Tobacco Documents Online

19.1s tobacco smoking a form of nicotine dependence? R KUMAR, E C COOKE. M H LAIDER ANO M A H RUSSELL Inrtrod'uctlon The pharmacologicalibasis of the tobacco-smoking habit remains surprisingly obscure, although it is generally assumedi that nicotine plays sorrte part in this bizarre and widespread!compulsionto burn dried leaves. An average-strengCh cigarette: delivers slightly over l mg of nicotine in its mainstream smoke, most of which can be rapidily, . absorbed into the blood-stream following inhalation (Armitage:eta4 1'975),. Such 'smoking doses"of the alkaloid produce many effects in the brain and peripherally ('Agwe, 1i974;,Brown, 1973; Coffman, 1969; Friedman, Horvath andMeares, 1974; Russell, 1'976);, but the:psychological actions of nicotine arevariable and there is oniycircumstantial evidence that tobacco-smoking is a form of nicotine dependence. Smokers can partially regulate their intakes of nicotine whenofferedicigarettes of varying strengths (Ashton, and Watson, 1970;'Finnegan, Larson and Haag, 1945; Frith, 1!971; Turner, Silletrand Ba11, 1'974),,,but other constituents of'tobaceo smoke such as tar, covary in arrtount with nicotine (Atussell eta{,1973), and factorssurh as the taste and 'quality' of the smoke can markedly influence the amounts of smoking, (Goldfarb, Jarvik and'Click, 1'970). Recent tests (Goldfarb cral, 1976)'inwhich tar and nicotine yields:of cigarettes were independently varied do, however, ilnplicate nicotine as a reinforcer of smoking. This view is also supported by the observation (Stolerman et a4 1973)~that smoking,inereases when subjects are given mecamylamine, whic4 is, among,ot'her things„a central antagonist of nicotine. Other evidence for the nicotine hypothesis comes frocnistudies of the effects of nicotine-eontaining chewing-gum upon smokirng~(Btantmark, Ohlinand Westling, 1973; Kozlowski, Jarvk and Crdtz,,1'975),, but'the most direct tests have been done with injected doses of t'he drug.. In 1942 Johnston commentied'i that when habitual smokers were gii+en hypodiermic injections of nicotine they `almost, invariably thought the sensation pleasant, and,, given an adeqtaate dose, were disinclined to smoke for some time thereafter'. The same aut'hor, also injected'himself repeatedly with nicotine and came to prefer the injections to inhaling cigarette smoke; he1ater experienced feelings of deprivation when the injections were discontinued. Thesearc all hallmarks of a dependence disorder and it can be argued that habitual smokers are physiolosically dependentt upon nicotiine and, that they repeatedly self-administer this drug in order to ward! off the onset of withdrawallsymptiorns: There is some evidence fora nicotine-abstinence syndrome compr~ising psychological responsessuclias craving, tiension, irritability, restlessness, impaired!attention and performance, as well as a number of minor 244 1005052973

248 SMOKING BEHAVIOUR to mood! and to somatic symptorns of'anxiety were administered twenty minutess after the start of the experiment an& twenty minutes after the endlof each dose of' the airug; these were completed by the subjects within two to~five minutes. Analysis of resulrs The scores for puffing and for the physiological measures were fust averaged over ten-minute blocks and this gave four consecutive scores for each measure after every dose. Multivariate analyses showed thaU the scores for the first ten minutes after the inhaled doses ('Experimea 1) were significantly different from, the scores over subsequent ten;minute blocks and it appearedl that the main effects due to doses had occurred' during the first ten-minute block. Further analyses of variance.were then done on the data for the first ten minutes after the doses iniboth experiments and also for selected measures that were taken during the times that the doses were being given (12 mihutes.in: ExperimenU I and tenmirtutes in Experirnent 2). Results and discussion Figure 19.2 illustrates segments of the polygraph, records for two of the subjects;; it shows how, once they had settled down, these subjects tended to pufl"in a regular way. Subjects differed considerably between themselves in their rates of puffing, but, individual rates tended to remain broadly stable during the test session. Further- more, there was a relatively good correlat2on between the overaDl rates of puffiutg by individlual subjects~across the two experiments which were about a month apart (r = 0.66 df 10 p <0.02): These puff-by-puff recordings are reminiscent of behavioural research into drug dependence in anirnala where drugs may be self-administered according to simple schedules of reinforcement. In this study the schedule canibe described as fiiced ratio - 1, i.e. one response (suckutg,at holder) producing one reinforcement (dose of smoke). It was not possible to measure the:amounts of'smoke actually inhaled and we elected'in this experiment not to disturb the smoking behaviour of'our subjects by taking repeated blood samples for nicotine and carbon monoxide estimations. Puffing and inhalation seem closely related, but our conclusions must remaut, tentative until the.method is further developed to incorporate estimates of smoke inhaledL This technique does, however, improve on studies in which either numbers of cigarettes smoked or numbers of puffs arrcounted. Estimates of the volume puffed add greatly to the sensitivity of the measures and the validity of these scores was checked by correlating them with estimates of nicotine remaining in the fiIter-tips. The falters firom Experiment 2'were pooled in batches of four correspondirtg to each forty-minute period; two batches were lost and, there werre therefore 46'possible comparisons (r = 0.88' d!f 44 p<0.00'1). The filter nicotine measures give a good indication of'the smoke that has passed througit the filter-tlp O and, this result confirms the validity of the puff voliame scores. ~ Effects of inhaled and intravenous doses of nicotine upon smoking, Q Figure.19:3'shows the average rates of puffing by the subjects after each of'three ~I doses of inhaled or intravenous nicptine. After t'he inhaled doscs (Esperiment 1) there were no overall differences during the full forty-mnnute periods (F <1)„ but (~ comparisons of'puffung scores over the successive ten-minute blt7cks shtuwed that, j

