Effects Of The Central Microinjection Of Neuropeptide W On Amino Acids Concentration In Hypothalamic Paraventricular Nucleus In Conscious Rats

Neuropeptide W (NPW) is a novel peptide which produced by neurons in hypothalamus. Two endogenous molecular forms of NPW that consist of 23-and 30-amino acid residues were identified. The receptors of NPW are orphan G protein-coupled receptors, which are identified two subtypes:GPR7 and GPR8. It is found that the NPW receptors, NPW mRNA and NPW-like immunoreactive (NPW-LI) cell bodies are obviously expressed in the hypothalamus paraventricular nucleus (PVN). In addition, it is reported that NPW acts as neurotransmitter or neuromediator to regulate PVN neuronal activity, which involves in modulation of the hypothalamus-pituitary-adrenal (HPA) axis and sympathetic outflow, and affects cardiovascular activity. The previous studies suggested that central NPW modulates PVN neuronal activities, which might be involved in the regulation of cardiovascular function. However, the neurouchemical mechanisms of NPW involves in the central regulation of cardiovascular activity is not clear.Objective:To investigate the effects of introcerebroventricular (i.c.v) or hypothalamic PVN administration of NPW on the blood pressure, heart rate and the PVN amino acids concentration in conscious rats by microinjection, microdialysis and high-performance liquid chromatography methods.Methods:Male SD rats (350-450 g) were anesthetized by an intraperitoneal injection of chloral hydrate (50 mg/kg). Stainless-steel guide cannula and cerebroventricular cannula were implanted with a lateral cerebroventricular and PVN area for using microdialysis probes and microinjection needles. The animal emoral artery and vein were intubated for measuring heart rate and blood pressure.I.c.v or PVN administered NPW30 by microinjection. After collection of perfusion fluid by microdialysis, the amino acids concentrations were measured by high-performance liquid chromatography (HPLC). All data are expressed as mean±S.E.M., and statistical analyses were performed using ANOVA for repeated measurements followed by Bonferroni multiple comparison tests using Prism 5.0 software. P< 0.05 was considered statistically significantResults:(1) I.c.v administration of 3 nmol NPW30 (5 μl) induced increases in blood pressure and heart rate, which were significant higher than the values in baseline, control group and 0.3 nmol NPW30 (5μl) group, respectively (P< 0.05).(2) PVN administration of 3 nmol NPW30 (0.2μl) induced increases in blood pressure and heart rate, which were significant higher than the values in baseline, control group and 0.3 nmol NPW30 (0.2 μl) group, respectively (P< 0.05).(3) I.c.v administration of 3 nmol NPW30 (5 μl) induced increases in the extracellular levels of Glutamate (GIu), Aspartic acid (Asp), but expressed a decrease in extracellular levels of γ-aminobutyric acid (GABA) in the PVN region, which were significant differ from the values in baseline, control group and 0.3 nmol NPW30 (5 μl) group, respectively (P< 0.05).(4) I.c.v administration of 0.3 (5μl) nmol and 3 nmol (5μl) NPW30 did not change the extracellular levels of Taurine (Tau), Glycine (Gly), Glutamine (Gln), Alanine (Ala) in the PVN region, which were no significant differ from the values in baseline and control group, respectively (P>0.05).(5) PVN administration of 3 nmol NPW30 (0.2μl) induced increases in the extracellular levels of Glu, Asp and Gln, but expressed a decrease in extracellular levels of GAB A in the PVN region, which were significant differ from the values in baseline, control group and 0.3 nmol NPW30 (0.2 μl) group, respectively (P< 0.05).(6) PVN administration of 0.03 nmol (0.2 μl) nmol and 0.3 nmol (0.2 μl) NPW30 did not change the extracellular levels of Tau, Gly, and Ala in the PVN region, which were no significant differ from the values in baseline and control group, respectively (P>0.05).Conclusion:Central (I.c.v. and PVN) administration of NPW induced increases in the concentration of Glu, Asp, but decreased GAB A level, in the PVN region and accompanied by changes in cardiovascular activities, which suggests that NPW in PVN region might be involved in the regulation of cardiovascular function in part through neurotransmitters of the Glu, Asp and GABA in the PVN.