PVH and Neuron Projections

It is widely accepted that the hypothalamus has neurons that are responsible for the regulation of arterial pressure. The PVH has known projects to the RVLM, which is a major brain stem region responsible for the regulation of sympathetic nerve activity. Furthermore, the PVH also has neuronal projections to the NTS which is paramount is receiving afferent inputs from the cardiovascular system and relaying vasomotor effects on the PVH and ultimately the RVLM. The NTS also has projections to presympathetic ganglionic neurons within the spinal cord that influence SNA and regulation cardiovascular function. The RVLM and NTS have been shown to have separate hypothalamic inputs however; no attempts have shown hypothalamic inputs to both structures. In this experiment by Badoer, they attempted to identify hypothalamic neurons having projections to functionally identified areas of the RVLM and NTS. Male Sprague Dawley rats were anesthetized and injected with tracers DY (diamidino yellow) and FB (fast blue). The animals were allowed to recover for 3-5 days for transport. Animals were sacrificed and the brains were sliced and studied using fluorescence microscopy. The results showed that numerus labeled neurons were shown to have projections to along the rostral-caudal axis of the hypothalamus. Most interestingly, the neurons in the hypothalamus had project to the RVLM and NTS were overlapping in the hypothalamus. Despite this finding, Badoer concludes that double labeled neurons were rare which would indicate that neurons from the hypothalamus to the RVLM and NTS have direct projections and influence to one or the other, not both. It does seem likely thought that both overlapping neurons that project to the RVLM or NTS may influence each other through synaptic contacts. Badoer also located neurons with the PVH that project to the NTS are found more ventral in the hypothalamus whereas projections to the RVLM were found more throughout the hypothalamus. Overall, this experiment by Badoer is critical in understanding neuronal projections to and from the hypothalamus to keep regions responsible for cardiovascular function.