Injection Of Dermorphin Research Articles

Dermorphin [D-Arg2, Lys4] (1-4) amide inhibits below-level heat hypersensitivity in mice after contusive thoracic spinal cord injury.

Opioid use for chronic pain is limited by severe central adverse effects. We examined whether activating mu-opioid receptors (MORs) in the peripheral nervous system attenuates spinal cord injury (SCI) pain-like behavior in mice. We produced a contusive SCI at the T10 vertebral level and examined motor and sensory dysfunction for 6 weeks. At 6 weeks, we tested the effect of subcutaneous (s.c.) injection of dermorphin [D-Arg2, Lys4] (1-4) amide (DALDA), a peripherally acting MOR-preferring agonist, on mechanical and heat hypersensitivity. Basso mouse scale score was significantly decreased after SCI, and mice showed hypersensitivity to mechanical and heat stimulation at the hind paw beginning at 2 weeks, as indicated by increased paw withdrawal frequency to mechanical stimulation and decreased paw withdrawal latency to heat stimulation. In wild-type SCI mice, DALDA (1 mg/kg, s.c.) attenuated heat but not mechanical hypersensitivity. The effect was blocked by pretreatment with an intraperitoneal injection of methylnaltrexone (5 mg/kg), a peripherally restricted opioid receptor antagonist, and was also diminished in Pirt-MOR conditional knockout mice. DALDA did not adversely affect exploratory activity or induced preference to drug treatment in SCI mice. In vivo calcium imaging showed that DALDA (1, 10 mg/kg, s.c.) inhibited responses of small dorsal root ganglion neurons to noxious heat stimulation in Pirt-GCaMP6s mice after SCI. Western blot analysis showed upregulation of MOR in the lumbar spinal cord and sciatic nerves at 6 weeks after SCI. Our findings suggest that peripherally acting MOR agonist may inhibit heat hypersensitivity below the injury level with minimal adverse effects.

Different effects of peptidase inhibitors on dermophin- and on [D-Arg 2] dermorphin-induced antinociceptive activity

The antinociceptive effects produced by the intracerebroventricular (i.c.v.) injection of dermorphin and [D-Arg 2] dermorphin were compared in conscious mice, using the combined administration of peptidase inhibitors. Nociception was assessed using a tail pressure assay. Dermorphin-induced antinociception was not potentiated by simultaneous administration of amastatin or captopril as judged from the ED 50 values. Co-administration of dermorphin and amastatin gave a longer duration than with dermorphin alone, whereas there was no significant effect on duration with captopril. The antinociceptive activity of dermorphin was significantly enhanced when the heptapeptide was injected simultaneously with both peptidase inhibitors. This result indicates that the heptapeptide sequence is required for the full expression of intrinsic opioid activity of dermorphin. In contrast, co-administration of amastanin brought about a significant enhancement of the antinociceptive activity induced by i.c.v. administration of [D-Arg 2]dermorphin, whereas the effect of [D-Arg 2]dermorphin was markedly decreased by the concurrent administration of captopril or thiorphan. The potency of captopril was much greater than that of thiorphan. The present results suggest that [D-Arg 2]dermorphin may be transformed metabolically to a peptide which has potent antinociceptive activity.

Effect of dermorphin on body temperature in rats

The effect of dermorphin on regulation of body temperature was studied in the rat under extreme and thermoneutral environmental temperatures and in different nutritional states. Intracerebroventricular (icv) injections of dermorphin at dose levels of 10, 50, 100 ng/rat produced hypothermia in animals placed in cold temperatures (-10 degrees C and +4 degrees C) and hyperthermia at ambient (+22 degrees C) and higher temperatures (+34 degrees C). These data emphasize the importance of using a wide range of environmental temperatures in studying drug effects on thermoregulation. To determine whether the effect of dermorphin on body temperature was related to the nutritional state of the animal, as observed with other neuropeptides (i.e., bombesin, litorin), the thermoregulatory response was followed in fed and fasted rats. The same results were obtained in both experimental groups. In all cases, dermorphin change in body temperature was mediated via an action on typical opioid receptors since it was completely prevented by pretreatment with naloxone.

Peripheral versus central components of the effects of dermorphin on intestinal motility in the fed rat

The effects of subcutaneous (s.c.), intraperitoneal (i.p.), intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of dermorphin (DER) on intestinal myoelectrical activity were examined in fed rats with chronically implanted electrodes on the small and large bowel. DER s.c. restored the ‘fasting’ pattern of duodenal activity, i.e., the migrating myoelectric complex (MMC), corresponding to an inhibition by about 40% of the fed pattern for 120 min at a dose as small as 0.5 nM per rat. DER i.p. strongly inhibited (about 65%) the fed pattern for 120 min. A fasting pattern lasting 80 min, or a marked inhibition lasting 150 min were recorded after 0.5 nM DER i.t. or i.c.v., respectively. On the contrary, the colonic pattern of activity was inhibited by DER whatever the route used, although the duration of inhibition was different from each other. For both the small and large intestine, similar doses of DER were more efficient by i.c.v. than by i.t. routes, and by i.p. than by s.c. routes. A plurality of sites of action is suggested, including local receptors which are activated, particularly at the duodenal level by i.p. DER (0.5 nM). The supraspinal component of the immediate effects of i.c.v. DER (0.1 nM) were demonstrated by a preferential effect on the colon that was even more intense than after i.t. DER.

