Intrathecal kynurenate but not benextramine blocks hypoxic sympathoexcitation in chemodenervated anesthetized rats.

In peripherally chemodenervated anesthetized and ventilated rats, inhalation of 100% N2 for 20 s rapidly excites reticulospinal vasomotor neurons of the rostroventrolateral reticular nucleus (RVL) and sympathetic nerves. After an initial fall, arterial pressure is also elevated. The sympathoexcitatory response and secondary increases in arterial pressure were abolished by microinjections of muscimol (250 pmol) into the RVL or by intrathecal administration of kynurenate (500 nmol), a broad-spectrum antagonist of excitatory amino acid receptors, but not by benextramine, an alpha-adrenoceptor antagonist. The results indicate that excitation of pre-ganglionic sympathetic neurons in the spinal cord by hypoxia results from excitation of RVL-spinal vasomotor neurons, probably the glutamatergic neurons.