Opioid systems,behavioral thermoregulation and shell polymorphism in the land snail,Cepaea nemoralis

Summary Numerous ecological studies have dealt with the shell color and banding polymorphism of the land snail Cepaea nemoralis. The present field and laboratory investigations focus on the roles of opioid systems in modulating the thermal preferences and behavioral thermoregulation of various morphological types of Cepaea. Evidence is presented that differences in opioid modulation of the thermal responses of Cepaea are associated with shell polymorphism. It is shown that the effects of the prototypic opiate agonist, morphine, and antagonist, naloxone, on behavioral thermoregulation in Cepaea vary with the shell banding pattern and thermal microhabitat. In both the field and laboratory, morphine (0.10, 1.0 and 10 g per snail) caused significant dose- and time-dependent increases in the temperatures selected by various morphological types of Cepaea. The palest shell type (yellow, unbanded) with the highest basal preferred temperature displayed the greatest response to morphine, the shell type (yellow, 2-banded) with an intermediate basal preferred temperature showed an intermediate response to morphine, and the darkest shell type (yellow, 5-banded) with lowest basal preferred temperature showed the least increase in preferred temperature after administration of morphine. These effects of morphine were blocked and reversed by naloxone (1.0 g), with the opiate antagonist by itself (1.0 and 10 g) causing a significant decrease in behaviorally selected temperatures. The unbanded and 2-banded morphs displayed significantly greater decreases in preferred temperatures after treatment with naloxone than did the 5-banded morph, which showed minimal responses. It is suggested that these differences in opioid modulation of thermal preferences and behavioral thermoregulation may contribute to the polymorphic thermal preferences of natural populations of Cepaea.Abbreviations B yellow five-banded shell type - I yellow two-banded shell type - U yellow unbanded shell type     

Influence of altitude, habitat and microhabitat on thermal adaptation of cicadas from Southwest Texas (Hemiptera: Cicadidae)

The thermal responses of 12 cicada species inhabiting Big Bend National Park, Texas, USA are investigated to determine the influence of altitude, habitat and microhabitat. The park provides an opportunity to analyze the thermal responses in animals from a variety of habitats and altitudinal gradients within a limited geographic range. The data suggest that thermal responses of cicadas are adaptations to their specific habitats. No thermal responses are significantly correlated with body size. The maximum voluntary tolerance temperature (an upper behavioral thermoregulatory point) and heat torpor temperatures show significant correlations with altitude. Variability in thermal responses can also be related to the characteristics of the microhabitat selected or the behavioral pattern of a species.     

Effects of beta-endorphin on ornithine decarboxylase in tissues of developing rats: a potential role for this endogenous neuropeptide in the modulation of tissue growth

Ornithine decarboxlyase (ODC) catalyzes the initial step in the bio-synthesis of the polyamines spermidine and spermine, which are key regulators of cell growth, proliferation and differentiation. Intracisternal administration of beta-endorphin (1 microgram) to 6 day-old rats markedly decreased brain, liver, heart and kidney ODC activity. Conversely, subcutaneous administration of beta-endorphin increased ODC activity in the heart and liver. Thus, ODC inhibition in peripheral organs in rat pups given beta-endorphin intracisternally appears to reflect central effects of this neuropeptide. Experiments were also carried out to test whether opioid receptors are involved in these tissue ODC responses. Naloxone prevented the decreases in brain ODC indicating the participation of opioid receptors in that process. In contrast, naloxone did not alter ODC responses in peripheral organs in rat pups given beta-endorphin intracisternally, indicating that these effects are independent of its classical opioid character. These results support the view that endogenous beta-endorphin may play an important role in organogenesis by modulating the growth-related enzyme ODC. The data also suggest that the regulation of peripheral organ development by beta-endorphin may be mediated through the release of growth regulatory substances from the CNS.     

Plasma glucose-lowering effect of beta-endorphin in streptozotocin-induced diabetic rats.

