Chronic Nicotine Treatment Research Articles

Chronic nicotine interactions with clozapine and risperidone and attentional function in rats

Although antipsychotic drugs are therapeutically effective in attenuating the hallmark symptoms of schizophrenia, these improvements do not return most patients to normative standards of cognitive function. Thus, complementary drug treatment may be needed to treat the attentional deficits of schizophrenia as well as to counteract the potential attentional impairments caused by some antipsychotic drugs. Nicotine, a drug commonly self-administered by a great majority of individuals with schizophrenia, has been shown to significantly improve cognitive function in some studies. The current study was conducted to determine the interactive effects of the atypical antipsychotic drugs clozapine and risperidone with chronic nicotine administration on attentional performance. Adult female Sprague-Dawley rats ( N = 35) were trained to perform an attentional task using an operant visual signal detection task. After training, rats were infused with a dose of 5 mg/kg/day (s.c.) nicotine base ( n = 18) or saline ( n = 17) for 28 consecutive days via osmotic pump. In Exp. 1, while being administered chronic nicotine or saline, rats were given acute doses of clozapine (0, 0.625, 1.25 and 2.5 mg/kg, s.c.) and were tested for attentional function. In Exp. 2, while on chronic nicotine or saline, other rats were challenged with acute doses of risperidone (0, 0.025, 0.05 and 0.1 mg/kg, s.c.) and were tested for attentional function. Results showed that acute administration of clozapine caused a significant dose-dependent impairment in choice accuracy (percent hit) in animals treated with chronic saline. Chronic nicotine treatment itself lowered accuracy, but attenuated further declines with acute clozapine treatment. Acute administration of risperidone at high dose significantly reduced performance (percent correct rejection) in chronically saline-treated rats, but in a similar fashion as in Exp. 1, chronic nicotine lowered accuracy but attenuated further impairment with acute risperidone. In summary, atypical antipsychotic drugs clozapine and risperidone significantly impaired choice accuracy in the visual signal detection task. Clozapine was more detrimental than risperidone but the adverse effects of both clozapine and risperidone on attentional performance were masked in rats chronically treated with nicotine.

CYP2B6 is expressed in African Green monkey brain and is induced by chronic nicotine treatment

CYP2B6 is a drug-metabolizing enzyme expressed in human tissues that can activate bupropion (a smoking cessation drug) and tobacco smoke nitrosamines and can inactivate drugs such as nicotine. Smokers have higher brain CYP2B6 protein levels compared to non-smokers but the cause of this elevation is unknown. We investigated the basal expression and the effect of chronic nicotine treatment on CYP2B6 protein in African Green monkey ( Cercopithecus aethiops) brain. Basal expression of brain CYP2B6 was strong in specific cells such as the frontal cortical pyramidal cells, the cerebellar Purkinje cells and the neurons in the substantia nigra. Basal CYP2B6 protein levels varied 2.7-fold (non-significant) among 12 brain regions. All monkeys were given a subcutaneous 0.1 mg/kg nicotine test dose prior to treatment and the maximum plasma concentration achieved was 87 ± 69 ng/ml and the half-life was 2.6 ± 1.5 h. Monkeys were treated subcutaneously twice daily with nicotine at 0.05 mg/kg for 2 days, 0.15 mg/kg for 2 days followed by 0.3 mg/kg for 18 days ( n = 6) or saline ( n = 6). Chronic nicotine treatment induced CYP2B6 expression in specific cells such as astrocytes and neurons in the frontal cortex, caudate, thalamus and hippocampus. CYP2B6 protein levels were induced 1.5-fold in the frontal cortex ( p < 0.01). Hepatic CYP2B6 expression was not altered by nicotine. In conclusion, CYP2B6 protein is expressed in specific cells in monkey brain and is induced by chronic nicotine treatment which may impact central metabolism of CYP2B6 substrates such as bupropion and nicotine.

