Effects Of Hypothermia Research Articles

Effects of repeated treatment with the 5-HT1A and 5-HT1B agonists (R)-( +)-8-hydroxy-DPAT and CP-94253 on the locomotor activity and axillary temperatures of preweanling rats: evidence of tolerance and behavioral sensitization.

Drugs that stimulate 5-HT1A/1B receptors produce both tolerance and behavioral sensitization in adult rats and mice, yet it is unknown whether the same types of plasticity are evident during earlier ontogenetic periods. The purpose of this study was to determine whether repeated treatment with selective 5-HT1A and/or 5-HT1B agonists cause tolerance and/or sensitization in preweanling rats. In Experiments 1 and 2, male and female preweanling rats were given a single pretreatment injection of saline, the 5-HT1A agonist (R)-( +)-8-hydroxy-DPAT (8-OH-DPAT), or the 5-HT1B agonist CP-94253 on PD 20. After 48h, rats received a challenge injection of 8-OH-DPAT or CP-94253, respectively. In Experiment 3, rats were pretreated with saline or DPAT + CP on PD 20 and challenged with the same drug cocktail on PD 22. In Experiment 4, the tolerance- or sensitization-inducing properties of 8-OH-DPAT, CP-94253, or DPAT + CP were tested after a 4-day pretreatment regimen on PD 17-20. On the first pretreatment day, 8-OH-DPAT, CP-94253, and DPAT + CP increased locomotion and caused hypothermia. Repeated treatment with 8-OH-DPAT (2 or 8mg/kg) or DPAT + CP caused locomotor sensitization in preweanling rats. In contrast, tolerance to the hypothermic effects of 8-OH-DPAT (8mg/kg), CP-94253 (5-20mg/kg), or DPAT + CP was evident after repeated drug treatment. During the preweanling period, a single injection of a selective 5-HT1A or 5-HT1B agonist is capable of producing drug-induced plasticity. A pretreatment administration of 8-OH-DPAT causes both tolerance (hypothermia) and behavioral sensitization (locomotor activity) in preweanling rats, whereas repeated CP-94253 treatment results in tolerance.

The Hypothermic Effect of Hydrogen Sulfide Is Mediated by the Transient Receptor Potential Ankyrin-1 Channel in Mice.

Hydrogen sulfide (H2S) has been shown in previous studies to cause hypothermia and hypometabolism in mice, and its thermoregulatory effects were subsequently investigated. However, the molecular target through which H2S triggers its effects on deep body temperature has remained unknown. We investigated the thermoregulatory response to fast-(Na2S) and slow-releasing (GYY4137) H2S donors in C57BL/6 mice, and then tested whether their effects depend on the transient receptor potential ankyrin-1 (TRPA1) channel in Trpa1 knockout (Trpa1−/−) and wild-type (Trpa1+/+) mice. Intracerebroventricular administration of Na2S (0.5–1 mg/kg) caused hypothermia in C57BL/6 mice, which was mediated by cutaneous vasodilation and decreased thermogenesis. In contrast, intraperitoneal administration of Na2S (5 mg/kg) did not cause any thermoregulatory effect. Central administration of GYY4137 (3 mg/kg) also caused hypothermia and hypometabolism. The hypothermic response to both H2S donors was significantly (p < 0.001) attenuated in Trpa1−/− mice compared to their Trpa1+/+ littermates. Trpa1 mRNA transcripts could be detected with RNAscope in hypothalamic and other brain neurons within the autonomic thermoeffector pathways. In conclusion, slow- and fast-releasing H2S donors induce hypothermia through hypometabolism and cutaneous vasodilation in mice that is mediated by TRPA1 channels located in the brain, presumably in hypothalamic neurons within the autonomic thermoeffector pathways.

Pharmacokinetic and pharmacodynamic properties of aerosolized ("vaped") THC in adolescent male and female rats.