The effect of beta-endorphin on plasma glucose levels was investigated in streptozotocin-induced diabetic rats (STZ-diabetic rats). A dose-dependent lowering of plasma glucose was observed in the fasting STZ-diabetic rat fifteen minutes after intravenous injection of beta-endorphin. The plasma glucose-lowering effect of beta-endorphin was abolished by pretreatment with naloxone or naloxonazine at doses sufficient to block opioid mu-receptors. Also, unlike wild-type diabetic mice, beta-endorphin failed to induce its plasma glucose-lowering effect in the opioid mu-receptor knock-out diabetic mice. In isolated soleus muscle, beta-endorphin enhanced the uptake of radioactive glucose in a concentration-dependent manner. Stimulatory effects of beta-endorphin on glycogen synthesis were also seen in hepatocytes isolated from STZ-diabetic rats. The blockade of these actions by naloxone and naloxonazine indicated the mediation of opioid mu-receptors. In the presence of U73312, the specific inhibitor of phospholipase C (PLC), the uptake of radioactive glucose into isolated soleus muscle induced by beta-endorphin was reduced in a concentration-dependent manner, but it was not affected by U73343, the negative control of U73312. Moreover, chelerythrine and GF 109203X diminished the stimulatory action of beta-endorphin on the uptake of radioactive glucose at a concentration sufficient to inhibit protein kinase C (PKC). The data obtained suggest that activating opioid mu-receptors by beta-endorphin may increase glucose utilization in peripheral tissues via the PLC-PKC pathway to lower plasma glucose in diabetic rats lacking insulin.     

The insensitivity of thermal preferences to various thermal gradient profiles in newts

Many ectotherms possess the ability to behaviourally regulate their body temperatures. Thermoregulatory behaviour is affected by various biotic and abiotic factors, which may cause a substantial bias in the laboratory estimates of preferred body temperatures (T _p). We examined thermoregulatory behaviour in alpine newts, Ichthyosaura (formerly Triturus) alpestris, in both horizontal linear and vertical nonlinear thermal gradients, to evaluate the influence of a disparate water temperature distribution on their thermal preferences. Newt positions in thermal gradients differed from those in constant temperatures, which indicates their thermal preferences in both experimental setups. The mean and range of body temperatures showed similar values in both types of aquatic thermal gradients. We concluded that under a sufficiently wide range of environmental temperatures, newt thermal preferences are largely insensitive to the thermal gradient profile. This supports the suitability of T _p estimates for further experimental and comparative studies in newts.     

Thermoregulatory and endocrine effects of a low dose of danazol in postmenopausal women: interaction with the effect of naloxone

Before and on the 30th day of danazol administration (200 mg/day), in six postmenopausal women the activity of endogenous opioid peptides has been indirectly evaluated by the effect on LH secretion and body temperature (measured as rectal temperature) exerted by the infusion of the opioid antagonist naloxone (1.6 mg/h x 4 h preceded by 1.6 mg iv bolus). Before and during danazol administration a GnRH test (100 mcg iv bolus) was also performed to evaluate possible variations in pituitary responsiveness to GnRH. Danazol significantly reduced mean plasma levels of LH and FSH (p less than 0.01), and their response to GnRH stimulus (p less than 0.05). Either before or during danazol administration mean plasma LH and FSH levels did not vary during the infusion of naloxone, while body temperature significantly decreased (p less than 0.01). The decrease in body temperature was significantly greater (p less than 0.05) during danazol than before treatment. The present data suggest that in postmenopausal women a low dose of danazol exerts an antigonadotropic effect mainly reducing the pituitary responsiveness to GnRH. The enhanced hypothermic response to naloxone observed during danazol administration also seems to suggest that in postmenopausal women a low dose of danazol enhances the thermoregulatory role of endogenous opioid peptides.     

Effect of beta-endorphin on the thermal excitability of preoptic neurons in the unanesthetized rabbit

The opioid peptide, beta-endorphin (beta-E), will promote changes in body temperature when injected into the brain. It is possible that beta-E alters body temperature by affecting the activity of thermoregulatory neurons in the preoptic anterior hypothalamus (POAH). Single unit activity in the POAH was recorded in unanesthetized rabbits while radiant heat was applied to the dorsal skin. Beta-E was then microinjected into the POAH, and the peripheral heating was repeated. Seventy-seven percent of the POAH neurons were responsive to skin heating. Beta-E and equal excitatory and inhibitory effects on warm-excited and warm-inhibited neurons. Four of six warm-excited neurons were converted to warm-inhibited or unresponsive following beta-E injection. Six out of ten warm-inhibited neurons were converted to warm-excited or unresponsive by beta-E. Beta-E-induced shifts in thermal excitability of POAH neurons may be responsible for the ability of POAH injections of beta-E to elevate body temperature in the rabbit.     

Identification of functionally important dipeptide in sequences of atypical opioid peptides

The occurrence of individual amino acids and dipeptide fragments in the sequences of 60 known atypical opioid peptides was analyzed. An expressed predominance of Tyr-Pro fragment suggested a high probability of analgesic activity for this dipeptide, and it was experimentally studied. It was shown on the somatic and visceral pain sensitivity models that, at the i.p. administration of Tyr-Pro in doses of 1.0–10 mg/kg of body mass, it exhibits an analgesic activity eliminated by naloxone and naloxone metiodide. However, in tests on ileum preparations of guinea pig and mouse vas deference in vitro, Tyr-Pro was devoid of opioid activity, which proved its indirect influence on opioid receptors.     

