Research reportErythropoietin prevents long-term sensorimotor deficits and brain injury following neonatal hypoxia–ischemia in rats
Introduction
Hypoxic–ischemic (HI) brain injury in the perinatal period is an important cause of long-term neurological disabilities, such as sensorimotor deficits, learning and memory dysfunctions that can be observed throughout development and during adulthood [39], [51]. It is therefore important to study the mechanisms and explore the protective agents against HI injury in the immature brain. The most well-established and widely used animal model of perinatal asphyxia was proposed by Rice et al. based on the Levine preparation and consists of unilateral occlusion of carotid artery followed by exposure to hypoxia in 7-day-old rats [32], [38]. Morphological and biochemical changes associated with HI brain insult have been extensively studied in the experimental model of perinatal asphyxia [10], [14], [22], [37], [50], [57]. A few studies dealing with the long-term behavioral alterations after HI insult demonstrated obvious sensorimotor deficits, learning and memory impairments [4], [6], [7], [20], [49].
Neurological examination and developmental evaluation of the infant or a child are the sine qua non in the follow up of the patients with history of brain damage. It is therefore very important for the neuropathological assessment to be combined with neurofunctional evaluation. To date, various therapeutic strategies have shown neuroprotection against HI-induced brain injury in immature animals in the short-term perspective. However, it remains uncertain whether such findings are accompanied by long-term functional and structural improvements [15], [18], [42], [55].
Erythropoietin (Epo) is a cytokine that is commonly associated with a central role in erythropoiesis [21]. Recently, scientific interest was turned to the possible role of Epo and its receptor (EpoR) in the nervous system. Epo and EpoR expression significantly changed during brain development and EpoR signaling is required for normal brain development, indicating that Epo/EpoR system might play a pivotal role in neurodevelopment [23], [25], [26], [56]. In vitro evidence and various experimental models of nervous system injury demonstrate the effectiveness of Epo as a neuroprotective agent [1], [5], [8], [33], [36], [41]. Epo acts in a coordinated fashion at multiple levels in the nervous system, including activation of specific protein kinases, inhibition of reactive oxygen species and glutamate overproduction, modulation of neurotransmission, attenuation of apoptosis and stimulation of angiogenesis [11], [16], [27], [34], [44], [53].
Recent studies have also pointed to a neuroprotective role for Epo in perinatal asphyxia animal models, based on morphological and biochemical data [3], [29], [30], [35], [45], [46], [47]. However, little emphasis has been placed on assessing the effectiveness of Epo on long-lasting behavioral alterations [31].
The aim of the present study is to investigate whether Epo treatment immediately after neonatal hypoxic–ischemic insult prevents brain damage and improves long-lasting behavioral impairment.
Section snippets
Animal model and drug administration
Cerebral hypoxia–ischemia was performed as described by Rice et al. [38]. Seven-day-old Wistar rats of either sex, weighing 12–16 g, were anesthetized with diethyl ether and their left common carotid artery was permanently ligated through a midline neck incision. After surgery, the rat pups were returned to their dams for 2–3 h recovery. Hypoxia was induced by placing the animals in a chamber, submerged in a 37 °C water bath and subjected to a humidified mixture of 8% oxygen–92% nitrogen for 1
Effects of Epo on sensorimotor tests
To investigate the effect of Epo on muscle strength, motor coordination and limb placing reflexes of adult rats subjected to HI during neonatal period 5 different sensorimotor tests were conducted. In all behavioral tests, sham-operated animals treated with Epo exhibited a successful performance similar to that of sham-operated–saline treated rats (data not shown).
Discussion
Erythropoietin and its receptor (EpoR) have been implicated in the development of the CNS. The observation that Epo and its receptor show a specific distribution that changes with development has further paved the way for new studies aimed at investigating whether endogenous Epo/EpoR system possesses a prominent role in the developing brain [23], [56]. Neuroprotective effect of Epo has also been demonstrated on various animal models of cerebral ischemia [5], [34], [41], [44]. In our previous
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