The parabrachial nuclei (medial and lateral; visceral and gustatory) form some of the most important links between the BRAINSTEM and SPINAL CORD and the FOREBRAIN. The rich diversity of inputs and widespread efferent projections implicate the parabrachial nuclei in neural systems subserving and integrating GUSTATION, visceral and AUTONOMIC function and NOCICEPTION. The parabrachial nuclei consist of groups of cells located in the dorsolateral PONTINE TEGMENTUM, positioned medially and laterally adjacent to the SUPERIOR CEREBELLAR PEDUNCLE (BRACHIUM CONJUNCTIVUM) with which they are not, however, functionally related. Up to 12 distinct parabrachial sub-nuclei have been identified according to cell morphology, relationships to the superior cerebellar peduncle and neuroanatomical connectivity. The subnuclei receive specific afferent connections from many levels of the NEURAXIS and, in turn, send widespread ascending projections to the DIENCEPHALON and forebrain, and descending projections to the brainstem and spinal cord. Anatomical and physiological studies point to specific functions for individual sub-nuclei but substantial overlap and reciprocal connections also indicate that the parabrachial nuclei play integrative roles.
Gustatory regions of the rostral NUCLEUS OF THE SOLITARY TRACT project to the external medial, medial and ventral lateral sub-nuclei.
Respiratory and eardiovascular regions of the nucleus of the solitary tract project most strongly to the central lateral and external lateral sub-nuclei while cardiorespiratory regions of the ventrolateral medullary reticular formation are reciprocally connected with the KÖLLIKER-FUSE sub-nucleus. General visceral sensory (gastric) regions of the caudal nucleus of the solitary tract project to the dorsal lateral and central lateral sub-nuclei. The AREA POSTREMA, a circumventricular organ involved in body fluid HOMEOSTASIS and blood pressure regulation, projects rather discretely to the external lateral sub-nucleus. Nociceptive neurons in superficial and deeper laminae of the SPINAL CORD and DORSAL HORN of the MEDULLA send topographically organized projections to the superior lateral and external lateral sub-nuclei. The ascending projections of the various parabrachial sub-nuclei have functionally significant connections to gustatory regions of the THALAMUS, the ventromedial nucleus of the HYPOTHALAMUS, the central nucleus of the AMYGDALA, and the INSULA CORTEX and lateral FRONTAL CORTEX. These connections and physiological studies indicate that the parabrachial nucleus is involved in gustatory, cardiorespiratory and visceral functions as well as nociception. Thus, the parabrachial nuclei represent an important anatomical and functional link between gastric, visceral and nociceptive afferent signals that modulate or are important for autonomic components of emotion.
