Interpeduncular

Interpeduncular is an anatomical term used to describe structures located between the cerebral peduncles of the midbrain. It commonly refers to the interpeduncular fossa, a shallow ventral depression on the underside of the midbrain bounded laterally by the two cerebral peduncles, and to the interpeduncular nucleus, a midline group of neurons within the tegmentum near the floor of the third ventricle.

The interpeduncular fossa is a notable surface landmark on the ventral midbrain. On its upper part, cranial nerve III, the oculomotor nerve, emerges to supply most of the extraocular muscles. The fossa lies in a region where several vascular and neural structures traverse the ventral brainstem, and it serves as a reference point in neuroanatomical descriptions and imaging.

The interpeduncular nucleus (IPN) is a small, midline structure embedded in the tegmentum of the caudal midbrain. It forms part of the habenulo-interpeduncular system, receiving major input from the habenula via the fasciculus retroflexus and projecting to brainstem centers such as the raphe nuclei. Through these connections, the IPN is thought to participate in modulation of monoaminergic systems and in aversive learning and motivational processes, with relevance to nicotine dependence and related pathways.

Clinical relevance is often indirect but important. The interpeduncular region is adjacent to pathways involved in oculomotor control, so lesions or vascular lesions in this vicinity can affect CN III function. The term interpeduncular serves as a directional and locational descriptor in neuroanatomy, reflecting its position between the cerebral peduncles.