Beta-endorphin-(10-16) antagonizes behavioral responses elicited by melatonin following injection into the nucleus accumbens of rats

Beta-endorphin 1-31 biotransformation and cAMP modulation in inflammation

A large body of evidence now exists for the immune cell expression, production, and the release of beta-endorphin (BE 1–31) within inflamed tissue. The inflammatory milieu is characterised by increased acidity, temperature and metabolic activity. Within these harsh conditions BE 1–31 is even more susceptible to increased enzymatic degradation over that of plasma or other non-injured tissue. To elucidate the biotransformation pathways of BE 1–31 and provide an insight to the impact of inflamed tissue environments, BE 1–31 and three of its major N-terminal fragments (BE 1–11, BE 1–13 and BE 1–17) were incubated in inflamed tissue homogenates at pH 5.5 for 2 hrs. In addition, the potency of BE 1–31 and five main N – terminal fragments (BE 1–9, BE 1–11, BE 1–13, BE 1–17, BE 1–20) was assessed at mu-opioid receptors (MOR), delta-opioid receptors (DOR), and kappa-opioid receptors (KOR). Opioid receptor potency was investigated by examining the modulation of forskolin induced cAMP accumulation. The majority of the N-terminal fragment of BE 1–31 had similar efficacy to BE 1–31 at MOR. The shortest of the major N-terminal fragments (BE 1–9), had partial agonist activity at MOR but possessed the highest potency of all tested peptides at DOR. There was limited effect for BE 1–31 and the biotransformed peptides at KOR. Major N-terminal fragments produced within inflamed tissue have increased presence within inflamed tissue over that of the parent molecule BE 1–31 and may therefore contribute to BE 1–31 efficacy within disease states that involve inflammation.

The behavior of rats in response to changes in the light regime and administration of melatonin

This report describes studies of the effects of shifts in the daily light/dark rhythm and administration of different doses of melatonin on the behavior of rats with different activity in the open field test. Experiments were performed on 172 Wistar rats kept in a natural or an inverted light/dark regime. Groups of rats received 1 ml of physiological saline or melatonin (1 or 2 mg/kg, i.p.) or were not injected. Inversion of the light/dark regime led to a shift in the rhythm of movement activity and eliminated differences between measures of daytime and night-time activity in control rats not given injections. The effect of melatonin on the movement activity of rats in conditions of natural and inverted light regimes depended on the dose given, the time of administration, and the initial characteristics of the animals' behavior. The data obtained here show that use of melatonin to correct impairments induced by the shift in the light/dark cycle should take consideration of the individual behavioral characteristics of the subjects.

Acute low doses of melatonin restore full sexual activity in impotent male rats

Evidence exists that repeated injections of melatonin in rather large doses inhibit sexual performance in male rats. In contrast, systemic injection of small doses of this hormone stimulates sexual activity of normal male rats. In these experiments, systemic acute administration of melatonin in small doses (10-100 microg/kg) induced the appearance of ejaculations in impotent Wistar male rats that were selected as showing null sexual approach or showing mounts, intromissions but no ejaculations. This effect was partially abolished by the simultaneous peripheral injection of the non-selective melatonin receptor antagonist, luzindole, or by the acute administration of serotonin or of the 5HT(2A) receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), into the amygdala or the ventral hypothalamus. These results suggest that melatonin may stimulate, in a dose-dependent manner, several copulatory parameters of male sexual behavior and may restore sexual activity in impotent animals by interacting with brain receptors, i. e. melatonin and serotonin receptors.

Melatonin acts on the nucleus accumbens to increase acetylcholine release and modify the motor activity pattern of rats

Brain microdialysis coupled to high performance liquid chromatography with electrochemical detection (HPLC-ED) was used to evaluate the influence of melatonin on extracellular concentration of acetylcholine (ACh) in the nucleus accumbens (NAc) of rats. Motor activity was simultaneously monitored during the dialysis sessions with an activity meter. Melatonin and prazosin were administered locally through the dialysis probe. It was found that melatonin dose-dependently increased accumbens ACh. Melatonin (3 microM) decreased horizontal activity and increased vertical activity, while another dose (100 microM) enhanced both horizontal and vertical activity. Prazosin, a putative melatonin antagonist, blocked the effects of melatonin on both motor activity and ACh release when given 20 min before melatonin. Overall, these results suggest that melatonin modulates the release of ACh in the NAc and the pattern of motor activity in the rat.

Acute low doses of melatonin stimulate rat sex behavior: the role of serotonin neurotransmission

Melatonin is known to inhibit male and female sex behavior, but this effect has been reported only after repeated administration of sustained doses of the hormone. The present experiments were performed in order to study the effects of acute treatment with low doses of melatonin on rat male and female sex behavior in a dose-response paradigm. After four mating tests with a receptive female, sexually active male rats of the Wistar strain were injected intraperitoneally (i.p.) with small doses of melatonin (10, 50 and 100 microg/kg) administered acutely 1 h before a 30-min mating test. Melatonin (50 and 100 ng/2 microl) or its analogs, 6-chloromelatonin (2 and 4 ng/2 microl) and 2-iodomelatonin (5 and 10 ng/2 microl) were also injected intracerebroventricularly (i.c.v.) 30 min before mating. Either treatments caused a reduction of the latency to the first mount, intromission and ejaculation. An increase in the frequency of mounts, intromissions and ejaculations was also observed. Inhibition of sexual activity was observed when a greater dose (1 mg/kg) of melatonin was repeatedly injected for 14 days. Female sex behavior, measured by the lordosis quotient in Wistar female rats, was not affected by acute treatment with the hormone, while it appeared to be inhibited by the repeated injection. The facilitating effect of acute i.p. or i.c.v. melatonin low doses on sexual activity of male rats was partially abolished by the pre-treatment with the non-selective melatonin antagonist, luzindole (0.25 mg/kg, injected subcutaneously), and totally suppressed by the injection of small quantities of serotonin or the 5H(2A)-5H(2C) receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane into the amygdala. These results suggest that melatonin may exert opposite effects on male and female sex behavior depending on the dose and duration of treatment.

