Cerebral uptake of nicotine and of amino acids

Central administration of nicotine suppresses tracheobronchial cough in anesthetized cats

We tested the hypothesis that nicotine, which acts peripherally to promote coughing, might inhibit reflex cough at a central site. Nicotine was administered via the vertebral artery [intra-arterial (ia)] to the brain stem circulation and by microinjections into a restricted area of the caudal ventral respiratory column in 33 pentobarbital anesthetized, spontaneously breathing cats. The number of coughs induced by mechanical stimulation of the tracheobronchial airways; amplitudes of the diaphragm, abdominal muscle, and laryngeal muscles EMGs; and several temporal characteristics of cough were analyzed after administration of nicotine and compared with those during control and recovery period. (-)Nicotine (ia) reduced cough number, cough expiratory efforts, blood pressure, and heart rate in a dose-dependent manner. (-)Nicotine did not alter temporal characteristics of the cough motor pattern. Pretreatment with mecamylamine prevented the effect of (-)nicotine on blood pressure and heart rate, but did not block the antitussive action of this drug. (+)Nicotine was less potent than (-)nicotine for inhibition of cough. Microinjections of (-)nicotine into the caudal ventral respiratory column produced similar inhibitory effects on cough as administration of this isomer by the ia route. Mecamylamine microinjected in the region just before nicotine did not significantly reduce the cough suppressant effect of nicotine. Nicotinic acetylcholine receptors significantly modulate functions of brain stem and in particular caudal ventral respiratory column neurons involved in expression of the tracheobronchial cough reflex by a mecamylamine-insensitive mechanism.

The short-term effect of nicotine chewing gum in patients with Parkinson's disease

Because of the inverse association of cigarette smoking with the risk of Parkinson's disease, we performed a short-term, double-blind, randomized controlled trial of nicotine polacrilex resin gum in patients with this disease. Forty-eight subjects were randomly assigned to chew either nicotine gum or placebo gum three times at 2-h intervals, with evaluation of symptoms before and after the trial. The nicotine gum was reasonably well tolerated, but there were no substantial differences in Parkinson's disease symptoms between the two treatment groups.

A sensitive period in gestation for nicotine acceleration of neuromuscular maturation

Nicotine, administered to pregnant Sprague-Dawley rat dams during gestation, altered the maturation of the developing extensor digitorum longus (EDL) muscle-peroneal nerve complex of the 2-week-old offspring. Initial isometric twitch time to peak and rate of rise of tension and tetanus time to peak tension of the group treated with nicotine during gestational (G) days G3-G8 were faster than controls indicating accelerated maturation of EDL muscle. Contractile parameters of the group treated with nicotine during G9-G13, a period immediately prior to muscle innervation, differed little from control. Nicotine administered during G14-G21 significantly increased twitch and tetanus tension and twitch rate of rise. There was little to no effect on motor unit size or number of motor units with nicotine during any of the three prenatal periods. Thus, while late prenatal nicotine administration primarily altered the strength of muscle, early gestational administration of nicotine increased the rate of muscle development suggesting a possible sensitive period for the accelerative action of nicotine on muscle maturation at this time.

The antiestrogenic effect of cigarette smoking in women

Epidemiologic results indicate that women who smoke cigarettes are relatively estrogen-deficient. Smokers have an early natural menopause, a lowered risk of cancer of the endometrium, and an increased risk of some osteoporotic fractures. Moreover, women who smoke may have a reduced risk of uterine fibroids, endometriosis, hyperemesis gravidarum, and benign breast disease. Several possible mechanisms for these effects have been identified. Smoking does not appear to be clearly related to estradiol levels, at least in postmenopausal women, although levels of adrenal androgens are increased. Moreover, smoking appears to alter the metabolism of estradiol, leading to enhanced formation of the inactive catechol estrogens.

Accelerated neuromuscular development in the rat with prenatal exposure to nicotine

Nicotine, administered to pregnant Sprague-Dawley rats either throughout gestation or during two selective prenatal periods before or after muscular innervation (i.e. before or after gestational day 13), accelerated the maturation of developing nerve and muscle as viewed in 2-week-old offspring. Prenatal treatment of rats with nicotine (tartrate salt; 0.25 mg/kg twice a day; i.p.) induced marked changes in the contractile force and speed of the developing extensor digitorum longus (EDL) muscle when tested in situ on 14 to 15-day-old pups. In all nicotine treatment groups isometric twitch and tetanus half contraction durations were shorter than controls. Use of 2,3,5-triphenyltetrazolium chloride, a biochemical indicator for cellular respiration, showed that totigestational nicotine administration increases cellular metabolic activity of EDL muscle. Hypertrophy of adrenal glands in these animals also was noted. While each of the three courses of nicotine administration accelerated muscle development and maturation, nicotine during the first half of prenatal development, prior to EDL muscle innervation, produced a more dramatic effect than nicotine during the second half of prenatal life.

Nicotinic stimulation of [3H]acetylcholine release from mouse cerebral cortical synaptosomes

The effects of nicotine and 1,1-dimethyl-4-phenylpiperazinium (DMPP) on the release of newly synthesized [3H]acetylcholine in mouse cerebral cortical synaptosomes were examined. Nicotine and DMPP produced increases in [3H]acetylcholine release, over the level of spontaneous release, of 24% and 30%, respectively, of a maximum depolarization-induced release produced by 50 mM potassium. The maximum effect was achieved at a concentration of 1 X 10(-4) M for both agents. The time course of release indicated a slow onset of action, reaching a maximum effect at 15 min of incubation. Both nicotine and DMPP also produced a slightly greater release of total tritium, measured in the absence of cholinesterase inhibition, than of [3H]acetylcholine. The release induced by nicotine was completely antagonized by hexamethonium and was largely (58%) calcium-dependent. Nicotine also produced an increase in [3H]choline accumulation into synaptosomes. These results indicate that the nicotinic agonists nicotine and DMPP can produce a moderate enhancement of acetylcholine release by a receptor-mediated action on cholinergic nerve terminals in the central nervous system.

Sex-linked differences in avoidance learning in the offspring of rats treated with nicotine during pregnancy

The offspring of rats treated with nicotine (0.5 mg/kg/day SC) on days 1-20 of gestation, were trained for active avoidance conditioning when 60 days old. Although learning was similar in both control groups of males and females, nicotine exposure during fetal life improved learning in females but reduced it in males, the difference between these two groups being statistically significant from day 17 until the end of the training period (day 25).

Effects of prenatal administration of nicotine on amino acid pools, protein metabolism, and nicotine binding in the brain

The effects of nicotine on brain protein metabolism and on the properties of the nicotine binding site were investigated in newborn animals exposed to nicotine during gestation. Brain protein synthesis rates measured in vivo were lower by 18% in newborn of treated animals. Protein degradation rates measured in vitro in the presence of nicotine were lower by 13%. The effect was specific for L-(-)nicotine, since D-(+)nicotine, nicotinic acid, or nicotinamide had no effect on degradation rates. Newborn brain amino acid levels, mainly nonessential amino acids and amino acids of putative neurotransmitter function, were changed somewhat; an increase in the level of taurine (13%), threonine (21%), serine (35%) and glycine (35%), and a decrease in lysine (14%) was observed in the offspring of nicotine treated animals (0.5 mg/kg, s.c., 2 x daily throughout gestation). These changes could not account for the decrease in protein metabolism. Nicotine binding was higher by 25% in the offspring of animals exposed to nicotine during gestation. No such increase was found after treatment of adult rats with nicotine, indicating that the properties of the nicotine binding site change with age.