Glutamatergic activation of A1 and A2 noradrenergic neurons in the rat brain stem

AIM: To analyze the effects of glutamatergic agonists and antagonists on the activation of the A1 and A2 noradrenergic neurons localized in caudal ventrolateral medulla and nucleus tractus solitarii, respectively. METHODS: Rats were injected with glutamatergic agonists – kainic acid, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), or N-methyl-D-aspartic acid (NMDA), and the brain sections were prepared for immunohistochemistry. Before agonist injections, antagonists – 6-cyano-7-nitroquinoxaline-2,3-dione or dizocilpine were administered. The expression of c-Fos, as the neuronal activation marker, and tyrosine hydroxylase (TH), as the marker of noradrenergic neurons was assessed with dual immunohistochemistry. The percentage of c-Fos-positive noradrenergic neurons relative to all TH-positive neurons in the respective areas of the brain stem was calculated. RESULTS: All three glutamatergic agonists significantly increased the number of the c-Fos-positive noradrenergic neurons in both the A1 and A2 area when compared with control animals. Kainic acid injection activated about 57% of TH-positive neurons in A1 and 40% in A2, AMPA activated 26% in A1 and 38% in A2, and NMDA 77% in A1 and 22% in A2. The injections of appropriate glutamatergic antagonists greatly decreased the number of activated noradrenergic neurons. CONCLUSION: Our results suggest that noradrenergic neurons are regulated and/or activated by glutamatergic system and that these neurons express functional glutamate receptors.