Reasons for Increased Cigarette Consumption

Cigarette฀smoke฀inhibits฀the฀activity฀of฀monoamine฀oxidase฀MAO฀B,฀which฀is฀partly฀ responsible฀for฀the฀catabolism฀of฀serotonin฀5-HT,฀dopamine฀and฀noradrenaline฀in฀the฀brain.฀ Inhibition฀of฀MAO฀B,฀causing฀up฀to฀40฀loss฀of฀activity,฀probably฀does฀not฀occur฀until฀heavy฀ smoking฀has฀taken฀place฀for฀months฀or฀even฀years฀ [91,฀92] .฀It฀is฀probable฀that฀MAO฀B฀reacts฀ sensitively฀to฀peroxidation฀processes,฀and฀thus฀to฀oxidative฀stress,฀with฀neurodegenerative฀ manifestations฀ [93] .฀MAO฀A฀inhibition฀has฀also฀been฀observed฀after฀many฀years฀of฀smoking฀ [94] .฀Suppression฀and฀inhibition฀of฀both฀forms฀of฀MAO฀apparently฀contribute฀to฀the฀tendency฀ of฀smokers฀to฀react฀depressively฀ [95,฀96] .฀Smokers฀with฀a฀depressive฀disease฀reportedly฀show฀ lower฀noradrenaline฀levels฀at฀rest฀than฀smokers฀with฀no฀depressive฀tendency฀ [81] .฀The฀effect฀ of฀tobacco฀smoke฀can฀be฀interpreted฀as฀analogous฀to฀an฀MAO฀inhibitor.฀In฀contrast฀to฀earlier฀ assumptions,฀MAO฀activity฀itself฀is฀unchanged฀in฀people฀at฀high฀risk฀of฀depression฀or฀with฀a฀ history฀of฀depression,฀and฀is฀therefore฀not฀a฀marker฀for฀a฀depressive฀tendency฀ [81] .฀The฀action฀ of฀antidepressants฀is฀also฀similar฀to฀that฀of฀an฀MAO฀inhibitor,฀suggesting฀that฀various฀antide- pressants฀could฀also฀be฀supportive฀in฀smoking฀cessation,฀especially฀in฀depressive฀patients.

7.1.5.4 Comorbidity Between Depression and Smoking

A฀frequently฀described฀comorbidity฀might฀result฀from฀social,฀familial฀and฀individual฀risk฀ factors,฀inally฀manifesting฀in฀the฀form฀of฀depression฀and฀nicotine฀dependence,฀a฀hypoth- esis฀that฀is฀supported฀by฀numerous฀study฀indings฀ [55,฀76,฀89,฀97–100] . Another฀hypothesis฀is฀derived฀from฀the฀self-medication฀theory฀of฀increased฀substance฀use฀ [2,฀7,฀101,฀102] .฀Raised฀cigarette฀consumption฀could฀be฀a฀way฀of฀easing฀depressive฀symptoms฀ and฀the฀accompanying฀stress฀symptoms.฀The฀adolescent฀age฀range฀up฀to฀20฀years฀in฀which฀ these฀symptoms฀occur฀is฀particularly฀interesting฀ [72,฀87,฀103,฀104] .฀Another฀documented฀fact฀ is฀that฀cigarette฀consumption฀increases฀signiicantly฀between฀the฀ages฀of฀14฀and฀18฀ [80,฀88] ฀ and฀there฀is฀also฀a฀greater฀frequency฀of฀depressive฀disturbances฀in฀this฀age฀group฀ [89,฀100,฀ 105,฀106] .฀These฀results฀were฀conirmed฀in฀investigations฀involving฀1,265฀16-year-olds฀within฀ the฀framework฀of฀a฀longitudinal฀study.฀Here,฀as฀well,฀an฀odds฀ratio฀of฀4.6฀95฀CI:฀2.5–8.4฀ was฀determined฀for฀additional฀nicotine฀dependence฀with฀concomitant฀depression฀ [107] . Yet,฀a฀third฀hypothesis฀assumes฀that฀nicotine฀or฀one฀of฀the฀other฀inhaled฀substances฀induces฀ a฀depressive฀reaction฀by฀way฀of฀toxic฀effects฀ [108] ,฀as฀relected฀in฀a฀longitudinal฀study฀involv- ing฀a฀thousand฀subjects฀aged฀between฀21฀and฀30:฀only฀4.8฀of฀the฀non-smokers,฀but฀12฀of฀ the฀heavy฀smokers฀20฀cigarettes฀a฀day,฀developed฀depressive฀symptoms฀ [108,฀109] .