Experimental Manipulation of Melanism Demonstrates the Plasticity of Preferred Temperature in an Agricultural Pest (Phaulacridium vittatum)

Phenotypic plasticity is a key trait of successful pest species, and may increase the ability to cope with higher, more variable temperatures under climate change. We investigate the plasticity of preferred temperature in a widespread agricultural pest, the wingless grasshopper (Phaulacridium vittatum). Preferred temperature is a measure of thermoregulatory behaviour through habitat selection. It is influenced by melanism, which affects body temperature by determining the amount of radiation absorbed by the body. First we demonstrate that body temperature and preferred temperature in P. vittatum is influenced by melanism, by comparing the preferred temperature of the colour morphs in laboratory thermal gradients and field body temperatures in natural populations. We then test whether preferred temperature changes in response to changes in body temperature, by determining preferred temperature before and after manipulation of melanism by painting. When melanism was manipulated experimentally in live grasshoppers, preferred temperature changed to reflect the thermal qualities of the new colour. The preferred temperature of light grasshoppers increased after they were painted black, and decreased after being painted white. Similarly, dark individuals that were painted white behaved like a light individual, maintaining a lower body temperature. Preferred temperature in P.vittatum is a plastic thermoregulatory response to ambient temperature, mediated by the influence of melanism on body temperature.     

Antagonism of diazepam-induced feeding in rats by antisera to opioid peptides

Diazepam-induced feeding in rats is antagonized not only by the opiate antagonist naloxone but also intraventricular administration of specific antisera to the endogenous opioid peptides met-enkephalin or beta-endorphin. Pituitary beta-endorphin is probably not implicated in the diazepam effect since blockade with the glucocorticoid dexamethasone of the release of beta-endorphin from the anterior pituitary does not modify the diazepam-induced feeding, which is however prevented by TRH, a suggested physiological antagonist of some of the effects of opioid peptides. The possible central participation of both beta-endorphin and met-enkephalin in the ingestive behavior induced by diazepam gives further support to the postulated physiological role of endogenous opioids in appetite regulation.     

Beta-endorphin activity and hypercapnic ventilatory responsiveness after marathon running

To investigate the hypothesis that endurance exercise may lead to a decrease in ventilatory chemosensitivity as possibly mediated by an increase in endogenous beta-endorphins, we measured hypercapnic ventilatory responsiveness (HCVR) and circulating beta-endorphin immunoreactivity in six runners before and after a marathon (42.2 km) race and after administration of 10 mg iv naloxone. Similar testing was performed at identical time periods on the day before the marathon as control data. On each occasion, HCVR was measured twice 15 min apart, and the mean value was used for analysis. Six active (training distance 50-104 km/wk) and experienced (no. of marathons completed, 1-25) runners participated in the study. There were no significant changes in beta-endorphin activity or HCVR on the control day. All runners experienced a rise in beta-endorphin activity from premarathon (21.3 +/- 16.0 pg/ml) to immediate postmarathon (89.6 +/- 84.9 pg/ml) values (P less than 0.05). However, HCVR showed no significant change at any of the three testing periods on the marathon day. To investigate whether a time delay may have affected the lack of response to naloxone, additional testing was performed in five subjects, except that 10 mg iv naloxone was given within 10 min after completion of the marathon, and then HCVR was measured. Although there was a greater than fourfold increase in beta-endorphin immunoreactivity after the marathon, there was no significant change in HCVR after naloxone administration. We conclude that natural increases in endogenous beta-endorphin activity associated with marathon running do not modulate central chemosensitivity.     

Endogenous opioids and ventilatory responses to hypercapnia in normal humans

Though administration of opioid peptides depresses ventilation and ventilatory responsiveness, the role of endogenous opioid peptides in modulating ventilatory responsiveness is not clear. We studied the interaction of endogenous opioids and ventilatory responses in 12 adult male volunteers by relating hypercapnic responsiveness to plasma levels of immunoactive beta-endorphin and by administering the opiate antagonist naloxone. Ventilatory responsiveness to hypercapnia was not altered by pretreatment with naloxone, and this by itself suggests that endogenous opioids have no role in modulating this response. However, there was an inverse relationship between basal levels of immunoactive beta-endorphin in plasma and ventilatory responsiveness to CO2. Furthermore, plasma beta-endorphin levels rose after short-term hypercapnia but only when subjects had been pretreated with naloxone. We conclude that measurement of plasma endorphin levels suggests relationships between endogenous opioid peptides and ventilatory responses to CO2 that are not apparent in studies limited to assessing the effect of naloxone.     

