dark phase of the cycle in all the brain areas studied except the adenohypophysis, cerebellum, hippocampus and hypothalamus. These findings expand earlier observations on the circadian variation in rat brain AChE activity and suggests a relationship with reported circadian variation in the acetylcholine levels of rat brain.     

Chronic Stress Increases Serotonin and Noradrenaline in Rat Brain and Sensitizes Their Responses to a Further Acute Stress

The effects of 1 h/day restraint in plastic tubes for 24 days on the levels of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), tryptophan (TP), and noradrenaline (NA) in six regions of rat brain 20 h after the last restraint period were investigated. The levels of 5-HT, 5-HIAA, and NA but not TP increased in several regions. The effects of 1 h of immobilization on both control and chronically restrained rats were also studied. Immobilization per se did not alter brain 5-HT, 5-HIAA, and TP levels, but decreased NA in the pons plus medulla oblongata and hypothalamus. However, immobilization after chronic restraint decreased 5-HT, increased 5-HIAA, and decreased NA in most brain regions in comparison with values for the chronically restrained rats. We suggest that chronic restraint leads to compensatory increases of brain 5-HT and NA synthesis and sensitizes both monoaminergic systems to an additional acute stress. These changes may affect coping with stress demands.     

Disorder of catecholamine synthesis in early ontogeny and hypophyseal-adrenal cortical function in adult rats

The effects of daily intraperitoneal (150 mg/kg of body weight) injections of alpha-methyl-dl-tyrosine (MT), an inhibitor of tyrosine hydroxylase, on the 2nd to 4th, 5th to 7th or 10th to 12th days of life on the pituitary-adrenal function and brain adrenaline level in 3 to 4-month old rats were studied. MT treatment on the 5th to 7th days resulted in a decrease of noradrenaline content in hypothalamus and midbrain and chronic decrease of basal corticosterone level in blood, its diurnal fluctuations being preserved. MT injections on the 10th to 12th days were accompanied by a decrease of the basal corticosterone level, but the brain noradrenaline level remained unchanged. A study of pituitary-adrenal stress reactivity of adult rats has revealed no specific MT effect. A conclusion was drawn that the MT treatment applied exerted a long-term effect, predominantly, on the regulation of tonic corticosterone secretion.     

Regional Distribution and Production Rate of 3-Methoxy-4-Hydroxyphenylethyleneglycol Sulphate (MHPG-SO4) in Rat Brain

The levels of noradrenaline (NA) and 3-methoxy-4-hydroxyphen-ylethyleneglycol sulphate (MHPG-SO₄) in 15 brain regions showed a parallel distribution in male Wistar rats. The differences in regional distribution of MHPG-SO₄ were similar to those in the rate of NA turnover reported by other investigators. The accumulation rates of MHPG-SO₄ during 45 and 90 min after probenecid injection significantly correlated to the steady state levels of MHPG-SO₄ in nine regions studied. With the results, the regional levels of MHPG-SO, either in untreated or in probenecid-treated rats, are considered to be a useful index of NA turnover.     

Beta-adrenoceptor mediated inhibition of behavioral action of desipramine and of central noradrenergic activity in forced swimming rats

The immobility-reducing action of desipramine (DMI) in forced swimming rats was attenuated by intracerebroventricular (i.c.v.) injection of isoproterenol (ISO) and potentiated by i.c.v. atenolol (ATE), a beta 1-adrenoceptor antagonist. The effect of ISO was blocked by ATE. When administered i.c.v. in normal rats, ISO reduced the contents of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), a major metabolite of noradrenaline, in the septal area, thalamus and hypothalamus while ATE had no effect in most of the brain regions. However, in forced swimming rats treated with DMI, ISO reduced MHPG-SO4 in 6 out of 8 brain regions tested and conversely, ATE increased the levels in the amygdala, septal area and hypothalamus. Similar to the behavioral effect, the effect of ISO was antagonized by ATE. These results support the hypothesis that central beta 1-adrenergic mechanisms inhibit the immobility-reducing action of DMI by reducing the activity of noradrenergic neurons in the brain.     

