The Interpeduncular nucleus is thought to have a broad inhibitory effects on many other brain regions.

As the name suggests, the interpeduncular nucleus lies in between the cerebral peduncles.

The Interpeduncular nucleus is an unpaired, ovoid cell group at the base of the midbrain tegmentum.

Interpeduncular nucleus (brain region)

The presence of non-homologous subdivisions of the Interpeduncular nucleus was first noticed by Cajal over a hundred years ago.

The sites of action in the brain include the medial habenula, interpeduncular nucleus, dorsolateral tegmentum and basolateral amygdala.

Other axons arising from these cells descend through the medial forebrain bundle to terminate in a region dorsal to the interpeduncular nucleus.

The medial habenula sends outputs of substance P and acetylcholine to the interpeduncular nucleus as well as to the pineal gland.

By way of the fasciculus retroflexus (habenulointerpeduncular tract) it projects to the interpeduncular nucleus and other paramedian cell groups of the midbrain tegmentum.

The Interpeduncular nucleus is primarialy GABAergic and contains at least two neuron clusters of different morphologies.

The receptor is also widely distributed in the brain, including in the cortex, anterior olfactory nucleus, lateral septum, hypothalamus, hippocampus, amygdala, central gray, pontine nuclei, interpeduncular nucleus, substantia nigra, raphe complex, locus coeruleus, and spinal cord.

Most of the trigonum habenulæ's fibers are, however, directed downward and form a bundle, the fasciculus retroflexus of Meynert, which passes medial to the red nucleus, and, after decussating with the corresponding fasciculus of the opposite side, ends in the interpeduncular nucleus.

Moreover, in the midbrain of the rat those authors described NKA in the substantia nigra, the interpeduncular nucleus and the periaqueductal gray [ 29 ] , just as we found NK-ir structures in these nuclei of the human brainstem when using immunocytochemical techniques.

This pathway presents the IPN with several excitatory neurotransmitters including ACh and Substance P. Other brain regions that project to the Interpeduncular nucleus include: the Nucleus of diagonal band, the dorsal Tegmentum, the Raphe nuclei, the Central grey, and the Locus coeruleus.