Nicotine tolerance in chromaffin cell cultures: acute and chronic exposure to smoking-related nicotine doses

Elevated Norepinephrine may be a Unifying Etiological Factor in the Abuse of a Broad Range of Substances: Alcohol, Nicotine, Marijuana, Heroin, Cocaine, and Caffeine

A wide range of commonly abused drugs have effects on the noradrenergic neurotransmitter system, including alterations during acute intoxication and chronic use of these drugs. It is not established, however, that individual differences in noradrenergic signaling, which may be present prior to use of drugs, predispose certain persons to substance abuse. This paper puts forth the novel hypothesis that elevated noradrenergic signaling, which may be raised largely due to genetics but also due to environmental factors, is an etiological factor in the abuse of a wide range of substances, including alcohol, nicotine, marijuana, heroin, cocaine, and caffeine. Data are reviewed for each of these drugs comprising their interaction with norepinephrine during acute intoxication, long-term use, subsequent withdrawal, and stress-induced relapse. In general, the data suggest that these drugs acutely boost noradrenergic signaling, whereas long-term use also affects this neurotransmitter system, possibly suppressing it. During acute withdrawal after chronic drug use, noradrenergic signaling tends to be elevated, consistent with the observation that norepinephrine lowering drugs such as clonidine reduce withdrawal symptoms. Since psychological stress can promote relapse of drug seeking in susceptible individuals and stress produces elevated norepinephrine release, this suggests that these drugs may be suppressing noradrenergic signaling during chronic use or instead elevating it only in reward circuits of the brain. If elevated noradrenergic signaling is an etiological factor in the abuse of a broad range of substances, then chronic use of pharmacological agents that reduce noradrenergic signaling, such as clonidine, guanfacine, lofexidine, propranolol, or prazosin, may help prevent or treat drug abuse in general.

Nicotine as an Addictive Substance: A Critical Examination of the Basic Concepts and Empirical Evidence

The present review is a critical analysis of the concepts behind and the empirical data supporting the view that tobacco use represents an addiction to nicotine. It deals with general aspects of the notion of addiction, while concentrating on specific problems associated with incorporating nicotine into current frameworks. The notion of addiction suffers from unprecedented definitional difficulties. The definitions offered by various authorities are very different, even contradictory. Definitions that reasonably include nicotine are so broad and vague that they allow many trivial things, such as salt, sugar, and watching television, to be considered addictive. Definitions that exclude the trivia also exclude nicotine. The addiction hypothesis, in general, is strongly shaped by views that certain drugs bring about a molecular level subversion of rationality. The main human evidence for this is verbal reports of smokers who say that they can't quit. On the other hand, the existence of many millions of successful quitters suggests that most people can quit. Some smokers don't quit, but whether they can't is another matter. The addiction hypothesis would be greatly strengthened by the demonstration that any drug of abuse produces special changes in the brain. It has yet to be shown that any drug produces changes in the brain different from those produced by many innocuous substances and events. The effects of nicotine on the brain are similar to those of sugar, salt, exercise, and other harmless substances and events. Apart from numerous conceptual and definitional inadequacies with the addiction concept in general, the notion that nicotine is addictive lacks reasonable empirical support. Nicotine does not have the properties of reference drugs of abuse. There are so many findings that conflict so starkly with the view that nicotine is addictive that it increasingly appears that adhering to the nicotine addiction thesis is only defensible on extra-scientific grounds.

Differing temporal roles of Ca2+ and cAMP in nicotine-elicited elevation of tyrosine hydroxylase mRNA

