Effect of baseline MAP on cardiovascular responses elicited by microinjections of NMDA into the ARCN.

*<p>Significantly smaller compared with ‘†’ (P<0.01). **Significantly greater compared with ‘‡’ (P<0.01). ***Significantly greater compared with ‘§’ (P<0.05). ARCN, the hypothalamic arcuate nucleus; HR, heart rate (beats/min); MAP, mean arterial pressure, NMDA, N-methyl-D-aspartic acid (10 mM, 20 nl); SNP, sodium nitroprusside (150–300 µg/kg/hr).</p

Group data showing the effect of melanocortin receptor blockade in the PVN on ARCN responses.

<p>A: In barodenervated rats, microinjections of NMDA (10 mM, 20 nl) into the ARCN before the blockade of MC 3/4 receptors in the ipsilateral PVN by SHU9119 (open bar) elicited increases in MAP (n = 5). Microinjections of SHU9119 (2 mM, 30 nl) into the ipsilateral PVN elicited no changes in baseline MAP, GSNA or HR (not shown). Microinjections of NMDA (10 mM, 20 nl) into the ARCN after the blockade of MC 3/4 receptors in the ipsilateral PVN (dark bar) elicited smaller increases in MAP than those before microinjections of SHU9119 (**P<0.01). B: Increases in GSNA elicited by microinjections of NMDA into the ARCN were attenuated by the blockade of melanocortin 3/4 receptors in the PVN (*P<0.05). C: Increases in HR elicited by the ARCN stimulation were attenuated by the blockade of melanocortin 3/4 receptors in the PVN (*P<0.05).</p

Histological identification of microinjection sites in the ARCN.

<p>A: A typical microinjection site in the ARCN marked with green retrobeads IX (20 nl). B–D: Composite diagrams of ARCN sections at levels 2.40 mm (rostral region), 3.24 mm (middle region) and 3.84 mm (caudal region) showing microinjection sites (n = 21 rats); the coordinates mentioned below each drawing are caudal to the bregma. Each dark spot represents one microinjection site in one animal. Bar in panel A = 500 µm. DMN: the hypothalamic dorsomedial nucleus; ME: the hypothalamic median eminence; VMN: the hypothalamic ventromedial nucleus; 3V: the third ventricle.</p

Histological identification of microinjection sites in the ARCN.

<p>A: Microinjection site in the ARCN marked with green retrobeads IX (20 nl) (a typical site). B–D: Composite diagrams of ARCN sections at levels 3.12 mm, 3.60 mm and 3.84 mm caudal to the bregma showing microinjection sites (n = 11). Each dark spot represents one microinjection site in one animal. Calibration bar in panel A = 500 µm. Abbreviations: DMN, the hypothalamic dorsomedial nucleus; ME, the hypothalamic median eminence; PH, the posterior hypothalamic nucleus; VMN, the hypothalamic ventromedial nucleus; 3V, the third ventricle.</p

ARCN stimulation: effect of gabazine microinjections into the same nucleus.

<p>Bar graphs (n = 5) showing conversion of decreases in MAP and GSNA elicited by microinjections of NMDA into the ARCN to increases in MAP and GSNA (*P<0.01) following the blockade of GABA-A receptors in the same nucleus (A and B, respectively). Tachycardic responses elicited by the microinjections of NMDA into the ARCN were not altered significantly by the blockade of GABA-A receptors in the same nucleus (C). GSNA: greater splanchnic nerve activity.</p

ARCN stimulation: effect of GABA-A receptor blockade in the PVN.

<p>Bar graphs (n = 6) showing significant (*P<0.01) attenuation of depressor responses (A), but not tachycardic responses (B), elicited by microinjections of NMDA into the ARCN following the blockade of GABA-A receptors in the ipsilateral PVN. In this and other figure legends: ARCN, the hypothalamic arcuate nucleus; GABA, gamma-aminobutyric acid; HR, heart rate (beats/min); MAP, mean arterial pressure (mmHg); NMDA, N-methyl-D-aspartic acid; PVN, the hypothalamic paraventricular nucleus; Gabazine, GABA-A receptor antagonist.</p

Identification of GAD67, NPY and beta-endorphin immunoreactive ARCN cells retrogradely labeled from the PVN.

<p>A: Retrogradely labeled neurons in the ARCN after unilateral microinjection (30 nl) of green retrobeads IX into the ipsilateral PVN. B: GAD67 immunoreactive neurons in the section shown in A. C: The merged images of A and B indicated that some retrogradely labeled cells in the ARCN contained GAD67 (white arrows). D: ARCN neurons retrogradely labeled from PVN (different rat). E: NPY immunoreactive neurons in the section shown in D. F: The merged images of D and E indicated that some retrogradely labeled cells in the ARCN contained NPY (white arrows). G: ARCN neurons retrogradely labeled from PVN (different rat). H: Beta-endorphin immunoreactive neurons in the section shown in G. I: The merged images of G and H indicated that some retrogradely labeled cells in the ARCN contained beta-endorphin (white arrows). GAD67: glutamic acid decarboxylase 67.</p

Group data showing the effect of barodenervation on ARCN responses.

<p>A: Microinjections of NMDA (10 mM, 20 nl) into the ARCN before barodenervation (open bars) elicited decreases in MAP (n = 5). Bilateral barodenervation elicited increases in baseline MAP, GSNA and HR (not shown) which lasted for 60 min. When baseline MAP was completely recovered, microinjections of NMDA (10 mM, 20 nl) into the ARCN after barodenervation (dark bars) elicited increases in MAP (**P<0.01). B: Decreases in GSNA elicited by microinjections of NMDA into the ARCN were converted to increases in GSNA by barodenervation (**P<0.01). C: Increases in HR elicited by the ARCN stimulation were exaggerated by barodenervation (*P<0.05).</p

ARCN stimulation: effect of opioid receptor blockade in the PVN.

<p>Bar graphs (n = 5) showing significant (*P<0.05) attenuation of depressor responses (A), but not tachycardic responses (B), elicited by microinjections of NMDA into the ARCN following the blockade of opioid receptors in the ipsilateral PVN. Naloxone: opioid receptor antagonist.</p

ARCN stimulation: data showing effect of GABA-A, NPY1 and opioid receptor blockade in the PVN.

<p>Bar graphs (n = 6) showing conversion of decreases in MAP and GSNA elicited by microinjections of NMDA into the ARCN to increases in MAP and GSNA (*P<0.01) following the combined blockade of GABA-A, NPY1 and opioid receptors in the ipsilateral PVN (A and B, respectively). Tachycardic responses elicited by the microinjections of NMDA into the ARCN were not altered significantly by the combined blockade of these receptors in the PVN (C).</p