Nicotine exerts its psychopharmacological effects by activating the nicotinic acetylcholine receptor (nAChR), composed of alpha and/or beta subunits, giving rise to a diverse population of receptors with a distinct pharmacology. β4-containing (β4*) nAChRs are located almost exclusively in the habenulo-interpeduncular pathway. We examined the role of β4* nAChRs in the medial habenula (MHb) and the interpeduncular nucleus (IPN) in nicotine reinforcement using behavioral, electrophysiological, and molecular techniques in transgenic mice. Nicotine intravenous self-administration (IVSA) was lower in constitutive β4 knockout (KO) mice at all doses tested (7.5, 15, 30, and 60 μg/kg/infusion) compared with wild-type (WT) mice. In vivo microdialysis showed that β4KO mice have higher extracellular dopamine (DA) levels in the nucleus accumbens than in WT mice, and exhibit a differential sensitivity to nicotine-induced DA outflow. Furthermore, electrophysiological recordings in the ventral tegmental area (VTA) demonstrated that DA neurons of β4KO mice are more sensitive to lower doses of nicotine than that of WT mice. Re-expression of β4* nAChRs in IPN neurons fully restored nicotine IVSA, and attenuated the increased sensitivity of VTA DA neurons to nicotine. These findings suggest that β4* nAChRs in the IPN have a role in maintaining nicotine IVSA.

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Introduction: Prior to implementation of Haemophilus influenzae type b (Hib)-conjugate vaccination programs in the 1990s, Hib was the commonest cause of bacterial meningitis in children aged <5 years. While the burden of all Hib disease has significantly decreased in the post-vaccination era, Hib still accounted for >29,000 deaths worldwide in children aged <5 years in 2015. Areas covered: We reviewed literature data on the most widely used Hib vaccines and vaccination strategies which led to the global prevention and control of Hib disease and aim to highlight important factors for continued disease control and elimination in the future. Expert commentary: More than 90% of countries worldwide have implemented Hib-conjugate vaccination in their national immunization programs. Vaccines containing Hib polyribosylribitol phosphate (PRP) conjugated with tetanus toxoid (Hib-TT) are the most commonly used. Neisseria meningitidis outer membrane protein complex of PRP (Hib-OMP) is also used. Although the kinetics of the immune response varies with Hib vaccine and schedule used, high control of Hib disease was observed in all settings/scenarios. Further improving global Hib vaccination coverage may result in disease elimination.

Nicotine addiction, through smoking, is the principal cause of preventable mortality worldwide. Human genome-wide association studies have linked polymorphisms in the CHRNA5-CHRNA3-CHRNB4 gene cluster, coding for the a5, a3, and b4 nicotinic acetylcholine receptor (nAChR) subunits, to nicotine addiction. b4*nAChRs have been implicated in nicotine withdrawal, aversion, and reinforcement. Here we show that b4*nAChRs also are involved in non-nicotinemediated responses that may predispose to addiction-related behaviors. b4 knockout (KO) male mice show increased novelty-induced locomotor activity, lower baseline anxiety, and motivational deficits in operant conditioning for palatable food rewards and in reward-based Go/No-go tasks. To further explore reward deficits we used intracranial selfadministration (ICSA) by directly injecting nicotine into the ventral tegmental area (VTA) in mice. We found that, at low nicotine doses, b4KO self-administer less than wild-type (WT) mice. Conversely, at high nicotine doses, this was reversed and b4KO self-administered more than WT mice, whereas b4-overexpressing mice avoided nicotine injections. Viral expression of b4 subunits in medial habenula (MHb), interpeduncular nucleus (IPN), and VTA of b4KO mice revealed dose-and region-dependent differences: b4*nAChRs in the VTA potentiated nicotine-mediated rewarding effects at all doses, whereas b4*nAChRs in the MHb-IPN pathway, limited VTA-ICSA at high nicotine doses. Together, our findings indicate that the lack of functional b4*nAChRs result in deficits in reward sensitivity including increased ICSA at high doses of nicotine that is restored by re-expression of b4*nAChRs in the MHb-IPN. These data indicate that b4 is a critical modulator of reward-related behaviors.