Opioid receptor types for endogenous enkephalin in the thoracic ganglion of the crab, Carcinus maenas

Mu opioid receptor in spermatozoa, eggs and larvae of gilthead sea bream (Sparus Aurata) and its involvement in stress related to aquaculture

In aquaculture, unfavourable conditions experienced during early development may have strong downstream effects on the adult phenotype and fitness. Sensitivity to stress, leading to disease, reduced growth and mortality, is higher in larvae than in adult fish. In this study, conducted on sea bream (Sparus aurata), we evidenced the presence of the mu opioid receptor in gametes and larvae at different developmental stages. Moreover, we evaluated the possibility of reducing the effects of artificially produced stress, altering temperature, salinity and pH, by naloxone (an opioid antagonist) and calcium. Results evidenced that mu opioid receptor is present in larvae and in gametes of both sexes and that, during larval growth, its expression level changes accordingly; furthermore, naloxone/calcium association is efficacious in increasing the survival period of treated larvae compared to controls. We conclude that in sea bream rearing, the use of naloxone/calcium against stress can improve fish farming techniques by reducing larval mortality and consequently increasing productivity.

Analgesia in amphibians: preclinical studies and clinical applications

Preclinical studies of analgesia in amphibians or recommendations for clinical use of analgesics in amphibian species are extremely limited. This article briefly reviews the issues surrounding the use of analgesics in amphibians, starting with common definitions of pain and analgesia when applied to nonhuman animals. Nociceptive and endogenous opioid systems in amphibians are reviewed, and results of preclinical research on opioid and nonopioid analgesics summarized. Recommended opioid and nonopioid analgesics are summarized, and practical recommendations made for their clinical use.

The presence of delta and mu-, but not kappa or ORL(1) receptors in bovine pinealocytes

Physicians have noted since antiquity that their patients complained of less pain and required fewer analgesics at night-time. In humans, the circulating levels of melatonin, a pineal substance with analgesic and hypnotic properties, exhibit a pronounced circadian rhythm with serum levels being high at night and low during day-time. Moreover, pinealectomy abolishes the analgesic effects of melatonin, and naloxone disrupts the day-night rhythm of nociception. In this study, we have attempted to identify and characterize the nature and types of opioid receptor in bovine pinealocyte membranes, using a radioligand binding technique with the selective radioligands [3H]DAMGO, [3H]DPDPE, [3H]U69593 and [3H]orphanin-FQ (OFQ) for identifying mu (mu)-, delta (delta)-, kappa (kappa)- and opioid receptor-like (ORL(1)) receptors, respectively. The saturation experiments on bovine pinealocyte membranes for [3H]DPDPE binding provided B(max) and K(d) values of 553+/-24 fmol/mg protein and 1.3+/-0.6 nM; and for [3H]DAMGO binding provided B(max) and K(d) values of 6.3+/-1.3 fmol/mg protein and 1.2+/-0.4 nM, respectively. On the other hand, the specific radioligands ([3H]U69593 and [3H]OFQ) binding of kappa and ORL(1) receptors were undetectable in bovine pinealocyte membranes. Furthermore, competitive experiments with opioid agonist and antagonist and related compounds confirmed the presence of mu- and delta-opioid binding sites in bovine pinealocyte membranes. These results indicate that neither kappa nor ORL(1) receptors are present on the pinealocytes, and the majority of opioid receptors found in the bovine pineal gland are delta (possibly, both delta(1) and delta(2)) types, with a minority being mu type, and that both are primarily located on the bovine pinealocyte membranes. These opioid receptors, by stimulating the activity of N-acetyltransferase, enhance the synthesis of melatonin.

Enkephalinergic control of the secretory activity of neurons producing stereoisomers of crustacean hyperglycemic hormone in the eyestalk of the crayfish Orconectes limosus

A subgroup of neurons in the classical X organ sinus gland neuroendocrine system of the crayfish (Orconectes limosus) eyestalk produces two chiral forms of the crustacean hyperglycemic hormone (CHH) in two different types of neurons: CHH in 22 cells and D Phe(3) CHH in eight cells. Previous reports have demonstrated that release of CHH from the sinus gland is inhibited by enkephalins. Here, we have addressed the questions of 1) whether this inhibition affects one or both types of CHH neurons, 2) where the site of enkephalinergic control of CHH and/or D Phe(3) CHH is, and 3) whether the inhibitory effect is due to direct or indirect interactions of enkephalinergic neurons with CHH cells. In vitro incubations of neurosecretory complexes followed by immunoassays of CHH isoforms indicated that both methionine and leucine enkephalins inhibit release of the two CHH isoforms from crayfish eyestalks, by a receptor mediated process. Whole mount double or triple immunofluorescence labelings combined with confocal microscopy revealed enkephalin immunostaining in all neuropils of the eyestalk, except in the sinus gland. Virtual thin confocal sections showed many close appositions between terminals of enkephalinergic neurons and dendritic arborizations of specific CHH immunoreactive cells in the medulla terminalis neuropil. This provides the first evidence for direct inputs from enkephalinergic neurons into dendrites of both CHH cell types, which suggests that enkephalins inhibit release of both CHH isoforms via synaptic contacts.

Cloning, molecular characterization, and distribution of a gene homologous to delta opioid receptor from zebrafish (Danio rerio)

A full-length cDNA, ZFOR1, has been isolated from the teleost zebrafish (Danio rerio) using a probe from rat mu opioid receptor. ZFOR1 encodes a 373 amino acid protein with seven potential transmembrane domains that shows a high degree of homology to mammalian delta opioid receptor. We have also isolated a genomic clone which contains two exons of ZFOR1, homologous to exons 2 and 3 in mouse and human delta opioid receptor. Expression of ZFOR1 appears to be restricted to nervous tissue as assessed by Northern blot. In situ hybridization in zebrafish brain with specific probes revealed several discrete areas of ZFOR1 expression; higher levels are detected in dorsal telencephalic areas, the periventricular layer of the optic tectum, and the granular layer of the cerebellum. This is the first molecular evidence of the presence of the delta opioid receptor in a non-mammalian species and suggests that it has been highly conserved throughout vertebrate evolution.