The Parabrachial Nucleus: CGRP Neurons Function as a General Alarm

The PBN relays sensory information to the forebrain. Some functions of a few genetically identified PBN neurons have been delineated. CGRPPBN neurons relay a wide variety of aversive signals (e.g., food poisoning, pain, itch, and hypercapnia) to the central nucleus of the amygdala, the bed nucleus of the stria terminalis, and other brain regions. Activation of CGRPPBN neurons is necessary and sufficient to establish robust foot-shock and taste memories. Chronic activation of CGRPPBN neurons can lead to severe anorexia and starvation. Other PBN neurons transmit taste, temperature, respiratory, satiety, thirst, salt-appetite, or glucose counter-regulatory signals. The parabrachial nucleus (PBN), which is located in the pons and is dissected by one of the major cerebellar output tracks, is known to relay sensory information (visceral malaise, taste, temperature, pain, itch) to forebrain structures including the thalamus, hypothalamus, and extended amygdala. The availability of mouse lines expressing Cre recombinase selectively in subsets of PBN neurons and viruses for Cre-dependent gene expression is beginning to reveal the connectivity and functions of PBN component neurons. This review focuses on PBN neurons expressing calcitonin gene-related peptide (CGRPPBN) that play a major role in regulating appetite and transmitting real or potential threat signals to the extended amygdala. The functions of other specific PBN neuronal populations are also discussed. This review aims to encourage investigation of the numerous unanswered questions that are becoming accessible. The parabrachial nucleus (PBN), which is located in the pons and is dissected by one of the major cerebellar output tracks, is known to relay sensory information (visceral malaise, taste, temperature, pain, itch) to forebrain structures including the thalamus, hypothalamus, and extended amygdala. The availability of mouse lines expressing Cre recombinase selectively in subsets of PBN neurons and viruses for Cre-dependent gene expression is beginning to reveal the connectivity and functions of PBN component neurons. This review focuses on PBN neurons expressing calcitonin gene-related peptide (CGRPPBN) that play a major role in regulating appetite and transmitting real or potential threat signals to the extended amygdala. The functions of other specific PBN neuronal populations are also discussed. This review aims to encourage investigation of the numerous unanswered questions that are becoming accessible.