Disinhibition of neurons of the nucleus of solitary tract that project to the superior salivatory nucleus causes choroidal vasodilation: Implications for mechanisms underlying choroidal baroregulation.
Preganglionic neurons in the superior salivatory nucleus (SSN) that mediate parasympathetic vasodilation of choroidal blood vessels receive a major excitatory input from the baroresponsive part of the nucleus of the solitary tract (NTS). This input appears likely to mediate choroidal vasodilation during systemic hypotension, which prevents decreases in choroidal blood flow (ChBF) due to reduced perfusion pressure. It is uncertain, however, how low blood pressure signals to NTS from the aortic depressor nerve (ADN), which fires at a low rate during systemic hypotension, could yield increased firing in the NTS output to SSN. The simplest hypothesis is that SSN-projecting NTS neurons are under the inhibitory control of ADN-receptive GABAergic NTS neurons. As part of evaluating this hypothesis, we assessed if SSN-projecting NTS neurons, in fact, receive prominent inhibitory input and if blocking GABAergic modulation of them increases ChBF. We found that SSN-projecting NTS neuronal perikarya identified by retrograde labeling are densely coated with GABAergic terminals, but lightly coated with excitatory terminals. We also found that, infusion of the GABA-A receptor antagonist GABAzine into NTS increased ChBF. Our results are consistent with the possibility that low blood pressure signals from the ADN produce vasodilation in choroid by causing diminished activity in ADN-receptive NTS neurons that tonically suppress SSN-projecting NTS neurons.
['Li|Chunyan|C|', 'Fitzgerald|Malinda E C|ME|', 'Del Mar|Nobel|N|', 'Reiner|Anton|A|']
D000818:Animals D001794:Blood Pressure D002829:Choroid D065828:Facial Nucleus D058787:GABA-A Receptor Antagonists D008297:Male D009474:Neurons D017729:Presynaptic Terminals D011724:Pyridazines D017207:Rats, Sprague-Dawley D012039:Regional Blood Flow D017552:Solitary Nucleus D014664:Vasodilation D005680:gamma-Aminobutyric Acid
Disinhibition Nucleus of solitary tract Superior salivatory nucleus Parasympathetic Choroidal blood flow Autonomic GABA