Acute stimulation of vagus nerve modulates brain neurotrophins, and stimulates neuronal plasticity in the hippocampus of adult male rats

Abstract

The present study was aimed at evaluating whether single intermittent acute cervical vagus nerve stimulation (ACVS), pro-vided at a frequency which exhibits a clinical efficacy, may influence brain neurotrophins and hippocampal plasticity. With this purpose, the brain of adult male rats undergoing ACVS was used to analyze the expression of Nerve Growth Factor (NGF) and Brain-Derived Neurotrophic Factor (BDNF) in brain areas known to synthetize these growth factors, and the expression the neural cell adhesion molecule (NCAM), the synaptophysin (SYP) and biosynthetic GABA (GAD67) in the hippocampus. The effects of ACVS on NGF and BDNF protein and mRNA in hippocampus, hypothalamus and cortex two hours after stimulation were shown to be dependent on the frequencies of ACVS stimulation. Prolonged (three days post stimulation) modifications of NGF and BDNF were also observed in the hippocampus of ACVS rats. An early enhancement of the plasticity markers NCAM, SYP and GAD67 was also found in ACVS hippocampus. Three days after stimulation, NCAM and GAD67 levels were still higher than controls. Immunohistochemistry confirms the stimulatory effects of ACVS on GABA showing an increase in GAD67-positive cells in the dentate gyrus and CA3 hippocampal areas. This study shows that ACVS affects brain NGF and BDNF synthesis in a frequency-dependent manner. Neurotrophins changes are associated with increased hippocampal plasticity, as demonstrated by the observed molecular and morphological modifications. These findings support the role of brain neurotrophins in the ACVS mechanism of action.