Effect of acute administration of nicotine on in vivo release of noradrenaline in the hippocampus of freely moving rats: a dose-response and antagonist study

In search of a mechanism for receptor-mediated neurobehavioral teratogenesis by nicotine: catecholamine release by nicotine in immature rat brain regions

Nicotine disrupts central nervous system development through interactions with nicotinic cholinergic receptors found in immature brain, leading to discoordination of target cell replication and differentiation. However, it is unclear whether the net result is achieved by nicotine's actions on its specific target cells, or indirectly through receptor-mediated release of other neurotransmitters, such as catecholamines, that possess neurotrophic properties. In the current study, developing rats (1, 7, 14 and 21 days old) were challenged acutely with nicotine (0.3 mg/kg) and the release of catecholamines was evaluated in vivo (AMPT method) in three brain regions that differ in nicotinic receptor concentrations. Nicotine did not stimulate catecholamine release at birth, but developed the capacity to do so in parallel with the ontogeny of nicotinic cholinergic receptors in the midbrain+brainstem and in the forebrain. In the cerebellum, which remains poor in nicotinic receptors, no response was obtained at any age. Superimposed on this general pattern, changes in sensitivity to nicotine were also seen that corresponded to ontogenetic changes in endogenous cholinergic tone, suggesting that receptor desensitization occurs normally during developmental stages in which neuronal activity is high. The absence of a catecholamine response to nicotine at birth in the rat indicates that neurobehavioral teratology associated with fetal nicotine exposure does not reflect secondary actions mediated through catecholamines. However, because brain development in the neonatal rat corresponds to fetal stages in man, the onset of these mechanisms may be relevant to human fetal exposure.

Nicotine-induced activation of locus coeruleus neurons--an analysis of peripheral versus central induction

Previous electrophysiological experiments have shown that the marked but short-lasting excitation of locus coeruleus (LC) neurons seen after systemic administration of low doses of nicotine is of a peripheral origin. In addition, nicotine induces a weak but more long-lasting activation of LC neurons which is preferentially observed following administration of high doses of the drug. In the present study this latter activation was pharmacologically analysed. Whereas low intravenous doses of nicotine caused a marked but short-lasting excitation of most LC cells recorded from, higher doses of nicotine were associated with a moderate but durable (> 20 min) activation. In contrast to the short-lasting activation of the LC, the long-lasting effect of the drug was not counteracted by chlorisondamine (0.3 mg/kg, i.v.; n = 5). On the other hand, administration of mecamylamine (4 mg/kg, i.v.; n = 5) rapidly and effectively decreased the elevated spontaneous firing rate of LC neurons (as observed following repeated nicotine injections) to the original baseline firing rate. Intravenous administration of tetramethylammonium (TMA, 50-800 mg/kg, i.v.), activated most LC neurons in a manner resembling that of nicotine at low doses, i.e. a marked but short-lasting excitation with no tachyphylaxis. However, in contrast to nicotine, TMA administered in higher doses did not affect the baseline firing rate of LC neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Unilateral AMPA lesions of nucleus basalis magnocellularis induce a sensorimotor deficit which is differentially altered by arecoline and nicotine

One week after unilateral alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) lesions of nucleus basalis magnocellularis, rats showed significant lateralised bias in spontaneous turning and in turning induced by tail pinch or by placing the rat on a 45 degrees grid. Turning was biased to the lesioned side and this side also showed increased responsiveness to pin-prick stimulation of the skin (somaesthesia), snout and whisker stimulation and ammonia olfaction. Arecoline (0.5 mg/kg), at a dose which did not affect responses to sensorimotor stimulation in sham-operated rats, corrected the lesion-induced biased turning to tail pinch and the 45 degrees grid test and reduced the bias in the open field. In contrast, nicotine (0.05 mg/kg), at a dose which also did not substantially affect responses to sensorimotor stimulation in sham-operated rats, switched the lesion-induced turning bias towards the contralateral side. Neither cholinoceptor agonist reduced the lesion-induced increased sensory responsiveness. The effects of nicotine were blocked by the centrally acting nicotinic antagonist, mecamylamine (1.0 mg/kg), but not by hexamethonium (1.0 mg/kg), or ondansetron (0.01 mg/kg). Amphetamine (up to 1.0 mg/kg) did not affect the lesion-induced motor asymmetry. The results confirm that the basal forebrain cholinergic system plays a role in sensorimotor cortical functions, but suggest different functional roles for muscarinic and nicotinic receptors.

