Nicotine-induced hypothermia through an indirect dopaminergic mechanism

Age is associated with altered locomotor and hypothermic response to acute nicotine

Cigarette smoking is at an all-time low. However, nicotine consumption has diversified with the introduction of commercial tobacco products that include Electronic Nicotine Delivery Systems. Nicotine is the main psychoactive component of tobacco and contributes to the addictive properties of tobacco products. Prolonged nicotine exposure induces neural adaptations that promote addiction-related behaviors in an age-dependent manner. Here, we investigated nicotine sensitivity among young adult and middle-aged male mice by comparing initial responses to nicotine tartrate from different suppliers. We observed that all nicotine compounds tested in the present study induced a robust reduction in locomotor activity and body temperature, and nicotine exposure resulted in increased serum cotinine concentration. We observed age-related differences in the magnitude and the time course of nicotine responses for locomotor and hypothermic effects. Reduction in locomotor activity was larger among young adult mice, but the time course of this response was similar for both age groups. Nicotine-induced reduction in body temperature was of a comparable magnitude for both age groups but young adults showed a faster decrease than middle-aged mice. These results suggest that age of exposure is a key factor contributing to nicotine sensitivity and its potential addictive effects. These responses were consistently produced for nicotine tartrate from different sources. Our findings reveal distinct responses between young adults and middle-aged mice, suggesting that age-specific neurobiological mechanisms in nicotine sensitivity continue developing into adulthood. These age-related variations in nicotine response are crucial for developing targeted interventions and understanding the risk factors for nicotine dependence across the lifespan.

Health Literacy and Health-Related Habits among Conscripts in the Norwegian Armed Forces-A Cross-Sectional Survey

INTRODUCTION

Although health information is widely available to the Norwegian population a lack of health literacy is still common and considered a public health challenge. However, there is limited information on the health literacy of the adolescent population in Norway. The purpose of this pilot study was to assess health literacy and self-reported health habits among soldiers in basic military training, both in field, camp, and home settings. Furthermore, we aimed to investigate which health habits characterize soldiers with inadequate health literacy.

METHODS

An electronic questionnaire was sent out to conscripts who completed first-time military service in 2022 and was answered by 2,225 conscripts. Descriptive statistics were performed using cross-tabulations, correlations, and chi-squared tests. The survey is part of an internal quality study of the Norwegian Armed Forces routines. It is approved by the Norwegian Armed Forces joint medical services.

RESULTS

In the study population, 43% scored inadequate health literacy on the European Health Literacy Survey Questionnaire-Q12 (HLS-Q12), and 57% scored adequate health literacy. We found a significant difference between those having inadequate and adequate HLS-Q12 scores in categories of self-rated health habits of oral health and diet with lower scores in the inadequate score group. The use of tobacco during field exercise in camp and at home was higher in the group of conscripts with adequate health literacy scores. The conscripts generally reported a lower standard of health habits during field exercises with significantly less brushing and flossing, higher use of tobacco products and higher consumption of energy drinks and sugary snacks compared to reported habits in camp and at home.

CONCLUSION

The results from our study suggest that the conscripts in the Norwegian Armed Forces have a lower health literacy than the general population, and this is reflected in reported higher frequency of unhealthy habits in service settings than at home. The Armed Forces have an opportunity to take responsibility to optimize the health skills of their soldiers and to encourage them to make informed decisions about their own health. Improved adaptation to the national recommendations regarding nutrition, tobacco use, and oral health are areas having the potential to greatly improve the overall health habits of conscripts.

