Disruption of VGLUT1 in Cholinergic Medial Habenula Projections Increases Nicotine Self-Administration

Abstract

Cholinergic projections from the medial habenula (MHb) to the interpeduncular nucleus (IPN) have been studied for their complex contributions to nicotine addiction and have been implicated in nicotine reinforcement, aversion, and withdrawal. While it has been established that MHb cholinergic projections co-release glutamate, no direct evidence has demonstrated a role for this glutamate projection in nicotine consumption. In the present study, a novel floxed Slc17a7 (VGLUT1) mouse was generated and used to create conditional knockout (cKO) mice that lack VGLUT1 in MHb cholinergic neurons. Loss of Slc17a7 expression in ventral MHb cholinergic neurons was validated using fluorescent in situ hybridization, and immunohistochemistry was used to demonstrate a corresponding reduction of VGLUT1 protein in cholinergic terminals in the IPN. We also used optogenetics-assisted electrophysiology to evoke excitatory post-synaptic currents in IPN and observed a reduction of glutamatergic currents in the cKO, supporting the functional disruption of VGLUT1 in MHb to IPN synapses. cKO mice exhibited no gross phenotypic abnormalities and displayed normal thigmotaxis and locomotor behavior in the open-field assay. When trained to lever press for food, there was no difference between control and cKO. However, when tested in a nicotine self-administration procedure we found that the loss of VGLUT1-mediated glutamate co-release led to increased responding for nicotine. These findings indicate that glutamate co-release from ventral MHb cholinergic neurons opposes nicotine self-administration, and provide additional support for targeting this synapse to develop potential treatments for nicotine addiction.Significance statement: Excitatory projections from the medial habenula (MHb) to interpeduncular nucleus (IPN) have been studied for their role in mediating the aversive properties of nicotine and nicotine intake behaviors. Although these projections are known to corelease acetylcholine and glutamate, the present study is the first investigation of a function for 2 this glutamate signaling in nicotine consumption. We demonstrate that a loss of VGLUT1 from cholinergic MHb neurons promotes increased nicotine self-administration in mice. Thus, we outline a role for glutamate release from MHb cholinergic projections in mediating the aversive properties of nicotine, expanding our knowledge of the neurobiology underlying nicotine consumption and identifying a possible substrate for therapeutic intervention.

Specialized astrocytes mediate glutamatergic gliotransmission in the CNS

“…The GFAP creERT2 gene was always maintained in heterozygosis. To produce a conditional allele of the mouse Slc17a7 gene encoding VGLUT1, GFAP creERT2 tdTomato lsl/lsl mice were back-crossed with Slc17a7 fl/fl mice 38 to obtain GFAP creERT2 Slc17a7 fl/fl tdTomato lsl/lsl mice and Slc17a7 fl/fl tdTomato lsl/lsl littermates. Likewise, to produce GFAP CreERT2 Slc17a6 fl/fl tdTomato lsl/lsl mice, we back-crossed GFAP creERT2 tdTomato lsl/lsl mice to VGLUT2-flox mice ( Slc17a6 fl/fl ; B6;129/Sv-Slc17a6tm1.1Edw, Jackson, 636372 48 ).…”

“…To determine whether astrocyte release occurred through exocytosis, we sought to impede glutamate filling in vesicles. We took advantage of a recently developed Slc17a7 fl/fl mouse line 38 carrying a conditional allele of Slc17a7 , encoding VGLUT1, the main VGLUT isoform in hippocampus 35 , expressed also in glutamatergic astrocytes (Fig. 1e,g ; Extended Data Figs.…”

Habenula bibliometrics: Thematic development and research fronts of a resurgent field

“…According to our co-citation analysis, the medial habenula cholinergic system has attracted current attention because of its potential relationship between the MHb and nicotine withdrawal, drug addiction, and mood disorders ( McLaughlin et al, 2017 ; Lee et al, 2019 ). Moreover, MHb-IPN (interpeduncular nucleus) pathway showed left-right functional asymmetry in the level of neurotransmitter acetylcholine ( Hong et al, 2013 ), which also revealed the involvement of this pathway in nicotine addiction ( Souter et al, 2022 ). Notably, the CHRNA5 gene encoding the nicotinic receptor alpha 5 subunit, which is strongly implicated in smoking dependence, is expressed at highest mRNA levels in the IPN, while the A3/B5 genes encoding channel-forming α3 and β4 receptor subunits are prominently expressed in the ventral MHb ( Morton et al, 2018 ).…”

New medications development for smoking cessation

“…Within the mesolimbic circuit, nicotine facilitates glutamate release from presynaptic terminals in both the VTA and NAc, which is believed to play a role in its reinforcing actions [ 120 ]. Evidence suggests that blocking glutamatergic transmission within these brain circuits attenuates nicotine reward-related behaviors in rodents [ 120 , 125 , 126 ]. Conversely, facilitation of inhibitory GABAergic transmission attenuates nicotine seeking behaviors in rodent models of tobacco dependence [ 120 , 127 , 32 ].…”