An assessment of skin temperature gradients in a tropical primate using infrared thermography and subcutaneous implants

Infrared thermography has become a useful tool to assess surface temperatures of animals for thermoregulatory research. However, surface temperatures are an endpoint along the body's core-shell temperature gradient. Skin and fur are the peripheral tissues most exposed to ambient thermal conditions and are known to serve as thermosensors that initiate thermoregulatory responses. Yet relatively little is known about how surface temperatures of wild mammals measured by infrared thermography relate to subcutaneous temperatures. Moreover, this relationship may differ with the degree that fur covers the body. To assess the relationship between temperatures and temperature gradients in peripheral tissues between furred and bare areas, we collected data from wild mantled howling monkeys (Alouatta palliata) in Costa Rica. We used infrared thermography to measure surface temperatures of the furred dorsum and bare facial areas of the body, recorded concurrent subcutaneous temperatures in the dorsum, and measured ambient thermal conditions via a weather station. Temperature gradients through cutaneous tissues (subcutaneous-surface temperature) and surface temperature gradients (surface-ambient temperature) were calculated. Our results indicate that there are differences in temperatures and temperature gradients in furred versus bare areas of mantled howlers. Under natural thermal conditions experienced by wild animals, the bare facial areas were warmer than temperatures in the furred dorsum, and cutaneous temperature gradients in the face were more variable than the dorsum, consistent with these bare areas acting as thermal windows. Cutaneous temperature gradients in the dorsum were more closely linked to subcutaneous temperatures, while facial temperature gradients were more heavily influenced by ambient conditions. These findings indicate that despite the insulative properties of fur, for mantled howling monkeys surface temperatures of furred areas still demonstrate a relationship with subcutaneous temperatures. Given that most mammals possess dense fur, this provides insight for using infrared imaging in thermoregulatory studies of wild animals lacking bare skin.     

Food consumption does not affect the preferred body temperature of Yarrow's spiny lizard (Sceloporus jarrovi)

When animals consume less food, they must reduce their body temperature to maximize growth. However, high temperatures enhance locomotion and other performances that determine survival and reproduction. Therefore, thermoregulatory behaviors during different metabolic states reveal the relative importance of conserving energy and sustaining performance. Using artificial thermal gradients, we measured preferred body temperatures of male spiny lizards (Sceloporus jarrovi) in fed and fasted states. Both the mean and maximal body temperatures (33° and 35 °C, respectively) were unaffected by metabolic state. This finding suggests that the benefits of foraging effectively, evading predators, and defending territory outweigh the energetic cost of a high body temperature during fasting.     

D-amphetamine-induced hypothermia and hypermotility in rats: Changes after systemic administration of beta-endorphin

Systemically administered beta-endorphin was tested in rats for its ability to modify the hypothermia and hypermotility induced by d-amphetamine. Colonic temperature and motor activity were measured in a cold (4°C) ambient temperature in animals given IP injections of beta-endorphin (0.1, 1.0, or 3.0 mg/kg), naloxone (10 mg/kg), or morphine (30 mg/kg). The same measurements were taken in animals given beta-endorphin (1.0 mg/kg) in combination with naloxone or saline pretreatment and d-amphetamine (15 mg/kg) or saline post-treatment. Morphine alone had a biphasic effect on thermoregulation, but did not affect d-amphetamine-induced hypothermia. Activity scores were decreased by morphine, in both d-amphetamine and saline treated animals. The thermal response of rats to beta-endorphin alone was variable, depending on dosage, but all 3 dosages partially blocked the hypothermic effect of d-amphetamine. Naloxone blocked the thermal effects of both beta-endorphin and d-amphetamine. Motor activity tended to be decreased by naloxone, regardless of amphetamine treatment, but beta-endorphin tended to increase activity in amphetamine-treated animals and reduce it in saline-treated controls. In their actions on both thermoregulation and activity, naloxone and beta-endorphin appeared to interact independently with d-amphetamine, often producing effects in the same direction, but in combination, they tended to be mutually inhibitory.     

Endogenous opioid peptides: do they mediate the acute antihypertensive action of clonidine in humans?

