Cytoarchitecture and efferent projections of the nucleus incertus of the rat

Abstract

The nucleus incertus is located caudal to the dorsal raphe and medial to the dorsal tegmentum. It is composed of a pars compacta and a pars dissipata and contains acetylcholinesterase, glutamic acid decarboxylase, and cholecystokinin-positive somata. In the present study, anterograde tracer injections in the nucleus incertus resulted in terminal-like labeling in the perirhinal cortex and the dorsal endopyriform nucleus, the hippocampus, the medial septum diagonal band complex, lateral and triangular septum medial amygdala, the intralaminar thalamic nuclei, and the lateral habenula. The hypothalamus contained dense plexuses of fibers in the medial forebrain bundle that spread in nearly all nuclei. Labeling in the suprachiasmatic nucleus filled specifically the ventral half. In the midbrain, labeled fibers were observed in the interpeduncular nuclei, ventral tegmental area, periaqueductal gray, superior colliculus, pericentral inferior colliculus, pretectal area, the raphe nuclei, and the nucleus reticularis pontis oralis. Retrograde tracer injections were made in areas reached by anterogradely labeled fibers including the medial prefrontal cortex, hippocampus, amygdala, habenula, nucleus reuniens, superior colliculus, periaqueductal gray, and interpeduncular nuclei. All these injections gave rise to retrograde labeling in the nucleus incertus but not in the dorsal tegmental nucleus. These data led us to conclude that there is a system of ascending projections arising from the nucleus incertus to the median raphe, mammillary complex, hypothalamus, lateral habenula, nucleus reuniens, amygdala, entorhinal cortex, medial septum, and hippocampus. Many of the targets of the nucleus incertus were involved in arousal mechanisms including the synchronization and desynchronization of the theta rhythm.

Theta oscillations and sensorimotor performance

“…Changes in hippocampal theta rhythm have also been correlated with respiratory state changes in rodents (31). Thus, it is likely that the HPC theta rhythm during the sniffing period is influenced by and influences respiratory processes and other theta-related brainstem-limbic system projections (32,33). At the same time, afferent and centrifugal inputs drive a similar theta rhythm in the OB, producing a coherent signal by means of the common respiratory process.…”

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…Miscellaneous subcortical afferents of the perirhinal cortex include the nucleus incertus (Olucha-Bordonau et al, 2003) and the substantia innominata (Grove, 1988b). Miscellaneous subcortical efferents of the perirhinal cortex include the suprachiasmatic nucleus (Krout et al, 2002) and the substantia innominata (Grove, 1988a).…”

Central relaxin-3 receptor (RXFP3) activation reduces elevated, but not basal, anxiety-like behaviour in C57BL/6J mice

“…The largest population of relaxin-3 expressing neurons is located within the tegmental area known as the nucleus incertus (NI), and these neurons project broadly throughout the brain [15][16][17][18][19]. The neuroanatomy of the relaxin-3/RXFP3 system suggests a broad role as an ascending neuromodulatory network [20,21], akin to the monoamine systems including serotonin, and noradrenaline [22][23][24][25].…”