Nicotine prevents stress‐induced enhancement of long‐term depression in hippocampal area CA1: Electrophysiological and molecular studies

Nicotine treatment prevents chronic psychosocial stress-induced impairment of hippocampus-dependent spatial memory and long-term potentiation (LTP). In this study, we investigated the effect of chronic nicotine treatment on stress-induced enhancement of long-term depression (LTD). After paired-pulse stimulation, LTD was evoked in area CA1 of anesthetized control, stressed, nicotine-treated, and nicotine-treated stressed rats. In stressed rats, a significantly greater LTD magnitude was seen than in control rats. Stress also facilitated the induction of LTD. Nicotine treatment of stressed rats prevented stress-induced enhancement and facilitation of LTD. For chronically stressed rats, we previously reported marked decreases in the basal levels of brain-derived neurotrophic factor (BDNF), CaMKII, P-CaMKII, and calmodulin as well as a significant increase in calcineurin basal levels. Herein, Western blot analysis conducted 1 hr after induction of LTD by paired-pulse stimulation showed that the levels of calcineurin and P-CaMKII were increased in the stressed group compared with the other groups and were normalized by chronic nicotine treatment. Additionally, after paired-pulse stimulation, the levels of total CaMKII were increased in all groups with no change in the levels of BDNF and calmodulin. Therefore, the increase in the levels of calcineurin and P-CaMKII during expression of LTD in area CA1 may explain the enhanced magnitude of LTD in chronically stressed rats.

Selective down-regulation of [ 125I]Y 0-α-conotoxin MII binding in rat mesostriatal dopamine pathway following continuous infusion of nicotine

Prolonged exposure to nicotine, as occurs in smokers, results in up-regulation of all the neuronal nicotinic acetylcholine receptor subtypes studied so far, the only differences residing in the extent and time course of the up-regulation. α6β2*-Nicotinic acetylcholine receptors are selectively enriched in the mesostriatal dopaminergic system and may play a crucial role in nicotine dependence. Here we show that chronic nicotine treatment (3mg/kg/day for two weeks, via s.c. osmotic minipumps) caused a significant decrease (36% on average) in the binding of [ 125I]Y 0-α-conotoxin MII (a selective ligand for α6β2*-nicotinic acetylcholine receptors in this system) to all the five regions of the rat dopaminergic pathway analyzed in this study. After one week of withdrawal, binding was still lower than control in striatal terminal regions (namely the caudate putamen and the accumbens shell and core). In somatodendritic regions (the ventral tegmental area and the substantia nigra) the decrease was significant at the end of the treatment and recovered within one day of withdrawal. This effect was not due to displacement of [ 125I]Y 0-α-conotoxin MII binding by residual nicotine. In fact the binding was not changed by 565 ng/g nicotine (obtained with a single injection of nicotine), a concentration much higher than that found in the brain of rats chronically treated with nicotine (240 ng/g). In addition, consistent with previous studies reporting an up-regulation of other subtypes of nicotinic acetylcholine receptors, we found that nicotine exposure significantly increased (40% on average) the binding of [ 125I]epibatidine (a non-selective agonist at most neuronal heteromeric nicotinic acetylcholine receptors) in three up to five regions containing only α-conotoxin MII-insensitive [ 125I]epibatidine binding sites, namely the primary motor, somatosensory and auditory cortices. In conclusion, this work is the first to demonstrate that α6β2*-nicotinic acetylcholine receptors, unique within the nicotinic acetylcholine receptor family, are down-regulated following chronic nicotine treatment in rat dopaminergic mesostriatal pathway, a finding that may shed new light in the complex mechanisms of nicotine dependence.

