Evaluation of the neuronal activity and neuroanatomical characterization of purinergic circuitry in the hypothalamic and brainstem nuclei under hyperosmotic condition.

• Grant number: 23/04290-5
• Support Opportunities: Scholarships in Brazil - Master
• Start date: August 01, 2023
• End date: February 28, 2025
• Field of knowledge: Biological Sciences - Physiology - Physiology of Organs and Systems
• Principal Investigator: Vagner Roberto Antunes
• Grantee: Giovanna Arielle de Oliveira
• Host Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Among the cardiovascular diseases may be related to a high-salt diet, the neurogenic hypertension is one of them. Although there are many studies in this field, there are still gaps to fully understand the mechanisms involved in neurotransmission between hypothalamic and brainstem nuclei that participate in the neural control of circulation during hyperosmotic stimuli with salt loading. More than a decade ago, our laboratory published a succession of papers demonstrating that salt loading activates neurons of the paraventricular nucleus of the hypothalamus (PVN), in which the nucleotide adenosine triphosphate (ATP) is one of the neurotransmitters involved in neuronal excitability as part of the circuitry in the sympathoexcitatory leading to high blood pressure. Recently, our laboratory shows that one of the sources of ATP in the central nervous system is from the glial cells in PVN. Here we hypothesized that another source of ATP could be provide from the inputs of osmosensitive neurons located in the circumventricular organs, more specifically in the subfornical organ (SFO) and organum-vasculosum of lamina terminalis (OVLT), with monosynaptic connections with the PVN, and the later with connections with the rostral ventrolateral medulla (RVLM) where the pre-sympathetic neurons are located. To study neuronal connections involved in the hypothalamic-brainstem pathways and the involvement of ATP as a neurotransmitter during hyperosmotic stimulus, we will be using the murine experimental animal model (Wistar rats) divided into two cohorts: 1) GROUP 1 (SALT) which will receive an intravenous injection of 3M NaCl solution and GROUP 2 (CONTROL) injected with isotonic 0.9% NaCl solution. To analyze the neuronal connections between SFO/OVLT and the PVN we will inject a retrograde neuronal tracer (fluorogold - FG) in the PVN, and to study the connections between the PVN and the medulla, FG will be microinjected into the RVLM using the stereotactic surgery technique. In these same groups, neuronal activation with hyperosmotic stimulus will be evaluated by c-Fos protein expression combined with purinergic neuronal phenotype analysis subsequent to the presence of the vesicular nucleotide transporter (V-NUT) using the immunohistochemistry technique. We expect that neurons activated by hyperosmotic stimulation with salt loading have monosynaptic connections between SFO/OVLT - PVN - RVLM and that ATP participates in the neurotransmission among these nuclei that are part of the sympathetic autonomic circuitry involved in the neural control of circulation.