MilliporeSigma
  • Home
  • Search Results
  • Spontaneously hypertensive rats have more orexin neurons in their medial hypothalamus than normotensive rats.

Spontaneously hypertensive rats have more orexin neurons in their medial hypothalamus than normotensive rats.

Experimental physiology (2015-02-03)
Liam Clifford, Bruno W Dampney, Pascal Carrive
ABSTRACT

What is the central question of this study? Blockade of orexin receptors reduces blood pressure in spontaneously hypertensive rats (SHRs) but not in normotensive Wistar-Kyoto (WKY) rats, suggesting that upregulation of orexin signalling underlies the hypertensive phenotype of the SHR. However, it is not known what causes this upregulation. What is the main finding and its importance? Using orexin immunolabelling, we show that SHRs have 20% more orexin neurons than normotensive WKY and Wistar rats in the medial hypothalamus, which is a good match to their blood pressure phenotype. In contrast, there is no such match for the orexin neurons of the lateral hypothalamus. Essential hypertension may be linked to an increase in orexin neurons in the medial hypothalamus. The neuropeptide orexin contributes to the regulation of blood pressure as part of its role in the control of arousal during wakefulness and motivated behaviour (including responses to psychological stress). Recent work shows that pharmacological blockade of orexin receptors reduces blood pressure in spontaneously hypertensive rats (SHRs) but not in normotensive Wistar-Kyoto (WKY) rats. It is not clear why orexin signalling is upregulated in the SHR, but one possibility is that these animals have more orexin neurons than their normotensive WKY and Wistar relatives. To test this possibility, SHRs, WKY and Wistar male rats (6-16 weeks old) were killed, perfused and their brains sectioned and immunolabelled for orexin A. Labelled neurons were plotted and counted in the six best labelled hemisections (120 μm apart) of each brain. There were significantly more orexin neurons (+20%) in the medial hypothalamus (medial to fornix) of SHRs compared with WKY and Wistar rats (126 ± 4 versus 106 ± 5 and 104 ± 5 per hemisection, respectively, P < 0.05), which matches well the blood pressure phenotypes. In contrast, counts in the lateral hypothalamus did not match the blood pressure phenotypes (69 ± 2 versus 50 ± 3 and 76 ± 4, respectively). The results support the idea that orexin signalling is upregulated in the SHR and suggest that this is due, at least in part, to a greater number of orexin neurons in the medial hypothalamus. These medial orexin neurons, which are also involved in hyperarousal and stress responses, may contribute to the development of essential hypertension.

MATERIALS
Product Number
Brand
Product Description

Supelco
Dehydrated Alcohol, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
Ethanol solution, certified reference material, 2000 μg/mL in methanol
Supelco
Hydrogen peroxide solution, 30 % (w/w), for ultratrace analysis
Sigma-Aldrich
Hydrogen peroxide solution, contains potassium stannate as inhibitor, 30-32 wt. % in water, semiconductor grade, 99.999% trace metals basis
Sigma-Aldrich
Ethanol Fixative 80% v/v, suitable for fixing solution (blood films)
Supelco
Ethanol standards 10% (v/v), 10 % (v/v) in H2O, analytical standard
Sigma-Aldrich
Hydrogen peroxide solution, tested according to Ph. Eur.
Supelco
Hydrogen peroxide solution, ≥30%, for trace analysis
Sigma-Aldrich
Hydrogen peroxide solution, 34.5-36.5%
Millipore
Hydrogen peroxide solution, 3%, suitable for microbiology
Sigma-Aldrich
Hydrogen peroxide solution, 30 % (w/w) in H2O, contains stabilizer
Sigma-Aldrich
Hydrogen peroxide solution, contains inhibitor, 30 wt. % in H2O, ACS reagent
Sigma-Aldrich
Hydrogen peroxide solution, purum p.a., ≥35% (RT)
Sigma-Aldrich
Hydrogen peroxide solution, contains inhibitor, 30 wt. % in H2O, meets USP testing specifications
Sigma-Aldrich
Hydrogen peroxide solution, contains ~200 ppm acetanilide as stabilizer, 3 wt. % in H2O
Sigma-Aldrich
Hydrogen peroxide solution, contains inhibitor, 35 wt. % in H2O
Sigma-Aldrich
Hydrogen peroxide solution, 50 wt. % in H2O, stabilized
Sigma-Aldrich
Hydrogen Peroxide Solution, 30% (w/w), puriss. p.a., reag. ISO, reag. Ph. Eur.
USP
Dehydrated Alcohol, United States Pharmacopeia (USP) Reference Standard
Sigma-Aldrich
Ethanol, anhydrous, denatured
Sigma-Aldrich
Ethyl alcohol, Pure, 190 proof, meets USP testing specifications
Sigma-Aldrich
Ethyl alcohol, Pure, 190 proof, ACS spectrophotometric grade, 95.0%
Sigma-Aldrich
Ethyl alcohol, Pure, 200 proof, anhydrous, ≥99.5%
Sigma-Aldrich
Ethanol, ACS reagent, prima fine spirit, without additive, F15 o1
Sigma-Aldrich
Ethyl alcohol, Pure, 190 proof, for molecular biology
Sigma-Aldrich
Ethyl alcohol, Pure, 200 proof, for molecular biology
Sigma-Aldrich
Ethyl alcohol, Pure, 200 proof, ACS reagent, ≥99.5%
Sigma-Aldrich
Ethanol, puriss., meets analytical specification of Ph. Eur., BP, 96.0-97.2%
Sigma-Aldrich
Ethyl alcohol, Pure, 200 proof, meets USP testing specifications
Sigma-Aldrich
Ethyl alcohol, Pure, 200 proof, HPLC/spectrophotometric grade