Adolescent exposure to ∆9-tetrahydrocannabinol (THC), the psychotropic constituent of cannabis, might affect brain development, and in rodent models leads to long-term behavioral and physiological alterations. Yet, the basic pharmacology of this drug in adolescent rodents, especially when ingested via ecologically relevant routes like aerosol inhalation, commonly referred to as "vaping," is still poorly characterized. Moreover, sex differences exist in THC metabolism, kinetics, and behavioral effects, but these have not been rigorously examined after vapor dosing in adolescents. We investigated the pharmacokinetics and pharmacodynamics of aerosolized THC (30min inhalation exposure, 25 or 100mg/ml) in adolescent Wistar rats of both sexes. Liquid chromatography/mass spectrometry analysis of THC and its major metabolites was conducted on blood plasma and brain tissue at 5, 30, 60, and 120min following a 30-min aerosol dosing session. Effects on activity in a novel environment for 120min after aerosol, and temperature, were measured in separate rats. We found sex-dependent differences in the pharmacokinetics of THC and its active (11-OH-THC) and inactive (11-COOH-THC) metabolites in the blood and brain, along with dose- and sex-dependent effects on anxiety-like and exploratory behaviors; namely, greater 11-OH-THC levels accompanied by greater behavioral effects in females at the low dose but similar hypothermic effects in both sexes at the high dose. These results provide a benchmark for dosing adolescent rats with aerosolized (or "vaped") THC, which could facilitate adoption by other labs of this potentially human-relevant THC exposure model to understand cannabis effects on the developing brain.

Sex-specific mechanisms of tolerance for the cannabinoid agonists CP55,940 and delta-9-tetrahydrocannabinol (Δ9-THC).

Tolerance to cannabinoids could limit their therapeutic potential. Male mice expressing a desensitization-resistant form (S426A/S430A) of the type-1 cannabinoid receptor (CB1R) show delayed tolerance to delta-9-tetrahydrocannabinol (∆9-THC) but not CP55,940. With more women than men using medical cannabis for pain relief, it is essential to understand sex differences in cannabinoid antinociception, hypothermia, and resultant tolerance. Our objective was to determine whether female mice rely on the same molecular mechanisms for tolerance to the antinociceptive and/or hypothermic effects of cannabinoids that we have previously reported in males. We determined whether the S426A/S430A mutation differentially disrupts antinociceptive and/or hypothermic tolerance to CP55,940 and/or Δ9-THC in male and female S426A/S430A mutant and wild-type littermates. The S426A/S430A mutation conferred an enhanced antinociceptive response for ∆9-THC and CP55,940 in both male and female mice. While the S426A/S430A mutation conferred partial resistance to ∆9-THC tolerance in male mice, disruption of CB1R desensitization had no effect on tolerance to ∆9-THC in female mice. The mutation did not alter tolerance to the hypothermic effects of ∆9-THC or CP55,940 in either sex. Interestingly, female mice were markedly less sensitive to the antinociceptive effects of 30mg/kg ∆9-THC and 0.3mg/kg CP55,940 compared with male mice. Our results suggest that disruption of the GRK/βarrestin2 pathway of desensitization alters tolerance to Δ9-THC but not CP55,940 in male but not female mice. As tolerance to Δ9-THC appears to develop differently in males and females, sex should be considered when assessing the therapeutic potential and dependence liability of cannabinoids.

Potentiation of (α4)2(β2)3, but not (α4)3(β2)2, nicotinic acetylcholine receptors reduces nicotine self-administration and withdrawal symptoms

The low sensitivity (α4)3(β2)2 (LS) and high sensitivity (α4)2(β2)3 (HS) nAChR isoforms may contribute to a variety of brain functions, pathophysiological processes, and pharmacological effects associated with nicotine use. In this study, we examined the contributions of the LS and HS α4β2 nAChR isoforms in nicotine self-administration, withdrawal symptoms, antinociceptive and hypothermic effects. We utilized two nAChR positive allosteric modulators (PAMs): desformylflustrabromine (dFBr), a PAM of both the LS and HS α4β2 nAChRs, and CMPI, a PAM selective for the LS nAChR. We found that dFBr, but not CMPI, decreased intravenous nicotine self-administration in male mice in a dose-dependent manner. Unlike dFBr, which fully reverses somatic and affective symptoms of nicotine withdrawal, CMPI at doses up to 15 mg/kg in male mice only partially reduced nicotine withdrawal-induced somatic signs, anxiety-like behavior and sucrose preference, but had no effects on nicotine withdrawal-induced hyperalgesia. These results indicate that potentiation of HS α4β2 nAChRs is necessary to modulate nicotine's reinforcing properties that underlie nicotine intake and to reverse nicotine withdrawal symptoms that influence nicotine abstinence. In contrast, both dFBr and CMPI enhanced nicotine's hypothermic effect and reduced nicotine's antinociceptive effects in male mice. Therefore, these results indicate a more prevalent role of HS α4β2 nAChR isoforms in mediating various behavioral effects associated with nicotine, whereas the LS α4β2 nAChR isoform has a limited role in mediating body temperature and nociceptive responses. These findings will facilitate the development of more selective, efficacious, and safe nAChR-based therapeutics for nicotine addiction treatment.

