Effects of morphine on body temperature of squirrel monkeys of various ages

Naltrexone alters responses to social and physical warmth: implications for social bonding

Socially warm experiences, when one feels connected to others, have been linked with physical warmth. Opioids, hypothesized to support social bonding with close others and, separately, physical warmth, may underlie both experiences. In order to test this hypothesis, 80 participants were randomly assigned to the opioid antagonist, naltrexone or placebo before neural and emotional responses to social and physical warmth were collected. Social and physical warmth led to similar increases in ventral striatum (VS) and middle-insula (MI) activity. Further, feelings of social connection were positively related to neural activity to social warmth. However, naltrexone (vs placebo) disrupted these effects by (i) reducing VS and MI activity to social and physical warmth, (ii) erasing the subjective experience-brain association to social warmth and (iii) disrupting the neural overlap between social and physical warmth. Results provide additional support for the theory that social and physical warmth share neurobiological, opioid receptor-dependent mechanisms and suggest multiple routes by which social connections may be maintained.

Blocking opioids attenuates physical warmth-induced feelings of social connection

"Heartwarming" social experiences, when one feels interpersonally connected to others, have recently been linked with physical warmth. According to one theory (Panksepp, 1998), "social warmth" and physical warmth may be closely linked because both experiences are supported by similar neurobiological mechanisms; however, the neurochemical substrates underlying this overlap have not been explored. Here, an opioid antagonist, naltrexone, was administered in order to examine the role of opioids, previously shown to alter temperature and social bonding behavior, on perceived thermal intensity, general positive affect, and feelings of social connection from physical warmth. Thirty-one participants took both naltrexone and a placebo and completed a temperature manipulation task (held a warm pack, cold pack, and neutral object) while on each drug. Replicating previous research, holding a warm (vs. a cold or neutral) object increased feelings of social connection. Moreover, blocking opioids reduced this effect. Hence, naltrexone specifically reduced feelings of social connection to holding a warm (vs. neutral) object but not to holding a cold (vs. neutral) object. These results lend further support to the theory that social and physical warmth share neurobiological, opioid receptor dependent mechanisms.

Shared neural mechanisms underlying social warmth and physical warmth

Many of people's closest bonds grow out of socially warm exchanges and the warm feelings associated with being socially connected. Indeed, the neurobiological mechanisms underlying thermoregulation may be shared by those that regulate social warmth, the experience of feeling connected to other people. To test this possibility, we placed participants in a functional MRI scanner and asked them to (a) read socially warm and neutral messages from friends and family and (b) hold warm and neutral-temperature objects (a warm pack and a ball, respectively). Findings showed an overlap between physical and social warmth: Participants felt warmer after reading the positive (compared with neutral) messages and more connected after holding the warm pack (compared with the ball). In addition, neural activity during social warmth overlapped with neural activity during physical warmth in the ventral striatum and middle insula, but neural activity did not overlap during another pleasant task (soft touch). Together, these results suggest that a common neural mechanism underlies physical and social warmth.

Persistent hypothermia after intrathecal morphine: case report and literature review

PURPOSE

To describe a case of persistent hypothermia following spinal anesthesia with intrathecal morphine.

CLINICAL FEATURES

Following elective right total knee arthroplasty under spinal anesthesia with isobaric 0.5% bupivacaine 11 mg, fentanyl 15 μg, and preservative-free morphine 150 μg, a 57-yr-old female (93.5 kg, 151 cm) developed postoperative hypothermia with a nadir rectal temperature of 33.6°C four hours after surgery. At times, her temperature could not be measured by tympanic, temporal arterial, oral, axillary, or rectal routes. In spite of the low temperature, the patient complained of feeling hot and was diaphoretic without shivering. With the exception of her temperature, her vital signs were normal postoperatively, and aside from hyperglycemia, complete blood count, electrolytes, thyroid-stimulating hormone, serum cortisol, troponin, and twelve-lead electrocardiogram were normal. Her temperature did not respond to warming efforts with a forced-air warming blanket, infusion of warmed intravenous crystalloid, and hourly bladder irrigation with warm saline through an indwelling urinary catheter. Normothermia returned after she received a small dose of sublingual lorazepam eight hours after surgery. The remainder of her postoperative stay was uneventful.

CONCLUSION

Patients undergoing spinal anesthesia with intrathecal morphine may develop postoperative hypothermia that is resistant to warming measures. This complication may be treated successfully with lorazepam.

Hypothermia after cesarean delivery and its reversal with lorazepam

BACKGROUND

Intrathecal morphine can produce hypothermia in animals. This side effect has been reported in humans, but has not been thoroughly studied in obstetrics.

METHODS

We report a series of 14 patients with presumed morphine-induced hypothermia. All patients had post-cesarean temperatures <35.8 degrees C, and complained of associated symptoms of diaphoresis and subjective feeling of being hot. After collecting this series, we determined the incidence of this side effect in an observational study of 100 consecutive patients. All patients had spinal anesthesia with bupivacaine, morphine and fentanyl.