Role of the locus coeruleus in the noradrenergic response to a systemic administration of nicotine

Experiments were conducted using in vivo microdialysis to ascertain the role of nicotinic receptors in the terminal, or the cell body area, in the hippocampal noradrenaline response provoked by a systemic administration of nicotine. These experiments combined systemic administration of nicotine with local administration of antagonists into the hippocampus via the microdialysis probe, or close to the LC via a cannula, while continuously monitoring extracellular levels of NA in the hippocampus. Systemic administration of nicotine (0.4 mg/kg, s.c.) produced a rapid and prolonged increase in extracellular levels of noradrenaline in the hippocampus of conscious animals, reaching a maximum in the first 10 min sample. In anaesthetised animals the maximum occurred 20 min after administration, but the subsequent response profile was similar. In both anaesthetised and freely moving animals nicotine increased extracellular levels of dihydroxyphenylacetic acid and homovanillic acid in the hippocampus, but failed to alter levels of dopamine or 5-hydroxyindoleacetic acid. In anaesthetised animals intrahippocampal administration of nicotine (250 microM over 10 min via the dialysis probe) significantly increased extracellular levels of noradrenaline; the response was shortlasting, being evident only in the 10 min sample during exposure to the drug. Local administration of nicotine failed to alter extracellular levels of any other amine or metabolite measured. Mecamylamine (25 microM), a nicotinic channel blocker, administered intrahippocampally 10 min prior to an intrahippocampal administration of nicotine completely blocked the increase in noradrenaline. However, intrahippocampal administration of mecamylamine (25 microM) for 10 min, or for the duration of recording, failed to antagonise the effect of a systemic administration of nicotine (0.4 mg/kg, s.c.) on extracellular levels of noradrenaline, dihydroxyphenylacetic acid or homovanillic acid. In contrast administration of mecamylamine (50 microM) close to the locus coeruleus abolished the increase in noradrenaline levels in the ipsilateral hippocampus following a systemic administration of nicotine (0.4 mg/kg, s.c.), while trimethaphan (50 microM), a nicotine receptor antagonist, significantly reduced the response. Administration of mecamylamine also attenuated increases in dihydroxyphenylacetic acid and homovanillic acid, suggesting that the response of these metabolites may be associated with the functional metabolism of noradrenergic neurones. Locus coeruleus administration of kynurenic acid (1 mM), a non-specific excitatory amino acid antagonist, was without effect. Finally, application of nicotine (50 microM) close to the locus coeruleus significantly increased extracellular levels of noradrenaline in the ipsilateral hippocampus.(ABSTRACT TRUNCATED AT 400 WORDS)

Increases in tyrosine hydroxylase messenger RNA in the locus coeruleus after a single dose of nicotine are followed by time-dependent increases in enzyme activity and noradrenaline release

We have utilized biochemical, molecular biological, and functional neurochemical measurements to investigate the integrated and long-term effects of a single dose of nicotine on the noradrenergic system in the central nervous system of the rat, from enzyme induction to transmitter release. We have found that a single systemic injection of nicotine (0.8 mg/kg) increases messenger RNA for the rate-limiting enzyme in the synthesis of catecholamines, tyrosine hydroxylase, two to six days later in the noradrenergic cell body region, the locus coeruleus (and not in the dopaminergic cell body regions, substantia nigra and ventral tegmental area). This was then followed by a time-dependent increase in enzyme activity, measured in vitro, in terminal regions of the ascending dorsal noradrenergic bundle up to four weeks later. Functionally, the increase in tyrosine hydroxylase activity in the terminals four weeks after a single administration was associated with an increase in the capacity to release noradrenaline in the hippocampus, measured using in vivo microdialysis in freely moving animals. This occurred in response to an acute systemic nicotine injection (0.4 mg/kg) but not to a local, intrahippocampal, challenge with 250 microM nicotine. These experiments have revealed a long-term effect of nicotine on noradrenergic activity in the central nervous system, associated with induction of tyrosine hydroxylase. This is accompanied by a time-dependent increase in terminal tyrosine hydroxylase activity and an increase in noradrenaline release.

Effects of systemic nicotine on serotonin release in rat brain

We used in vivo microdialysis to examine the acute effects of systemically administered nicotine (0.8-8.0 mg/kg, s.c.) on extracellular levels of serotonin (5-HT) in the frontal cortex of awake rats and animals anesthetized with chloralose/urethane. In anesthetized animals, 5-HT efflux was elevated during the initial 15 min after nicotine administration (2-8 mg/kg), but then returned to baseline values. All of the effective nicotine doses also lowered and then raised blood pressure in these animals. However, other drugs which raised (methoxamine, 0.07 mg/kg, i.v.) or lowered (mecamylamine, 5 mg/kg, i.p.) blood pressure without directly activating nicotinic receptors failed to alter 5-HT release. Moreover, pretreatment with a centrally active dose of mecamylamine, a known nicotinic antagonist, blocked the effects of nicotine (4 mg/kg) on 5-HT release. For studies on awake rats the perfusion fluid also contained fluoxetine, since basal 5-HT levels were barely detectable without this uptake blocker. In such animals, 1.6 mg/kg of nicotine significantly increased 5-HT release, an effect apparent in the initial 20 min after treatment and persisting for at least 2 h. These observations demonstrate that systemically administered nicotine increases frontocortical 5-HT release, that this effect is independent of the cardiovascular responses to the drug, and that it probably results from the activation of previously described nicotinic receptors on raphe neurons. The present findings are consistent with the hypothesis that the appetitive and mood disturbances associated with nicotine withdrawal may be mediated by diminished serotoninergic transmission.

