Summary Background Chronic exposure to nicotine elicits physical dependence in smokers, yet the mechanism and neuroanatomical bases for withdrawal symptoms are unclear. As in humans, rodents undergo physical withdrawal symptoms after cessation from chronic nicotine characterized by increased scratching, head nods, and body shakes. Results Here we show that induction of physical nicotine withdrawal symptoms activates GABAergic neurons within the interpeduncular nucleus (IPN). Optical activation of IPN GABAergic neurons via light stimulation of channel rhodopsin elicited physical withdrawal symptoms in both nicotine-naïve and chronic nicotine-exposed mice. Dampening excitability of GABAergic neurons during nicotine withdrawal through IPN-selective infusion of an NMDA receptor antagonist or through blocking IPN neurotransmission from the medial habenula reduced IPN neuronal activation and alleviated withdrawal symptoms. During chronic nicotine exposure, nicotinic acetylcholine receptors containing the β4 subunit were upregulated in somatostatin interneurons clustered in the dorsal region of the IPN. Blockade of these receptors induced withdrawal signs more dramatically in nicotine-dependent compared to nicotine-naïve mice and activated non-somatostatin neurons in the IPN. Conclusions Together, our data indicate that therapeutic strategies to reduce IPN GABAergic neuron excitability during nicotine withdrawal, for example, by activating nicotinic receptors on somatostatin interneurons, may be beneficial for alleviating withdrawal symptoms and facilitating smoking cessation.

The complement system functions during the early phase of infection and directly mediates pathogen elimination. The recent identification of complement-like factors in arthropods indicates that this system shares common ancestry in vertebrates and invertebrates as an immune defense mechanism. Thioester (TE)-containing proteins (TEPs), which show high similarity to mammalian complement C3, are thought to play a key role in innate immunity in arthropods. Herein, we report that a viral recognition cascade composed of two complement-related proteins limits the flaviviral infection of Aedes aegypti. An A. aegypti macroglobulin complement-related factor (AaMCR), belonging to the insect TEP family, is a crucial effector in opposing the flaviviral infection of A. aegypti. However, AaMCR does not directly interact with DENV, and its antiviral effect requires an A. aegypti homologue of scavenger receptor-C (AaSR-C), which interacts with DENV and AaMCR simultaneously in vitro and in vivo. Furthermore, recognition of DENV by the AaSR-C/AaMCR axis regulates the expression of antimicrobial peptides (AMPs), which exerts potent anti-DENV activity. Our results both demonstrate the existence of a viral recognition pathway that controls the flaviviral infection by inducing AMPs and offer insights into a previously unappreciated antiviral function of the complement-like system in arthropods.

Increased anxiety is a predominant withdrawal symptom in abstinent smokers, yet the neuroanatomical and molecular bases underlying it are unclear. Here, we show that withdrawal-induced anxiety increases activity of neurons in the interpeduncular intermediate (IPI), a subregion of the interpeduncular nucleus (IPN). IPI activation during nicotine withdrawal was mediated by increased corticotropin releasing factor (CRF) receptor-1 expression and signaling, which modulated glutamatergic input from the medial habenula (MHb). Pharmacological blockade of IPN CRF1 receptors or optogenetic silencing of MHb input reduced IPI activation and alleviated withdrawal-induced anxiety; whereas IPN CRF infusion in mice increased anxiety. We identified a meso-interpeduncular circuit, consisting of ventral tegmental area (VTA) dopaminergic neurons projecting to the IPN, as a potential source of CRF. Knock-down of CRF synthesis in the VTA prevented IPI activation and anxiety during nicotine withdrawal. These data indicate that increased CRF receptor signaling within a VTA-IPN-MHb circuit triggers anxiety during nicotine withdrawal.