Age-dependent memory impairment induced by co-exposure to nicotine and a synthetic cannabinoid in mice

Co-use of marijuana and tobacco products is the second most common drug combination among adolescents. Nicotine (NIC) and cannabinoid use during adolescence induce similar detrimental changes, raising the hypothesis that simultaneous exposure could result in even more severe outcomes. Thus, we investigated whether the co-exposure to NIC and the synthetic cannabinoid WIN 55,212-2 (WIN) in adolescent mice causes behavioral outcomes different from those observed after exposure to a single drug. Male Swiss mice were exposed twice daily to NIC, WIN, or NIC + WIN during adolescence (PND28-47) or adulthood (PND70-89). Drug combination led to a greater reduction in weight gain in adolescent mice, while NIC-induced weight loss was observed in adults. During administration, NIC provoked hypothermia, and WIN produced hyperlocomotion in adolescent and adult mice. Animals exposed to NIC + WIN presented a profile of changes similar to those exposed to NIC. After drug exposure, changes in locomotion, thigmotaxis, social preference, prepulse inhibition, and working and recognition memory were evaluated. Adolescent but not adult mice exposed to NIC showed withdrawal-related hyperlocomotion unaffected by WIN co-administration. An age-specific impairment in object recognition memory was induced only by drug co-exposure during adolescence, which resolved spontaneously before reaching early adulthood. A transient decrease in hippocampal α7 nAChR subunit and CB1 receptor mRNA levels was induced by NIC exposure, which may be involved but is not enough to explain the memory impairment. Our work confirms the potential of NIC and cannabinoids association to aggravate some of the individual drug effects during critical neurodevelopmental periods.

Genetic differences in nicotine sensitivity and metabolism in C57BL/6J and NOD/ShiLtJ mouse strains

Genetic background impacts sensitivity to nicotine's rewarding and aversive effects and metabolism, which influences susceptibility to nicotine addiction. This is important because sensitivity to nicotine influences susceptibility to nicotine addiction. Thus, understanding genetic contribution to nicotine sensitivity can aid in identifying risk factors for nicotine addiction. Genetic variability in addiction phenotypes can be modeled in rodent systems, and comparisons of nicotine sensitivity in inbred mice can identify contributing genetic substrates. Our laboratory has identified differences in nicotine sensitivity in male mice from two inbred mouse strains, C57BL/6J and NOD/ShiLtJ. We found that the NOD/ShiLtJ strain experienced greater nicotine-induced locomotor depression and hypothermia than the C57BL/6J strain. To investigate possible differences in nicotine metabolism between strains, subjects were treated with acute nicotine and serum and urine samples were analyzed using LC-MS/MS to quantify nicotine and metabolites. This analysis revealed that NOD/ShiLtJ mice had similar serum nicotine but lower cotinine and 3'-hydroxycotinine levels after nicotine treatment when compared to C57BL/6J mice. Possible genetic factors mediating strain differences were identified by surveying nicotine sensitivity- and metabolism-related genes within the Mouse Phenome Database SNP retrieval tool. Polymorphisms were found in 15 of the 26 examined gene sequences. Liver expression levels of nicotine metabolism-related genes (Cyp2a5, Cyp2a4, and Aox1) were measured using qPCR. NOD/ShiLtJ mice showed lower expression of Cyp2a5 and Cyp2a4 and greater expression of Aox1 in liver tissue. These data demonstrate complex differences in nicotine sensitivity and metabolism driven by genetic differences between C57BL/6J and NOD/ShiLtJ inbred mouse strains.

Multigenerational nicotine exposure affects offspring nicotine metabolism, nicotine-induced hypothermia, and basal corticosterone in a sex-dependent manner

Parental nicotine exposure can impact phenotypes in unexposed offspring. Our laboratory recently published data showing that nicotine reward and hippocampal gene expression involved in stress pathways were perturbed in F1 offspring of male C57BL/6J mice chronically exposed to nicotine. For the current study, we aimed to further test nicotine and stress-sensitivity phenotypes that may predict vulnerability to nicotine addiction in new cohorts of F1 offspring derived from nicotine-exposed males. We tested locomotor and body temperature sensitivity to acute nicotine administration, serum concentration of nicotine and nicotine metabolites after acute nicotine dosing, and serum corticosterone levels in male and female F1 offspring of nicotine- or saline-exposed males. Paternal nicotine exposure reduced sensitivity to nicotine-induced hypothermia in males, altered nicotine metabolite concentrations in males and females, and reduced serum basal corticosterone levels in females. These findings may point to reduced susceptibility to nicotine addiction-related phenotypes as a result of parental nicotine exposure.