Chronic treatments with cholinoceptor drugs influence spatial learning in rats

Nicotine, scopolamine, oxotremorine, diisopropyl-fluorophosphate (DFP) and tetrahydroaminoacridine (THA) were administered chronically to different groups of rats in doses reported to alter central muscarinic and/or nicotinic receptor numbers. Beginning 24 h after final drug injection, the groups were compared to a vehicle control group on acquisition of a hidden platform position in the Morris water maze over 20 trials with a 30-min inter-trial interval. Chronic treatment with either nicotine or scopolamine significantly improved the rate of learning, but oxotremorine and DFP retarded learning and THA had no effect on learning. The chronic drug effects on behaviour were consistent with known effects of the injected drugs on muscarinic and nicotinic binding in the forebrain and on the sensitivity of frontal cortex neurones to iontophoretically applied cholinoceptor agonists. However, alternative explanations for the observed changes cannot be ruled out, since the drugs used are known to have a wide range of effects on other neurotransmitters.

Fetal nicotine exposure ablates the ability of postnatal nicotine challenge to release norepinephrine from rat brain regions

Exposure of the fetus to nicotine is known to affect the function of noradrenergic pathways in the central nervous system. In the current study, synaptic mechanisms underlying the functional defects were evaluated in the offspring of pregnant rats given nicotine infusions of 2 mg/kg/day throughout gestation, administered by osmotic minipumps. At 30 days postpartum, norepinephrine levels in brain regions of the offspring were significantly reduced. More importantly, acute challenge with either 0.1 mg/kg or 0.3 mg/kg of nicotine evoked significant norepinephrine release from brain regions of control animals, but failed to do so in the fetal nicotine cohort. These results suggest that prenatal exposure to nicotine produces a deficit in subsequent noradrenergic responsiveness, deficits which may participate in behavioral and neuroendocrine abnormalities.

Effects of acute subcutaneous nicotine on attention, information processing and short-term memory in Alzheimer's disease

This single-blind, placebo controlled study reports on the effects of administering three acute doses of nicotine (0.4, 0.6 and 0.8 mg) subcutaneously to a group of Alzheimer's disease (DAT) patients (n = 22), young adult controls (n = 24), and normal aged controls (n = 24). The study extends our previous findings obtained using smaller groups of subjects. Drug effects were examined on three computerised tests: the first measuring rapid visual information processing, sustained visual attention and reaction time (RVIP task); a delayed response matching to location-order task measuring sustained visual attention and visual short-term memory (DRMLO task); and a finger tapping test measuring simple reaction time (FT task). The critical flicker fusion test (CFF) was used as a measure of perception and the WAIS digit span forwards (DS), of auditory short-term memory. Tests were graded in difficulty, titrated to avoid floor and ceiling effects so that meaningful, direct comparisons between groups could be made. Nicotine significantly improved sustained visual attention (in both RVIP and DRMLO tasks), reaction time (in both FT and RVIP tasks), and perception (CFF task--both ascending and descending thresholds). Nicotine administration did not improve auditory and visual short-term memory. There were no consistent, overall patterns of difference in performance between smokers and non-smokers in the control groups, or between males and females in any group. Despite the absence of change in memory functioning, these results demonstrate that DAT patients have significant perceptual and visual attentional deficits which are improved by nicotine administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicotinic systems and cognitive function

Nicotinic acetylcholine receptors have been found to be important for maintaining optimal performance on a variety of cognitive tasks. In humans, nicotine-induced improvement of rapid information processing is particularly well documented. In experimental animals nicotine has been found to improve learning and memory on a variety of tasks, while the nicotinic antagonist mecamylamine has been found to impair memory performance. Nicotine has been found to be effective in attenuating memory deficits resulting from lesions of the septohippocampal pathway or aging in experimental animals. Nicotinic receptors are decreased in the cortex of patients with Alzheimer's disease. Preliminary studies have found that some aspects of the cognitive deficit in Alzheimer's disease can be attenuated by nicotine. Nicotine may prove to be useful therapeutic treatment for this and other types of dementia.