Active immunisation against nicotine blocks the reward facilitating effects of nicotine and partially prevents nicotine withdrawal in the rat as measured by dopamine output in the nucleus accumbens, brain reward thresholds and somatic signs

We recently showed that active immunisation with the nicotine immunoconjugate IP18-KLH reduces the nicotine-induced increase in dopamine (DA) output in the nucleus accumbens (NAC) and prevents reinstatement of nicotine-seeking behaviour in rats. These effects are mediated by altered distribution of nicotine, resulting in reduced amounts of nicotine reaching the brain, thereby interfering with the rewarding properties of the drug. The present study was designed to explore the effect of immunisation against nicotine on mecamylamine-precipitated nicotine withdrawal as assessed by the reduction in DA output in the NAC in rats. Measuring brain reward thresholds and somatic signs of nicotine withdrawal, the effects of immunisation were also tested during chronic nicotine treatment and after its withdrawal. Finally, we examined the effect of immunisation on challenge injections of nicotine on brain reward thresholds after the increases in somatic signs and reward thresholds associated with nicotine withdrawal had dissipated. The results show that immunisation with IP18-KLH prevented the decrease in DA output in the NAC associated with mecamylamine-precipitated nicotine withdrawal. Moreover, immunisation against nicotine did not precipitate a withdrawal syndrome, as measured by brain reward thresholds and somatic signs, in rats chronically exposed to nicotine. Furthermore, the withdrawal syndrome elicited after cessation of chronic nicotine administration was attenuated in immunised rats compared to that of mock-immunised rats. Finally, the lowering in reward thresholds after nicotine challenge injections was attenuated in both naïve and previously nicotine-exposed immunised rats. In conclusion, the present results show that immunisation with IP18-KLH did not precipitate nicotine withdrawal in rats. Thus, immunisation with IP18-KLH may not elicit nicotine withdrawal in smokers either. Furthermore, since the withdrawal syndrome in rats was attenuated by immunisation, the nicotine withdrawal in smokers should not be worsened but may even be ameliorated during a quit attempt.

Nicotine blocks stress-induced impairment of spatial memory and long-term potentiation of the hippocampal CA1 region

The effect of chronic nicotine treatment on chronic psychosocial stress-induced impairment of short-term memory and long-term potentiation (LTP) was determined. An "intruder" stress model was used to induce psychosocial stress for 4-6 wk, during which rats were injected with saline or nicotine (1 mg/kg s.c.) twice a day. The radial arm water maze memory task was used to test hippocampus-dependent spatial memory. Chronic psychosocial stress impaired short-term memory without affecting the learning phase or long-term memory. Concurrent chronic nicotine treatment prevented stress-induced short-term memory impairment. In normal rats chronic nicotine treatment had no effect on learning and memory. Extracellular recordings from the CA1 region of anaesthetized rats showed severe reduction of LTP magnitude in stressed rats, which was normalized in nicotine-treated stressed rats. Nicotine had no effect on LTP in control animals. These results showed that chronic nicotine treatment improved hippocampus-dependent spatial memory and LTP only when impaired by stress.

Deletion of the beta 2 nicotinic acetylcholine receptor subunit alters development of tolerance to nicotine and eliminates receptor upregulation

Chronic nicotine exposure induces both tolerance and upregulation of [3H]nicotine binding sites in rodent and human brain. However, the mechanism for chronic tolerance is unclear because a direct relationship between tolerance and receptor upregulation is not consistently observed. In the present experiments, the role of beta2* nicotinic acetylcholine receptors (nAChRs) on tolerance development and nAChR upregulation was examined following chronic nicotine treatment of beta2 wild-type (+/+), heterozygous (+/-), and null mutant (-/-) mice. Saline or nicotine (1, 2, or 4 mg/kg/h) was infused intravenously for 10 days. Locomotor activity and body temperature responses were measured before and after nicotine challenge injection to observe changes in nicotine sensitivity. [3H]Epibatidine binding was then measured in ten brain regions. Beta2+/+ mice developed dose-dependent tolerance and upregulation of [3H]epibatidine binding sites. In contrast, beta2-/- mice, initially less sensitive to acute nicotine's effects, became more sensitive following treatment with the lowest chronic dose (1 mg/kg/h). Beta2-/- mice treated with 4.0 mg/kg/h nicotine were no longer supersensitive, indicating that tolerance developed at this higher dose. However, these changes in nicotine sensitivity occurred in the absence of any nAChR changes in either low- or high-affinity [3H]epibatidine sites. Responses of beta2+/- mice were intermediate between wild-type and mutant mice. Upregulation of nAChRs in vivo requires the presence of the beta2 subunit. Changes in nicotine sensitivity occurred both in the presence (beta2+/+) and absence (beta2-/-) of beta2* nAChRs and suggest that mechanisms involving both beta2* and non-beta2* nAChR subtypes modulate adaptation to chronic nicotine exposure.

