Comorbidity Between Depression and Smoking

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฀