[Hypothermic Action of Oseltamivir Not Dependent on Its Anti-influenza Virus Action]

Although the anti-influenza virus drug oseltamivir ameliorates the fever of influenza, adverse events related to its hypothermic effect have been reported. We found that oseltamivir causes dose-dependent hypothermia in normal mice, and have been studying the pharmacological mechanisms responsible for 12 years. Oseltamivir blocks nicotinic cholinergic transmission at sympathetic ganglia and reduces sympathetic modulation of brown adipose tissue (BAT), a heat generator. Oseltamivir was found to target the ion channels of nicotinic acetylcholine receptors, as demonstrated by patch clamp experiments with cells expressing the human α3β4 nicotinic receptor. Metabolized oseltamivir carboxylate, which inhibits the influenza virus neuraminidase, did not elicit hypothermia and ion channel suppression. Body temperature was decreased by intracerebroventricular administration of oseltamivir. Because this hypothermic effect was inhibited by dopamine D₂ receptor blockade, it was suggested that oseltamivir centrally stimulates the D₂ receptor. In Japan, the package inserts for oseltamivir and amantadine indicate very similar adverse neuropsychiatric reactions for the two drugs (abnormal behavior, consciousness disturbance, convulsion, delirium, delusion, hallucination). A literature search revealed that in some previous studies, oseltamivir and amantadine were shown to block the ion channel systems and activate the dopaminergic nervous system via several mechanisms. Therefore the similarity of the adverse reactions elicited by oseltamivir and amantadine was considered attributable to their similar pharmacological effects.

Induction of cross-tolerance between protective effect of morphine and nicotine in 6-hydroxydopamine-induce neurotoxicity in SH-SY5Y human dopaminergic neuroblastoma cells

PURPOSE

Parkinson's disease is a progressive neurodegenerative disease characterized by progressive and selective death of dopaminergic neurons. It has been reported that nicotine and morphine have protective roles during neuronal damage in Parkinson's disease. In addition, the induction of cross-tolerance between their biological effects has been shown in numerous reports.

METHODS

Here, we investigated the effects of nicotine and morphine on 6-OHDA-induced neurotoxicity in human neuroblastoma SH-SY5Y cell line as an in vitro model of Parkinson's disease. Cell damage was induced by 150 μM 6-OHDA and the cells viability was examined by MTT assay. Intracellular reactive oxygen species, calcium level, and mitochondrial membrane potential were determined by fluorescence spectrophotometer method. Biochemical markers of apoptosis were also evaluated by immunoblotting.

RESULT

The data showed that morphine and nicotine prevent 6-OHDA- induced cell damage and apoptosis. However, the protective effects of nicotine were not observed in chronic morphine-pretreated cells. Morphine had no protective effects in chronic nicotine-incubated cells.

CONCLUSION

A cross-tolerance between protective effects of morphine and nicotine was occurred in 6-OHDA-induced SH-SY5Y cell toxicity.

Oseltamivir produces hypothermic and neuromuscular effects by inhibition of nicotinic acetylcholine receptor functions: comparison to procaine and bupropion