Neurochemical Correlates of Nicotine Neurotoxicity on Rat Habenulo-Interpeduncular Cholinergic Neurons

Chronic administration of high doses of nicotine results in axonal degeneration in the central core of the fasciculus retroflexus, a fiber tract connecting the habenulae (Hb) to the interpeduncular nucleus (IPN). An important part of this connection is cholinergic and neurons of origin are located in the medial Hb. We have undertaken the present investigation in order to ascertain whether the cholinergic Hb–IPN neurons are the actual target of nicotine toxicity and to begin studying molecular correlates of this action. In the present report, we demonstrate that 7-day-long continuous administration of nicotine through osmotic minipumps, results in a significant (−13%) decrease in the volume of the medial Hb, where cholinergic neurons projecting to the IPN are located, and in a drop of a specific marker for cholinergic neurons, choline acetyltransferase (ChAT), in Hb (−36%) and IPN (−28%). At various intervals (2–6 days) during continuous nicotine administration, some apoptotic neurons were visualized in the medial Hb by the TUNEL technique. The chronic nicotine treatment also resulted, after 2 days of continuous administration in significant activation of the transcription factor CREB and the ERK/MAPK survival kinase in the Hb, suggesting that these alterations in expression are in some way related to the neurodegenerative/neuroreparative process. The present observations demonstrate that the cholinergic Hb–IPN neurons are a target for nicotine neurotoxicity and confirm the usefulness of the experimental model used here not only to study the consequences of chronic stimulant abuse, but also to study the neurochemistry of the affected neural systems and the role of signaling factors in neurodegenerative and repair mechanisms. Medical relevance of the data on unique vulnerability of the Hb–IPN connection to nicotine in relation to heavy smoking habits, is briefly discussed.

Exocytic Trafficking Is Required for Nicotine-induced Up-regulation of α4β2 Nicotinic Acetylcholine Receptors

The primary target for nicotine in the brain is the neuronal nicotinic acetylcholine receptor (nAChR). It has been well documented that nAChRs respond to chronic nicotine exposure by up-regulation of receptor numbers, which may underlie some aspects of nicotine addiction. In order to investigate the mechanism of nicotine-induced nAChR up-regulation, we have developed a cell culture system to assess membrane trafficking and nicotine-induced up-regulation of surface-expressed alpha(4)beta(2) nAChRs. Previous reports have implicated stabilization of the nAChRs at the plasma membrane as the potential mechanism of up-regulation. We have found that whereas nicotine exposure results in up-regulation of surface receptors in our system, it does not alter surface receptor internalization from the plasma membrane, postendocytic trafficking, or lysosomal degradation. Instead, we find that transport of nAChRs through the secretory pathway to the plasma membrane is required for nicotine-induced up-regulation of surface receptors. Therefore, nicotine appears to regulate surface receptor levels at a step prior to initial insertion in the plasma membrane rather than by altering their endocytic trafficking or degradation rates as had been previously suggested.

Up‐regulation of β2 and α7 subunit containing nicotinic acetylcholine receptors in mouse striatum at cellular level

