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C. Li, M. E. C. Fitzgerald, S. L. Cuthbertson, M. S. LeDoux, A. Reiner; Neural Regulation of Choroidal Blood Flow May Involve a Paraventricular Nucleus Projection to the Superior Salivatory Nucleus. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2262.
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The vasodilatory response of the choroid in the eye is mediated by parasympathetic input from pterygopalatine ganglion (PPG), which receives preganglionic input from the superior salivatory nucleus (SSN) of the facial motor complex. As part of an effort to understand the role of SSN-mediated choroidal blood flow (ChBF) control, we sought to determine the higher order neural structures involved in its regulation of ChBF.
We used transneuronal retrograde and anterograde pathway tracing methods, the latter in conjunction with nitric oxide synthase (NOS) immunolabeling. For the transneuronal retrograde study, pseudo-rabies virus (PRV) was injected into the choroid of 10 rats, followed by post-injection transport intervals of 65-87 hours. Immunostaining was used to visualize the PRV. For anterograde labeling, injections (by pressure or iontophoresis) of 10K biotinylated dextran amine (BDA10K) were made into the paraventricular nucleus (PVN) of six rats in order to determine the efferent projections from PVN.
In addition to PRV+ neurons in SSN, PRV+ neurons were observed in dorsal and lateral PVN, in its parvocellular subdivision. Anterograde labeling with BDA10K from PVN confirmed that it projects directly to the part of SSN containing neurons that control the choroid. Using NOS+ neurons as a marker of choroidal SSN (as per Cuthbertson et al., 2003), BDA10K+ terminals arising from PVN were observed to overlap the SSN field of NOS+ neurons, as judged from adjacent single-labeled sections. More direct evidence was obtained by labeling NOS+ neurons with a brown diaminobenzidine tetrahydrochloride (DAB) reaction and BDA10K+ fibers with a nickel-intensified black DAB. The double-labeled tissue showed choroidal SSN receives a highly selective input from PVN. In SSN, NOS+ cells were contacted by BDA10K+ positive boutons, with an individual axon giving rise to boutons contacting many neurons and individual SSN neurons receiving boutons from multiple axons.
The parvocellular part of the hypothalamic PVN selectively innervates, within SSN, the part that controls choroidal blood flow. These findings suggest a role of the PVN in the regulation of choroidal blood flow, such as in the compensatory vasodilation observed in the choroid during systemic hypotension.
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