The involvement of cAMP- and Ca2+-mediated pathways in the activation of tyrosine hydroxylase (TH) gene expression by nicotine was examined in PC-12 cells. Extracellular Ca2+ and elevations in intracellular Ca2+ concentration ([Ca2+]i) were required for nicotine to increase TH mRNA. The nicotine-elicited rapid rise in [Ca2+]i was inhibited by blockers of either L-type or N-type, and to a lesser extent P/Q-, but not T-type, voltage-gated Ca2+ channels. With continual nicotine treatment, [Ca2+]i returned to basal levels within 3-4 min. After a lag of approximately 5-10 min, there was a smaller elevation in [Ca2+]i that persisted for 6 h and displayed different responsiveness to Ca2+ channel blockers. This second phase of elevated [Ca2+]i was blocked by an inhibitor of store-operated Ca2+ channels, consistent with the observed generation of inositol trisphosphate. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (BAPTA-AM), when added before or 2 h after nicotine, prevented elevation of TH mRNA. Nicotine treatment significantly raised cAMP levels. Addition of the adenylyl cyclase inhibitor 2', 5'-dideoxyadenosine (DDA) prevented the nicotine-elicited phosphorylation of cAMP response element binding protein. DDA also blocked the elevation of TH mRNA only when added after the initial transient rise in [Ca2+]i and not after 1 h. This study reveals that several temporal phases are involved in the induction of TH gene expression by nicotine, each of them with differing requirements for Ca2+ and cAMP.

Dose-related cardiovascular and endocrine effects of transdermal nicotine

BACKGROUND

Transdermal nicotine in doses up to 21 mg/24 hr is used to facilitate smoking cessation. However, this dose does not achieve the nicotine plasma levels seen among heavy smokers, and underdosing may be one of the reasons for the limited efficacy of transdermal nicotine. There are some concerns about the adverse cardiovascular effects of nicotine, especially with concomitant smoking. Treatment with higher doses of transdermal nicotine has been proposed for highly dependent smokers, but the effects of such treatment on the cardiovascular system have not been determined. The objective of this study was to determine the cardiovascular effects of high-dose transdermal nicotine with concomitant smoking.

METHODS

Twelve healthy male smokers received three doses of transdermal nicotine (21, 42, and 63 mg/24 hr) and placebo, each for 5 days, in a balanced order. The subjects smoked during the first 4 days of each treatment and abstained from smoking during the fifth day. Ambulatory 24-hour daytime and nighttime heart rate and blood pressure values were determined for each treatment; plasma nicotine, cotinine, and carboxyhemoglobin levels and urinary catecholamines with aldosterone were measured on days 4 and 5. The data were compared by means of repeated-measures ANOVA.

RESULTS

There was no difference in heart rate or blood pressure and no changes in the pattern of circadian variations with various transdermal nicotine doses compared with smoking alone, consistent with the development of tolerance. Urinary epinephrine level was significantly higher (p < 0.05) with transdermal nicotine compared with no nicotine but was not higher with transdermal nicotine and smoking compared with smoking alone. No change was found in fibrinogen and lipid profiles with different nicotine doses.

CONCLUSIONS

High-dose nicotine treatment, even with concomitant smoking, caused no short-term adverse effects on the cardiovascular system.

Ibogaine acts at the nicotinic acetylcholine receptor to inhibit catecholamine release

In an effort to determine mechanisms of action of the putative anti-addictive agent ibogaine, we have measured its effects on catecholamine release in a model neuronal system, cultured bovine chromaffin cells. Various modes of stimulating catecholamine release were used including nicotinic ACh receptor activation, membrane depolarization with elevated K+ and Na+ channel activation with veratridine. In addition, because ibogaine has been reported to interact with kappa opioid receptors, we tested whether kappa receptor antagonists could reverse ibogaine's effects on catecholamine release. Ibogaine, at low concentration (<10 microM) was found to selectively inhibit nicotinic receptor-mediated catecholamine release, while having no significant effect on release evoked by either veratridine or membrane depolarization with elevated K+. The inhibitory actions of ibogaine and the kappa agonists were not reversed by preincubation with the opioid antagonists nor-binaltorphimine or naltrexone, suggesting that these inhibitory effects are not mediated by the kappa opioid receptor. The effects of low dose (10 microM) ibogaine were rapidly reversible, while the inhibitory effects of higher ibogaine doses persisted for at least 19 h following ibogaine washout. The results provide evidence for a mechanism of action ibogaine at the nicotinic ACh receptor. The results are consistent with a model in which the initial high transient brain concentrations (100 microM) of ibogaine act at multiple cellular sites and then have a selective action at the nicotinic ACh receptor cation channel following its metabolism to lower brain concentrations. The present findings are relevant to potential anti-addictive actions of ibogaine and to the development of drugs to combat nicotine addiction.