Nicotine releases dopamine in the brain by activating neuronal nicotinic acetylcholine receptors (nAChRs). Chronic nicotine treatment increases the number of nAChRs, which represents plasticity of the brain. Together these phenomena have been suggested to have a role in the development of nicotine addiction. In the brain nAChRs can be localized synaptically, extrasynaptically or intracellularly. The purpose of these studies was to clarify the effects of chronic nicotine treatment on the localization of beta2 and alpha7 nAChR subunits in brain areas involved in nicotine addiction. Nicotine was administered orally in drinking water to male NMRI mice for 7 weeks. At the end of chronic nicotine treatment the localization of the nAChR subunits was studied in the dorsal striatum and in the ventral tegmental area (VTA) by using electron microscopy. In the brain areas studied beta2 and alpha7 subunits were localized presynaptically and postsynaptically in axon endings and in dendrites. In both areas the majority of the beta2 and alpha7 subunits were localized at extrasynaptic sites. In response to chronic nicotine treatment the beta2 and alpha7 nAChR subunit labelling was increased at synaptic and extrasynaptic sites as well as intracellularly. This suggests that the trafficking of nAChR subunits is increased as a result of chronic nicotine treatment and nAChRs in all parts of neurons could have functional roles in the formation of nicotine addiction.

Time and brain region specific up-regulation of low affinity neuronal nicotinic receptors during chronic nicotine administration in mice

We studied the effects of chronic oral nicotine on brain low affinity nicotine binding sites. Mice received nicotine in the drinking water for 4 or 7 weeks. Receptor binding was measured at 24 or 48 h after cessation of nicotine administration with [3H]methyllycaconitine, an antagonist in α7 and α3/α6β2β3* nicotinic receptors in striatum, midbrain, hippocampus and cortex. Chronic nicotine for 4 weeks resulted in a significant increase in the [3H]methyllycaconitine binding in the striatum and cortex, whereas after 7 weeks the increase in binding could be found in the hippocampus but not in the other brain areas studied. For comparison, high affinity nicotine binding sites (mostly α4β2) were measured with [3H]epibatidine after 7-week chronic nicotine treatment. [3H]Epibatidine binding sites were increased in the hippocampus, midbrain and cortex, but not in the striatum. The up-regulation of [3H]methyllycaconitine binding was significant at 24 h but that of [3H]epibatidine binding sites was not observed until at 48 h after cessation of chronic nicotine. These results suggest that up-regulation of low affinity nicotine binding sites does occur during chronic nicotine administration. Furthermore, the low affinity and high affinity binding differ clearly as regards regions and duration suggesting that different nicotinic receptors respond differently to nicotine administration.

Chronic nicotine differentially affects the function of nicotinic receptor subtypes regulating neurotransmitter release

It is known that nicotine can activate several subtypes of release-regulating presynaptic nicotinic receptors (nAChRs) including those situated on central noradrenergic, dopaminergic, cholinergic and glutamatergic axon terminals. The objective of this study was to investigate the effects of chronic administration of (-)nicotine on the function of the above autoreceptors and heteroreceptors using rat superfused synaptosomes. In hippocampal synaptosomes prelabelled with [3H]noradrenaline (NA) the nicotine-evoked overflow of [3H]NA was higher in rats treated with nicotine for 10 days (via osmotic mini-pumps) than in vehicle-treated rats. In striatal synaptosomes, prelabelled with [3H]dopamine (DA), chronic nicotine did not modify the releasing effect of nicotine. No significant change was observed in experiments with synaptosomes from nucleus accumbens prelabelled with [3H]DA. Exposure of hippocampal synaptosomes prelabelled with [3H]choline to nicotine elicited release of [3H]acetylcholine; this effect was almost abolished in synaptosomes from animals administered nicotine for 10 days, suggesting down-regulation of nicotinic autoreceptors. In hippocampal synaptosomes prelabelled with [3H]D-aspartate, the releasing effect of epibatidine following chronic nicotine treatment did not differ from that in controls. The K+-evoked exocytotic release of the neurotransmitters tested was not modified by long-term nicotine administration. The results show that chronic nicotine differentially affects the function of release-regulating nAChR subtypes.

