Tabac mice showed a prominent enrichment of Chrnb4 transcripts in α3β4∗-positive areas, such as MHb and IPN, and in brain Screening Library areas that have been shown to express lower levels of Chrnb4, such as SuM ( Dineley-Miller and Patrick,

1992) and VTA ( Yang et al., 2009) ( Figures 3I and 3J). RT-PCR studies showed that Chrna4, Chrna7, and Chrnb2 transcripts (which are not present in the BAC) are not altered in Tabac mice ( Figure S2). Taken together these data show that Tabac mice express high levels of β4, but not α5, in α3/eGFP-labeled cells in CNS and PNS structures known to express the Chrnb4-Chrna3-Chrna5 nicotinic gene cluster, and are thus a useful mouse model in which to test the consequences of enhanced β4 expression at endogenous sites. Given the demonstration that the level of β4 expression is rate limiting for the function of α3β4α5 receptors in vitro (Figure 1), we were next interested in determining whether enhanced expression of www.selleckchem.com/products/incb28060.html Chrnb4 in Tabac neurons resulted in elevated nicotine-evoked currents in vivo. Previous studies have shown that neurons in the MHb express high levels of α3β4α5 receptors ( Quick et al., 1999). Accordingly, we employed patch-clamp recordings

to measure nicotine-evoked currents in MHb neurons of Tabac mice. A large proportion of MHb neurons in WT mice (n = 20 of n = 23 neurons recorded) responded to local fast application (50 ms) of nicotine ( Figures 4A and 4B). In Chrna3/eGFP-labeled MHb neurons of Tabac mice, nicotine elicited significantly increased peak currents in comparison to WT littermates (on average, 3.4-fold at 100 μM nicotine, two-way ANOVA, p < 0.05) ( Figure 4B). Similarly increased responses were obtained using acetylcholine (ACh) (data not shown). Dose-response curves for nicotine showed no significant differences between WT and Tabac mice, indicating that the

affinity of the receptors in the transgenic mice is not altered ( Figure 4C). Application of mecamylamine (MEC), a nonselective potent inhibitor of α4β2∗ and α3β4∗ nAChRs ( Bacher et al., 2009), resulted in a blockade of as much as 90% of the nicotine-elicited responses in Tabac Metalloexopeptidase mice ( Figure 4D), demonstrating that the enhanced nicotine responses in Tabac neurons result directly from elevated levels of functional nAChRs. To determine whether these additional receptors cause enhanced neuronal excitability, the firing rate of habenular neurons was measured in current-clamp assays in response to nicotine. Neurons from WT and Tabac mice were silent at rest (−70 mV). Local nicotine application (1 μM for 3 s) elicited single action potentials in WT neurons, whereas nicotine induced a robust burst of action potentials with a 13-fold higher firing frequency on average in Tabac neurons (p < 0.005) ( Figures 4E and 4F).