Basal forebrain-lateral habenula inputs and control of impulsive behavior

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Neuropharmacology

Background:

• Impulse control deficits are characteristic of attention deficit hyperactivity disorder (ADHD), substance use disorders (SUDs), and traumatic brain injury (TBI).
• The lateral habenula (LHb) plays a crucial role in regulating impulsivity, with its intact function being necessary to limit impulsive behaviors.
• Understanding the specific brain circuits and mechanisms underlying impulsivity is vital for developing effective therapeutic interventions.

Purpose of the Study:

• To investigate the involvement of synaptic inputs to the LHb in regulating response inhibition and impulsive behavior.
• To elucidate the neurochemical and circuit-level mechanisms, particularly those involving cannabinoid signaling, that modulate LHb function related to impulse control.

Main Methods:

• Utilized retrograde fluorogold tracing to identify basal forebrain (BF) inputs to the LHb, specifically from the ventral pallidum and nucleus accumbens shell (VP/NAcs).
• Employed cellular and circuit approaches, including optogenetics, to manipulate and assess the function of VP/NAcs inputs to the LHb.
• Conducted behavioral experiments in rats to measure response inhibition and impulsivity, and examined the effects of systemic Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and LHb CB1R antagonism.

Main Results:

• Identified a GABAergic pathway from VP/NAcs to LHb, modulated by cannabinoid CB1 receptors (CB1R), which tonically suppresses LHb neuron activity.
• Optogenetic stimulation of VP/NAcs inputs to LHb impaired response inhibition, while inhibition of this pathway did not affect impulse control.
• Systemic administration of Δ⁹-THC increased impulsivity in male rats, an effect blocked by LHb CB1R antagonism, but this did not involve the VP/NAcs pathway.

Conclusions:

• An inhibitory afferent to the LHb, originating from the VP/NAcs and modulated by CB1Rs, plays a role in regulating impulsive behavior.
• The pro-impulsive effects of Δ⁹-THC are likely mediated through CB1Rs in the LHb but not exclusively via the identified VP/NAcs inhibitory pathway.
• This research identifies a novel cannabinoid-sensitive circuit influencing impulse control, offering potential targets for treating disorders characterized by impulsivity.