Effect of Nicotine on Lung S-Adenosylmethionine and Development of Pneumocystis Pneumonia

Because S-adenosylmethionine (AdoMet) is required by Pneumocystis carinii in vitro, Pneumocystis infection depletes plasma AdoMet of rats and humans, nicotine reduces AdoMet of guinea pig lungs, and smoking correlates with reduced episodes of Pneumocystis pneumonia (PCP) in AIDS patients, we tested the effect of nicotine treatment on PCP using a rat model. Intraperitoneal infusion of 400 microg of R-(+) nicotine kg(-1) h(-1) intraperitoneal for 21 days caused a 15-fold reduction in lung AdoMet although neither plasma nor liver were changed. Infusion of 4 and 400 microg kg(-1) h(-1) into immunosuppressed rats, beginning when rats were inoculated with P. carinii, caused 85 and 99.88% reductions, respectively, in P. carinii cysts at sacrifice 21 days later; P. carinii nuclei were reduced by 91.2 and >99.99%, respectively. This effect was reversed by concomitant administration of AdoMet with nicotine. Treatment with AdoMet alone increased infection intensity. We conclude that AdoMet is a critical and limiting nutrient for Pneumocystis thus can serve as a therapeutic target for PCP. Regarding the mechanism, nicotine treatment caused no change in rat lung activity of AdoMet synthesizing methionine ATP transferase activity nor was there any evidence of increased AdoMet utilization for methylation reactions. Except of a doubling of putrescine, nicotine treatment also did not change lung polyamine content. However, key polyamine anabolic and catabolic enzymes were upregulated, and there were corresponding changes in polyamine metabolic intermediates. We conclude that chronic nicotine treatment increases lung polyamine catabolic/anabolic cycling and/or excretion leading to increased AdoMet-consuming polyamine biosynthesis and depletion of lung AdoMet.

Taurine treatment protects against chronic nicotine‐induced oxidative changes

Experiments have shown that chronic nicotine administration caused oxidative damage in various organs by increasing lipid peroxidation products and decreasing the activity of endogenous antioxidants. The aim of this study was to investigate the effects of taurine treatment on nicotine-induced oxidative changes in rat thoracic aorta and heart and to explore the possible mechanisms of action. Male Wistar albino rats (200-250 g) were injected with nicotine hydrogen bitartrate (0.6 mg/kg; i.p.) or saline for 21 days. Taurine was administered (50 mg/kg; i.p.) alone or along with nicotine injections. After decapitation, the thoracic aorta and heart tissues were excised. The aorta was used for in vitro contractility studies or stored along with the heart samples for the measurement of malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity and collagen content. Tissue samples were also examined histologically. Serum samples were stored for the measurement of MDA, GSH and lactate dehydrogenase (LDH) activity. Chronic nicotine treatment impaired both the contraction and relaxation responses of the aortic rings to phenylephrine and acetylcholine, respectively. It increased lipid peroxidation, MPO levels and tissue collagen content of both aorta and heart samples. Taurine supplementation to nicotine-treated animals reversed the contractile dysfunction and restored the endogenous GSH levels and decreased high lipid peroxidation and MPO activities in both tissues. These data suggest that taurine supplementation effectively attenuates the oxidative damage because of chronic nicotine administration possibly by its antioxidant effects.

Functional Proteins Involved in Regulation of Intracellular Ca2+ for Drug Development: Chronic Nicotine Treatment Upregulates L-Type High Voltage-Gated Calcium Channels

Neurochemical mechanisms underlying drug dependence and withdrawal syndrome remain unclear. In this review, we discuss how chronic nicotine exposure to neurons affects expression of diazepam binding inhibitor (DBI), an endogenous anxiogenic neuropeptide supposed to be a common substance participating drug dependence, and function of L-type high voltage-gated Ca2+ channels (HVCCs). We also discuss the functional interaction between DBI and L-type HVCCs in nicotine dependence. Both DBI levels and [45Ca2+] influx significantly increased in the brain from mice treated with nicotine for long term, which was further enhanced after abrupt cessation of nicotine and was abolished by nicotinic acetylcholine receptor (nAChR) antagonists. Similar responses of DBI expression and L-type HVCC function were observed in cerebral cortical neurons after sustained exposure to nicotine. In addition, increased DBI expression was inhibited by antagonists of nAChR and L-type HVCCs. Sustained exposure of neurons to nicotine significantly enhanced expression of α1 and α2/δ1 subunits for L-type HVCCs and caused an increase in the Bmax value of [3H]verapamil binding to the particulate fractions. Therefore, it is concluded that the alterations in DBI expression is mediated via increased influx of Ca2+ through upregulated L-type HVCCs and these neurochemical changes have a close relationship with development of nicotine dependence and/or its withdrawal syndrome.