7.1.6 Schizophrenia

7.1.6.1 Prevalence

The฀“normal”฀population฀has฀30–40฀smokers.฀The฀risk฀of฀heavy฀smoking฀is฀increased฀ signiicantly฀in฀cases฀of฀schizophrenia฀ [2] .฀The฀prevalence฀of฀smoking฀among฀schizophrenics฀ is฀ estimated฀ at฀ 62–81฀ [12,฀ 105,฀ 110] ฀ and฀ the฀ correlation฀ with฀ the฀ paranoid฀ form฀ of฀ ฀schizophrenia฀ is฀ particularly฀ noticeable฀ [7,฀ 101,฀ 105,฀ 110] .฀ Schizophrenic฀ smokers,฀ fre- quently฀young฀men,฀are฀more฀likely฀to฀have฀the฀most฀severe฀forms,฀with฀earlier฀onset฀and฀ more฀frequent฀hospitalisation฀ [101] .

7.1.6.2 Reasons for Increased Cigarette Consumption

Although฀ the฀ changes฀ to฀ the฀ a 7 -ACh N ฀ receptor฀ are฀ clearly฀ psychosis-associated฀ most฀ clearly฀ with฀ schizoaffective฀ types,฀ moderately฀ with฀ bipolar฀ types,฀ and฀ least฀ of฀ all฀ with฀ schizophrenic฀disorders฀and฀smoking฀is฀particularly฀widespread฀among฀schizophrenics,฀ the฀craving฀to฀smoke฀cannot฀be฀seen฀as฀directly฀related฀to฀the฀receptor฀change฀since฀no฀such฀ links฀exist฀in฀healthy฀smokers฀and฀non-smokers฀ [111] .฀Reversible฀changes฀in฀event-evoked฀ potentials฀also฀raise฀the฀question฀of฀whether฀brain฀function฀is฀altered฀by฀smoking฀ [112] .฀ The฀following฀three฀observations฀are฀made฀in฀connection฀with฀the฀smoking฀behaviour฀of฀ schizophrenics:฀1฀they฀have฀greater฀dificulty฀in฀quitting฀smoking;฀2฀smoking฀is฀often฀ taken฀up฀after฀the฀psychosis฀breaks฀out;฀3฀in฀many฀cases,฀however,฀these฀people฀tend฀to฀ start฀smoking฀earlier฀in฀youth฀than฀the฀average฀age฀in฀the฀normal฀population,฀i.e.฀before฀any฀ outbreak฀of฀a฀psychosis,฀leading฀to฀the฀hypothesis฀that฀starting฀smoking฀early฀in฀adoles- cents฀might฀be฀a฀marker฀for฀a฀later฀schizophrenic฀outbreak฀where฀there฀is฀a฀familial฀dispo- sition฀ to฀ schizophrenia฀ [108] .฀ As฀ is฀ the฀ case฀ with฀ depression,฀ alcoholism฀ and฀ phobias,฀ reduced฀MAO฀activity฀in฀the฀thrombocytes฀of฀schizophrenics฀was฀found฀to฀be฀tobacco- induced฀and฀not฀to฀be฀a฀marker฀for฀a฀disposition฀to฀develop฀the฀disease฀ [109] .฀One฀change฀ seen฀in฀schizophrenics฀that฀may฀be฀signiicant฀in฀a฀pathogenic฀sense,฀an฀abnormal฀expres- sion฀and฀function฀of฀the฀gene฀family฀for฀the฀neuronal฀a 7 -ACh N ฀receptor,฀appears฀to฀be฀ compensated฀for฀by฀nicotine฀use:฀a฀deicit฀in฀acoustically฀evoked฀potentials฀recognised฀in฀ schizophrenics฀is฀not฀seen฀during฀nicotine฀use฀ [113] . Another฀indication฀of฀an฀altered฀a 7 -ACh N ฀receptor฀in฀schizophrenics฀is฀the฀fact฀that฀the฀ use฀of฀nicotine฀by฀this฀group฀does฀not฀stimulate฀the฀proliferation฀of฀pulmonary฀neuroendo- crine฀tissue,฀which฀is฀mediated฀by฀this฀receptor,฀as฀strongly฀as฀in฀healthy฀subjects฀mea- sured฀in฀terms฀of฀the฀secretion฀of฀bombesin-like฀peptides฀by฀the฀neuroendocrine฀tissue฀ [114] .฀This฀could฀also฀be฀one฀of฀the฀reasons฀for฀the฀lower฀incidence฀of฀lung฀cancer฀among฀ schizophrenics.

7.1.6.3 Extent of Cigarette Consumption

The฀severity฀of฀the฀smoking฀habit฀correlates฀with฀the฀severity฀of฀impairment฀of฀cognitive฀ functions฀caused฀by฀the฀schizophrenia,฀so฀that฀smoking฀is฀in฀some฀cases฀considered฀self- treatment฀in฀that฀it฀increases฀dopaminergic฀neurotransmission฀in฀prefrontal฀areas฀ [102] .฀ According฀to฀other฀indings,฀the฀number฀of฀cigarettes฀smoked฀does฀not฀correlate฀with฀the฀ severity฀of฀psychotic฀symptoms,฀but฀rather฀with฀non-speciic฀neurotic฀and฀anxiety-related฀ symptoms฀ [105] .฀The฀“self-therapy”฀smoking฀hypothesis฀is฀supported฀by฀a฀New฀Zealand฀