Journal of Neuroscience, Vol 14, 871-888, Copyright © 1994 by Society for Neuroscience
Emetic reflex arc revealed by expression of the immediate-early gene c- fos in the cat
AD Miller and DA Ruggiero
Rockefeller University, New York, New York 10021.
The organization of the central neuronal circuitry that produces vomiting
was explored by mapping the distribution of c-fos protein (Fos)-like
immunoreactivity (FLI) as a monitor of functional activity. The brainstem
and spinal cord were examined in cats administered multiple emetic drugs
(cisplatin, lobeline, protoveratrine, naloxone, apomorphine) or control
saline injections. Some animals were decerebrated, paralyzed, and
artificially ventilated to avoid possible Fos expression induced by sensory
feedback or fluid depletion during vomiting. Fictive vomiting was
identified in these animals by a characteristic pattern of respiratory
muscle nerve (phrenic and abdominal) coactivation. Tissues were
immunoprocessed using an antibody raised against amino acids 1-131 of Fos
and the avidin-biotin peroxidase complex method. Enhanced nuclear FLI was
observed in experimental animals along portions of the sensorimotor emetic
reflex arc, including the nodose ganglia, area postrema, nuclei of the
solitary tract (especially medial and subpostrema subnuclei), intermediate
reticular zone of the lateral tegmental field, nucleus retroambiguus, C2
inspiratory propriospinal cell region, and dorsal vagal and phrenic motor
nuclei. Enhanced FLI was also detected in the raphe magnus, subretrofacial
nucleus, and spinal dorsal horn. Regions showing no recognizable
differences in FLI between experimental and control animals included the
vestibular, cochlear, spinal trigeminal, subtrigeminal, and lateral
reticular nuclei. Only minor differences were observed in the distributions
of FLI between intact and decerebrate animals. No unique, well-defined
group of labeled neurons that might function as a "vomiting center" could
be identified. Instead, the pattern of c-fos expression suggests that
neurons involved in coordinating the emetic response may radiate from the
area postrema and nucleus of the solitary tract to an arc in the lateral
tegmental field implicated in somato-autonomic integration.
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