Increased expression of L-type high voltage-gated calcium channel α1 and α2/δ subunits in mouse brain after chronic nicotine administration

We investigated the effect of chronic nicotine administration on high voltage-gated calcium channels (HVCCs) in the mouse cerebral cortex. The treatment significantly increased expression of α1C, α1D, α1F, and α2/δ1 subunits with no changes of β4 subunit of L-type HVCCs. [ 3H]Diltiazem binding to the particulate fractions increased with increased Bmax value. These results indicate that chronic nicotine treatment up-regulates L-type HVCCs, which is due to increased expression of α1 and α2/δ1 subunits.

Chronic nicotine and smoke treatment modulate dopaminergic activities in ventral tegmental area and nucleus accumbens and the γ‐aminobutyric acid type B receptor expression of the rat prefrontal cortex

Dopaminergic afferents from the mesencephalic areas, such as ventral tegmental area (VTA), synapse with the gamma-aminobutyric acid (GABA)-ergic interneurons in the prefrontal cortex (PFC). Pharmacological and electrophysiological data show that the reinforcement, the dependence-producing properties, as well as the psychopharmacologic effects of nicotine depend to a great extent on activation of nicotinic receptors within the mesolimbocortical dopaminergic projection. To explore further the relationship between the mesencephalic dopaminergic neurons and PFC GABAergic neurons, we investigated the effects of nicotine and passive exposure to cigarette smoke on the regulation of tyrosine hydroxylase (TH) in VTA and substantia nigra (SNC) and dopamine (DA) D1 receptor levels in nucleus accumbens (NAc) and caudate-putamen (CPu). Also, the simultaneous changes in GABAB receptors mRNAs in the PFC were studied. The results showed that chronic nicotine and smoking treatment differentially changed the levels of TH protein in VTA and SNC and DA D1 receptor levels in Nac and CPu. GABAB1 and GABAB2 receptor mRNA levels also showed different change patterns. Ten and thirty minutes of smoke exposure increased GABAB1 receptor mRNA to a greater extent than that of GABAB2, whereas GABAB2 was greatly enhanced after 1 hr of smoke exposure. The TH levels in VTA were closely related to DA D1 receptor levels in NAc and with GABAB receptor mRNA changes in PFC. These results suggest that the mesolimbic pathway and GABAB receptor mRNA in PFC are modulated by nicotine and cigarette smoke, implying an important role in nicotine's psychopharmacological effects.

P.1.080 Assessment of cerebral regions associatedwith sexual arousal in depressive women before and after antidepressant treatment by using BOLD-fMRI

Chronic nicotine treatment has deleterious effects on vascular functioning and catecholamine modulation, which may compromise erectile functioning. Evidence that long-term cigarette smoking is an independent risk factor for introducing impotence is robust. However, limited studies have focused on the acute effects of smoking on physiological sexual response, and none have investigated the deleterious effects of isolated nicotine on human sexual arousal. Consequently, pathophysiological underpinnings of tobacco-induced—and particularly, nicotine-induced—erectile dysfunction are not well understood.To provide the first empirical examination of the acute effects of isolated nicotine on sexual arousal in nonsmoking men.Twenty-eight sexually functional heterosexual men (mean age 21 years), each with less than 100 direct exposures to nicotine, participated in a double-blind, randomized, placebo-controlled, crossover trial. Participants received either Nicorette polacrilex gum (SmithKline Beecham Consumer Healthcare, Pittsburgh, PA, USA) (6 mg; approximately equivalent to smoking one high-yield cigarette) or placebo gum, matched for appearance, taste, and consistency, approximately 40 minutes prior to viewing an erotic film.Physiological (circumferential change via penile plethysmography) and subjective (continuous self-report) sexual responses to erotic stimuli were examined, as well as changes in mood.Nicotine significantly reduced erectile responses to the erotic films (P = 0.02), corresponding to a 23% reduction in physiological sexual arousal. This occurred in 16 of 20 men with valid physiological recordings. Nicotine had no significant effect on continuous subjective ratings of sexual arousal (P = 0.70) or on mood (all Ps > 0.05).Isolated nicotine can significantly attenuate physiological sexual arousal in healthy nonsmoking men. These findings have implications for elucidating physiological mechanisms responsible for the effects of nicotine on sexual dysfunction, and for assisting public health policy in considering the deleterious effects of nicotine on sexual health. Harte CB, and Meston CM. Acute effects of nicotine on physiological and subjective sexual arousal in nonsmoking men: A randomized, double-blind, placebo-controlled trial.

