Tobacco Documents Online

PROSPECTIVES FOR'CTR IN RELATION TO CNS STUDIES Several investigators in recent years have been interested in the effeets of smoking,or nicotine on the CNS'(See review, Annals of the New York Academy of Sciences, vol. 142, art. 1, 1967; Smoking Behaviour: Motives & Incentives, Ed W.C. Dunny 1973; See Also Tobacco Suppl. III, Larson & Silvette, 1975). Regional localizati~on of nicotine, effects of brai!nstem neurons, effects on arousal, EEG and evoked responses and behavioural responses were described, amongst other effects. Despite the considerable efforts of these investigators and others, the resulits remain preliminary. Basic quest'ions concerning mechanisms of action in relationships between neurons, neurons and supporting cells as well as intracellular functions remain unresolved. Ten, years since the 1967 conference, with more information accumuliated (See Tobacco, Suppl. III, Larson & Silvette, 1975), the situation remains much the saime i although it now seems evident that nicotine like narcotics, influences the CNS in multiple ways involving effects related to most of the knovn neurotransmitt'ers. 1 (Chemical mediators of neurone activity). Further, the dependence which develops to tobacco in humans (+ withdrawal symptoms during cessation of'smoking) and the degree of tolerance to nicotine which occurs in certain onimali paradigms strongly suggest that nicotine is anihabituat'ing agent. While numerous avenues exiist whereby the effects of smoking, nicotine ' (and metabolites or nicotine derivatives), nitrosamines, beneo(a) pyrene and CO on the CNS'may be determined, the results could be diffuse if some attempt were 6- . not first made to define which particular areas of study might be most profitable. The following represents some degree of consolidation into five major research C 4== w fields which might be approached simultaneously. Then, as progress is made on one or the other front,,an emphasis might then be made in t'hat'field which seems ~ N C!t ~ ~ ~~ I

C 2. mosti ~.axely Lo proviue cne answers un cne oasic mecuanismms oi actiion. nvwever, while one may speak of limiting approaches to five major types of investigation, the technological method's available in each area are sufficiently diverse to, produce an appearance of uncoordinated programing. Primary Catagories of Investigation 1. Receptors andisites of nicotine action: Identification and localization of nicotine receptors within the CT15. Are they all cholinergic (associate&with acetylcholine, a neurotransmitter), or is there a novel non-cholinergic nicotine receptor, as suggested, by Abood? Are the receptors all at synapses (interneuronal junctions) or are there al!so "acceptor" molecules for nicotine in neurons or glia (supporting cells) which relate to non-connectivLty functions? Are the synaptic receptors all post synaptic?' What is the degree of stereospecificity of nicotine? Does nicotine receptor localiization mimic that of opiate narcotics in the liimbic system (that part of brain associated with pain perception, pleasure andivarious emotional responses) and can specific receptors be identified whose role is associated with the dependency component of smoking? Are there effects on non-niootinic receptors, ~ moduliating their activity. To what degree can nicotine act to modulate the effects of any, of the neurotransmitters? Current technological advances in receptor chemistry should facilitate studies in this area. II. Basic Neurochemical Studies: Whilie it might be of interest to consider pursuing all or'several of the various neurochemical lines of study (protein, carbohydrate, lipid, RPZA, DNA, ions, ami'nes, etc.) available, it seems more profitable to cozcentrate on protein (as an end product already knownito be influenced by nicotine) and then work backwards to RNA and~DNA as progress is made. This is alsolbecause consider- able advances have been made in the iso]a tion and characterization of many brain 46----T-

3. . • specific proteins. (S-100, 14-3-2, Tubulin, Synaptin, Neuractin + M(yosi'n, contractile proteins, Neurophysin, Glial acetic protein, etc.). Antisera to . the S-100-and synaptic membrane proteins have produced difficulties in learning paridigms in experimental animalis; the 1k-3-2'neuron specific protein has been shown to consist of 3'isozymes of enolase, (a cellul'ar respiratory enzyme) Tubulin (from Neurotubul!es) appears as anlimportant structurali protein as well as playing a significant role iniaxonal +ransport. This may relate specifically to transport from the cell bod'y of a nicotine receptor protein to the synapse. Firther, a protein has beenlisolated fran the neurons of the electric eel which migrates down the axon (presumably associated with the microtubules). This protein has been demonstrated to have immunological identity with the nicotinee acetylcholine receptor of'the electric organ. Considerable advances have also been made in defining the properties of neurophysin, the protein associated with the neural hormones, vasopressin and oxcytocin of the posterior pituitary which regulate blood pressure and sodium clearance. Another pair of neuronal nroteins are neuractin and neuromyosin. These two contractile proteins have chemical properties similar to those of the actin and myosin of muscle, yet they are not completely identical. They are believed to play a role in the release of transmitter at the synapse. Finally, there are a number of proteins associated with glia (glial acidic proteins)~which are believed to be important in normal glial function and which increase markedly in amount in diseases involving,glia. These could be important in normal nerve lunetion in as much as glia are essential for neuronal viability. Iit is believed by neurochemists that a major disruption of these proteins by any drug at the level of synthesis (RNA transcription, etc.) or degradation may have profound effects on CPIS function. A more mild disruption could lead to a variety of behavioural disorders or perhaps only to changes which could only be monitoredobjectiveLy by neurochemical procedures. An initial phase in the

