Rostromedial tegmental nucleus

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 dopaminergic neuronal activity in the central nervous system by endogenous opioids and opiate drugs. The GABAergic neurons that project from the RMTg to the midbrain dopaminergic nuclei (i.e., the ventral tegmental area and substantia nigra pars compacta) express μ-opioid receptors. Current evidence suggests that exogenous opiates (e.g., morphine and heroin) excite the 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 the dopaminergic pathways that are implicated in addiction (e.g., the mesolimbic pathway), the RMTg plays a significant role in the development of opiate addictions.

Psychostimulants have been shown to increase expression of the FosB and ΔFosB in the RMTg; as of 2012, the effects of stimulant-induced increases in ΔFosB expression in the RMTg are not known.