β-amyloid infusion into lateral ventricle alters behavioral thermoregulation and attenuates acquired heat tolerance in rats

Abstract

We investigated behavioral thermoregulatory function and acquired heat tolerance of β-amyloid (Aβ)-infused rats. Male Wistar rats were anesthetized and implanted in the intraperitoneal cavity with a temperature transmitter. Aβ peptide (4.9-5.5 nmol) was dissolved in a solvent of 35% acetonitrile and 0.1% trifluoroacetic acid (pH 2.0). The solvent was used as the vehicle. An osmotic pump contained 234 ± 13.9 μl of Aβ solution was subcutaneously implanted in the back and was cannulated into the left cerebral ventricle. Moreover, 0.5 µg of AlCl3 was injected into the right cerebral ventricle with a micro syringe pump (Aβ-infused rats). The solvent-infused rats were used as control rats (CN rats). After 2 weeks, rats were placed in a thermal gradient and their intra-abdominal temperature (T ab ) and their ambient temperatures (T a ) selected (T s ) were measured for 3 consecutive days. In an additional study, rats were kept at a T a of 32°C for 4 weeks to attain heat acclimation. Then, rats were subjected to a heat tolerance test, i.e. they were exposed to a T a of 36°C for 160 min. Although there were clear day-night variations of T s and T ab in CN rats, patterns were significantly abolished in Aβ-infused rats. Moreover, heat tolerance obtained by heat acclimation was attenuated in Aβ-infused rats. These results suggest that Aβ-infusion in the lateral ventricle modifies behavioral thermoregulation and lowers an ability to acclimate to heat in rats.

Keywords: behavioral thermoregulation; heat acclimation; hypothalamus; rats; β-amyloid.

Figure 1.

The mean T_ab in CN and Aβ–infused rats. (A) Before surgery, T_ab levels of CN (black circle) did not differ from those of Aβ-infused rats (red circle). (B) Twelve days after surgery, T_ab of the light phase in Aβ-infused rats was significantly higher than that of CN. Dark bars above abscissa indicate the dark phase of the day. Values are the means ±S.E.Ms (n = 6 in each group).

Figure 2.

The mean T_s in CN and Aβ–infused rats. (A) T_s value of day in CN (black circle) and Aβ-infused rats (red circle). Dark bar above abscissa indicates the dark phase of the day. (B) Mean T_s of CN (black bar) and Aβ-infused rats (red bar) in the light and dark phase. In the light phase, mean T_s of Aβ-infused rats was significantly lower than that of CN. However, in the dark phase, mean T_s of Aβ-infused rats was significantly higher than that of CN. Values are the means±S.E.Ms (n = 6 in each group). *Shows significant difference of the light phase and dark phase. # shows significant difference between CN and Aβ-infused rats.

Figure 3.

Heat tolerance test in CN and Aβ–infused rats. (A) T_a of the chamber in the heat tolerance test. T_a was gradually raised from time at 0 min. (B) T_ab responses to gradient heat of CN (black circle) and Aβ-infused rats (red circle). The T_ab values of all rats were monitored by a telemetry system. T_ab responses of CN and Aβ-infused rats did not significantly change. (C) c-Fos+ cells in the PO/AH. Green signals show c-Fos+ cells. The expression level of c-Fos+ cells of CN (left) and Aβ-infused rats (right) did not alter. Scale bar: 50 μm. (D) Over view of PO/AH of hypothalamic section. Red box shows immuno-stained area of (C). ac, anterior comm. ox, optic chiasm.

Figure 4.

Ability of acquired heat tolerance in CN and Aβ-infused rats. (A) Heat tolerance test in CN (black circle) and Aβ–infused rats (red circle) after long term heat exposure. The increase in the T_ab values was slower for CN rats than that for the Aβ-infused rats. #, significant difference between CN and Aβ-infused rats. Values are the mean ±SEM (n = 4). (B) PCNA and (C) Dcx immunostaining in the hypothalamus. Scale bar, 100 µm. (D) Western blot analysis of Dcx protein in the hypothalamus. (Left) Western blot analyses were performed using anti-Dcx antibody. Blots were then stripped and reprobed with anti-GAPDH antibody to verify that equal amount of protein was electrophoresed in each lane. (Right) The densitometric data on Dcx/GAPDH of CN (black bar) and Aβ-infused rats (red bar). # shows significant difference between CN and Aβ-infused rats. Values are the mean ±SEM (n = 4).