Oseltamivir, an anti-influenza virus drug, induces marked hypothermia in normal mice. We have proposed that the hypothermic effect arises from inhibition of the nicotinic acetylcholine receptor function of sympathetic ganglion neurons which innervate the brown adipose tissue (a heat generator). It has been reported that local anesthetics inhibit nicotinic acetylcholine receptor function by acting on its ionic channels, and that bupropion, a nicotinic antagonist, induces hypothermia. In this study, we compared the effects of oseltamivir, procaine and bupropion on body temperature, cardiovascular function and neuromuscular transmission. Intraperitoneal administration of oseltamivir (100mg/kg), procaine (86.6mg/kg) and bupropion (86.7mg/kg) lowered the core body temperature of normal mice. At lower doses (10-30mg/kg oseltamivir, 8.7-26mg/kg procaine and bupropion), when administered subcutaneously, the three drugs antagonized the hypothermia induced by intraperitoneal injection of nicotine (1mg/kg). In anesthetized rats, intravenous oseltamivir (30-100mg/kg), procaine (10mg/kg) and bupropion (10mg/kg) induced hypotension and bradycardia. Oseltamivir alone (100mg/kg) did not inhibit neuromuscular twitch contraction of rats, but at 3-30mg/kg it augmented the muscle-relaxing effect of d-tubocurarine. Similar effects were observed when lower doses of procaine (10-30mg/kg) and bupropion (3-10mg/kg) were administered, suggesting that systemic administration of oseltamivir inhibits muscular nicotinic acetylcholine receptors. These results support the idea that the hypothermic effect of oseltamivir is due to its effects on sympathetic ganglia which innervate the brown adipose tissue, and suggest that oseltamivir may exert non-selective ion channel blocking effects like those of ester-type local anesthetics.

Effects of the sazetidine-a family of compounds on the body temperature in wildtype, nicotinic receptor β2-/- and α7-/- mice

Nicotine elicits hypothermic responses in rodents. This effect appears to be related to nicotinic receptor desensitization because sazetidine-A, an α4β2 nicotinic receptor desensitizing agent, produces marked hypothermia and potentiates nicotine-induced hypothermia in mice. To determine the specificity of sazetidine-A induced hypothermia to β2 subunit-containing nicotinic receptors, we tested its efficacy in β2 knockout (β2(-/-)) mice. These effects were compared with wildtype (WT) and α7 knockout (α7(-/-)) mice. Confirming our earlier results, sazetidine-A elicited a pronounced and long-lasting hypothermia in WT mice. In comparison, sazetidine-A induced a much attenuated and shorter hypothermic response in β2(-/-) mice. This indicates that the greater proportion of sazetidine-A induced hypothermia is mediated via actions on β2-containing nicotinic receptors, while a smaller component of hypothermia induced by sazetidine-A is mediated by non-β2 receptors. Similar to WT mice, α7(-/-) mice showed the full extent of the sazetidine-A effect, suggesting that the hypothermia produced by sazetidine-A did not depend on actions on α7 nicotinic receptor subtype. Three other novel nicotinic receptor desensitizing agents derived from sazetidine-A, triazetidine-O, VMY-2-95 and YL-1-127 also produced hypothermia in WT and α7(-/-) mice. Furthermore, unlike sazetidine-A, triazetidine-O and YL-1-127 did not show any hint of a hypothermic effect in β2(-/-) mice. VMY-2-95 like sazetidine-A did show a residual hypothermic effect in the β2(-/-) mice. These studies show that the hypothermic effects of sazetidine-A and the related compound VMY-2-95 are mainly mediated by nicotinic receptors containing β2 subunit, but that a small component of the effect is apparently mediated by non-β2 containing receptors.

Potentiation of imipramine-induced antinociception by nicotine in the formalin test

In this study, the effect of cholinergic agents on imipramine antinociception in mice, in the formalin test, has been investigated. Intraperitoneal (i.p.) administration of different doses of imipramine (2.5, 5, 10, 20 and 30 mg/kg) or nicotine (0.25, 0.5, 0.75 and 1 mg/kg) induced a dose dependent antinociception in both the first and second phases of the formalin test in mice. The combination of imipramine with doses of 0.5 and 0.75 mg/kg of nicotine showed a potentiated response, in both phases of the test. However, neither hexamethonium (5 and 10 mg/kg), atropine (0.25 mg/kg) or mecamylamine (0.25 mg/kg) altered the antinociception induced by imipramine. It is concluded that nicotinic receptor activation but not the cholinergic muscarinic mechanism is involved in the imipramine-induced antinociception.

