Nicotine binding and nicotinic receptor subunit RNA after chronic nicotine treatment

Abstract

DBA mice were chronically treated with nicotine by continuous intravenous infusion of 4.0 mg/kg/hr for 10 d. Drug-treated mice were tolerant to the acute effects of nicotine on locomotor activity and body temperature. The effect of chronic treatment on the amount of L-3H-nicotine binding and RNA encoding for alpha 4, the most widely expressed nicotinic alpha-subunit, was measured in three brain regions. Chronic treatment increased L-3H-nicotine binding in cortex and midbrain but had no effect in cerebellum. In contrast, chronic treatment had no effect on the levels of mRNA encoding for alpha 4 in any of the three brain regions. Subsequently brains were sectioned and L-3H-nicotine binding was measured using quantitative autoradiographic methods. In addition, the relative amounts of mRNA for the major nicotinic receptor subunits (alpha 4 and beta 2), as well as for three additional minor subunits (alpha 2, alpha 3, and alpha 5), were determined by in situ hybridization histochemistry followed by quantitation of image intensity. Chronic nicotine treatment resulted in increases in the amount of L-3H-nicotine binding in many but not all brain areas measured. In contrast, chronic treatment had little effect on the intensity of the hybridization signal for the nicotinic subunit mRNA. The results suggest that chronic treatment with nicotine under conditions resulting in maximal steady-state increases in L-3H-nicotine binding has little effect on RNA levels encoding any of four nicotinic alpha-subunits and the beta 2-subunit.

Abnormal Regulation of High Affinity Nicotinic Receptors in Subjects with Schizophrenia

“…Interestingly, schizophrenics failed to show any upregulation in thalamus from baseline levels. In thalamus, upregulation in response to nicotine can be reduced and variable, particularly at low doses of nicotine (Marks et al 1992;Flores et al 1997;Ulrich et al 1997;Breese et al 1997a), indicating that thalamus may be refractory to nicotinic receptor upregulation. While neuroleptic treatment may have affected receptor upregulation of the high affinity receptors in thalamus, the lack of correlation may be related to the expression of other receptor subtypes (Marks et al 1992) that do not demonstrate the same degree of receptor upregulation to chronic nicotine treatment as the ␣4␤2 subtype (Fenster et al 1999).…”

“…This increase was shown to be dosedependent, based on the number of cigarettes smoked at death, and was reversible, with binding levels returning to control values in subjects who had quit smoking for at least two months prior to death (Breese et al 1997a). The up-regulation of receptor numbers does not appear to be under transcriptional regulation (Marks et al 1992). Rather, the increases may be related to changes in receptor turnover based on receptor desensitization, subunit composition, secondary structural changes in the receptor, or to modification of the receptor by protein kinases (Peng et al 1994;Baenziger and Chew 1997;Eilers et al 1997;Flores et al 1997;Hsu et al 1997;Xiao et al 1998;Fenster et al 1999).…”

The subtypes of nicotinic acetylcholine receptors on dopaminergic terminals of mouse striatum

“…The experiments described here used molecular biological, biochemical and pharmacological approaches in a series of studies that were designed to identify the subunit compositions of the nAChR subtypes that are expressed In situ hybridization has been used to characterize mRNA expression patterns in brain tissue. Figure 1 presents the results of in situ hybridization experiments that determined the mRNA expression patterns of the α2, α3, α4, α5, α6, α7, β2, β3, and β4 subunits in coronal sections of mouse (C57BL/6) brain [64]. The coronal sections shown in Figure 1 include the ventral tegmental area (VTA) and the substantia nigra (SN), brain regions that have high concentrations of dopaminergic neurons.…”

“…Figure 1 presents the results of in situ hybridization experiments that determined the mRNA expression patterns of the α2, α3, α4, α5, α6, α7, β2, β3, and β4 subunits in coronal sections of mouse (C57BL/6) brain [64]. The coronal sections shown in Figure 1 include the ventral tegmental area (VTA) and the substantia nigra (SN), brain regions that have high concentrations of dopaminergic neurons.…”

“…in situ at level of SN/VTA. Frozen sections (14μm) from a C57Bl6 mouse at the level of SN/ VTA (∼-3.0mm bregma) were hybridized with full length riboprobes complementary to the α2, α3, α4, α5, α6, α7, β2, β3 and β4 nAChR subunits [64,100]. nAChR binding sites measurable with radiolabeled epibatidine.…”