Preautonomic neurones of the paraventricular nucleus of the hypothalamus receive inputs from the cardiovascular region of the nucleus tractus solitarius

The paraventricular nucleus of the hypothalamus (PVN) and nucleus tractus solitarius (NTS) are critical components of the neural circuit that regulate sympathetic nerve activity. The NTS projects to the PVN but there is no evidence to indicate this projection targets those preautonomic neurones in the PVN that regulate sympathetic activity. It is important to establish this as studies suggest elevated sympathetic nerve activity, strongly associated with cardiovascular disease including heart failure, is partly generated from the preautonomic neurones of the PVN. We used anterograde (Biotin dextran amine‐BDA) and retrograde (Fluorogold‐FG or cholera toxin subunit B‐CTB) labelling methods to identify the terminal neuronal targets of the ascending axonal projection from the NTS to the PVN. Ascending axons from the NTS coursed through and around the PVN nucleus. The NTS terminals showed numerous varicosities closely apposed to the somata and dendrites of the preautonomic neurones. This is the first demonstration that axonal fibres from the NTS target preautonomic neurones of the PVN. Functionally, this pathway can modulate the activity of the neurones controlling sympathetic outflow. This pathway may contribute to the generation of abnormal sympathetic activity by the PVN. Supported by the British Heart Foundation.