Noradrenergic α1, α2, and β1receptors mediate VNS-induced theta oscillations

Although vagal nerve stimulation (VNS) has been employed with success for almost four decades in many central nervous system disturbances, the physiological and pharmacological processes underlying this therapy are still unclear. Searching for central mechanisms of VNS is clinically limited. Hence, in many experiments, VNS technique is tested on the model of laboratory animals. In the present study we proceed with the experiments to verify some central effects of VNS. Specifically, we focussed on the hippocampal formation (HPC) noradrenergic profile which underlines the VNS-induced theta oscillations in anesthetized rats (Broncel et al., 2017; 2021). The effects of noradrenaline (NE) and selective noradrenergic α and β agonists and antagonists were tested in experiments organized in three stages. Initially, a nonspecific noradrenergic agonist, noradrenaline, was administrated. In the second stage, noradrenergic α and β agonists were applied. In the last stage, the administration of selected agonists was pretreated by specific antagonists. The results of the present study provide evidence that the selective activation of HPC α1, α2, and β1 noradrenergic receptors produce the inhibition of VNS-induced theta oscillations. Hippocampal β2 and β3 receptors were found not to be involved in the modulation of oscillations produced by the vagal nerve stimulation. The obtained outcomes are discussed in light of the effects of increased exogenous NE and induced release of endogenous NE.