Chronic nicotine treatment leads to induction of tyrosine hydroxylase in locus ceruleus neurons: the role of transcriptional activation.

Chronic nicotine treatment (two daily subcutaneous injections administered approximately 12 h apart for 14 days) is associated with long-term inductions of tyrosine hydroxylase (TH) protein and TH mRNA in locus ceruleus (LC) neurons. These increases persist for at least 3 days after the final nicotine injection in LC cell bodies and for at least 7 to 10 days in LC nerve terminal regions. We tested whether this long-term response is due to sustained stimulation of TH gene transcription rate. A semiquantitative reverse transcription-polymerase chain reaction assay was developed to assess changes in the levels of TH RNA primary transcripts; these changes are an indirect measurement of changes in TH gene transcription rate. TH RNA primary transcript levels increase rapidly in the LC after a single nicotine administration and return to basal levels by 24 h. A similar rapid and transient induction of LC TH RNA primary transcripts occurs after chronic nicotine administration. In contrast, TH RNA primary transcript levels remain elevated for a sustained period of time (at least 1 day) in the adrenal medulla after chronic nicotine administration. Similar rapid, but transient changes in LC TH RNA primary transcript levels are observed after repeated immobilization stress. These results suggest that TH gene transcription rate in the LC is stimulated rapidly after each nicotine injection; however, in contrast to the adrenal medulla, there is no sustained transcriptional response elicited by chronic nicotine treatment or repeated immobilization stress in the LC, suggesting that post-transcriptional mechanisms may also play a role in these long-term responses.

Nicotinic and muscarinic acetylcholine receptors are essential for the long-term response of tyrosine hydroxylase gene expression to chronic nicotine treatment in rat adrenal medulla

Nicotine induces tyrosine hydroxylase (TH) mRNA by interacting with nicotinic acetylcholine receptors (nAChRs) in cultured adrenal medullary cell systems; however, the mechanisms responsible for the induction of adrenal TH in response to systemically administered nicotine under in vivo conditions are more complex. In the present study, we tested whether nAChRs and muscarinic acetylcholine receptors (mAChRs) participate in the induction of adrenal TH observed after long-term treatment with nicotine. Chronic nicotine treatment (1.6 mg/kg, two daily injections spaced 12 h apart for 7 days) induced TH mRNA, TH protein and TH activity in rat adrenal medulla. This induction of TH gene expression was totally blocked when an antagonist of either nAChRs or mAChRs was administered prior to each nicotine injection. Repeated injections of the mAChR agonist bethanechol (5 mg/kg injected twice per day for 7 days) also produced increases in TH mRNA levels; however, TH protein levels and TH activity did not increase in response to bethanechol. In denervated adrenal glands chronic nicotine treatment did not lead to induction of either TH mRNA, TH protein or TH activity, whereas chronic bethanechol treatment led to induction of TH mRNA, but not TH protein or activity. These results suggest that agonist occupation of both nAChRs and mAChRs are essential for the complete response of TH gene expression to chronic nicotine treatment in rat adrenal medulla, but that stimulation of either cholinergic receptor by itself is not sufficient to elicit a full response. The results also suggest that both transcriptional and post-transcriptional mechanisms may potentially need to be regulated to induce TH protein in response to some stimuli.