Expression of nischarin, an imidazoline 1 receptor candidate protein, in the ventrolateral medulla of newborn rats

Abstract

The activation of imidazoline 1 (I₁) receptors is suggested to stimulate the respiratory drive in newborn rats. Here, we immunohistochemically examined whether nischarin, an I₁ receptor candidate protein, is expressed in the ventrolateral medulla, where cardiorespiratory centers are located. Newborn rats (age, 3-5 days) were deeply anesthetized with isoflurane; the brainstem was dissected, sectioned sagittally, and labeled with nischarin. Nischarin-associated signals were observed broadly throughout the newborn rat brainstem, including at motor nuclei (motor trigeminal nucleus and facial nucleus), sensory nuclei (lateral superior olive, medial and spinal vestibular nuclei, cuneate nucleus, spinal trigeminal nucleus, and solitary nucleus), and the rostral and caudal ventrolateral medullar regions. In particular, the rostral ventrolateral medulla included a layer of aggregated nischarin expression along the ventral surface, and the layer was in close contact with GFAP-positive processes. In addition, some Phox2b-positive neurons were positive for nischarin in the region. Our results reveal nischarin expression in the newborn rat brainstem and suggest that I₁ receptor activation at the level of the ventrolateral medulla contributes to central chemoreception and respiratory control in newborn rats.

Keywords: Immunohistochemistry; Parafacial respiratory group/retrotrapezoid nucleus; Respiratory control; Retrotrapezoid nucleus.