Adenosine 5’-monophosphate induces hypothermia and alters gene expressions in the brain and liver of chicks

The adenosine A1 receptor is important for body temperature regulation in mammals; however, little is known about its function in avian species. In this study, we investigated the effects of the adenosine A1 receptor agonist and antagonist (adenosine 5′-monophosphate [5′-AMP] and 8 p-sulfophenyl theophylline [8-SPT], respectively) on thermoregulation in chickens. Male chicks were used in this study. After administration of 5′-AMP and 8-SPT, the rectal temperature, plasma metabolites, and gene expressions in the hypothalamus and liver were measured. The rectal temperature was reduced by peripheral administration of 5′-AMP, and the hypothermic effect of 5′-AMP was attenuated by central injection of 8-SPT in chicks. In the hypothalamus, the mRNA level of the agouti-related protein (AgRP) was increased by 5′-AMP administration, whereas it was suppressed by 8-SPT. The plasma levels of free fatty acid were elevated in 5′-AMP-treated chicks and that elevation was suppressed by the 8-SPT treatment. The gene expression of proopiomelanocortin in the hypothalamus was affected by 8-SPT. Nevertheless, the gene expressions of the thermoregulation-related genes, such as the thyrotropin-releasing hormone, were not affected by 5′-AMP and 8-SPT. Hepatic gene expressions related to lipid intake and metabolism were suppressed by 5′-AMP. However, the gene expression of the uncoupling protein was upregulated by 5′-AMP. Based on these results, birds, like mammals, will undergo adenosine A1 receptor-induced hypothermia. In conclusion, it is suggested that 5′-AMP-mediated hypothermia via the adenosine A1 receptor may affect the central melanocortin system and suppress hepatic lipid metabolism in chickens.

Noxious cold stimulation: pro–con perspectives on the hypothermic effect on experimentally evoked cough

We read with great interest in the recent article by Hilton et al. [1] published in the European Respiratory Journal , about the effect of pain conditioning on experimentally evoked cough; the hypothesis and protocol are well thought out. The study showed that noxious cold-water-induced pain significantly reduced capsaicin-evoked cough; however, it was less effective in refractory chronic cough (RCC) patients than healthy volunteers. The results indicated that endogenous inhibitory control mechanisms, especially those activated by noxious stimuli-inducing pain (conditioned pain modulation, CPM), can modulate cough response evoked by capsaicin. Impairment of such mechanisms may contribute to persistent coughing in RCC patients. The cold stimulation effect on the body may have bidirectional influences on cough response in differential exposure temperature and areas <https://bit.ly/38nVohD>

Effects of Δ⁹-tetrahydrocannabinol (THC) vapor inhalation in Sprague-Dawley and Wistar rats.

An inhalation system based on e-cigarette technology produces hypothermic and antinociceptive effects of Δ⁹-tetrahydrocannabinol (THC) in rats. Indirect comparison of some prior investigations suggested differential impact of inhaled THC between Wistar (WI) and Sprague-Dawley (SD) rats; thus, this study was conducted to directly compare the strains across inhaled and injected routes of administration. Groups (N = 8 per strain) of age-matched male SD and WI rats were prepared with radiotelemetry devices to measure temperature and then exposed to vapor from the propylene glycol (PG) vehicle or THC (25-200 mg/mL of PG) for 30 or 40 min. Additional studies evaluated effects of THC inhalation on plasma THC (50-200 mg/mL) and nociception (100-200 mg/mL) as well as the thermoregulatory effect of intraperitoneal injection of THC (5-30 mg/kg). Hypothermic effects of THC were more pronounced in SD rats, where plasma levels of THC were identical across strains, under either fixed inhalation conditions or injection of a mg/kg equivalent dose. Strain differences in hypothermia were largest after i.p. injection of THC, with SD rats exhibiting dose-dependent temperature reduction after 5 or 10 mg/kg, i.p. and the WI rats only exhibiting significant hypothermia after 20 mg/kg, i.p. The antinociceptive effects of inhaled THC (100, 200 mg/mL) did not differ significantly across the strains. These studies confirm an insensitivity of WI rats, compared with SD rats, to hypothermia induced by THC following inhalation conditions that produced identical plasma THC and antinociception. Thus, quantitative, albeit not qualitative, strain differences may be obtained when studying thermoregulatory effects of THC. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Appetitive, antinociceptive, and hypothermic effects of vaped and injected Δ-9-tetrahydrocannabinol (THC) in rats: exposure and dose-effect comparisons by strain and sex

