Viscerosensory input drives angiotensin II type 1A receptor expressing neurons in the solitary tract nucleus.

Homeostatic regulation of visceral organ function requires integrated processing of neural and neurohormonal sensory signals. The nucleus of the solitary tract (NTS) is the primary sensory nucleus for cranial visceral sensory afferents. Angiotensin II (Ang II) is known to modulate peripheral visceral reflexes, in part, by activating Ang II type 1A receptors (AT_1AR) in the NTS. AT_1AR-expressing NTS neurons occur throughout the NTS with a defined sub-nuclear distribution and most of these neurons are depolarized by Ang II. In this study we determined whether AT_1AR-expressing NTS neurons receive direct visceral sensory input, and whether this input is modulated by Ang II. Using AT_1AR-GFP mice to make targeted whole cell recordings from AT_1AR-expressing NTS neurons, we demonstrate that two thirds (37 of 56) of AT_1AR-expressing neurons receive direct excitatory, visceral sensory input. In half of the neurons tested (4 of 8) the excitatory visceral sensory input was significantly reduced by application of the transient receptor potential vallinoid type 1 receptor agonist, capsaicin, indicating AT_1AR-expressing neurons can receive either C or A-fibre mediated input. Application of Ang II to a subset of second order AT_1AR-expressing neurons did not affect spontaneous, evoked or asynchronous glutamate release from visceral sensory afferents. Thus it is unlikely that AT_1AR-expressing viscerosensory neurons terminate on AT_1AR-expressing NTS neurons. Our data suggest that Ang II is likely to modulate multiple visceral sensory modalities by altering the excitability of second order AT_1AR-expressing NTS neurons.

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