The elevation of immunoreactive beta-endorphin in old male rats is related to alterations in dopamine and serotonin

Cocaine and inhibition of nitric oxide synthesis produce opioid-mediated antinociception

Cocaine and nitric oxide are known to influence the perception of pain. The present study sought to determine if the endogenous opioid peptide system participates in cocaine-induced antinociception and antinociception produced by antagonism of nitric oxide. Pain perception was measured using the hot plate test. Administration of cocaine (25 mg/kg) to male rats resulted in a significant increase in reaction time in the hot plate test, which was reversed by treatment with 3, 10, and 30 mg/kg of the opiate antagonist, naloxone. In rats that were not treated with cocaine, doses of 30 and 60 mg/kg of naloxone significantly reduced hot plate reaction Time. Treatment of animals with the nitric oxide synthase inhibitor, N omega nitro-L-arginine, produced a significant increase in response time to the hot plate, which was reversed by administration of naloxone. These data indicate that antinociception produced in the rat by cocaine appears to have a supraspinal component and to involve activation of endogenous opioid peptide activity in the brain. The results also suggest a tonic inhibition of endogenous opioid peptide activity by nitric oxide, which when antagonized, results in diminished response to pain.

Synaptophysin immunoreactivity in the aging rat pituitary gland

The density of synaptophysin (SN)-immunoreactivity (IR) was examined in pituitary glands of aging male Sprague-Dawley rats. SN-IR was observed as dense dots among endocrine cells of the intermediate lobe, while the neural lobe contained numerous, highly dense immunopositive regions. Some anterior lobe secretory cells contained SN-IR within the cytoplasm, suggestive of the presence of the protein in secretory granules, but no dot-like staining was observed between endocrine cells of that region. A quantitative analysis of the dot-like SN-immunostaining within the intermediate lobe found that tissue from groups of rats aged 13 months, or 15-17 months, contained significantly fewer SN-immunopositive areas than did tissues from 8-month-old animals. Diminished SN immunostaining is suggestive of reduced numbers of synapses in the intermediate lobe, which may lead to alterations in regulation of pituitary hormone secretion from endocrine cells in the older animals.

Interrelationships of neurochemicals, estrogen, and recurring headache

Recurring headache syndromes, such as migraine, are common problems for women throughout their adult lives. Headache symptoms often fluctuate over the years that they are present and, for most headache sufferers, these changes seem to occur randomly. For many women, however, chronic headache changes in predictable patterns in relation to alterations in hormonal states. Clinically, headache is often modified during menses, pregnancy, and menopause. Although sex hormones are changing with these clinical events, this paper will present the more important link between altered sex hormones and changes in neurochemicals believed to be responsible for recurring headache syndromes according to the neurobiological theory of migraine.

Regulation of pituitary beta-endorphin secretion in aging rats: in vitro responsiveness to dopamine

The intermediate lobe of the mammalian pituitary is highly responsive to dopamine inhibition of beta-endorphin secretion. In this study, the ability of aged (12 months) intermediate lobes to respond to dopamine was compared to that of young (6 weeks) tissue, using a short-term in vitro incubation of isolated rat neurointermediate lobes, with measurement of peptide release by radioimmunoassay. Tissue from the aged rats released greater amounts of beta-endorphin peptide than amounts measured from young tissue at all time periods studied. The aged lobes were also found to be significantly more sensitive to dopamine than young glands, as measured by percent change of each group compared to respective baseline release. In comparison, incubation of tissue from young animals in which the intermediate lobe had been acutely denervated by treating rats with injections of the catecholamine neurotoxin, 6-hydroxydopamine, did not differ in responsiveness to dopamine as compared to tissue from control rats. The observations suggest that aging intermediate lobe, while being hypersecretory, is supersensitive to dopamine, perhaps as the result of gradually reduced innervation.

Naltrexone administration effects on regional brain monoamines in developing rats

The effects of the opioid antagonist naltrexone (NALTX) daily administration (1 mg/kg SC) from birth on the levels of dopamine (DA), serotonin (5-HT), and their respective major metabolites, in the striatum, midbrain, and hypothalamus of 7-, 14-, and 22-day-old rats were investigated. Naltrexone treatment increased the striatal HVA/DA ratio on postnatal day 7. At day 14, two subpopulations (A and B) were found among the treated animals. The subpopulation A showed decreased HVA/DA and increased DOPAC/DA ratios, whereas the subpopulation B presented a higher DA concentration. No significant effect appeared on the striatal dopaminergic system in 22-day-old pups. The serotonergic system was affected by exposure to naltrexone only from day 14. The subpopulation A showed a reduction in all the parameters measured in the three regions studied, although in the subpopulation B, lower 5-HIAA/5-HT ratios appeared in the midbrain and hypothalamus. At 22 days of age NALTX treatment elevated striatal 5-HT and 5-HIAA and the ratio of 5-HIAA/5-HT in the midbrain and hypothalamus. These data suggest an endogenous opioid modulation on the central aminergic systems during the neonatal period and point out the consequences of opioid plasticity on related neurotransmitter systems.