TOBACCO~-SNUOKdNG A FORM OF NICOTINE D'EPENDENCE?' 249 EICG', GSR Tim. (minsi C .. .. 7.•. . . .. ... ..__. .. ., . .. . Puffs- GSR' Tim. lmins 1 U I l D ~ l 101 , io1' .c3 104 ~oS K Iw~ W L~ Figure 19:2. Sections of polygraph records of twn: subjects, The measures in, each case are of the heart-rate, puffdng, skin conductance and a time-ma!rirer indicating one*minute intexvals. lhdividual,puffs have:been numbered on the tracings. the rates at which puffing changedi were a linear functionlof the doseswhich had, previously been: inhaled'(F = 13.01 dl' 1,20 p<0.002'). For example, there was a marked initial'reduction al'ter the 1arge inhaled dose which was then followed by a gradual recovery. RougHly comparable doses of nicotine were given intzavenously in Experirnent 2 and it can be seen in Figure 19.3 that puffing rates remain unaffected over the! forty minutes (F G1). The subjects did, however, tend to puff more frequently irrespective of thcdose which, had been injected. 10050%532978

t. : doses of tobacco smoke the subjects took smaller puffs and this effect persisted ; The average volumes per puff are'shown in Figure' 1!9.4L After both the inhalcd - TOBACCO-S1v1oK1Nt7 A FORM OF NICOTINE DEPENDENCE? 251 throughout the forty minutes (F = 4.54 df 2,2D p<p105): The~siz'cs of the puffs that were taken, after the intravenous doses didlnot'd'iffer significantly from cach, other (F < 1), but, there was a strtking gpneral!rcductioni in the volumes per puff even before any doses were injected. 3nwk'inq elsaiekoLd dsars~ smekieaa+f/.riel.aroeeVS, dbs!.s, of Hicel7oo (E.p.rilw.n: I) - of NiceNn. (IEap.niin.es 21 nJw 700' E'. ^ 200 , e. a O. . ~CI 100 > r I i' 300 200 100 0 o ---o Dosr 0 r.--r~. Dew~ 1~. ~-+ Deso 2 2 3 4 Syec.ssi.o . bbck~s~ of 10 /einr1s Figure 19:S. Inahled doses of tobacco smoke:reduce the amount of smoke th'at is subsequently pu!ffed in a!dose-related way (ExpKriment' 1) and this effect is greatest during the first ten m'invtes after the doses. Comparable intravenous doses ofhicoaine have no eflfectupon the volumes that areipuffed,in Expernment,2: Althouighithe subjects are puiffing',more often (',see Fig. 19.3), the fact that they take smaiter'puiffs (see Fig. 1,9:4) resubts in a genKral fa/t in the volumes puffed in Experiment 2; this', difference betweenithe two experiments, whiich is evident before any doses are given, is also shown,by the crosses indicating the volumes'.pu!ffed during the',last'ten minutes of the settting-down, period. ~ The average volumes of smoke! puffed in successive ten-minute blocks are plotted in Figure 1'9,5; these scores are, in effect, the product'of the two previous measures (numbers of'puffs and volumes per puff). The i,nhaled doses reduced the vo'lumes subsequently puffed in an orderiy manner (F = 8.78 df 1,20 p<0101) and the clearest effect was seen in the first ten minutes after the doses. As might be expected (see Figures 19.3 and 19:4) the intravenous doses did not modify the amounts of' stnokesubs'equently puffed (F' <21),. The total votumes puffed were smaller in Experiment 2'inspite of the increased rates of puffing; perhaps this was a response to the more stressful conditions produced by the intravenous infusions„but a number of observations fail to support thiss interpretation. In Experiment 2 the subjects"check-iist scores showed that they were JL005052980

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