We found that the latency for find more the evoked PVN-RVLM depolarization was significantly longer when a prominent afterhyperpolarizing

potential (AHP) following the evoked bursts of action potentials was observed in the paired EGFP-VP neuron (n = 9; Figure 6B1), compared to neurons in which AHPs were absent (n = 6; Figure 6B2), or those in which a depolarizing afterpotential (DAP) was observed instead (n = 3; Figure 6D) (p < 0.001; Figure 6E). Moreover, a significant correlation between the EGFP-VP AHP duration and the PVN-RVLM latency was found (Pearson r = 0.89; p < 0.0001). The mean latency in paired recordings in which AHPs in EGFP-VP neurons were absent was similar to that observed following photolysis of caged NMDA (p > 0.3; see above), in which AHPs were not observed. In contrast to the effect on latency, the magnitude of the PVN-RVLM response was independent of the presence or

duration of an AHP in the stimulated EGFP-VP neurons (data not shown). Finally, to determine whether astrocytes participate Lapatinib research buy as intermediaries in the neurosecretory-presympathetic crosstalk, experiments were repeated following functional ablation of astrocytes with the selective gliotoxin L-aminoadipic acid (L-AAA; 250 μM, 30–60 min) (McBean, 1994 and Xu et al., 2008). Under this condition, stimulation of EGFP-VP neurons still efficiently evoked an excitatory response in PVN-RVLM neurons (p < 0.001, n = 5; (Figures 6D and 6F). In a few cases (n = 4) in which both neurons were intracellularly labeled with fluorescent dyes, segments of dendrites from the paired neurons were found in close proximity (12.5 ± 3.1 μm) (Figures 6G1–6G3). Our results demonstrate that evoked dendritic peptide release from an individual VP neuron can diffuse locally to affect the activity of a neighboring presympathetic neuron. We then tested whether the

basal average activity of the neurosecretory VP population as a whole was sufficient to generate a tonic-diffusing peptide pool, to continuously modulate presympathetic neuronal activity. Blockade of V1a receptors per se resulted in membrane hyperpolarization and inhibition of firing activity in presympathetic Non-specific serine/threonine protein kinase neurons (p < 0.001 and p < 0.01, respectively, n = 14; Figures 7A and 7B), unveiling the presence of a diffusible, tonic pool of VP. Conversely, the firing activity of EGFP-VP neurons was not affected (baseline, 2.2 ± 0.6 Hz; V1a antagonist, 2.2 ± 0.7 Hz; n = 5). To test whether the strength of the diffusible pool was dependent on the degree of activity of the VP population, we performed manipulations that either increased or decreased VP neuronal activity. The VP tone was enhanced by increasing extracellular K+ concentration (8.0 mM K+), as indicated by a more pronounced effect of the V1a antagonist in this condition, compared to normal K+ ACSF (p < 0.01; Figure 7D). Conversely, in the presence of the κ opioid receptor agonist U-50488 (1 μM), known to strongly inhibit VP neuronal activity (p < 0.01; Figure S7A; see also Brown et al.