Epinephrine, norepinephrine, dopamine and serotonin: differential effects of acute and chronic stress on regional brain amines

Following acute cold swim stress, hypothalamic epinephrine concentrations were markedly lowered and remained decreased for 24 h, while norepinephrine concentrations were decreased, but returned to baseline within 14 h. With oscillation stress repeated daily for 21 days, hypothalamic norepinephrine, hypothalamic epinephrine, and hippocampal norepinephrine turnover were decreased and absolute concentrations were increased. Repeated stress had little effect on serotonin, dopamine or their metabolites. These results suggest that hypothalamic epinephrine concentration and turnover are particularly responsive to acute and chronic stress. The decreased epinephrine and norepinephrine turnover under chronic stress may be responsible in part for the behavioral and endocrine changes observed in chronically stressed rats.

Immunohistochemical distribution of alpha-neo-endorphin/dynorphin neuronal systems in rat brain: evidence for colocalization

alpha-Neo-endorphin and dynorphin immunoreactivities in rat brain were visualized by double antibody immunofluorescence of frozen sections. Antibodies were used that were specific for their respective antigens. The pattern of neuronal immunostaining produced by alpha-neo-endorphin and dynorphin antisera in adjacent serial sections was completely superimposible. No areas were found in which alpha-neo-endorphin or dynorphin immunoreactivities existed alone. The following brain regions contained alpha-neo-endorphin/dynorphin-immunoreactive fibers and terminals: the median forebrain bundle, the internal capsule, the substantia nigra, the hypothalamus, the nucleus accumbens, the hippocampus, and the medulla oblongata. A few fibers were seen in the cerebral cortex and in the corpus striatum. In many regions, this neuronal fiber system seems to overlap the neuronal system previously described to contain [Met]-/[Leu]enkephalin-immunoreactive material. In brains from colchicine-treated animals, numerous alpha-neo-endorphin/dynorphin-immunoreactive neuronal cell bodies were seen in the supraoptic, retrochiasmatic supraoptic, paraventricular, and magnocellular accessory nuclei of the hypothalamus. It is concluded that alpha-neo-endorphin-like and dynorphin-like immunoreactivities are part of the same neuronal system.

Nicotinic-catecholaminergic interactions in rat brain: evidence for cholinergic nicotinic and muscarinic interactions with hypothalamic epinephrine

The i.p. injection of nicotine produced several changes in regional catecholamine concentrations in rat brain. These changes were blocked by the centrally active nicotinic antagonist mecamylamine, but not by the quaternary nicotinic antagonist hexamethonium. An examination of the effects of various cholinergic agents on hypothalamic epinephrine concentrations revealed several interesting findings. Central muscarinic antagonism or peripheral muscarinic agonism decreased hypothalamic epinephrine concentrations. The anticholinesterase physostigmine decreased hypothalamic epinephrine concentrations and this effect was blocked by the centrally acting nicotinic antagonist mecamylamine, but not by hexamethonium, scopolamine or methscopolamine. These findings indicate an interaction of cholinergic receptors, both nicotinic and muscarinic, with hypothalamic epinephrine.

Opioid peptides in human plasma: evidence for multiple forms

Studies were designed to assess whether the enkephalin-containing peptides and proteins present in the chromaffin granules of the adrenal medulla and in other secretory tissues, such as the neurohypophysis, could be found circulating in human blood. We analyzed human plasma acid acetone extracts chromatographed on Sephadex G-75 in acetic acid and found evidence for the existence of opioid peptides of several different molecular weights and a large number of peptides and small proteins which generate opioid activity after tryptic digestion. These compounds are different from and present in much greater quantities than previously described opioid peptides in human plasma, and are separate from dynorphin-immunoreactive compounds, which we also report in the blood. Expressed in leucine-enkephalin equivalents on a radioreceptor assay, we found 63.2 +/- 6.5 (n = 4; mean +/- SEM) pmol/ml plasma. One active peak from the Sephadex G-75 chromatography of human plasma (apparent mol wt, 3000) was examined by reverse phase high pressure liquid chromatography, tryptic digestion, and Sephadex G-50 chromatography. The results were consistent with the notion that this opioid active peptide contains an enkephalin sequence at its N-terminal, followed by a basic residue. Mild stress (2 min of deep knee bends) produced a 2-fold elevation in overall circulating opioid activity. The possibility is considered that the large enkephalin-containing peptides may have an endocrine function, independent of a role as enkephalin precursors.

