Region-specific effects of N,N'-dodecane-1,12-diyl-bis-3-picolinium dibromide on nicotine-induced increase in extracellular dopamine in vivo

Abstract

Background and purpose: Systemic administration of N,N'-dodecane-1,12-diyl-bis-3-picolinium dibromide (bPiDDB), an antagonist of nicotinic acetylcholine receptors (nAChRs) attenuated the nicotine-induced increase in dopamine levels in nucleus accumbens (NAcc).

Experimental approach: Using in vivo microdialysis, we investigated the effects of local perfusion of the novel nAChR antagonist bPiDDB into the NAcc or ventral tegmental area (VTA) on increased extracellular dopamine in NAcc, induced by systemic nicotine. We also examined the concentration-dependent effects of bPiDDB on the acetylcholine (ACh)-evoked response of specific recombinant neuronal nAChR subtypes expressed in Xenopus oocytes, using electrophysiological methods.

Key results: Nicotine (0.4 mg kg(-1), s.c.) increased extracellular dopamine in NAcc, which was attenuated by intra-VTA perfusion of mecamylamine (100 microM). Intra-VTA perfusion of bPiDDB (1 and 10 microM) reduced nicotine-induced increases in extracellular dopamine in NAcc. In contrast, intra-NAcc perfusion of bPiDDB (1 or 10 microM) failed to alter the nicotine-induced increase in dopamine in NAcc. Intra-VTA perfusion of bPiDDB alone did not alter basal dopamine levels, compared to control, nor the increased dopamine in NAcc following amphetamine (0.5 mg kg(-1), s.c.). Using Xenopus oocytes, bPiDDB (0.01-100 microM) inhibited the response to ACh on specific combinations of rat neuronal nAChR subunits, with highest potency at alpha3beta4beta3 and lowest potency at alpha6/3beta2beta3.

Conclusions and implications: bPiDDB-Sensitive nAChRs involved in regulating nicotine-induced dopamine release are located in the VTA, rather than in the NAcc. As bPiDDB has properties different from the prototypical nAChR antagonist mecamylamine, further development may lead to novel nAChR antagonists for the treatment of tobacco dependence.

Figure 1

Structure of N,N′-dodecane-1,12-diyl-bis-3-picolinium dibromide (bPiDDB).

Figure 2

Representative locations of microdialysis probe placements in the nucleus accumbens (NAcc; left) and ventral tegmental area (VTA; right) as indicated in black. Numbers to the right indicate distance in millimetres from bregma according to Paxinos and Watson (1986). The active probe protruded 2 mm below the distal end of the guide cannulae for NAcc and 1 mm for the VTA as described in the Methods.

Figure 3

(a) Time course of the effects of acute nicotine (NIC; 0.4 mg kg⁻¹, s.c.) alone or in combination with intra-VTA bPiDDB (0.1–10 μM) or mecamylamine (MEC; 100 μM) on extracellular dopamine levels in nucleus accumbens (NAcc). On the test day, after collection of stable basal samples, rats were perfused with bPiDDB or MEC for 40 min before NIC injection as indicated by arrow. Perfusion of bPiDDB or MEC continued for an additional 100 min. Dopamine levels represent the mean±s.e.mean of four–six rats. The average basal extracellular level of dopamine in these groups was 1.2±0.3 nM. (b) Area under the curve (AUC) for the effect of NIC alone or in combination with bPiDDB (0.1–10 μM) or MEC (100 μM). AUC values represent arbitrary units (mean ± s.e.mean) of four–six rats. ^*Different from control (artificial cerebral spinal fluid (ACSF)), P<0.05. ^#Different from NIC alone, P<0.05. (c) The effect of intra-VTA bPiDDB (1 or 10 μM) alone on extracellular dopamine levels in NAcc. After collection of basal samples, rats were perfused with ACSF or bPiDDB in the VTA, and dopamine levels were measured from NAcc. Data are the mean±s.e.mean of four–five rats. VTA, ventral tegmental area.

Figure 4

(a) Time course of the effects of acute nicotine (NIC; 0.4 mg kg⁻¹, s.c.) alone or in combination with intra-NAcc bPiDDB (0.1–10 μM) or mecamylamine (MEC; 100 μM) on extracellular dopamine levels in NAcc. On the test day, after collection of stable basal samples, the rats were perfused with bPiDDB or MEC for 40 min before NIC injection as indicated by arrow. Perfusion of bPiDDB or MEC continued for an additional 100 min. Data represent the mean±s.e.mean of four–six rats. (b) Area under the curve (AUC) for the effect of NIC alone or in combination with bPiDDB (0.1–10 μM) or MEC (100 μM). AUC values represent arbitrary units (mean±s.e.mean) of four–six rats. ^*Different from control (artificial cerebral spinal fluid (ACSF)), P<0.05. (c) The effect of intra-NAcc bPiDDB (1 or 10 μM) alone on extracellular dopamine levels in NAcc. After collection of basal samples, rats were perfused with ACSF or bPiDDB in the NAcc, and dopamine levels were measured from NAcc. Data are the mean±s.e.mean of four–five rats. NAcc, nucleus accumbens; VTA, ventral tegmental area.

Figure 5

(a) Time course effect of acute amphetamine (AMPH; 0.5 mg kg⁻¹, s.c.) alone or in combination with intra-VTA bPiDDB (10 μM) on extracellular dopamine levels in nucleus accumbens (NAcc). On the test day, after collection of stable basal samples, rats were perfused with bPiDDB for 40 min before AMPH injection as indicated by arrow. Perfusion of bPiDDB continued for an additional 100 min. Data represent the mean±s.e.mean of four–six rats. The average basal extracellular level of dopamine in these groups was 0.9±0.2 nM. (b) Area under the curve (AUC) for the effect of AMPH alone or in combination with bPiDDB (10 μM). AUC values represent arbitrary units (mean±s.e.mean) of four–six rats. ^*Different from control (artificial cerebral spinal fluid (ACSF)), P<0.05.

Figure 6

Inhibition of acetylcholine (ACh)-evoked responses obtained from oocytes expressing rat α4β2, α3β4, α3β2β3, α6/3β2β3, α3β4β3, α6β4β3, α7 and α1β1ɛδ nicotinic acetylcholine receptor (nAChR) subunits, by bPiDDB at varying concentrations. The mean net charges of coapplication responses (±s.e.mean, n⩾4) normalized to the net charge of the ACh controls obtained from the same cells are shown. Data obtained from oocytes expressing rat subunits are represented as follows: α4β2, α3β4, α3β2β3, α6/3β2β3, α3β4β3, α6β4β3, α7 and α1β1ɛδ.