Advances in drug vapor exposure systems have enabled evaluation of Δ-9-tetrahydrocannabinol (THC) vapor effects in laboratory animals. The purpose of this study was to 1) establish a range of parameters of THC vapor exposure in rats sufficient to produce a behavioral dose-effect curve in a battery of tasks sensitive to THC; and 2) to investigate sex differences in the effects of THC vapor exposure and THC injection (intraperitoneal, IP) on these behaviors in two strains of outbred rats. Male and female Sprague Dawley and Wistar rats (N = 22, 5–6/sex per group) received THC via passive vapor exposure (200 mg/mL; 5 conditions) and IP injection (1–20 mg/kg) in a within subject design. The effects of vaped and injected THC on appetite was determined using progressive ratio responding for food pellets. THC effects on nociception, measured using the tail withdrawal assay, and body temperature were also assessed during a 5-h test period for evaluation of time course of effects. Plasma THC concentrations were assessed after THC vapor and 10 mg/kg IP THC. THC vapor produced exposure-related increases and decreases in motivation to obtain food under the progressive ratio schedule. IP THC (3–20 mg/kg) reduced breakpoints. Vaped and injected THC produced exposure and dose-dependent antinociception and hypothermia. Sex and strain differences in THC effects were also observed. Plasma THC concentrations were higher after 10 mg/kg IP THC (152 ng/mL) compared to the highest vapor exposure condition tested (38 ng/mL), but magnitude of behavioral effects were comparable. THC vapor exposure produced reliable, dose orderly effects on food-maintained behavior, nociception, and body temperature that are comparable to effects of IP THC, although there were differences in the time course of behavioral outcomes.

Genetic deletion of dopamine D1 receptors increases the sensitivity to cannabinoid CB1 receptor antagonist-precipitated withdrawal when compared with wild-type littermates: studies in female mice repeatedly exposed to the Spice cannabinoid HU-210.

The emergence of the consumption of highly potent synthetic cannabinoid receptor agonists (spice drugs) that produce important neurological symptoms has prompted the research on the consequences of acute and chronic use of these new psychoactive substances. Most studies on cannabinoid dependence have been performed in male animals, and there is a need of studies using female subjects. In the present study, we evaluated only in female animals the role of dopamine D1 receptors in the behavioral responses induced by acute and repeated stimulation of cannabinoid CB1 receptors, including the development of physical dependence, since cannabinoid CB1 receptors are co-localized with dopamine D1 receptors on GABAergic neurons projecting to the substantia nigra. To this end, female dopamine D1 receptor-deficient mice and wild-type littermates were treated with HU-210, a potent synthetic cannabinoid agonist. Mutant mice displayed an enhanced response to acute motor and hypothermic effects to HU-210 when compared with wild-type females. The administration of SR141716A precipitated behavioral signs of withdrawal in mice treated subchronically with HU-210. Severity of cannabinoid withdrawal syndrome was potentiated in dopamine D1-deficient female mice. Indeed, 4 of 6 abstinence signs were increased in mutant mice. These results support for a role of dopamine D1 receptors in the acute, chronic, and withdrawal actions of spice drugs.

An Overview of the Potential Effects of Melatonin Supplementation on Athletic Performance

Context: Melatonin is a hormone synthesized principally in the pineal gland that has been classically associated with endocrine actions. Exogenous melatonin is often used to treat insomnia and enhance sleep quality in a range of situations, including jet lag. However, the benefit and safety profile of daytime melatonin dosing prior to exercise are unknown and warrant additional exploration. Objectives: We aimed to give (i) a brief overview of the beneficial effects of exogenous melatonin administration on sports performance and (ii) some recommendations for acute use of melatonin with a special focus on humans’ physical activity and athletic performance. Evidence Acquisition: To ascertain the effect of exogenous melatonin administration on humans, a systematic search of the literature was undertaken using PubMed, ScienceDirect, Medline, Google Scholar, and Scopus. Numerous studies in animals have demonstrated the positive impact of melatonin treatment during physical exercise. However, uncertainty remains regarding exogenous melatonin administration on human’s physical performance. Therefore, the present review focuses almost entirely on data obtained from humans. Results: The gathered data indicate that consuming melatonin at night improves sleep quality. In terms of physical activity and sports performance, previous research has demonstrated that melatonin administration has a good effect on decreasing oxidative stress and inflammation induced by exercise. However, in some specific situations, the daily administration of melatonin may have an unfavourable influence on performance during acute and strenuous exercise. Conclusions: Exogenous melatonin administration prior to exercise shows significant chronobiotic, antioxidant, antiadrenergic, and hypothermic effects and may represent a fascinating potential weight loss method. However, consuming a high amount of melatonin (6 mg) 50 minutes prior to commencing exercise is not recommended as it may interfere with the physiological reactions to physical activity. Melatonin-related adverse effects were mainly transient and were associated with daytime doses. Melatonin should therefore be consumed at night whenever possible.