Prolyl-leucyl-glycinamide, thyrotropin-releasing hormone and beta-endorphin-(10-16), like antidepressants, antagonize melatonin-induced behavioural changes in rats

beta-Endorphin-(10-16), as well as a variety of antidepressants, has been reported to block the behavioural changes induced by injecting melatonin into the nucleus accumbens. In the present study the influence of subcutaneously administered prolyl-leucyl-glycinamide (PLG) and thyrotropin-releasing hormone (TRH) on the behavioural changes induced by melatonin administration in the nucleus accumbens were investigated and compared with that of beta-endorphin-(10-16). PLG and TRH were found to be as effective as beta-endorphin-(10-16) in counteracting the melatonin-induced behavioural changes. The data suggest that these peptides may serve as a starting point for the development of a new class of antidepressants.

Responses to cold, heat, and pain increase locomotion in rats and are attenuated by pinealectomy

The effects of pinealectomy on locomotor behavior responses to cold, heat or pain were assessed in freely moving rats. External cold (4 degrees C) or heat (36 degrees C) stress produced increases of locomotion (including horizontal and vertical movement, and total distance traveled), increases of number of turnings (including both clockwise and counterclockwise), and decreases of postural freezing in rats. In addition, pain (produced by intradermal injection of normal saline) was also shown to produce increases of locomotion (including horizontal and vertical movement, and total distance traveled) and decreases of postural freezing in rats. The increases of locomotion (including horizontal and vertical movement, and total distance traveled), as well as the decreases of postural freezing induced by either cold or pain, were attenuated by pretreatment of animals with pinealectomy. The heat-induced increases of vertical movement as well as the decreases of postural freezing were also attenuated by pinealectomy. The results indicate that these nonphotic, stress-provoking stimuli act through the pineal gland to induce escape behaviors to try to get out of the stressed conditions in rats.

Neuropeptides: animal behaviour and human psychopathology

Animal studies have demonstrated that neuropeptides modulate nervous system functions. It has been postulated that disturbances in neuropeptide systems may be aetiological factors in psychiatric and neurological disorders. Neuropeptides related to ACTH/MSH, including ORG 2766, increase motivation and attention and facilitate recovery processes after nerve damage. These peptides may be effective during the early stage of dementia. Vasopressin and related peptides improve memory processes in animals and humans. In addition, these peptides influence social behaviour, mood and addictive behaviour. The non-opioid gamma-type endorphins have neuroleptic-like activities in animals and antipsychotic effects in a category of schizophrenic patients. Peptides related to CCK have also been found to be effective in these patients. Some neuropeptides, e.g. TRH and PLG, have been reported to exert antidepressant effects. Further research may eventually produce neuropeptides with therapeutic action in psychiatric and neurological diseases.

Inhibiting noradrenergic overactivity by inhibition of thromboxane and concomitant activation of opiate receptors via dietary means

A yin-yang hypothesis is presented linking noradrenergic activity, thromboxane, melatonin, left hemisphere functioning, and cyclic AMP on the one hand, and dopamine, beta-endorphin, calcium, right hemisphere functioning, and cyclic GMP on the other. It is further suggested that there is a yoking of NA, TXA2, serotonin and melatonin in the left hemisphere, and a similar yoking of DA, BE, calcium and cGMP in the right. Evidence is presented to support the hypothesis that each element (NA, TXA2, etc.) on one side can modulate or balance a corresponding element (DA, BE, etc.) on the other. It is suggested that thromboxane is the key element in noradrenergic overactivity and that not taking this into consideration has confounded much prior research. This theory takes into account information processing models as well as pharmacological data and neurochemical theory on coupling of adenylate cyclase to its hormone receptors. Inhibiting noradrenergic overactivity can be obtained by inhibiting thromboxane and concomitantly activating opiate receptors. This protocol may have clinical utility in treating a wide range of disorders such as: anxiety, depression, schizophrenia, sleeplessness, withdrawal states, enuresis, Gilles de la Tourette syndrome, Parkinsonism, Alzheimers, dementia, anorexia, infant ruminations, essential tremor, spasticity of spinal cord injury, diarrhoea, ulcerative colitis, extrapyramidal symptoms, akathisia, neuroleptic malignant syndrome, attention deficit disorder, hyperhidrosis, and possibly AIDS.

Endogenous opiates: 1985

This paper is the eighth installment of our annual review of research involving the endogenous opiate peptides. It is restricted to the non-analgesic and behavioral studies of the opiate peptides published in 1985. The specific topics this year include stress, tolerance and dependence, eating, drinking and alcohol consumption, gastrointestinal and renal activity, mental illness, learning and memory, cardiovascular responses, respiration and thermoregulation, seizures and neurological disorders, activity, and some other selected topics.