Rostromedial tegmental nucleus

The rostromedial tegmental nucleus (RMTg), or tail of the ventral tegmental area (tVTA), is a GABAergic nucleus which functions as a "master brake" for the midbrain dopamine system. It is poorly differentiated from the rest of the ventral tegmental area (VTA) and possesses robust functional and structural links to the dopamine pathways. Notably, both acute and chronic exposure to psychostimulants have been shown to induce FosB and ΔFosB expression in the RMTg; no other drug type has been shown to induce these proteins in the RMTg.

Inputs

The RMTg receives incoming projections from the following structures:

• Medial prefrontal cortex
• Cingulate cortex
• Preoptic area
• Lateral hypothalamus
• Lateral habenula
• Superior colliculus
• Periaqueductal gray
• Dorsal raphe
• Laterodorsal tegmental nucleus
• Substantia nigra
• Nucleus accumbens
• Pontine tegmentum
• Ventral pallidum

Outputs

GABA projections from the RMTg include:

• RMTg → Raphe nuclei
• RMTg → Preoptic area
• RMTg → Lateral hypothalamus
• RMTg → Substantia nigra
• RMTg → VTA
• RMTg → Periaqueductal gray
• RMTg → Pontine tegmentum

Clinical significance

The RMTg plays a "crucial role" in the regulation of CNS dopaminergic activity by endogenous opioids and opiate drugs. The GABAergic neurons that project from the RMTg to midbrain dopamine systems express μ-opioid receptors. Current models of this system suggest that exogenous opiates (e.g., morphine) excite dopamine pathways originating in the VTA by activating the μ-opioid receptors in neurons projecting from the RMTg; opioid activation of these neurons leads to disinhibition of the GABAergic brake on dopamine networks. Since RMTg projections to the VTA are the primary inhibitor of VTA-originating addiction pathways (most notably the mesolimbic pathway), the RMTg plays a dominant role in the development of opiate addictions.

Psychostimulants have been shown to increase expression of the FosB and ΔFosB in the RMTg; the involvement in stimulant addiction and effects of ΔFosB expression in the RMTg have not yet been identified.