In vitro and in vivo pharmacological activity of minor cannabinoids isolated from Cannabis sativa

The Cannabis sativa plant contains more than 120 cannabinoids. With the exceptions of ∆9-tetrahydrocannabinol (∆9-THC) and cannabidiol (CBD), comparatively little is known about the pharmacology of the less-abundant plant-derived (phyto) cannabinoids. The best-studied transducers of cannabinoid-dependent effects are type 1 and type 2 cannabinoid receptors (CB1R, CB2R). Partial agonism of CB1R by ∆9-THC is known to bring about the ‘high’ associated with Cannabis use, as well as the pain-, appetite-, and anxiety-modulating effects that are potentially therapeutic. CB2R activation by certain cannabinoids has been associated with anti-inflammatory activities. We assessed the activity of 8 phytocannabinoids at human CB1R, and CB2R in Chinese hamster ovary (CHO) cells stably expressing these receptors and in C57BL/6 mice in an attempt to better understand their pharmacodynamics. Specifically, ∆9-THC, ∆9-tetrahydrocannabinolic acid (∆9-THCa), ∆9-tetrahydrocannabivarin (THCV), CBD, cannabidiolic acid (CBDa), cannabidivarin (CBDV), cannabigerol (CBG), and cannabichromene (CBC) were evaluated. Compounds were assessed for their affinity to receptors, ability to inhibit cAMP accumulation, βarrestin2 recruitment, receptor selectivity, and ligand bias in cell culture; and cataleptic, hypothermic, anti-nociceptive, hypolocomotive, and anxiolytic effects in mice. Our data reveal partial agonist activity for many phytocannabinoids tested at CB1R and/or CB2R, as well as in vivo responses often associated with activation of CB1R. These data build on the growing body of literature showing cannabinoid receptor-dependent pharmacology for these less-abundant phytocannabinoids and are critical in understanding the complex and interactive pharmacology of Cannabis-derived molecules.

Hypothermic Effect of Acute Citral Treatment during LPS-induced Systemic Inflammation in Obese Mice: Reduction of Serum TNF-α and Leptin Levels.

Citral is a mixture of monoterpenes present in the essential oil of several plants, such as Cymbopogon citratus and Zingiber officinale, possessing anti-inflammatory, anti-ulcerogenic, and antipyretic actions. We investigated the action of citral on body temperature (Tb) and inflammatory signaling in eutrophic and obese mice during Systemic Inflammation (SI) induced by Lipopolysaccharide (LPS). Thus, we assessed the effect of citral (25, 100, and 300 mg/kg) and ibuprofen in LPS-induced SI in Swiss male mice fed a standard diet (SD) or high-fat diet (HFD) for 12 weeks. Following SI induction, we measured Tb and collected the serum, hypothalamus, and gastric mucosa for biochemical measurements. Acute treatment with citral decreased the Tb of both SD and HFD-fed animals. Citral (300 mg/kg) treatment caused a significantly lower Tb variation in HFD-fed animals than in those fed the SD. Citral reduced peripheral levels of tumor necrosis factor (TNF)-α in SD and HFD mice and decreased serum leptin concentration in HFD mice 90 min after the LPS challenge. Furthermore, citral also reduced interleukin (IL)-6 levels in the hypothalamus of obese mice. In summary, citral effectively reduced Tb during SI by reducing inflammatory mediators with a distinct action profile in HFD mice when compared with SD.

