Assessment of functional neuroprotection in a rat model of neonatal stroke

One type of neonatal stroke, hypoxic-ischemic encephalopathy (HIE), represents a major cause of brain damage in the human term neonate. There have been relatively few studies published to date that assess the neurobehavioural consequences associated with HIE, or use behavioural studies in rats to investigate potential therapies for HIE. To address this issue, we conducted two separate studies. First, we subjected neonatal Sprague-Dawley (SD) rats to an episode of unilateral hypoxia-ischemia (HI) (modified Levine method) and tested both neonatal and adult animals in a behavioural battery developed "in house." This battery consisted of various physical and sensory developmental, neuromotor and cognitive assessments. Preliminary analysis revealed a significant difference between male and female animals on a number of these assessments and all subsequent analyses were conducted separately for males and females. Results revealed a significant difference between HI and sham animals on neuromotor (pivoting, forelimb grip strength and, wire mesh ascending) and cognitive tests (spontaneous alternation, radial arm maze and, Morris Water Maze) with HI animals exhibiting deficits in each of these assessments.

Second, using the same surgical method and behavioural test battery deemed sensitive to detecting functional deficits following neonatal HI from the first study, we assessed the neuroprotection offered by a single high dose of erythropoietin. Immediately following hypoxia, postnatal day (pnd) 7 SD rats were administered recombinant murine erythropoietin (rmEPO; 5,000 U/kg i.p.). Results revealed that EPO offered only moderate protection in physical developmental and cognitive assessments and that these effects were different between male and female animals. Further, there was no observed protection offered in assessments of sensorimotor (both male and female) or neuromotor (males; negative geotaxis) abilities. Post-mortem measures of lesion area and brain morphology revealed that EPO did not offer significant structural neuroprotection although there was a trend towards moderate protection offered by EPO in male animals.

In conclusion, the results from these two studies show that neonatal SD rats subjected to HI exhibit various functional deficits and structural damage that can be used to measure neuroprotection. Administration of the putative neuroprotective compound, EPO, in the present dosage regime however, does not appear to offer significant long-term functional or structural neuroprotection.