Long-Term Motor Deficit and Diffuse Cortical Atrophy Following Focal Cortical Ischemia in Athymic Rats

Abstract

Development of new stroke therapies requires animal models that recapitulate the pathophysiological and functional consequences of ischemic brain damage over timeframes relevant to the therapeutic intervention. This is particularly relevant for the rapidly developing area of stem cell therapies, where functional replacement of circuitry will require maturation of transplanted human cells over months. An additional challenge is the establishment of models of ischemia with stable behavioral phenotypes in chronically immune-suppressed animals to allow for long-term survival of human cell grafts. Here we report that microinjection of endothelin-1 into the sensorimotor cortex of athymic rats results in ischemic damage with a sustained deficit in function of the contralateral forepaw that persists for up to 9 months. The histological post-mortem analysis revealed chronic and diffuse atrophy of the ischemic cortical hemisphere that continued to progress over 9 months. Secondary atrophy remote to the primary site of injury and its relationship with long-term cognitive and functional decline is now recognized in human populations. Thus, focal cortical infarction in athymic rats mirrors important pathophysiological and functional features relevant to human stroke, and will be valuable for assessing efficacy of stem cell based therapies.

Ischemic Injury Does Not Stimulate Striatal Neuron Replacement Even during Periods of Active Striatal Neurogenesis

“…The widespread loss of striatal neurons following injection of ET-1 into the adult forebrain is consistent with the pattern of ischemic damage we (Ermine et al, 2019;Somaa et al, 2017) and others (Gilmour et al, 2004) have previously reported and shown to be associated with a deficit in motor function that is stable over months. The robust proliferative response to injury, shown as a significant increase in BrdU+ cells relative to saline-treated controls, is a well-described response to acute brain injuries (Cavanagh, 1970;Nait-Oumesmar et al, 1999;Wright et al, 2016) including those arising from ischemic damage (Arvidsson et al, 2002;Liu et al, 2009;Parent et al, 2002).…”

Focal Ischemic Injury to the Early Neonatal Rat Brain Models Cognitive and Motor Deficits with Associated Histopathological Outcomes Relevant to Human Neonatal Brain Injury

“…Moreover, this is commonly observed in HI models, where atrophy occurs ipsilateral to the ligation site [ 26 , 27 , 29 ]. Quantification of neuronal density showed that the atrophy was indeed associated with neuronal loss, as opposed to collapse of the extra-cellular compartment as we have reported previously for both neonatal [ 17 ] and adult [ 41 ] models of ET-1 induced ischemic injury in rats. We also observed significant atrophy of white matter structures including the CC and PVWMBs in the dorso-medial striatum; comparable to human clinical data [ 1 , 6 , 25 , 42 , 43 , 44 , 45 , 46 ].…”

Hemispheric cortical atrophy and chronic microglial activation following mild focal ischemic stroke in adult male rats

“…Animals under deep anesthesia (2% isoflurane) were placed in a stereotaxic frame, and focal ischemic injury was induced by injection of the vasoconstrictor, ET-1 (800 pmol in saline; AusPep), into the sensorimotor cortex at two sites (0.5 and 2.0 mm rostral and 2.8 mm lateral to the bregma and 1.5 mm below the surface of the brain) as previously described (Ermine et al, 2019). Control animals received the same volume of saline injected at the same coordinates.…”

“…A first cohort of animals was used for histological analysis at 1, 4, 12, 24, 36, and 48 weeks postsurgery (n = 6 allocated per group for each time point, based on our previous work using this model (Ermine et al, 2019)). Two rats died during the surgical procedure and two others spontaneously developed tumor growth during the course of the experiment leading to immediate euthanasia.…”

“…Microinjection of the potent vasoconstrictor endothelin-1 has become a widely used approach to model focal ischemic injury in rodents with the capacity to modulate severity based on dosage (Abeysinghe & Roulston, 2018). We recently reported that ET-1 injection into the sensorimotor cortex of athymic rats that have a compromised immune system resulted in a focal ischemic injury associated with a stable motor impairment over 36 weeks (Ermine et al, 2019). It prompted us to explore motor and cognitive impacts in the present study using Long-Evans, an outbred strain most commonly employed in rat behavioral studies.…”