Online Seminar: Unconventional neurovascular coupling modality in the hypothalamus in response to a systemic homeostatic challenge
The supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus play critical roles in the regulation of bodily homeostasis, including the generation of coordinated neurosecretory and autonomic responses during challenges to fluid and electrolyte balance. In addition to major output neurons, including vasopressinergic (VP) and oxytocinergic (OT) magnocellular neurons, the SON and PVN also harbor a rich network of astroglial cells, and are some of the most vascularized regions in the brain. Still, a detailed characterization of the neurovascular unit within nuclei, and the functional significance of this uniquely rich vascularization remains puzzling.
The classical model of neurovascular coupling (NVC) implies that activity-dependent axonal glutamate release at synapses evokes the production and release of vasoactive signals from both neurons and astrocytes, which dilate arterioles, increasing in turn cerebral blood flow (CBF) to areas with increased metabolic needs. One limitation in the field is than In vivo imaging of neurovascular coupling has largely been limited to superficial brain areas, which has led to the conventional view that this modality of NVC is common to all brain regions. However, whether this model is also applicable to brain areas that also use less conventional neurotransmitters, such as neuropeptides, and which generally process information at a very different spatio-temporal scale, is currently unknown.
To start addressing some of these critical gaps in the field, we developed a surgical approach to allow in vivo two-photon imaging from the ventral surface of the brain. Using this approach, we aimed to measure NVC the SON in response to a systemic homeostatic challenge. Using a transgenic rat expressing eGFP driven by the vasopressin promoter, in conjunction with the delivery of intravascular fluorescent dyes, we were able to successfully image SON neurons and the local microvasculature in vivo in anesthetized rats. During my presentation, I will summarize the results obtained thus far using this novel approach, which overall support the presence of an unconventional NVC modality in the SON evoked by activity-dependent, local dendritic release of VP. Furthermore, I will discuss the potential functional implication for this form of NVC within the context of fluid/electrolyte homeostasis.
This seminar will be given online via Zoom. See attached poster for details.
