[PubMed] [Google Scholar] 36. HTS-evoked increases of integrated sSNA and PNA ( 0.001) and attenuated the accompanying pressor response ( 0.01). Blockade of PVN NMDA receptors with d-(2= 6) had similar effects. Analysis of respiratory rhythmic bursting of sSNA revealed that ICA HTS increased mean voltage TNR ( 0.001) without affecting the amplitude of inspiratory or expiratory bursts. Analysis of cardiac rhythmic sSNA likewise revealed that ICA HTS increased mean voltage. Cardiac rhythmic sSNA oscillation amplitude was also increased, which is consistent with activation of arterial baroreceptor during the accompanying pressor response. Increased mean sSNA voltage by HTS was blocked by prior PVN inhibition (muscimol) and blockade of PVN NMDA receptors (AP5). We conclude that even acute glutamatergic activation of PVN (i.e., by hypertonicity) is PEG3-O-CH2COOH sufficient to selectively increase a tonic component of vasomotor SNA. = 6) were used to determine contributions of PVN neuronal activity and NMDA receptors in mediating responses to ICA HTS. Neuronal inhibition was achieved by microinjecting the long-acting GABAA receptor agonist muscimol (100 pmol/side; Sigma). Blockade of NMDA receptors was achieved with the selective antagonist AP5 (6 nmol/side; Sigma). Drugs were injected 20 min prior to infusion of HTS, as previously described (14, 42). Briefly, rats were placed in a stereotaxic frame, and the skull was leveled between bregma and lambda. A midline craniotomy was performed and a single-barreled glass micropipette (tip: 50 m OD) was lowered into the PVN bilaterally at the following coordinates with respect to bregma (in mm): AP: ?1.8C2.1, ML: 0.2C0.4, DV: ?7.5 from dura. Drugs were dissolved in artificial cerebrospinal fluid and delivered in a volume of 50 nl using a pneumatic picopump (World Precison Instruments). Each injection was made over 20C30 s, first on one side of the PVN and then around the other. Injections were separated by 2C3 min, and sites were marked by including 0.2% rhodamine beads in the injected solution. Histology At the end of experiments, rats received an overdose of -chloralose-urethane, and the brains were removed, postfixed in 4% paraformaldehyde for 24C48 h, cryoprotected in 30% sucrose-PBS, and sectioned at 50 m with a freezing microtome. Injection sites were identified by mapping the outermost distribution of fluorescent beads onto plates of a standard stereotaxic atlas. Images from comparable rostrocaudal levels of PVN from all subjects within each treatment group were overlaid so that the outermost distribution of beads represents an overestimate of the range of injection sites within each group. Hematology Hematocrit (Hct) was measured from duplicate capillary tubes using a Lancer microhematocrit reader (Brunswick). Plasma osmolality (PosM) was decided from the average of duplicate plasma samples using a freezing-point depressive disorder osmometer (model 3320; Advanced Instruments). Refractometry (VWR International) was used to determine plasma protein concentration (Pprotein). Data Analysis Values of sSNA, PNA, and MAP were quantified from 5-min segments of stable data immediately before and 15 min after PVN injections. Effects of ICA ITS and HTS were quantified during the last 5 min of infusion, while recorded variables were stable. PEG3-O-CH2COOH Values of sSNA are expressed in microvolt units (V) decided after subtracting voltage due to noise, which was decided from a 3-min average of signal remaining 5 min after administration of hexamethonium. MAP was calculated as the sum of the average diastolic pressure and one-third of the average pulse pressure. Respiratory rhythmic sSNA was quantified from averages constructed using the onset of 150 consecutive phrenic nerve bursts as trigger events. Averages generated before and 15 min after PVN injection of muscimol or AP5 were compared to assess the influence of ongoing PVN neuronal discharge or NMDA receptor activity to sSNA bursting. These were compared, as appropriate, with averages PEG3-O-CH2COOH generated during the stable period of response to ICA infusion of ITS or HTS. Each sSNA average consisted of a 0.3-s pretrigger and 1.6-s posttrigger period. The posttrigger period was chosen to be equal to the average respiratory cycle duration across all experiments. Respiratory rhythmic sSNA oscillation amplitudes were calculated as the difference between the mean voltage of the brought on average and the posttrigger peaks or trough (Fig. 2=.