Hypothalamo-pituitary-interrenal responses to opioid substances in the trout. II. Effects of morphine and D-Ala2, Met5-enkephalinamide on plasma cortisol titres in vivo

Effects of Restraint Stress on Circulating Corticosterone and Met Enkephalin in Chickens: Induction of Shifts in Insulin Secretion and Carbohydrate Metabolism

This study examined the effects of acute restraint stress in the presence or absence of naltrexone on the circulating concentrations of insulin, glucose, Met-enkephalin and corticosterone in 14-week-old chickens [design: 2 sex × 2 stress/non-stress × 2 +/- naltrexone]. In chickens (five male and five females per treatment) subjected to restraint for 30 min, there were increases in the plasma concentrations of corticosterone and Met-enkephalin. The plasma concentrations of insulin and glucose were also increased in the chickens during restraint. Moreover, there were increases in the plasma concentrations of insulin and glucose in the chickens. The patterns of expression of the proenkephalin gene (PENK) in both the anterior pituitary gland and the adrenal gland were very similar to that of plasma Met-enkephalin. There were relationships between the plasma concentrations of corticosterone, Met-enkephalin, insulin and glucose after 30 min of restraint. The effects of naltrexone treatment on both untreated and stressed chickens were also examined, with naltrexone attenuating the stress-induced increases in the plasma concentrations of corticosterone, Met-enkephalin and glucose but not in those of insulin. The present study demonstrates that stress increases insulin secretion in chickens but also induces insulin resistance.

Expression of ZFOR1, a delta-opioid receptor, in the central nervous system of the zebrafish (Danio rerio)

Opioid receptors, besides mediating the effects of analgesic compounds, are involved in drug addiction. Although a large amount of work has been done studying these receptors in mammals, little information has been obtained from nonmammalian vertebrates. We have studied the regional distribution in the central nervous system (CNS) of the zebrafish of the recently cloned delta-opioid receptor homologue ZFOR1 using nonradioactive in situ hybridization. Our findings show that different nuclei within the main subdivisions of the brain displayed specific mRNA signal. The expression is widespread throughout the brain, but only specific cells within each nucleus displayed ZFOR1. Stained cells were abundant in the telencephalon, both in the olfactory bulb and telencephalic hemispheres, and in the diencephalon, where expression was observed in all the different subdivisions. In the mesencephalon, expression of ZFOR1 was abundant in the periventricular layer of the optic tectum. In the cerebellum, expression of ZFOR1 was detected in valvula cerebelli, corpus cerebelli, and lobus vestibulolateralis in both granule and Purkinje cells. In the myelencephalon, cells expressing ZFOR1 were also distributed in the octavolateralis area, the reticular formation, and the raphe nuclei, among others. Also, ZFOR1 was detected in cells of the dorsal and ventral horn of the spinal cord. This work presents the first detailed distribution of a delta-opioid receptor in the CNS of zebrafish. Distribution of ZFOR1 expression is compared with that of the delta-opioid receptor described in mammals.

In vivo and in vitro effects of β-endorphin and naloxone on corticosterone and cortisol release in male and female water frog, Rana esculenta

1. beta-Endorphin and naloxone effects on corticosterone and cortisol production in male and female Rana esculenta, were studied in vivo and in vitro. 2. The in vivo and in vitro results were in agreement. 3. beta-Endorphin caused a decrease in corticosterone and cortisol release. 4. Naloxone induced an increase in the two corticosteroids at the same times as the decrease caused by beta-endorphin. 5. beta-Endorphin plus naloxone treatment did not change corticosterone and cortisol levels. 6. These results suggest that in Rana esculenta opioids are involved in the regulation of the hypothalamo-pituitary-interrenal axis; in particular, opioids directly modulated interrenal steroidogenesis.

Opioid binding sites in the fish brain: an autoradiographic study

Cryostat sections of trout brains were incubated with tritiated opioid ligands (5 nM [3H]etorphine or 4 nM D-[3H]Ala2, Met5 enkephalinamide) with the initial aim of locating opioid binding sites associated with the hypothalamo-pituitary axis. Naloxone-displaceable binding was observed in all regions of the brain, with a density ranking order of cerebellum greater than telencephalon greater than optic tectum greater than hypothalamus greater than brain stem greater than pituitary gland. Within the hypothalamus and pituitary gland binding was unexpectedly low, apart from a slightly enhanced binding anteriorly in the preoptic region and posteriorly associated with presumptive sensory fibres. A similar distribution of opioid binding sites was seen in the eel and lamprey brain. The high level of opioid binding in the cerebellum permitted a tentative identification of opioid subtypes using [3H]etorphine binding to membrane preparations from trout cerebellum. Scatchard analysis indicated the presence of a single class of high-affinity binding sites with a density of 0.38 pmol/mg protein and affinity constant (KD) of 2.6 nM. Displacement by unlabelled ligands suggested the existence of mu and/or kappa receptors.