The possible cross-tolerance between morphine- and nicotine-induced hypothermia in mice

In the present study, cross-tolerance between hypothermia induced by morphine and nicotine in mice has been investigated. Different doses of morphine or nicotine induced dose-dependent hypothermia. The sub-maximal doses of both drugs were used for interaction studies. Administration of mecamylamine either intracerebroventricularly (2-6 microg/animal icv) or intraperitoneally (0.5 and 1 mg/kg ip) decreased both morphine- or nicotine-induced hypothermia. Naloxone either intracerebroventricularly (2-6 microg/animal) or intraperitoneally (1 and 2 mg/kg) reduced the response to morphine, but not nicotine's response. Hexamethonium (5 and 10 mg/kg ip) caused a slight decrease in morphine's hypothermia, but not that of nicotine. Nicotine's response was decreased in the animals which were made tolerant to hypothermic effect of morphine. Pre-treatment of the animals with low doses of morphine (12.5 or 25 mg/kg), once daily for 3 days, did not cause significant tolerance to the hypothermic response to morphine or nicotine. However, the administration of low doses of morphine (12.5 or 25 mg/kg) plus nicotine (2 mg/kg), once daily for 3 days, increased levels of tolerance to hypothermia induced by either drug. It is concluded that nicotinic receptor mechanism may play a role in morphine-induced hypothermia and there is cross-tolerance between the two drugs.

Effect of nicotine on sniffing induced by dopaminergic receptor stimulation

Effects of nicotine on sniffing induced by amphetamine and apomorphine have been tested in rats. Intraperitoneal (i.p.) administration of nicotine (0.5 and 1 mg/kg), amphetamine (1-6 mg/kg) or apomorphine (0.1-1 mg/kg) induced sniffing. Nicotine (0. 25-1 mg/kg) potentiates sniffing induced by amphetamine (1 mg/kg). Nicotine (1 mg/kg) also potentiates the response induced by different doses (0.1-1 mg/kg) of apomorphine. Atropine induced sniffing and increased the response of both amphetamine and nicotine. Higher doses of hexamethonium decreased the sniffing response induced by amphetamine and the response induced by combination of amphetamine and nicotine. Sulpiride reduced the response induced by nicotine or amphetamine plus nicotine, while SCH23390 reduced normal sniffing behaviour of the animals and sniffing induced by either amphetamine or amphetamine plus nicotine. The data may indicate that nicotinic receptor mechanism(s) may be involved in the sniffing induced by dopaminergic receptor stimulation.

Nicotine-induced grooming: a possible dopaminergic and/or cholinergic mechanism

The ability of nicotine, to induce grooming in rats was studied. Grooming was induced by i.p. injection of different doses (0.0675-0.5 mg/kg) of nicotine to rats. The effect was dose-dependent. However, the response was decreased with increasing doses of the drug from 0.25-0.5 mg/kg. Administration of the dopamine (DA) D1/D2 receptor agonist apomorphine (0.025-5 mg/kg, i.p.) also caused grooming in a dose-dependent manner. High doses of apomorphine (0.1-0.5 mg/kg, i.p.) also induced a lower degree of response. Combination of a low dose of nicotine (0.0675 mg/kg) with different doses of apomorphine did not show any interaction. However, there was an interaction between a high dose of nicotine and apomorphine. Thus, combination of a higher dose of nicotine (0.125 mg/kg) with apomorphine, reduced apomorphine-induced grooming. The muscarinic receptor antagonist atropine (5 and 10 mg/kg), peripheral nicotinic receptor antagonist hexamethonium (5 and 10 mg/kg), central nicotinic receptor antagonist mecamylamine (1 and 3 mg/kg) and D1 DA receptor antagonist SCH23390 (0.05 and 0.1 mg/kg) all decreased the response to nicotine. Atropine, mecamylamine and SCH23390 by themselves reduced spontaneous grooming. It is concluded that nicotine elicits grooming indirectly through a possible D1 dopaminergic mechanism. However, muscarinic and nicotinic cholinergic mechanism(s) may be involved.

