Abstract
Purpose: :
We have been using intrachoroidal injection of pseudorabies virus (PRV) to identify the central neuronal cell groups involved in parasympathetic regulation of choroidal blood flow via the pterygopalatine ganglion (PPG). Due to our interest in the possible role of parts of this circuit in compensatory choroidal vasodilation to diminished systemic blood pressure, we compared in detail the distribution of neurons labeled after intrachoroidal PRV injection to those activated by systemic hypotension (as assessed by cfos immunolabeling).
Methods: :
In some rats, PRV was injected into the right choroid. After a post-injection period of about 70 hours, fixed brains were sectioned and immunostained with goat anti-PRV. Other rats were subjected to 1-3 hrs of hypotension by blood withdrawal, and their fixed brains were sectioned and immunostained with anti-cfos. Brains from control rats not subjected to hypotension were also immunostained for cfos.
Results: :
A pool of neurons within the superior salivatory nucleus (SSN), which projects to the PPG, were labeled after intrachoroidal PRV. Higher order PRV labeling was also observed in diverse nuclei of the forebrain such as the suprachiasmatic nucleus (SCN) and paraventricular nucleus (PVN), of the midbrain such as the ventral tegmental area (VTA) and central gray, and hindbrain such as the parabrachial complex, locus coeruleus, raphe magnus and the nucleus of the solitary tract (NTS). Among the various PRV+ cell groups, notable cfos induction by hypotension was observed in the SSN, PVN, the central gray, the parabrachial complex, the raphe magnus, and the NTS. Within SSN, the location of the hypotension-responsive neurons corresponded precisely to the location of the prechoroidal neurons of SSN. Within PVN, nearly all neurons showed cfos induction, including in its caudal part that was most enriched in choroidal circuit PRV+ neurons. Finally, within NTS, PRV+ neurons and cfos+ neurons were both localized within the caudodorsal part of NTS that it is known to receive baroreceptive input (Ciriello, Neurosci Lett 1983).
Conclusions: :
The SSN and several of its major afferent cell groups respond to systemic hypotension. These findings are consistent with the notion that the SSN-PPG input to the choroid may play a role in compensatory choroidal vasodilation in response to diminished systemic blood pressure.
Keywords: choroid • anatomy • neurotransmitters/neurotransmitter systems