Evidence for involvement of the lateral parabrachial nucleus in mediation of cholinergic inputs to neurons in the rostral ventrolateral medulla of the rat

We examined whether sites in the lateral parabrachial nucleus (PBN) where l-glutamate produced increases in arterial pressure were involved in mediation of cholinergic inputs to neurons in the rostral ventrolateral medulla (RVLM). Male Wistar rats were anesthetized, paralyzed and artificially ventilated. Unilateral microinjection of l-glutamate into the lateral PBN produced a pressor response. Microinjection of the muscarinic receptor antagonist scopolamine into the unilateral RVLM inhibited the pressor response to l-glutamate injected ipsilaterally into the lateral PBN, whereas microinjection of the cholinesterase inhibitor physostigmine into the RVLM enhanced it. PBN microinjection of l-glutamate also enhanced the firing rate of RVLM sympathoexcitatory neurons and the enhancement of the firing rate was inhibited by scopolamine iontophoretically applied on neurons. PBN injection of l-glutamate produced a tetrodotoxin (TTX)-sensitive release of ACh in the RVLM. Unilateral microinjection of TTX into the lateral PBN inhibited the pressor response induced by RVLM microinjection of physostigmine. These results provide evidence that neurons in the pressor sites of the lateral PBN are involved in mediation of cholinergic inputs responsible for pressor responses in the RVLM.