Distribution of norepinephrine, epinephrine, dopamine, serotonin, 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindole-3-acetic acid in dog brain

The distribution and endogenous concentrations of norepinephrine, epinephrine, dopamine, serotonin, 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindole-3-acetic acid were determined in the brains of adult dogs. Norepinephrine and epinephrine were localized primarily in 'central core' areas in brain stem and hypothalamus. Dopamine (DA) and its major metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acids (HVA), were localized primarily in basal ganglia with relatively high concentrations also found in amygdala, septum and substantia nigra. HVA was also found in relatively high concentrations in areas where DA concentrations was very low. Serotonin and 5-hydroxyindole-3-acetic acid levels were highest in brain stem, hypothalamus, globus pallidus and nucleus accumbens. Epinephrine levels were higher than in previously studied species, at times as much as 25-30% of norepinephrine and frequently greater than dopamine in brain stem and hypothalamus. Using the ratios 5-hydroxyindole-3-acetic acid/serotonin and homovanillic acid/dopamine as indicators of serotonin and dopamine turnover and utilization, both putative transmitters were found to be generally more highly utilized in areas of lower concentration, especially in brain stem and cortex. Catecholamines were found to be unconjugated in dog brain. DOPAC and HVA were found to exist primarily in the unconjugated form. DOPAC was found to be slightly conjugated in most areas while 10-20% of HVA was present in the conjugated form in most cases.

Corticosterone: a critical factor in an opioid form of stress-induced analgesia

The finding that some opioid-mediated forms of stress-induced analgesia are antagonized by hypophysectomy and dexamethasone has led to the suggestion that beta-endorphin, released from the pituitary, may mediate these analgesic reactions. "Long-term analgesia" (an opioid-mediated form of stress-induced analgesia), which is blocked by dexamethasone and hypophysectomy, was also blocked by adrenalectomy and reinstated with corticosterone therapy. Corticosterone is proposed to play a permissive role in long-term analgesia and to be a critical hormone mediating this phenomenon.

Opioid peptides as neuroregulators: potential areas for the study of genetic-behavioral mechanisms

The opioid peptides have been related to behavior in both animal and human studies. Further investigation can be anticipated which could lead to the elucidation of genetic controls over enzymes which process these peptides and the receptors upon which the peptides act. The enzymes, both synthetic and degradative, can lead to the formation of different forms of the opiate peptides. Differential control of these enzymes or of the multiple forms of opiate receptors could lead to discrete changes in opiate status and subsequent behavioral changes. Conversely, genetically regulated behavioral modification could also lead secondarily to opiate changes.

Measurement of methionine-enkephalin [Arg6,Phe7] in rat brain by specific radioimmunoassay directed at methionine sulphoxide enkephalin[Arg6,Phe7]

A specific and sensitive radioimmunoassay procedure for Met-enkephalin[Arg6,Phe7] which allows its measurement in regions of the rat brain is described. The antiserum as raised against the methionine sulphoxide derivative of the peptide, and all samples and standards were oxidized with hydrogen peroxide prior to use in the assay with chloramine T-oxidized 125I-labelled Met(O)-enkephalin[Arg6,Phe7]. The only significant cross-reactivity was 30% with the reduced heptapeptide Met-enkephalin[Arg6,Phe7]. The assay showed less than 0.15% cross-reactivity with fragments of the heptapeptide and with leucine-enkephalin-containing peptides. Acid acetone extraction of rat striatum followed by Sephadex G-50 chromatography and reverse-phase high pressure liquid chromatography showed that essentially all immunoreactivity co-chromatographed with Met-enkephalin[Arg6,Phe7]. This confirmed the specificity of the assay and showed that the striatum does not contain a high concentration of larger molecular weight forms with the heptapeptide at the COOH terminus. Distribution of the heptapeptide followed that of methionine enkephalin, with highest concentrations in the globus pallidus, intermediate levels in caudate-putamen and hypothalamus, and low levels in cortex and cerebellum.