Effect of nicotine on apomorphine-induced licking behaviour in rats

In the present study, the dopaminergic receptor agonist apomorphine (0.1, 0.25 and 0.5 mg/kg) induced a dose-dependent licking in rats. Nicotine administration (0.025-250 microg/kg) altered the apomorphine-induced licking. The lower doses of nicotine (0.05 and 0.5 microg/kg) increased while the higher dose of the drug (250 microg/kg) reduced the apomorphine response. The antimuscarinic drug atropine (2.5 and 5 mg/kg) reduced the effects of apomorphine or nicotine plus apomorphine. The central nicotinic receptor antagonist mecamylamine (0.05, 0.25 and 0.5 mg/kg) also reduced the response induced by apomorphine or nicotine plus apomorphine. However, the peripheral nicotinic receptor antagonist hexamethonium (2.5, 5 and 10 mg/kg) reduced the response induced by nicotine plus apomorphine but not that elicited by apomorphine alone. The results indicate that the nicotinic receptor mechanism(s) may interact with apomorphine-induced licking in rats. Although central nicotinic and cholinergic mechanisms may be involved in the licking induced by apomorphine, peripheral nicotinic mechanism may be involved in the nicotine-induced increased apomorphine effect.

Chronopharmacological effects on nicotine repeated administration on heart rate, body temperature and locomotor activity circadian rhythms in rats

The aim of this study was to compare morning and evening repeated nicotine administration on the circadian rhythms of heart rate (H), body temperature (T) and locomotor activity (A) in unrestrained rats by using implanted radio-telemetry transmitters. The study was divided into three 7-day periods: a control period (P1), a treatment period (P2) and a recovery period (P3). During P2, four rats received nicotine (1mg.kg(-1)) subcutaneously at 09.00 h and four rats received nicotine in the same conditions at 21.00 h. For P1, P2 and P3, a power spectrum analysis was applied in order to determine the dominant period of rhythmicity. If H, T and A circadian rhythms were detected, the characteristics of these rhythms were determined by cosinor analysis, expressed as means+/-SEM and compared by ANOVA. Our results indicated: (1) a lack of detection of A circadian rhythm during P2 for the morning group while H and T circadian rhythms were detected for the morning and evening group whatever the period. (2) alterations of mesors, amplitudes and acrophases of H and T circadian rhythms for the morning and evening group during P2 and alterations of mesor, amplitude and acrophase of A circadian rhythm for the evening group. Furthermore these alterations were significantly different for the morning and evening group during P2. These results showed that the time of administration of nicotine differently affect H, T and A rhythms. The authors suggest that these effects can be mediated by central cholinergic and/or monoaminergic mechanisms.

Nicotine-induced perturbations on heart rate, body temperature and locomotor activity daily rhythms in rats

The aim of this study was to evaluate the influence of nicotine on the daily rhythms of heart rate, body temperature and locomotor activity in unrestrained rats by use of implanted radiotelemetry transmitters. The study was divided into three seven-day periods: a control period, a treatment period and a recovery period. The control period was used for baseline measurement of heart rate, body temperature and locomotor activity. During the treatment period three rats received nicotine (1 mg kg(-1), s.c.) at 0900 h. Three rats received saline under the same experimental conditions. Heart rate, body temperature and locomotor activity were continuously monitored and plotted every 10 min. During the three periods a power spectrum analysis was used to determine the dominant period of rhythmicity. If daily rhythms of heart rate, body temperature and locomotor activity were detected, the characteristics of these rhythms, i.e. the mesors, amplitudes and acrophases, were determined by cosinor analysis, expressed as means +/- s.e.m. and compared by analysis of variance. Nicotine did not suppress daily rhythmicity but induced decreases of amplitudes and phase-advances of acrophases for heart rate, body temperature and locomotor activity. These perturbations might result from the effects of nicotine on the suprachiasmatic nucleus, the hypothalamic clock that co-ordinates biological rhythms.

