Functional magnetic resonance imaging and immunohistochemical study of hypothalamic function following oral glucose ingestion in rats.
BACKGROUND
The hypothalamus plays a central role in the regulation of metabolism by sensing metabolic demands and releasing regulatory neurotransmitters. This study investigated the response of the hypothalamus to glucose ingestion in rats by blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI) and immunohistochemical techniques to determine the role of the hypothalamus in glyco-regulation during disturbances in carbohydrate metabolism.


METHODS
The signal intensity of the hypothalamus was monitored by fMRI for 60 minutes after oral glucose intake in 48 healthy rats (age 14 months), which included 24 normal weight rats (weighing (365 +/- 76.5) g) and 24 overweight rats (weighing (714 +/- 83.5) g). Then, 12 rats (6 normal, 6 overweight) underwent a repeat fMRI scan after consuming an equivalent amount of water without glucose on a separate day. The procedure for fMRI with water intake was the same as for glucose ingestion. fMRI data was processed using time cluster analysis and intensity averaging method. After fMRI, the expression of neuropeptide Y (NPY) and 5-hydroxytryptamine (5-HT) in the hypothalamus of all rats was determined by immunohistochemistry. Positive cells for NPY or 5-HT were counted.


RESULTS
There was a transient, but significant, decrease in fMRI signal intensity in all rats (mean (3.12 +/- 0.78)%) in the hypothalamus within 19.5 - 25.5 minutes of oral glucose ingestion. In overweight rats, the decrease in signal intensity in response to the glucose ingestion was more markedly attenuated than that observed in normal weight rats ((2.2 +/- 1.5)% vs (4.2 +/- 0.7)% inhibition, t = 2.12, P < 0.05). There was no significant response in the hypothalamus after oral water ingestion. The percentage of NPY positive cells in obese rats were slightly lower than those in control group (21% vs 23%, t = 0.71, P > 0.05); but there was no significant difference between the two groups; the percentage of 5-HT positive cells in obese rats were significantly lower than those in the control group (22% vs 31%, t = 3.25, P < 0.01).


CONCLUSIONS
There is a transient, but significant, decrease in BOLD signal intensity in the hypothalamus following glucose ingestion, which is similar to that observed in humans. The response of the hypothalamus to glucose ingestion was different in overweight and normal weight rats. The percentage of NPY positive cells in obese rats were lower than those in the control group, although this difference was not statistically significant. The percentage of 5-HT positive cells in obese rats was significantly lower than those in the control group.
Chen
Min
M
Department of Radiology, Beijing Hospital, Beijing 100730, China. cjr.chenmin@vip.163.com
Zhang
Tie-Mei
TM
Luo
Sen-Lin
SL
Zhou
Cheng
C
Wu
Xiao-Meng
XM
Zhou
Ni-Na
NN
Cai
Kui
K
Yang
Zhen-Han
ZH
Wang
Wen-Chao
WC
Zhao
Wei-Feng
WF
Li
Sa-Ying
SY
Wang
Zhi
Z
Zhang
Yun-Ting
YT
Li
Guo-Zhen
GZ
D000818:Animals; D005947:Glucose / Q000378:metabolism*; D007031:Hypothalamus / Q000502:physiology*; D007150:Immunohistochemistry; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009478:Neuropeptide Y / Q000032:analysis; D009765:Obesity / Q000378:metabolism; D010100:Oxygen / Q000097:blood; D051381:Rats; D012701:Serotonin / Q000032:analysis
D009478:Neuropeptide Y; D012701:Serotonin; D005947:Glucose; D010100:Oxygen