Galanin (GAL)‐immunoreactive (ir) axons closely appose parvalbumin (Parv)‐immunoreactive neurons in the rat ventral respiratory column (VRC)

Abstract

The neurochemistry of VRC neurons correlates with their function. Two‐thirds of large bulbospinal VRC neurons contain Parv and ~40% of chemosensitive neurons in the retrotrapezoid nucleus (RTN) contain GAL, which affects breathing when injected into the VRC. Here, we investigated whether GAL‐ir axons innervate Parv‐ir VRC neurons using double immunoperoxidase staining. In the VRC, GAL‐ir axons (black) closely apposed large Parv‐ir cell bodies (brown). We also identified two groups of black GAL‐ir somata. A rostral group occurred medial and ventral to the caudal end of the facial nucleus and are likely RTN neurons. A caudal group lay immediately ventral and slightly lateral to the column of Parv neurons, a location suggesting that some PreBötzinger (PreBöt) neurons might also be GAL‐ir. Since many PreBöt neurons contain the neurokinin‐1 receptor (NK1R), we double stained for GAL (brown) and NK1R (black). Some of the caudal GAL‐ir neurons were also NK1‐ir. These data suggest that GAL may influence respiration via PreBöt and/or RTN neurons releasing GAL onto Parv‐ir VRC neurons, which innervate spinal motor neurons that control respiratory pump muscles.Support: NH&MRC of Australia & NIH grant HL088580.