Identification and in vivo characterization of a brain-penetrating nanobody

BackgroundPreclinical models to determine blood to brain transport ability of therapeutics are often ambiguous. In this study a method is developed that relies on CNS target-engagement and is able to rank brain-penetrating capacities. This method led to the discovery of an anti-transferrin receptor nanobody that is able to deliver a biologically active peptide to the brain via receptor-mediated transcytosis.MethodsVarious nanobodies against the mouse transferrin receptor were fused to neurotensin and injected peripherally in mice. Neurotensin is a neuropeptide that causes hypothermia when present in the brain but is unable to reach the brain from the periphery. Continuous body temperature measurements were used as a readout for brain penetration of nanobody-neurotensin fusions after its peripheral administration. Full temperature curves were analyzed using two-way ANOVA with Dunnett multiple comparisons tests.ResultsOne anti-transferrin receptor nanobody coupled to neurotensin elicited a drop in body temperature following intravenous injection. Epitope binning indicated that this nanobody bound a distinct transferrin receptor epitope compared to the non-crossing nanobodies. This brain-penetrating nanobody was used to characterize the in vivo hypothermia model. The hypothermic effect caused by neurotensin is dose-dependent and could be used to directly compare peripheral administration routes and various nanobodies in terms of brain exposure.ConclusionThis method led to the discovery of an anti-transferrin receptor nanobody that can reach the brain via receptor-mediated transcytosis after peripheral administration. This method could be used to assess novel proteins for brain-penetrating capabilities using a target-engaging readout.

Sex and Strain Variation in Initial Sensitivity and Rapid Tolerance to Δ9-Tetrahydrocannabinol.

Background and Objectives: For cannabis and other drugs of abuse, initial response and/or tolerance to drug effects can predict later dependence and problematic use. Our objective is to identify sex and genetic (strain) differences in initial response and rapid tolerance to Δ9–tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, between highly genetically divergent inbred mouse strains—C57BL/6J (B6) and DBA/2J (D2).Experimental Approach: Sex and strain responses relative to baseline were quantified following daily exposure (i.p.) to 10 mg/kg THC or vehicle (VEH) over the course of 5 days. Dependent measures included hypothermia (decreased body temperature) and ataxia (decreased spontaneous activity in the open field), and antinociception (increase in tail withdrawal latency to a thermal stimulus). Initial sensitivity to THC was defined as the difference in response between baseline and day 1. Rapid tolerance to THC was defined as the difference in response between days 1 and 2.Results: B6 exhibited greater THC-induced motor activity suppression and initial sensitivity to ataxia relative to the D2 strain. Females demonstrated greater levels of THC-induced hypothermia and initial sensitivity relative to males. Higher levels of THC-induced antinociception and initial sensitivity were observed for D2 relative to B6. Rapid tolerance to THC was observed for hypothermia and antinociception. Much less tolerance was observed for THC-induced ataxia. D2 exhibited rapid tolerance to THC-induced hypothermia and antinociception at time points associated with peak THC initial response. Likewise, at the peak initial THC response time point, females demonstrated greater levels of rapid tolerance to hypothermic effects relative to males.Conclusions: Both sex and genetic factors drive variation in initial response and rapid tolerance to the ataxic, antinociceptive, and hypothermic effects of THC. As these traits directly result from THC activation of the cannabinoid receptor 1, gene variants between B6 and D2 in cannabinoid signaling pathways are likely to mediate strain differences in response to THC.

Explication of CB1 receptor contributions to the hypothermic effects of Δ9-tetrahydrocannabinol (THC) when delivered by vapor inhalation or parenteral injection in rats

The use of Δ9-tetrahydrocannabinol (THC) by inhalation using e-cigarette technology grows increasingly popular for medical and recreational purposes. This has led to development of e-cigarette based techniques to study the delivery of THC by inhalation in laboratory rodents. Inhaled THC reliably produces hypothermic and antinociceptive effects in rats, similar to effects of parenteral injection of THC. This study was conducted to determine the extent to which the hypothermic response depends on interactions with the CB1 receptor, using pharmacological antagonist (SR141716, AM-251) approaches. Groups of rats were implanted with radiotelemetry devices capable of reporting activity and body temperature, which were assessed after THC inhalation or injection. SR141716 (4 mg/kg, i.p.) blocked or attenuated antinociceptive effects of acute THC inhalation in male and female rats. SR141716 was unable to block the initial hypothermia caused by THC inhalation, but temperature was restored to normal more quickly. Alterations in antagonist pre-treatment time, dose and the use of a rat strain with less sensitivity to THC-induced hypothermia did not change this pattern. Pre-treatment with SR141716 (4 mg/kg, i.p.) blocked hypothermia induced by i.v. THC and reversed hypothermia when administered 45 or 90 min after THC (i.p.). SR141716 and AM-251 (4 mg/kg, i.p.) sped recovery from, but did not block, hypothermia caused by vapor THC in female rats made tolerant by prior repeated THC vapor inhalation. The CB2 antagonist AM-630, had no effect. These results suggest that hypothermia consequent to THC inhalation is induced by other mechanisms in addition to CB1 receptor activation.