Prolactin releasing and luteinizing hormone inhibiting activity of dermorphin shorter homologues in the rat

Dermorphin, a heptapeptide isolated from the skin of the frogs Phillomedusa sauvagei and Phillomedusa rhodei, is endowed with potent peripheral and central opioid-like activity. Intracerebroventricular (icv) injection of dermorphin (31.2, 62.5 and 125 pmol/100g) induced in ovariectomized (OVX) rats dose related rises and decreases in prolactin (PRL) and luteinizing hormone (LH) levels, respectively. The aim of this work was to evaluate the same endocrine responses after administration of shorter peptide amide homologues, related to the N-terminal sequence of dermorphin. These compounds retain a substantial analgesic activity although the latter decreases with the decrease in the number of amino acid residues. Icv administration of the hexapeptide homologue (dermorphin 1–6 amide) to OVX rats did not induce any PRL rise or LH inhibition, even at the high dose of 250 pmol/100g. The pentapeptide (dermorphin 1–5 amide), instead, increased PRL and decreased LH secretion, although the effect was significant only at the dose of 250 pmol/100g. Administration of the tetrapeptide (dermorphin 1–4 amide) induced a significant PRL rise and LH inhibition at both the doses of 125 and 250 pmol/100g. The tetrapeptide was the smallest fragment of the dermorphin moiety which caused endocrine responses while the tripeptide (dermorphin 1–3 amide) was completely ineffective in this context. These data indicate that a complete dissociation exists between the behavioral and endocrine effects of the dermorphin homologues examined. In fact, shorter dermorphins whose analgesic potency was directly related to the number of amino acids, exhibited an opposite pattern in evoking endocrine effects.

Development of tolerance to the effect of dermophin on gastric emptying in the rat

The development of tolerance to the effect of dermorphin on gastric emptying (G.E.) induced by repeated subcutaneous (s.c.), intracerebroventricular (i.c.v.) injections or by i.c.v. infusion of this peptide, was studied in rats. Dermorphin produced a delay in G.E. when it was injected i.c.v. or s.c., but when for 5 days rats were injected twice daily with the same dose of peptide, the acute i.c.v. injection of dermorphin no longer produced a significant delay in G.E. demonstrating an establishment of tolerance to this effect. However, 10 days were necessary to establish tolerance to s.c. injection of the peptide. When dermorphin was i.c.v. infused by a minipump, tolerance to delay of G.E. was inversely proportional to infusion time and it took 2 days to establish tolerance to this peripheral effect. These data suggest the possibility that different development mechanisms: of dermorphin-induced tolerance seem to exists for gastrointestinal responses as compared to other effects of dermorphin, analgesia and catalepsy.

Increases in heart rate and blood pressure produced by injections of dermorphin into discrete hypothalamic sites

Central cardiovascular sites of action for dermorphin were determined by injecting 40 pmol of the peptide into discrete sites within the hypothalamus of halothane anesthetized rats. Blood pressure and heart rate in 101 rats were 88 ± 1 mm Hg and 338 ± 3 beats/min, respectively, prior to 100 nl intrahypothalamic injections of either vehicle or dermorphin. In the caudal anterior hypothalamic nucleus (A5800-5300), dermorphin, but not vehicle, increased blood pressure 8% and heart rate 26%, without changing respiration rate. The peak response was at 32 ± 5 min, the duration > 90 min. Injections of naloxone (30 nmol) into the same anterior hypothalamic site, or 3 mg/kg naloxone administered i.m., completely reversed the cardiovascular actions. Similar increases in heart rate and blood pressure occurred at A6600–6300, the region between medial preoptic and anterior hypothalamic nuclei. Small increases in heart rate, but not blood pressure, resulted from dermorphin injections into the septal area, medial preoptic nucleus, paraventricular hypothalamic nucleus and the lateral ventricle, while injections in the posterior and dorsomedial hypothalamic nuclei were without effect on blood pressure and heart rate. These data provide support for anterior hypothalamic and medial preoptic sites for the cardiovascular actions of the opiate receptor agonist, dermorphin, and indicate greatest effects with this dose (primarily on heart rate) are produced at discrete sites (A6600–6300 and A5800-5300) within these nuclei.

Effects of dermorphin on gastrointestinal transit in rats.

The effects of subcutaneous (s.c.) and intracerebroventricular (i.c.v.) injections of dermorphin on gastric emptying and intestinal transit were studied in rats. Dermorphin injected i.c.v. delayed gastric emptying and this effect was dose-dependent. I.c.v. injections of dermorphin also inhibited intestinal transit but a dose level 5 to 10 times higher than that active on gastric emptying was required. Subcutaneous injections of dermorphin also inhibited gastrointestinal transit but inhibition of the two functions never exceeded 60%. The effect of i.c.v. and s.c. doses of dermorphin was antagonized by a 1 mg . kg-1 dose of naloxone s.c. The data suggest the possibility that dermorphin could affect gastrointestinal transit through an action on central and peripheral opiate receptors.

Neural regulation of gastric acid secretion in rats: influence of dermorphin.

The effects of subcutaneous (s.c.) and intracerebroventricular (i.c.v.) injections of dermorphin on gastric acid output both basal and stimulated by water distension of the stomach, insulin or histamine injections, were studied in conscious pylorus-ligated rats. Dermorphin injected i.c.v. suppressed the stimulation of gastric acid output by gastric water distension and this effect is dose-dependent, the threshold dose being 5 pmol . kg-1. Insulin stimulated gastric secretion is partially blocked by the peptide. Subcutaneous injections of dermorphin, at a dose of 625 nmol . kg-1, inhibited basal and water distension-induced gastric secretion. The effects of i.c.v. and s.c. doses of dermorphin were antagonized by a 1 mg . kg-1 dose of naloxone s.c. Injections (i.c.v.) of dermorphin were ineffective on histamine-induced gastric secretion. The strong inhibitory effect of dermorphin on basal and central or reflexly stimulated gastric acid output suggests that the brain plays a role in the modulation of gastric secretory functions.