Chronic haloperidol administration does not block acute nicotine-induced improvements in radial-arm maze performance in the rat

Nicotine has been found to improve cognitive performance in a variety of tasks including the radial maze. Nicotine has also been shown to promote the release of a variety of neurotransmitters including dopamine (DA). DA has been found to be important for nicotine's reinforcing effects. DA involvement with nicotine's cognitive effects is unclear. In the current study, the effects of acute nicotine injections (0, 0.1, 0.2, or 0.4 mg/kg) were examined on radial-arm maze performance in rats given chronic infusions the DA antagonist haloperidol (0, 0.2, or 0.6 mg/kg/day). Chronic haloperidol infusion was not found to attenuate the memory improvement caused by acute nicotine injection. In fact, the dose-related nicotine-induced memory improvement was clearer in the haloperidol-treated groups than in controls. This is similar to the effect of nicotine we saw in human subjects given chronic doses of haloperidol. Our previous studies demonstrated significant nicotinic-DA interactions with regard to memory function. The current results suggest that in the DA-nicotinic relationship DA stimulation is not necessary for the memory improvement caused by nicotine.

Effects of monoamine receptor antagonists on nicotine-induced hypophagia in the rat

(--)-Nicotine, in doses of 0.2-0.6 mg/kg intraperitoneally (i.p.), induced a dose-dependent anorexia 1 h, 2 h and 4 h after food presentation in 20-h food-restricted male rats. The anorectic response of nicotine (0.4 mg/kg, 30 min before the test) was prevented by pretreatment with the central nicotine receptor antagonist mecamylamine (0.5 and 1 mg/kg). The peripheral nicotine receptor antagonist hexamethonium (5 and 10 mg/kg), the muscarinic receptor antagonist atropine (5 and 10 mg/kg), the dopamine D2 receptor antagonist pimozide (0.5 and 1 mg/kg), the dopamine D1 receptor antagonist SCH23390 (R-(+)-8-chloro-2, 3, 4, 5-tetrahydro-3-methyl-5-phenyl-1 H-3-benzazepine-7ol maleate; 0.05 and 0.1 mg/kg), the alpha-adrenoceptor antagonist phenoxybenzamine (5 and 10 mg/kg), and the beta-adrenoceptor antagonist propranolol (5 and 10 mg/kg) amplified the nicotine response while promoting anorexia by themselves. The dopamine D2 receptor antagonist sulpiride (25, 50 and 100 mg/kg) increased food intake and amplified the anorectic effect of nicotine. The 5-HT receptor antagonists metergoline (0.5 and 1 mg/kg) and mianserin (1 and 2 mg/kg) increased the nicotine effect. When the antagonists were used alone, metergoline did not change food intake, while mianserin increased food intake. It can be concluded that part of nicotine-induced anorexia is mediated through central nicotinic receptors.

Effects of nicotine on memory retrieval in mice

The effect of nicotine was tested on retrieval 24 h after training on a passive avoidance task. Intraperitoneal (i.p.) injection of nicotine (0.25-1.5 mg/kg) increased the step-down latency in mice dose dependently. Pretreatment with the nicotinic receptor antagonist mecamylamine (0.5-1 mg/kg) decreased, whereas pretreatment with the dopamine D1 receptor antagonist SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol maleate) (0.01, 0.05 and 0.1 mg/kg) and the beta-adrenoreceptor antagonist propranolol (10 mg/kg) increased the nicotine response. The dopamine receptor D2 receptor antagonist sulpiride (5-10 mg/kg), the anti-muscarinic agent atropine (2.5-10 mg/kg), the peripheral nicotinic receptor antagonist hexamethonium (0.01-0.5 mg/kg), the alpha-adrenoceptor antagonist phenoxybenzamine (1 and 10 mg/kg) and the peripheral dopamine D2 receptor antagonist domperidone (5 and 10 mg/kg) did not change the response induced by nicotine. Single administration of the antagonists did not cause response; however, a high dose of domperidone (10 mg/kg) and propranolol alone increased the step-down latencies. It may be concluded that a nicotinic receptor mechanism is involved in the nicotine-induced improvement of memory retrieval.