Projection neurons from the central nucleus of the amygdala to the nucleus pontis oralis.

The present retrograde labeling study was designed to determine the presence and pattern of projections from individual subdivisions of the central nucleus of the amygdala (CNA) to the nucleus pontis oralis (NPO), which is a critical brainstem site involved in the generation and maintenance of active (REM) sleep. Projections from the CNA were labeled with the retrograde tracer cholera toxin B-subunit (CTB), which was injected, unilaterally, via microiontophoresis, into the NPO. Sections of the amygdala were immunostained in order to identify CTB-labeled CNA neurons and CNA neurons that contained CTB plus the vesicular glutamate transporter 2 (VGLUT2), which is a marker for glutamatergic neurons. Histological analyses revealed that retrogradely labeled neurons that project to the NPO were localized, ipsilaterally, within the medial, lateral, and capsular subdivisions of the CNA. In addition, a substantial proportion (24%) of all retrogradely labeled CNA neurons also exhibited VGLUT2 immunoreactivity. The present study demonstrates that glutamatergic neurons, which are present within various subdivisions of the CNA, project directly to the NPO. These data lend credence to the hypothesis that NPO neurons that are involved in the control of active sleep are activated by glutamatergic projections from the amygdala.