Brain-derived neurotrophic factor acts at neurons of the subfornical organ to influence cardiovascular function

Brain-derived neurotrophic factor (BDNF), a neurotrophin traditionally associated with neural plasticity, has more recently been implicated in fluid balance and cardiovascular regulation. It is abundantly expressed in both the central nervous system (CNS) and peripheral tissue, and is also found in circulation. Studies suggest that circulating BDNF may influence the CNS through actions at the subfornical organ (SFO), a circumventricular organ (CVO) characterized by the lack of a normal blood-brain barrier (BBB). The SFO, well-known for its involvement in cardiovascular regulation, has been shown to express BDNF mRNA and mRNA for the TrkB receptor at which BDNF preferentially binds. This study was undertaken to determine if: (1) BDNF influences the excitability of SFO neurons in vitro; and (2) the cardiovascular consequences of direct administration of BDNF into the SFO of anesthetized rats. Electrophysiological studies revealed that bath application of BDNF (1 nmol/L) influenced the excitability of the majority of neurons (60%, n = 13/22), the majority of which exhibited a membrane depolarization (13.8 ± 2.5 mV, n = 9) with the remaining affected cells exhibiting hyperpolarizations (-11.1 ± 2.3 mV, n = 4). BDNF microinjections into the SFO of anesthetized rats caused a significant decrease in blood pressure (mean [area under the curve] AUC = -364.4 ± 89.0 mmHg × sec, n = 5) with no effects on heart rate (mean AUC = -12.2 ± 3.4, n = 5). Together these observations suggest the SFO to be a CNS site at which circulating BDNF could exert its effects on cardiovascular regulation.