A breeding strategy to identify modifiers of high genetic risk for methamphetamine intake.

Trace amine-associated receptor 1 (Taar1) impacts methamphetamine (MA) intake. A mutant allele (Taar1m1J ) derived from the DBA/2J mouse strain codes for a non-functional receptor, and Taar1m1J/m1J mice consume more MA than mice possessing the reference Taar1+ allele. To study the impact of this mutation in a genetically diverse population, heterogeneous stock-collaborative cross (HS-CC) mice, the product of an eight-way cross of standard and wild-derived strains, were tested for MA intake. HS-CC had low MA intake, so an HS-CC by DBA/2J strain F2 intercross was created to transfer the mutant allele onto the diverse background, and used for selective breeding. To study residual variation in MA intake existing in Taar1m1J/m1J mice, selective breeding for higher (MAH) vs lower (MAL) MA intake was initiated from Taar1m1J/m1J F2 individuals; a control line of Taar1+/+ individuals (MAC) was retained. The lines were also examined for MA-induced locomotor and thermal responses, and fluid and tastant consumption. Taar1m1J/m1J F2 mice consumed significantly more MA than Taar1+/+ F2 mice. Response to selection was significant by generation 2 and there were corresponding differences in fluid consumed. Fluid consumption was not different in non-MA drinking studies. Taar1m1J/m1J genotype (MAL or MAH vs MAC mice) was associated with heighted MA locomotor and reduced hypothermic responses. MAL mice exhibited greater sensitization than MAH mice, but the selected lines did not consistently differ for thermal or tastant phenotypes. Residual variation among high-risk Taar1m1J/m1J mice appears to involve mechanisms associated with neuroadaptation to MA, but not sensitivity to hypothermic effects of MA.

Insightful Backbone Modifications Preventing Proteolytic Degradation of Neurotensin Analogs Improve NTS1-Induced Protective Hypothermia.

Therapeutic hypothermia represents a brain-protective strategy for multiple emergency situations, such as stroke or traumatic injury. Neurotensin (NT), which exerts its effects through activation of two G protein-coupled receptors, namely NTS1 and NTS2, induces a strong and long-lasting decrease in core body temperature after its central administration. Growing evidence demonstrates that NTS1 is the receptor subtype mediating the hypothermic action of NT. As such, potent NTS1 agonists designed on the basis of the minimal C-terminal NT(8-13) bioactive fragment have been shown to produce mild hypothermia and exert neuroprotective effects under various clinically relevant conditions. The high susceptibility of NT(8-13) to protease degradation (half-life <2 min) represents, however, a serious limitation for its use in pharmacological therapy. In light of this, we report here a structure-activity relationship study in which pairs of NT(8-13) analogs have been developed, based on the incorporation of a reduced Lys8-Lys9 bond. To further stabilize the peptide bonds, a panel of backbone modifications was also inserted along the peptide sequence, including Sip10, D-Trp11, Dmt11, Tle12, and TMSAla13. Our results revealed that the combination of appropriate chemical modifications leads to compounds exhibiting improved resistance to proteolytic cleavages (>24 h; 16). Among them, the NT(8-13) analogs harboring the reduced amine bond combined with the unnatural amino acids TMSAla13 (4) and Sip10 (6) or the di-substitution Lys11 - TMSAla13 (12), D-Trp11-TMSAla13 (14), and Dmt11-Tle12 (16) produced sustained hypothermic effects (−3°C for at least 1 h). Importantly, we observed that hypothermia was mainly driven by the increased stability of the NT(8-13) derivatives, instead of the high binding-affinity at NTS1. Altogether, these results reveal the importance of the reduced amine bond in optimizing the metabolic properties of the NT(8-13) peptide and support the development of stable NTS1 agonists as first drug candidate in neuroprotective hypothermia.

The Sigma1 Receptor Antagonist CM304 Potentiates the Antinociceptive but not the Discriminative Stimulus Effects of the Cannabinoid Receptor Agonist THC in Rats

