Interactions Between Vasoactive Intestinal Polypeptide and Dopaminergic Neurons in the Mammalian Olfactory Bulb

In the olfactory bulb (OB), vasoactive intestinal polypeptide (VIP) neurons have a role in modulation of the interneuronal network. It has been known to be expressed in the granule cell layer (GCL), external plexiform layer (EPL), and the glomerular layer (GL). One of the functions of VIP in the OB is maintaining olfactory circadian rhythms (Miller et al., 2014). In the OB, dopaminergic (DA) neurons help process olfactory information through the release of dopamine (DA) onto the presynaptic terminals of olfactory sensory neurons and the dendrites of mitral and tufted (M/T) cells, leading to inhibition of transmitter release (Berkowicz and Trombley, 2000; Davila et al., 2003; Ennis et al., 2001). Tyrosine hydroxylase (TH), the rate-limiting enzyme in the metabolic production of DA, is present in all DA neurons and is used as a histological marker. TH is involved in producing L-DOPA from L-Tyrosine which then enables the production of DA. DA neurons appear to be restricted to a sub-population of neurons within the GL (see Nagayama et al., 2014 for review). The distribution of VIP is less clear and appears to vary among mammalian species. The aim of this project is to determine whether VIP and/or VIP receptors (VPAC2) co-localize with DA in the GL using a combination of immunohistochemistry and fluorescence microscopy. Although the data for VIP remain inconclusive, some cells may show co-labeling of both VPAC2 and TH in the GL suggesting that glomerular DA neurons may be a target of VIP.