synthetic-degradative turnover pathway whieh might be altered by a drug (i.e. r nicotine or its metabolites) is the mechanism of amino acid transport, either from blood-to brain or within the compartments within the CNS. (Currently being investigated by C2R'grantee A. Lajtha). III. Effects on Development and Differentiations: Numerous reports relate heavy smoking among pregnant women to premature birth of their offspring which tend to also be sma]1~for date. These observations raise serious questions about the development of organ systems in the offspring, despite the fact that there have been many uncontrolled variablies in these studies (Consumption of alcohol, environmental pollutants, nutritional state of the mother) which make it difficult to interpret the results. Hudson et al demonstratedia dose related response of nicotine on the growth (depressed) of offspring of nicotine-treated pregnant rats. Further, nicotine influenced the level of the electroshock threshold (EST) in the offspring. (It was first elevated and then depressed in relation to controls at a dose level of 3.0'mg of nicotine/day throughout pregnancy)'. Nicotine and CUeffects on the uterus have aLso been reported which may influence fetal growth by impairing the supply of nutrients. Further, studies by Matalka demonstrate a perceptual defiei~t in offspring of pregnant rats treated rrith nicotine throughout pregnancy. Numerous morphological, biochemical and~physiologi'caL studies might be planned on the basis of these observations of defective perception, providing that adequate nutritional or st ress controls are established. Development of enzyme systems could be examined by both histo and neurochemical procedures, levelis of transmitters and their turnover could' be evaluated, growth of neuronal and glial populations determined, nerve cell 9 growth and~synaptogenesis measured, etc. One might also determine if there are delays in maturation (morphological or biochemical) in which there is a"catehing up". If so, to what degree does the dist.x .bance in the time table of maturation alter function. FinaJly, are there behavioural changes? I

i . . , C 5. If decrements in development and differentiation occur, they may be associated with disorders of neuroend'ocrine function, which can themselves readily lead to behavioural problems. Such effect's might be mediated by an altered degree of binding of various hormones to their specific receptors in neuronall nuclei, or as in the case of corticosterone, an interference with hormone association with some protein factor in the cell body prior toinuclear binding, to a receptor. This could disrupt the normal activity of the hormone at the level of'the nucl!ear material in the chromosomes. As is well known, the differentiation of various regions of the hypothalamus (part of the brain controlling pituitary, temperature, reprodtiction, feeding, etc.)',is particularly sensitive to inappropriately high or laa levels of male sex hormones in both sexes: High levels masculinize females and low levels lead to feminizat;ion in males. ThSmoU deficiency interferes with normal neuronal growth and delay,s dif£erentiation. Adrenal cortical hormones maintain normal rates of nerve cell division wi:thin~given period's...diffi- ciencies liead to shortening of the cell division period, hormone in excess prolongs cell division. Normally some sort of balance seems to exist betweenithyro3d and adrenal eortilcoids in regulating periods of cell division vs. maturation. Could smoking and the chemicals associated with smoking alter this balance or in any way alter the other delicate effects hormones have in the hypothalamus?' Since nicotine is knovm to stimulate vasopressin release (action at the supraoptic nucleus) and depresses the preovulatory surge of Lfi (influences ovulation) in adul!ts as well as the release of prolactin (associated with milk formation) in suckled mothers, it does not seem unreasonable to expeet that there may be other effects caused by exposure of the hypothalamus to nicotine during the period of differentiation or cell'di~vision when the neurons are more sensitive to external influences. -T

T. . . - Rah-i'nnre Certainly the most difficult data to:put into its proper perspective is that obtained from behavioural studies. This is perhaps due to communication difficulties between psychologists and the uninitiated or to an inherent resi~stenc. e to accepting bar pressing and maze data as relevent to "learning" and 'Snemory" or "emotional behaviour"'in primates. On the other hand, aetivity studies, state dependent and discriminative stimulus studies in relation to certain drugs do appear to have some relevance if the drugs used are not toxic or do not in andi of themselves produce effects (paralysis, seizures, etc.) whicl-, wouldiinterfere with a behavioural study. Thus,,many such studies do provide useful clues as to what may happemin~man with the same or similar druga. The ability of drug A to prevent or facilitate a rat from discriininat'ing,between saline and a very low dose of drug B~(a narcotic)lat doses below the threshold for pharmacological responses may be meaningful in terms of defining the response of the CIIS to either A or B. This is particularly true where both drugs are known to have an effect in man. Lesion or electrode stimulating studies in conjunction with applications of agents which influence transmitter release, re-uptake or degradation may further refine the results in relation to understanding,the pharmaeologic action of the drug. Ultimately, however, one must seek for answers at the molecular level. The behaviour which one observes is only an expression of what occurs at synapses, or in the synthesis and degradation of transmitters, or in the levels of interactions between~neurons. In~ huanan, terms, one arrives at the following in relation to behaviour as associated~withismoking, (These are self evident and appear almost as a quote from Dunn): 1. why,do people start smoking initiallyY' Is it simply peer pressuree or curiosityY

. e 7. 2. Why do people continue to smoke when there is so much evidence that it may be harmful' to their health? Is the habituation that overwhelming? 3. To what degree do people become physiologically and (of) psychologically dependent on smoking and nicotine? What is the basis of in- dividual differences in this respect? Is genetics the sole and only answer? 4. Why does it appear more difficult for women to give up smoking than men? . Is it simply because they are afraid of gaining weight or are there more eompLex psychological' issues which may be dependent or reinforced by the cyclic endoerine status of fernales with fluctuations of estrogens and progesterone (and metabol!ites)ias compared to the more static endocrine status of males? D. ff.~ Ford r Q

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