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Induction but not expression of behavioural sensitization to nicotine in the rat is dependent on glucocorticoids.

Artikel i vetenskaplig tidskrift
Författare D H Johnson
Anders I Svensson
Jörgen Engel
Bo Söderpalm
Publicerad i European journal of pharmacology
Volym 276
Nummer/häfte 1-2
Sidor 155-64
ISSN 0014-2999
Publiceringsår 1995
Publicerad vid Institutionen för fysiologi och farmakologi, Avdelningen för farmakologi
Sidor 155-64
Språk en
Länkar www.ncbi.nlm.nih.gov/entrez/query.f...
Ämnesord Adrenalectomy, Animals, Biogenic Monoamines, analysis, Brain Chemistry, drug effects, Glucocorticoids, physiology, Male, Motor Activity, drug effects, Nicotine, pharmacology, Rats, Rats, Sprague-Dawley, Receptors, Dopamine, physiology
Ämneskategorier Farmakologi, Beroendelära

Sammanfattning

Behavioural sensitization has been implicated in the development of addictive behaviour, and several studies suggest that corticosteroids may be involved in this phenomenon. In the present study, the effects of adrenalectomy and steroid replacement treatments on the behavioural sensitization observed after daily injections of nicotine (0.4 mg/kg s.c.) were investigated in the rat. Adrenalectomy completely prevented sensitization to the locomotor stimulating effect of nicotine after repeated injections but did not influence the acute locomotor activating effect of the drug or an already established sensitization to nicotine. In adrenalectomized animals receiving replacement treatment with corticosterone or dexamethasone, but not aldosterone, repeated administration of nicotine produced behavioural sensitization. Repeated dexamethasone treatment per se failed, however, to sensitize rats to nicotine. Post mortem neurochemical studies showed that repeated administration of nicotine significantly increased homovanillic acid (HVA) levels, as well as the dihydroxyphenylacetic acid (DOPAC)/dopamine quotient, in the limbic forebrain. Adrenalectomy per se significantly increased HVA levels and tended to elevate the DOPAC/dopamine quotient. When repeatedly treated with nicotine, adrenalectomized rats displayed a higher DOPAC/dopamine quotient, but no significant difference in HVA levels, compared to nicotine-treated sham-operated controls. In the striatum and the cortex, no significant effects of nicotine treatment or adrenalectomy were observed on any of the neurochemical measures. The present results suggest that glucocorticoid (type II) receptor activation is required for induction of sensitization to the locomotor stimulatory effect of nicotine, whereas corticosteroids are not required for the expression of the behavioural sensitization once established. Provided that HVA levels and the DOPAC/dopamine quotient relatively well reflect the presynaptic dopamine activating effect of nicotine, it may be suggested that corticosteroid-related mechanisms associated with behavioural sensitization to nicotine are post- rather than presynaptically located in relation to mesolimbic dopamine neurons.

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