The window of opportunity for neuronal rescue with insulin-like growth factor-1 after hypoxia-ischemia in rats is critically modulated by cerebral temperature during recovery
J. Guan et al., The window of opportunity for neuronal rescue with insulin-like growth factor-1 after hypoxia-ischemia in rats is critically modulated by cerebral temperature during recovery, J CEREBR B, 20(3), 2000, pp. 513-519
Insulin-like growth factor (IGF-I) is induced in damaged brain tissue after
hypoxia-ischemia, and exogenous administration of IGF-I shortly after inju
ry has been shown to be neuroprotective. However, it is unknown whether tre
atment with IGF-I delayed by more than a few hours after injury may be prot
ective. Hypothermia after brain injury has been reported to delay the devel
opment of ischemic neuronal death. The authors therefore hypothesize that a
reduction in the environmental temperature during recovery from hypoxia-is
chemia could prolong the window of opportunity for IGF-I treatment. Unilate
ral brain damage was induced in adult rats using a modified Levine model of
right carotid artery ligation followed by brief hypoxia (6% O-2, for 10 mi
nutes). The rats were maintained in either a warm (31 degrees C) or cool (2
3 degrees C) environment for the first 2 hours after hypoxia. All rats were
subsequently transferred to the 23 degrees C environment until the end of
the experiment. A single dose of IGF-I (501 mu g) or its vehicle was given
intracerebroventricularly at either 2 or 6 hours after hypoxia. Histologic
outcome in the lateral cortex was quantified 5 days after hypoxia. Finally,
cortical temperature was recorded from 1 hour before and 2 hours after hyp
oxia in separate groups of rats exposed to the "warm" and "cool" protocols.
In rats exposed to the warm recovery environment, IGF-1 reduced cortical d
amage (P < 0.05) when given 2 hours but not 6 hours after insult. In contra
st, with early recovery in the cool environment, a significant protective e
ffect of IGF-1 in the lateral cortex (P < 0.05) was found with administrati
on 6 hours after insult. In conclusion, a reduction in cerebral temperature
during the early recovery phase after severe hypoxia-ischemia did not sign
ificantly reduce the severity of injury after 5 days' recovery; however, it
markedly shifted and extended the window of opportunity for delayed treatm
ent with IGF-I.