Cerebrovascular alterations in mice lacking neuronal nitric oxide synthase gene expression

Area of Science:

• Neuroscience
• Physiology
• Cardiovascular Research

Background:

• Nitric oxide (NO) plays a key role in regulating regional cerebral blood flow (CBF).
• CO2 inhalation is a well-established method to increase CBF, with NO implicated in this response.
• Neuronal nitric oxide synthase (nNOS) is a primary source of NO in the brain.

Purpose of the Study:

• To investigate the role of neuronal nitric oxide synthase (nNOS) in mediating the cerebral blood flow (CBF) response to CO2 inhalation.
• To determine if the CBF response to CO2 is dependent on NO produced by nNOS.
• To explore potential compensatory mechanisms in the absence of nNOS.

Main Methods:

• Utilized knockout mice lacking the gene for neuronal nitric oxide synthase (nNOS).
• Measured regional cerebral blood flow changes in response to CO2 inhalation.
• Administered NOS inhibitor (N omega-nitro-L-arginine) and assessed cGMP levels.
• Evaluated endothelial NOS (eNOS) function using topical acetylcholine administration and immunohistochemistry.

Main Results:

• CO2 inhalation increased cerebral blood flow to a similar extent in both nNOS knockout and wild-type mice.
• The CO2-induced increase in CBF in nNOS knockout mice was not inhibited by NOS inhibition.
• CO2 exposure did not elevate brain cGMP levels in nNOS knockout mice.
• Endothelial NOS (eNOS) function remained intact in nNOS knockout mice, as evidenced by acetylcholine-induced vasodilation.

Conclusions:

• The cerebral circulatory response to CO2 inhalation is maintained independently of nitric oxide (NO) produced by neuronal nitric oxide synthase (nNOS).
• A compensatory mechanism, not involving NO, preserves the cerebral blood flow increase during hypercapnia in the absence of nNOS.
• Endothelial NOS (eNOS) function is not responsible for the NO-independent CBF regulation observed in this study.