The involvement of endogenous opioid peptides in the antihypertensive action of acutely administered clonidine, a centrally acting adrenergic agonist, was studied in humans. Eight hypertensive subjects received clonidine 0.2 mg orally, naloxone 8 mg i.v. followed by a 0.13 mg/min infusion, and both drugs together on separate days. Clonidine resulted in a significant decrease in mean blood pressure, which was not affected by concomitant treatment with naloxone. Naloxone alone or with clonidine caused significant elevations in plasma aldosterone, not mediated by increased plasma renin activity. Plasma beta-endorphin was not increased after clonidine administration. In humans, the antihypertensive effects of acute clonidine administration do not appear to be mediated by the release or action of endogenous opioids.     

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 altered responses were suppressed by the opioid antagonist naloxone. Non-invasive inhibition of the activity of the pineal gland by exposure to light also reduced nocturnal analgesia in schistosome infected animals. Naloxone antagonism and pineal inhibition of morphine- induced analgesia was obtained similarly in control, uninfected animals. Taken together, these findings suggest strongly that infection with S. mansoni results in a chronic activation of the endogenous opiate system.     

Effect of sex steroids on body temperature in postmenopausal women. Role of endogenous opioids.

The role of endogenous opioids on the thermoregulatory effect of sex steroids was investigated in six postmenopausal women before and during treatment with transdermal 17 B-estradiol (TTS 50; 50 mcg/day) with or without vaginal progesterone (P4; 100 mg twice daily). In all the different endocrine conditions, saline or the opioid antagonist naloxone (10 mg/hr. preceded by 10 mg iv bolus) were randomly infused for 4 hrs., on two consecutive days. Measurements of body temperature (BT) variations were performed by a thermistor probe placed in the rectum. BT did not significantly vary from baseline values during saline infusion, whereas it significantly decreased during the infusion of naloxone performed, either before treatment (p less than 0.01), during TTS 50 administration (p less than 0.01), or during TTS 50 + P4 (p less than 0.025). The naloxone induced decrease of BT was greater during TTS 50 administration than before treatment (p less than 0.025). The addition of P4 to TTS 50 administration increased baseline BT of 0.4 degrees C (p less than 0.01), and reduced the ability of naloxone to reduce BT (p less than 0.01 vs. TTS 50). The hyperthermic effect of P4 was not abolished by the infusion of naloxone. Our data show that in postmenopausal women the effect of endogenous opioid peptides on BT is enhanced by estradiol and reduced by progesterone. The hyperthermic effect of progesterone does not seem to be mediated by an increased endogenous opioid activity.     

Modulation of spontaneous seizures in the mongolian gerbil: effects of beta-endorphin

Intraventricular injection of beta-endorphin (0.1-3 micrograms) into gerbils from the UCLA seizure sensitive strain reduced the incidence and severity of spontaneous epileptiform seizures, both the motor manifestations and the preceding high voltage focal spiking and accompanying seizure activity in the cortical EEG. This "'anticonvulsant" effect of beta-endorphin was prevented by prior administration of naloxone (1 mg . kg-1 IP). These findings suggest that the endogenous opioid peptide may be involved in the normal suppression of the epileptic diathesis in these animals during the interictal periods.     

Lateral cerebral ventricle and preoptic-anterior hypothalamic area infusion and perfusion of beta-endorphin and ACTH to unrestrained rats: core and surface temperature responses

Both beta-endorphin and ACTH have been found in high concentrations within the hypothalami of mammals and each neuropeptide has been proposed to play a physiological role in regulating body temperature. In an attempt to determine how these peptides may alter thermoregulation, small, microgram concentrations of beta-endorphin and ACTH were injected either into lateral cerebral ventricle (ICV) or directly into the preoptic-anterior hypothalamic area (POAH) or perfused into the POAH of unrestrained rats. Core (rectal) and surface (tail) temperatures were recorded before and after ICV and POAH injection of 1 microgram of beta-endorphin or ACTH or perfusion (10 ng/microL) of either neuropeptide. POAH perfusion of naloxone HCl following the neuropeptide perfusion was tested to determine the specificity of the temperature responses. Regardless of the route of central administration, beta-endorphin, in the concentrations used, consistently evoked a hyperthermic core temperature response, that could be antagonized by naloxone. Increased core temperatures may, in part, have been due to peripheral vasoconstriction, as suggested by the decreases seen in tail temperature. The same concentrations of ACTH failed to show any prominent core temperature changes. Results suggest that beta-endorphin is a more potent modulator than ACTH in altering core temperatures of unrestrained rats. Whether beta-endorphin and ACTH act physiologically in an antagonistic manner to maintain a constant body temperature remains to be proven.