Desensitization and resensitization of norepinephrine release in the rat hippocampus with repeated nicotine administration

Desensitization of norepinephrine release was investigated with repeated intravenous (i.v.) infusions of nicotine and in vivo microdialysis of the hippocampus. At 100 min intervals, rats received three infusions of one of the following doses of nicotine: 0.045, 0.09 or 0.135 mg/kg. Doses of 0.09 mg/kg or higher increased norepinephrine release (F= 2.41, P < 0.05). However, the norepinephrine response to the second or third infusion was significantly reduced, compared to the first. The extent of desensitization and rate of resensitization was investigated further by administering consecutive infusions of nicotine (0.135 mg/kg) 40, 60, 100 or 200 min apart. Less norepinephrine was released after a second nicotine infusion given 40 to 100 min later, but this was not reduced further by a third infusion. Norepinephrine release was unchanged with a 200 min inter-infusion interval. Therefore, in the hippocampus, maximal desensitization of nicotine-stimulated norepinephrine release occurs as early as 40 min and persists for at least 100 min; thereafter, resensitization becomes the dominant process.

Stimulus coupling to transcription versus secretion in pheochromocytoma cells. Convergent and divergent signal transduction pathways and the crucial roles for route of cytosolic calcium entry and protein kinase C

How do chromaffin cell secretory stimuli program resynthesis of secreted peptides and amines? We previously showed that the physiologic nicotinic cholinergic signal for secretion also activates the biosynthesis of chromogranin A, the major protein released with catecholamines. Here, we examine signal transduction pathways whereby secretory stimuli influence exocytotic secretion versus chromogranin A transcription. Both secretion and transcription depended on initial nicotinic-triggered sodium entry into the cytosol, followed by calcium entry through -type voltage-gated channels. When calcium entered through -type channels, activation of secretion paralleled activation of transcription (r = 0.897, P = 0.002). Calcium entry from intracellular stores or through calcium ionophore channels activated secretion, though not transcription. Nicotinic-stimulated transcription depended upon protein kinase C activation; nicotine caused translocation of protein kinase C to the cell membrane fraction, and inhibition of protein kinase C blocked activation of transcription, while activation of protein kinase C mimicked nicotine effects. Transcriptional responses to both nicotine and protein kinase C mapped principally onto the chromogranin A promoter's cAMP response element (TGACGTAA; CRE box). KCREB, a dominant negative mutant of the CRE-binding protein CREB, blunted activation of chromogranin A transcription by nicotine, phorbol ester, or membrane depolarization. We conclude that activation of chromogranin A transcription by secretory stimulation in chromaffin cells is highly dependent upon precise route of calcium entry into the cytosol; transcription occurred after entry of calcium through -type channels on the cell surface, and was mediated by protein kinase C activation. The trans-acting factor CREB ultimately relays the secretory signal to the chromogranin A promoter's CRE box in cis.

Ibogaine and the dopaminergic response to nicotine

There is increasing evidence that the rewarding effect of nicotine is mediated by the mesolimbic dopamine system. The first objective of this study was to examine the dopamine response to repeated i.v. infusions of nicotine. Using in vivo microdialysis in awake and freely moving male Sprague-Dawley rats, we demonstrated that i.v. nicotine infusions (0.16 mg/kg or 0.32 mg/kg per infusion) produced increases in extracellular dopamine levels that were dose- and infusion order-dependent. Acute tolerance was evidenced by the smaller dopamine response produced by a second infusion of nicotine, administered 1 h after the first one. Tolerance was reversible, since the dopamine response to a second infusion of nicotine was unchanged when the interval between the infusions was increased to 3 h. Ibogaine, an alkaloid found in Tabernanthe iboga, is claimed to decrease smoking and to have an anti-nicotinic action. The second objective of this study was to establish whether this claim has any neurochemical basis. Pretreatment with ibogaine (40 mg/kg, i.p.) 19 h prior to the first nicotine infusion (0.32 mg/kg per infusion) significantly attenuated the increase in extracellular dopamine levels induced by-the nicotine infusions, suggesting that ibogaine may decrease the rewarding effect of nicotine.