Effect of reactive oxygen species on the metabolism of tryptophan in rat brain: Influence of age

In an earlier study, oxidation of tryptophan hydroxylase was implicated as its affinity was decreased with aging in rat brain. To establish any potential link between its oxidative damage and aging, we have determined the activities of antioxidant enzymes in midbrain, pons and medulla of 2, 12 and 24 month old Fisher 344 BNF1 rats. The results obtained suggest that the activities of antioxidant enzymes varied considerably with age and brain regions studied. Activities of Cu/Zn superoxide dismutase and glutathione peroxidase were found to increase from 2 to 12 months and then decrease in 24 month old rats. However catalase activity decreased consistently with the age. A parallel increase in the carbonyl content was observed in these brain regions indicating the oxidation of proteins. Reactive oxygen species when included in the incubation mixture decreased the activity of tryptophan hydroxylase in a concentration dependent manner. The loss of tryptophan hydroxylase activity induced by hydrogen peroxide and superoxide anion was prevented by catalase. However superoxide dismutase did not provide such protection. Sulfhydryl agents, cysteine, glutathione and dithiothreitol partially prevented the loss of activity. These studies suggest an involvement of reactive oxygen species for sulfhydryl oxidation of tryptophan hydroxylase in aging.     

Developmental plasticity of central noradrenaline neurons after neonatal damage—changes in transmitter functions

The effects of neonatal 6-hydroxydopamine (6-OH-DA) treatment (systemic administration) on norasrenaline (NA) metabolism, trun over, and receptor charasteristics have been investigated in rat brain in the adult atage. This treatment is known to preferentially affect the locus coeruleus (LC) NA system leading to a marked NA denervation in the cerebral cortex and a hyperinnervation of NA nerve terminals in the pons and medulla oblongata without influencing the LC perikarya. The main NA metabolite, 3-methoxy-4-hydroxyphenylglycol (MOPEG) was reduced by about 70% in the cerebral cortex after 6-OH-DA-treatment at birth while the endogenous NA was almost completely depleted (-92%). The MOPEG levels were not significantly changed in the pons medulla after 6-OH-DA treatment in contrast to the 60% increase of the endogenous NA concentration. The relative reduction of NA in the cerebral cortex of 6-OH-Da treated rats increased in the cerebral cortex is increased after 6-OH-DA, while decreased in the pons-medulla, possibly related to changes in the activation of presynaptic α-adrenoreceptors in both regions. NA-induced formation of cAMP in vitro was found to be markedly increased in the cerebral cortex after 6-OH-DA, whereas no consistent change was observed in the pons medulla. Measurements of α- and β-receptor binding in vitro using radioligand techniques showed an increase of binding sites (20%–50%) for both receptors in the neocortex after 6-OH-DA, whereas no changes were observed in the pons medulla. The 6-OH-Da induced changes in NA turnover, cAMP generating systems, and receptor density may all represent compensatory processes following the altered development of the NA neurons induced by 6-OH-DA.     

Sex differences in reserve capacity of the pituitary-adrenal system in rats

Female rats exposed to complex emotional stress for 1 hour (restriction in the penal, vibration, loud dissonance music, interrupt light) simultaneously showed more considerable increases in plasma and adrenal corticosterone values than did male animals. Female rat corticosterone levels returned to basal values within 20-120 minutes of stressor-off. As for males the processes of restoration were delayed and accompanied by a 6-fold decrease in the plasma corticosterone levels compared with basal values. The response to additional acute stress (immobilization for 10 minutes) in various times after termination of complex emotional stress (0, 40, 120, 180, 240 minutes) was facilitated in females and remained unchanged in males. Plasma corticosterone levels under stressful conditions were 2-4-fold higher in females than in males. It is concluded that reserve capacity of adaptation system is significantly higher in female rats than in male ones.