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Am J Physiol Regul Integr Comp Physiol (May 26, 2005). doi:10.1152/ajpregu.00222.2005
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Submitted on March 29, 2005
Accepted on May 19, 2005

Differential Role of the Paraventricular Nucleus of the Hypothalamus in Modulating the Sympathoexcitatory Component of Peripheral and Central Chemoreflexes

Maram K Reddy1, Kaushik P Patel1, and Harold D Schultz1*

1 Cellular & Integrative Physiology, University of Nebraska Medical Center, Omaha, NE, USA

* To whom correspondence should be addressed. E-mail: hschultz{at}unmc.edu.

In the present study we investigated the involvement of hypothalamic paraventricular nucleus (PVN) in the modulation of sympathoexcitatory reflex activated by peripheral and central chemoreceptors. We measured arterial blood pressure (MAP), heart rate (HR), renal sympathetic nerve activity (RSNA) and phrenic nerve activity (PNA) before and after blocking neurotransmission within the PVN by bilateral microinjection of 2% lidocaine (100nl) during specific stimulation of peripheral chemoreceptors by potassium cyanide (KCN) (75 µg/kg, i.v.; bolus dose) or stimulation of central chemoreceptors with hypercapnia (10% CO2). Typically stimulation of peripheral chemoreceptors evoked a reflex response characterized by an increase in MAP, RSNA and PNA and decrease in HR. Bilateral microinjection of 2% lidocaine into the PVN had no effect on basal sympathetic and cardiorespiratory variables; however, the RSNA and PNA responses evoked by peripheral chemoreceptor stimulation were attenuated (P<0.05). Bilateral microinjection of bicuculline (50 pmoles/50 nl, n=5) into the PVN augmented the RSNA and PNA response to peripheral chemoreceptor stimulation (P<0.05). Conversely, the GABA agonist, muscimol (0.2 nmoles/50 nl, n=5) into the PVN attenuated these reflex responses (P<0.05). Blocking neurotransmission within the PVN had no effect on the hypercapnia-induced central chemoreflex responses in carotid body denervated animals. These results suggest a selective role of the PVN in processing the sympathoexcitatory and ventilatory component of the peripheral, but not central, chemoreflex.




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