Opioid overdose is one of the leading causes of death in the United States in people under 50 years, which has resulted in a decline in life expectancy in the United States. Thus, there is a need for an alternative to prescription mu‐opioid agonists for pain treatment. Delta (9)‐tetrahydrocannabinol (THC), a cannabinoid (CB) agonist, has been shown to produce antinociceptive effects albeit less effectively than mu‐opioid receptor agonists. Sigma1 receptor (σ1R) antagonists in combination with THC may provide a viable and safe pharmacological alternative to prescription opioids for pain treatment. The present study compared the pharmacological effects of the σ1R antagonist CM304 alone and in combination with THC in Sprague Dawley rats. Hotplate latency was determined at 52°C followed by rectal temperature measurement and the drugs were administered intravenously (i.v.) and in cumulative doses every 5 min. THC dose‐dependently increased maximum possible effects (MPEs) up to 84% which were reversed by 10 mg/kg rimonabant (cannabinoid CB1 receptor antagonist). CM304 alone up to a dose of 10 mg/kg did not produce significant antinociceptive or hypothermic effects, but CM304 (1.0 and 3.2 mg/kg, i.v.) dose‐dependently left‐shifted the dose‐effect functions of the antinociceptive (7.3‐fold at 3.2 mg/kg CM304) and hypothermic effects of THC. In rats discriminating 3.2 mg/kg THC i.p. from vehicle under a fixed ratio (FR) 10 schedule of food delivery, the cannabinoid CB1 receptor agonist CP55,940 fully substituted for THC, whereas CM304 i.p. produced a maximum of 27 % THC‐lever responding at 17.8 mg/kg. CM304, at doses of 32 and 56 mg/kg, decreased response rate to 24 and 9 %, respectively. No dose of BD1063 (σ1R antagonist), rimonabant, SR144528 (cannabinoid CB2 receptor antagonist), morphine (μ‐opioid receptor agonist), or naltrexone (opioid antagonist) produced greater than 30% THC‐lever responding. Pretreatment with rimonabant (1.78 mg/kg) produced a rightward shift in the dose effect curve of THC (4.5‐fold) and CP55940 (4.5‐fold) while pretreatment with CM304, BD1063, SR144528, and naltrexone had no significant effect on the dose effect curve of THC. The present results may support the development of a σ1R antagonist as an adjunct to cannabinoids for treatment of acute pain without enhancing an undesirable side effect of THC.Support or Funding InformationThis work was supported by National Institute on Drug Abuse grants DA23205 and DA48353.

Structure‐Activity Relationships for Cumyl‐Containing Synthetic Cannabinoids to Induce Hypothermic, Cataleptic and Analgesic Effects in Mice

Synthetic cannabinoids (SCs), also known as “spice” or “K2”, are an evolving class of new psychoactive substances that pose public health risks. SCs exert their psychoactive effects by stimulating cannabinoid‐1 receptors (CB1) in the brain, yet few studies have systemically evaluated structure‐activity relationships (SAR) for newly‐emerging compounds. Here, we investigated the pharmacology of SCs which possess a fixed cumyl ‘head group’ but a variable N‐alkyl ‘tail group’ which ranged from 3 to 7 carbons in length. Cumyl‐PINACA, which contains a 5‐carbon pentyl tail, served as a reference compound. In vitro CB1 binding was assessed by displacement of [3H]SR141716 in mouse brain membranes. In vivo effects of subcutaneously (sc) administered drugs were examined in male C57Bl/6J mice bearing surgically‐implanted telemetric temperature transponders. Mice were subjected to a ‘triad’ test battery which assessed temperature, catalepsy, and analgesia every 30 min post‐injection for 2 h. Temperature was measured via a handheld receiver. Catalepsy was measured using the bar test, with a cut off of 60 sec, whereas analgesia was measured using a hot plate set at 52°C, with a cut off of 45 sec. Cumyl‐PINACA was the most potent inhibitor of CB1 binding with an IC50=1.8 nM. Decreasing N‐alkyl chain length to a 3‐carbon propyl markedly reduced binding affinity (IC50=44.8 nM), as did increasing chain length to a 7‐carbon heptyl (IC50=124.0 nM). Consistent with the in vitro findings, cumyl‐PINACA was the most potent compound to induce cannabinoid‐like effects in the triad test battery, with ED50s ranging from 0.06–0.09 mg/kg, sc. Importantly, all cumyl compounds induced hypothermic, cataleptic, and analgesic effects with a rank order of potency that matched their IC50s for inhibition of CB1 binding. THC exhibited ED50s in the triad test ranging from 18.7–30.3 mg/kg, sc. Overall, our data reveal that certain cumyl‐containing SCs are more potent CB1 agonists than THC. Furthermore, N‐alkyl chain length is a critical determinant for the pharmacological effects of cumyl SCs, with a 5‐carbon pentyl chain conferring optimal activity. More research examining the SAR for newly‐emerging SCs is needed to inform stakeholders involved with responding to the abuse of these compounds.Support or Funding InformationThis work was supported generously through IRP, NIDA, NIH.