Differential opiate influences on food hoarding and intake in the deer mouse, Peromyscus maniculatus.

The feeding behavior of the deer mouse, Peromyscus maniculatus, includes food hoarding as well as ingestion. In this animal the mu opiate agonist, morphine, and the kappa opiate agonist, U-50, 488H, selectively stimulate food hoarding and ingestion, respectively. This suggests that mu and kappa opiate systems may differentially mediate primary components of natural feeding behavior.

FMRFamide, a putative endogenous opiate antagonist: evidence from suppression of defeat-induced analgesia and feeding in mice.

Social conflict and defeat in mice leads to an activation of endogenous opiate systems. The effects of intracerebroventricular administration of the peptide FMRFamide (Phe-Met-Arg-Phe-NH2) and the opiate antagonist naloxone, on aggressive encounters, defeat-induced analgesia and defeat-induced feeding were examined in male mice. Both substances reduced the number of bites required to cause defeat in subordinate mice during aggressive encounters, as well as suppressing the subsequent defeat-induced analgesia.

Magnetic fields inhibit opioid-induced feeding in the slug, Limax maximus.

Exposure to rotating and elevated magnetic fields significantly reduced over three hours the ingestive effects of the opiate agonist, morphine (10 mg/kg), in free-feeding slugs, Limax maximus. Magnetic field exposure also inhibited the opioid-mediated increased ingestive responses of slugs that had been food-deprived for 24 hr. These results suggest that magnetic stimuli inhibit opiate-mediated behavioral and physiological functions in invertebrates in a similar manner as observed in vertebrates.

Exposure to nuclear magnetic resonance imaging procedure attenuates morphine-induced analgesia in mice.

Adult male mice exposed to a Nuclear Magnetic Resonance Imaging (NMRI) procedure during the mid-dark period and injected with morphine (10 mg/kg) failed to exhibit the normal nocturnally enhanced morphine analgesia response to a thermal stimulus that was displayed by mice exposed to a sham imaging procedure and treated with morphine (p less than .01). When tested during the mid-light period, animals exposed to the NMRI procedure and given morphine displayed attenuated analgesia levels relative to sham exposed mice (p less than .

Tolerance to morphine-induced analgesia in mice: magnetic fields function as environmental specific cues and reduce tolerance development.

Mice receiving daily injection of morphine (10 mg/kg) developed tolerance to morphine-induced analgesia, such that after 5-7 days of treatment their thermal response (paw licking) latencies in the hot plate test were indistinguishable from those of control animals. Exposure to a rotating magnetic field for thirty minutes before the daily morphine administrations significantly reduced the development of tolerance. These magnetic exposures also significantly increased over 7-10 days the basal nociceptive thresholds and paw licking response latencies of saline treated mice.

FMRFamide suppresses kappa opiate induced feeding in the mouse.

Intracerebroventricular administration of 0.01-1.0 micrograms of the peptide FMRFamide (Phe-Met-Arg-Phe-NH2) to mice suppressed feeding induced by the specific kappa opiate agonist, U-50, 488H.

The effects of opioid and FMRF-amide peptides on thermal behavior in the snail.

Administration of methionine-enkephalin, beta-endorphin or, as previously shown, the opiate agonist, morphine sulfate (0.10-10.0 micrograms per snail), resulted in significant dose-dependent increases in the latency of thermal (40 degrees C hot plate) avoidance behavior of the terrestrial snail, Cepaea nemoralis.

Inhibitory influences of FMRFamide on morphine- and deprivation-induced feeding.

Intracerebroventricular administration of 0.01-1.0 microgram of the peptide FMRFamide (Phe-Met-Arg-Phe-NH2) to mice reduced morphine-induced feeding.

Opioid systems and feeding in the slug, Limax maximus: similarities to and implications for mammalian feeding.

Substantial evidence is accumulating to implicate opioid systems in the regulation of behavioral and physiological functions in invertebrates in a manner analogous to that observed in vertebrates. This communication reviews opiate involvement in the mediation of the ingestive behaviors of the terrestrial slug, Limax maximus. The similarities to and implications for opioid modulation of mammalian feeding are considered.

Exposure to rotating magnetic fields alters morphine-induced behavioral responses in two strains of mice.

An exposure for 60 min to a 0.5 Hz rotating magnetic field (1.5-90 G) significantly reduced the day-time analgesic and locomotory effects of morphine (10 mg/kg) in CF-1 and C-57BL strains of mice, respectively.

Nocturnal feeding in the mouse--opiate and pineal influences.

Mice displayed daily rhythms in their basal and morphine-induced food intake, consuming significantly greater amounts of food at night. Non-invasive inhibition of the activity of the pineal gland by either exposure to a bright pulse of light or treatment with the L-amino-acid decarboxylase inhibitor, benserazide, reduced the elevated night-time food intakes. These effects on feeding were most evident on the first night the activity of the pineal was reduced.

Prolyl-leucyl-glycinamide reduces aggression and blocks defeat-induced opioid analgesia in mice.

The effects of Prolyl-leucyl-glycinamide (PLG, MIF-1) and the exogenous opiate antagonist naloxone, on aggressive interactions and defeat-induced analgesia were examined in male mice. Both substances reduced the number of bites required to obtain defeat in subordinate mice during aggressive encounters as well as blocking the subsequent defeat-induced analgesia. These results suggest that MIF-1 may function as an endogenous opioid antagonist and have an inhibitory influence on aggression.

The influence of opiate agonists on day-night feeding rhythms in young and old mice.