RESULTS

In the case series, four of 14 patients were treated conservatively, and 10 were given lorazepam. Those treated conservatively had 6h of hypothermia and symptoms; women given lorazepam had a cessation of symptoms and a rapid increase in temperature. In the observational study, 6% (95% Confidence Interval: 1-10%) experienced symptomatic hypothermia lasting for several hours after the end of surgery (120-360 min). We found no statistical association with any demographic or obstetric characteristic.

CONCLUSION

We conclude that symptomatic hypothermia is an occasional side effect of cesarean section under spinal anesthesia. We believe this syndrome is due to intrathecal morphine. While the duration is limited to 6h, lorazepam appears to treat both hypothermia and symptoms.

Refractory ventricular fibrillation in accidental hypothermia: salvage with cardiopulmonary bypass

A 20-year old woman presented with prolonged refractory ventricular fibrillation and pulmonary oedema following hypothermia while she was under self-administered heroin in an attempt to commit suicide. She was successfully resuscitated with cardiopulmonary bypass for core rewarming and internal defibrillation.

Intrahypothalamic injection of deltorphin-II alters body temperature in rats

The present study investigated the effect of H-Try-d-Ala-Phe-Glu-Val-Gly-NH2 deltorphin-II, a selective delta-2 agonist, and [d-Pen(2),d-Pen(5)]enkephalin, a selective delta-1 agonist, on body temperature in the rat. Microinjected into the preoptic anterior hypothalamus (POAH), deltorphin-II (0.1-1 microg) produced an immediate dose-related hyperthermia following injection. Injection of the delta-2 antagonist naltriben into the preoptic anterior hypothalamus (1 microg, 30 min prior to deltorphin-II) significantly attenuated the deltorphin-II-induced hyperthermia. Microinjection of [d-Pen(2),d-Pen(5)]enkephalin into the POAH (0.1-3 microg) did not affect Tb. The data demonstrate that delta-2 receptors are involved in the mediation of Tb effects, and deltorphin-II exerts its action directly on thermosensitive cells of the preoptic anterior hypothalamus. Delta-1 opioid receptors do not appear to be involved in the control of body temperature.

Role of the nitric oxide pathway in kappa-opioid-induced hypothermia in rats

The effect of central and peripheral administration of a nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME), on the hypothermia induced by the selective kappa-opioid receptor agonist trans-(+/-)3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl]-cyclohexyl)-benzeneacetamide methane sulfate (U50,488H) was studied in male Sprague-Dawley rats. In the first series of experiments, we examined the effect of subcutaneous (s.c.) administration of L-NAME on the hypothermia induced by s.c. injection of U50,488H. L-NAME, at a dose of 50 mg/kg s.c., had no influence on body temperature (Tb). Coadministration of L-NAME (50 mg/kg, s.c.) with U50,488H (10 mg/kg, s.c.) blocked the hypothermia induced by U50,488H. In the second series of experiments, we investigated the effect of intracerebroventricular (i.c.v.) administration of L-NAME on the hypothermia induced by s.c. injection of U50,488H. L-NAME itself, given i.c.v. at a dose of 1 mg/rat, did not evoke any change in Tb. Administration of L-NAME (1 mg/rat, i.c.v.) caused a significant suppression of U50,488H hypothermia. The results indicate that either central or peripheral nitric oxide synthesis is required for the production of hypothermia induced by U50,488H.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1979, but data from many earlier papers are also tabulated.

Beta-endorphin: effect on thermoregulation in aged monkeys

In previous experiments small doses of the opiate morphine produced greater hyperthermia in aged than in younger sub-human primates. To test whether this augmented response is due to enhanced sensitivity of CNS opioid receptors with age, beta-endorphin (0.625-5 micrograms), an endogenous opioid peptide, was injected into the lateral cerebral ventricle (ICV) of young (less than 9 years) and aged (greater than 9 years) squirrel monkeys. Significantly greater hyperthermias developed in the older primates after each dose. In the aged monkeys, all but the smallest dose increased core temperature about 1.5 degrees C within 1 hr after injection. Mean rectal temperature in the younger animals rose 0.5-0.7 degrees after all but the largest dose (1-1.5 degrees C rise). Both groups maintained an elevated body temperature after central beta-endorphin throughout the 5 hr recording period. 1.25 micrograms beta-endorphin given ICV in a hot environment (30 degrees C) caused greater hyperthermia in older animals. This dose given in the cold (18 degrees C) caused large changes in temperature of the aged monkeys, either hyperthermia or marked decreases, whereas the young primates developed only moderate rises in body temperature. The same dose of morphine sulfate (1.25 micrograms) ICV produced similar changes in core temperature in the two age groups in each ambient temperature. These results indicate that: (1) stimulation of CNS opioid receptors influences thermoregulation and (2) aging increases responsiveness to such stimulation.