Novel peptide neuronal system in rat brain and pituitary

Immunohistofluorescence studies of the rat central nervous system with antibodies to Phe-Met-Arg-Phe-NH2 (molluskan cardioexcitatory peptide) revealed a widespread neuronal system in the brain, spinal cord, and posterior pituitary. Immunoreactive axons and cell bodies were mainly located in cortical, limbic, and hypothalamic areas. Immunostaining of serial sections of the brain and pituitary showed that the Phe-Met-Arg-Phe-NH2 immunoreactive neurons were different from neurons labeled by antibodies to either Met-enkephalin or the putative Met-enkephalin precursor Tyr-Gly-Gly-Phe-Met-Arg-Phe, which is structurally related to Phe-Met-Arg-Phe-NH2. Control staining by antiserum absorption and radioimmunoassay indicated that the antibodies that caused the specific immunofluorescence recognized peptides with an amidated Arg-Phe sequence at the carboxyl terminus.

Neuroendocrine and neurochemical measurements in depression

The authors performed dexamethasone suppression tests (DST), TRH infusions, 72-hour urine collections, and lumbar punctures on a group of male depressed patients. Approximately 60% of the patients were DST positive and 33% had a blunted TSH response. Two biologic variables, the 8 a.m. postdexamethasone cortisol and the postprobenecid CSF 5-hydroxyindoleacetic acid (5-HIAA), accounted for over half of the variance in the behavioral measure, the Hamilton score. Plasma cortisol elevation was associated with high 3-methoxy-4-hydroxyphenyl glycol (MHPG) excretion; TSH blunting was associated with low urinary MHPG excretion. Comprehensive biologic measures showed certain significant interrelationships and correlations with the severity of depression.

Central and peripheral contributions to hypothalamic epinephrine

Hypothalamic epinephrine concentrations were examined following adrenal demedullation or after surgical hemisection of ascending projections to the hypothalamus. Following surgical transection epinephrine in the ipsilateral hypothalamus was depleted by approximately 60%. Adrenal demedullation had no effect on hypothalamic epinephrine concentrations. It was concluded that hypothalamic epinephrine was central in origin.

Clinical application of the probenecid test for measurement of monoamine turnover in the CNS

The probenecid-induced accumulation of the acidic metabolites of dopamine and serotonin is widely used to estimate the CNS turnover of these amines in human subjects. The theoretical basis of the probenecid test is discussed, including the assumptions on which the test is based, and the limitations of the procedure. Suggestions are offered on appropriate methods for analyzing test data. Available evidence suggests that maximal inhibition of the efflux of the acidic metabolites of dopamine and serotonin from the CSF is not achieved with probenecid doses up to 100 mg/kg. Therefore, before a comparison can be made between the accumulation of CSF metabolites from different groups of subjects, a correction for CSF probenecid concentrations is necessary. Moreover, in addition to the measurement of dopamine and serotonin turnover, the probenecid test can be extended to include comparisons of CNS turnover of other monoamines including octopamine, p-tyramine, and tryptamine.

The effects of naloxone in chronic schizophrenia

In a placebo-controlled, double-blind crossover study of 14 male chronic schizophrenic patients, high doses of the opiate antagonist naloxone were given intravenously. Hallucinations measured on a verbal-report scale were significantly decreased after naloxone administration. The authors suggest that this apparent action of naloxone is mediated by central opiate receptors and that it may result from an interaction between central endorphin systems and central catecholaminergic neurons.