Functional evidence of paraventricular nucleus involvement in cardiovascular and autonomic modulation in response to acute microgravity (head‐down tilt) in unanesthetized rats

Abstract

Exposure to microgravity induces autonomic and vestibular disorders such as alterations in cardiovascular function. The paraventricular nucleus of the hypothalamus (PVN) is known to be an important center for integrating autonomic and cardiovascular responses as blood volume reflexes. The acute effects promoted by microgravity and PVN involvement in cardiovascular and autonomic parameters have not yet been evaluated. Male Wistar rats were anesthetized to facilitate cannulae implantation in the PVN. After 3 days of surgical recovery, femoral artery and vein catheters were implanted for direct recording of blood pressure and heart rate (HR) in conscious animals to evaluate cardiovascular and autonomic changes in an acute protocol of head-down tilt (HDT) in nonanesthetized rats. During HDT, there was an increase in mean arterial pressure (11 ± 1 mmHg, P < 0.05) and a decrease in HR (-28 ± 5 bpm, P < 0.05). Spectral analysis of systolic arterial pressure showed an increase in the low-frequency (LF) component. In addition, HDT induced a reduction in the LF component and an increase in the high-frequency (HF) component of the pulse interval (PI). PVN inhibition with muscimol reversed bradycardia and blocked the reduction of the LF and HF increases in PI during HDT. These results suggest that the PVN participates in the cardiovascular compensation during HDT, especially modulating cardiac responses.

Glutamate and GABA neurotransmission are increased in paraventricular nucleus of hypothalamus in rats induced to 6‐OHDA parkinsonism: Involvement of nNOS

“…However, our unprecedented data was that bicuculline administered in the PVN of the 6‐OHDA group resulted in a higher increase of those parameters, suggesting an increase in the inhibitory tonic activity by the PVN in Parkinsonism. The microinjection of muscimol in the PVN did not promote cardiovascular changes in the sham groups, which agrees with previously published studies, and the same occurred with the 6‐OHDA group. Although studies have shown that PVN blockade with muscimol reduces MAP (Hassan et al, 2013) and HR under baseline and during pathological conditions .…”

“…We also performed unilateral microinjections of Nw‐Propyl‐L‐Arginine (N‐Propyl, 4 nmol/100 nL). The methodology for microinjection is in accordance with a previous study . It was performed one microinjection in each side of the PVN.…”

“…The chemicals were obtained from Sigma‐Aldrich. The functional identification of the PVN was performed by microinjecting bicuculline (1 mmol/L/100 nL) at the end of experimental protocols, according with previous work …”

“…After Evans blue dye (2%) microinjection in the PVN and decapitation, the hypothalamus was removed for histological identification of the injection sites, as previously described …”

Feeding-induced hepatokines and crosstalk with multi-organ: A novel therapeutic target for Type 2 diabetes

“…In addition, adropin may exert its physiological effects by acting directly on neurons in the PVN (165). PVN is a key autonomic control center that plays an important role in the regulation of fluid balance (166), energy homeostasis (167), and cardiovascular regulation (168). These findings further solidify that Adropin has an endocrine function as a hepatokine and provide the framework needed to link its peripheral effects to its role in the central nervous system.…”