Chemical stimulation of the laryngopharynx increases Fos-like immunoreactivity in the rat hypothalamus and amygdala.

Using immunohistochemical detection of the Fos protein as a cellular marker of neuronal activation, we examined forebrain areas that may be activated upon chemical stimulation of the laryngeal opening. Anesthetized rats were subject to multiple infusions of a chemical solution into the laryngopharynx. These animals were compared to two control groups: a surgical control group in which the animals were subject to the surgical procedure but received no stimulus infusions and a flow control group in which physiological saline replaced the chemical stimulus. Comparing the numbers of Fos-like-immunoreactive neurons in regions of the forebrain across groups revealed that infusing the chemical stimulus solution into the laryngopharyngeal opening selectively increased the number of Fos-like-immunoreactive nuclei in the paraventricular nucleus of the hypothalamus and the central nucleus of the amygdala, two autonomic-visceral related forebrain regions. Within the paraventricular nucleus of the hypothalamus, Fos-like-immunoreactive nuclei were significantly increased in the parvocellular subdivision while in the central nucleus of the amygdala, significant increases in Fos-like-immunoreactive nuclei were limited to the lateral capsular subdivision. These data suggest that in the rat laryngopharyngeal chemosensory stimulation activates forebrain regions that receive oral sensory information and are involved in visceral and autonomic functions.