Daily rhythms of feeding behavior and responses to ketocyclazocine, morphine and naloxone were measured in young (1-2 months) and old (24-30 months) male CF-1 mice. All of the mice consumed more food at night than in the day-time, though this nocturnal peak was markedly reduced in the old animals, who consumed more in the day. The young mice also displayed a significant nocturnal enhancement in ketocyclazocine- and morphine-stimulated feeding.

Magnetic fields as environmental specific cues for morphine-induced analgesia: interactions with tolerance development.

It has been previously demonstrated that weak fluctuating magnetic fields can act as environmental specific cues for the development of tolerance to morphine-induced analgesia in mice. During the course of this tolerance development the basal nociceptive response of the animals preexposed to magnetic fields are also increased. The magnetic field-induced increase in the basal nociceptive response can be blocked by the opiate antagonist, naloxone, suggesting an opioid-mediated stress effect of the magnetic stimuli.

PLG and FMRFamide--endogenous peptides with marked inhibitory effects on opioid-induced feeding.

Social conflict and defeat in mice leads to an activation of endogenous opiate systems and the display of marked feeding behavior. Intraperitoneal administrations of prolyl-leucyl-glycinamide (PLG 0.01-10 mg/kg) leads to a dose-dependent inhibition of defeat-induced feeding that is analogous to that obtained after treatment with either the endogenous peptide FMRFamide (Phe-Met-Arg-Phe-NH2), or the prototypic opiate antagonist, naloxone.

The effects of aging on day-night rhythms of kappa opiate-mediated feeding in the mouse.

Day-night rhythms in feeding behavior and response to the specific kappa opioid agonist U-50,488H (0.10-10. mg/kg) were measured in young (1-2 months), mature (8-12 months) and old (24-30 months) male CF-1 mice.

Evidence for the activation of the endogenous opiate system in hamsters infected with human blood flukes, Schistosoma mansoni.

Nociceptive thresholds were investigated in golden hamsters infected with the human blood fluke, Schistosoma mansoni. Increases in thermal thresholds suggestive of analgesia were evident by 20-25 days of infection. These increased further during a 40-42 day period.

The presence of an opioid system mediating behavioral thermoregulation in the terrestrial snail, Cepaea nemoralis.

Administration of the opiate agonist, morphine sulfate (0.1-10 micrograms per snail) resulted in a significant dose- and time-dependent increase in the temperatures selected by the terrestrial snail, Cepaea nemoralis, in a thermal gradient. These thermoregulatory effects could be blocked and reversed by naloxone hydrochloride, with the opiate antagonist by itself (1 and 10 micrograms) causing a significant decrease in preferred temperatures.

Opioid-induced feeding in the slug, Limax maximus.

Administration of the opioid agonist, morphine (1 and 10 mg X kg-1), resulted in significant, dose-dependent increases in the ingestive responses of food-deprived slugs, Limax maximus, and in the initiation of feeding in satiated animals. These effects could be blocked by the opiate antagonist, naloxone (1 mg kg-1), with naloxone by itself causing a significant decrease in the feeding of food-deprived slugs. These results suggest that opiates are involved in the control of the feeding behavior of Limax.

Ionizing radiation induces opioid-mediated analgesia in male mice.

The effects of exposure to ionizing radiation on the nociceptive thresholds of CF-1 mice were examined. Significant increases in thermal response latencies, indicative of analgesia were observed after exposure to either high or low doses of radiation. However, the onset of analgesia occurred significantly more rapidly after treatment with the high doses.

Age and day-night changes in clonidine-induced analgesia in mice.

Administrations of clonidine hydrochloride (0.1, 1.0 mg/kg) to young, mature, and old mice influenced their response time on a thermally aversive surface (50 degrees C) in an age-dependent manner.

Social conflict activates opioid analgesic and ingestive behaviors in male mice.

The activation of endogenous opioid mechanisms and their subsequent effects on rodent behavior and physiology has usually been characterized following artificial stress. In this study the more naturalistic stress arising from social conflict between male mice was used to investigate the involvement of opioid systems in post-conflict analgesic and ingestive behaviors. Both the aggressive encounters and the subsequent defeat experience resulted in marked analgesia and the induction of ingestive behaviors.

Opiates influence behavioral thermoregulation in the curly-tailed lizard, Leiocephalus carinatus.

Low doses of the opioid agonist, morphine (1-3 mg kg-1), significantly increased the behaviorally selected body temperatures of the curly-tailed lizard, Leiocephalus carinatus. A higher dose of morphine (10 mg kg-1) resulted in an initial behavioral hyperthermia that was followed by a significant decrease in preferred temperatures and a subsequent behavioral hypothermia which declined to control levels within 3-4 hr. These effects could be blocked and reversed by the opiate antagonist, naloxone, with naloxone (1 and 10 mg kg-1) by itself causing significant dose-dependent decreases in preferred temperatures.

Magnetic fields abolish the enhanced nocturnal analgesic response to morphine in mice.

Mice given morphine displayed diel rhythms in the latency of their behavioral response to placement on a hot plate, there being a several fold increase in their nocturnal reaction times. Exposure to a rotating magnetic field eliminated the day-night analgesia rhythms, reducing over 5-10 days the enhanced nocturnal latencies to those found during the day. The attenuation returned to normal nocturnal levels several days after removal of the rotating magnetic field and could be subsequently re-established by reapplication of the magnetic field condition.

Aging and daily rhythms of analgesia in mice: effects of natural illumination and twilight.

Day-night rhythms in aversive thresholds and morphine-induced analgesia were assessed in young (1-3 months) and old (22-30 months) male mice exposed to natural summer (43 degrees N lat.) lighting using a hot-plate technique. In both age groups peak aversive thresholds and morphine-induced analgesia were present at night, with significantly reduced response times in the day.