The effects of nitric oxide (NO) and noradrenergic activation in the posterior hypothalamus on arterial pressure tolerance induced by subcutaneous injection of nitroglycerin (NTG) was investigated in anesthetized Sprague-Dawley rats. Intravenous injections of NTG (3, 10, and 30 microg/kg) and sodium nitroprusside (1, 3, and 10 microg/kg) produced dose-dependant decreases in arterial blood pressure. Tolerance to NTG was produced by subcutaneous administration of 4.0 mg of NTG as 4 separate hourly injections of 1.0 mg each, affecting the dose-dependent response of NTG IV injection. The 4 high-dose NTG pulse injections produced a marked shift in the dose-response curves for arterial pressure depression induced by intravenous injection of the challenge doses of NTG, but did not alter hypotensive responses to sodium nitroprusside. The tolerance responses to arterial pressure depression were enhanced by a bilateral microinjection of NTG (1 nmol) and by diethylamine NONOate (1 nmol), an NO donor, into the posterior hypothalamus. Bilateral microinjection of guanethidine (1.5 nmol), a noradrenergic blocker, into the posterior hypothalamus inhibits NTG tolerance in a period of time within 2 hours. We conclude that exogenous NO and noradrenergic activation in the posterior hypothalamus play an important role in arterial pressure tolerance to systemically administered NTG.

Numerous researchers have investigated the extent to which human listeners are able to localize free-field and virtual acoustic stimuli. Despite the abundance of this research, few studies have focused on the number of sounds a listener is able to localize simultaneously, and even fewer have employed naturally occurring or real-world sounds. Results from these types of experiments may have important implications at the basic research level within the fields of perception and attention, and may also prove useful for guiding the design of spatial audio displays in applied disciplines such as engineering and human factors. In the present study, listeners localized between one and three virtual acoustic stimuli, the positions of which were restricted to the horizontal plane under factorial combinations of seven spatial locations, three set sizes (one, two, or three sources), and three distinct acoustical sounds of a real-world nature (e.g., a crying baby). The paradigm employed required participants to monitor a set of simultaneously presented sounds and localize one specific sound when prompted. Performance was measured in terms of average localization error and percentages of front–back confusions. These results will be discussed in terms of their implication for the design of spatial audio interfaces for complex, multitask environments.

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