Ibogaine selectively inhibits nicotinic receptor-mediated catecholamine release

The effects of ibogaine, a putative anti-addictive drug, on stimulated catecholamine release were examined in cultured chromaffin cells to clarify its mechanism(s) of action. Low concentrations of ibogaine (1-10 microM) had a selective inhibitory action on nicotinic receptor-mediated catecholamine release, while higher concentrations (100 microM) inhibited additional modes of stimulated catecholamine release. These results suggest a selective inhibitory action of ibogaine at the nicotinic acetylcholine receptor, possibly at the receptor ion channel site.

Stimulus-transcription coupling in pheochromocytoma cells. Promoter region-specific activation of chromogranin a biosynthesis

To explore stimulus-transcription coupling in pheochromocytoma cells, we studied the biosynthetic response of chromogranin A, the major soluble protein co-stored and co-released with catecholamines, to chromaffin cells' physiologic nicotinic cholinergic secretory stimulation. Chromogranin A mRNA showed a time-dependent 3.87-fold response to nicotinic stimulation, and a nuclear run-off experiment indicated that the response occurred at a transcriptional level. Transfected chromogranin A promoter/luciferase reporter constructs were activated by nicotinic stimulation, in time- and dose-dependent fashions, in both rat PC12 pheochromocytoma cells and bovine chromaffin cells. Cholinergic subtype agents indicated that nicotinic stimulation was required. Promoter deletions established both positive and negative nicotinic response domains. Transfer of candidate promoter domains to a heterologous (thymidine kinase) promoter conferred region-specific nicotinic responses onto that promoter. A proximal promoter domain (from -93 to -62 base pairs) was activated in copy number- and distance-dependent fashion, and thus displayed features of a promoter element. Its activation was sufficient to account for the overall positive response to nicotine. Within this proximal region, a cAMP response element (CRE) was implicated as a major nicotinic response element, since a CRE point-gap mutation decreased nicotinic induction, transfer of CRE to a thymidine kinase promoter augmented the promoter's response to nicotine, and nicotine activated the CRE-binding protein CREB through phosphorylation at serine 133. We conclude that secretory stimulation of pheochromocytoma cells also activates the biosynthesis of the major secreted protein (chromogranin A), that the activation is transcriptional, and that a small proximal domain, including the CRE box, is, at least in part, both necessary and sufficient to account for the positive response to nicotine.

Nicotine-related brain disorders: the neurobiological basis of nicotine dependence

1. This paper was written at a moment when the dependence liability of nicotine, the psychoactive component from tobacco, was the center of a dispute between the tobacco manufacturing companies and the scientific community (Nowak, 1994a-c). Without being comprehensive, it tries to summarize evidence compiled from several disciplines within neuroscience demonstrating that nicotine produces a true psychiatric disease, behaviorally expressed as dependence to the drug (American Psychiatric Association, 1994). Nicotine dependence has a biological substratum defined as "neuroadaptation to nicotine." 2. The first part of the article defines terms such as "abuse," "tolerance," "dependence," and "withdrawal." It discusses clinical and experimental facts at the whole-organism level, showing that animals and humans will seek and self-administer nicotine because of its rewarding properties. 3. The second part discusses the neurobiological basis of neuroadaptation to nicotine. It presents information on neuroanatomical circuits which may be involved in nicotine-related brain disorders, such as the mesocorticolimbic pathway and the basal forebrain-frontal cortex pathway. It also discusses work from several laboratories, including our own, that support the notion of a molecular basis for neuroadaptative changes induced by nicotine in the brain of a chronic smoker. 4. Although still under experimental scrutiny, the hallmark of neuroadaptation to nicotine is up-regulation of nicotinic receptors, possibly due to nicotine-induced desensitization of their function (Marks et al., 1983; Schwartz and Kellar, 1985). A correlation between these plastic changes and the behavioral data obtained from animal and human experiments is still needed to understand dependence to nicotine fully.