Theodore K. Koutouzis

3-Nitropropionic acid animal model and Huntington's disease.

Huntingtons disease (HD) is a progressive neurodegenerative disorder associated with severe degeneration of basal ganglia neurons, especially the intrinsic neurons of the striatum, and characterized by progressive dementia and involuntary abnormal choreiform movements. Despite our increasing knowledge of the pathophysiology of HD, culminating with the discovery of the gene underlying HD, there has been no cure available to completely cease or reverse the progressive neurodegeneration and behavioral consequences of the disease. Animal models that closely mimic the neurobiological and clinical symptoms of the disease continue to offer alternative approaches for studying HD. Recently, we have reported that systemic administration of 3-nitropropionic acid (3-NP), an inhibitor of the mitochondrial citric acid cycle, results in a progressive locomotor deterioration resembling that of HD. Furthermore, we observed congruent with other reports, that 3-NP produces a very selective striatal degeneration. It differs mechanistically from excitotoxic lesions in that 3-NP irreversibly inhibits the mitochondrial citric acid cycle and leads to depressed ATP levels and elevated lactate concentrations. Recent neurochemical studies have implicated lowered glutamate levels and impaired oxidative energy metabolism as underlying mechanisms for many neurodegenerative disorders, including HD. Because of the mechanistic and pathologic similarities between 3-NP lesions and HD, 3-NP has been proposed as an alternative HD model. We further demonstrated that manipulating the time course of 3-NP injections leads to sustained hyperactivity (early HD) or hypoactivity (late HD). The present review will primarily discuss this progressive behavioral pathology induced by 3-NP that closely resembles that of HD. This body of evidence suggests that the 3-NP model is an improved HD model and may offer a unique system wherein testing of experimental treatments for HD can be carried out across different stages of the disease. This future application of the 3-NP model will be very useful especially in assessing the efficacy of treatment modalities, e.g. neural transplantation, during the progression of the disease.

Behavioral pathology induced by repeated systemic injections of 3-nitropropionic acid mimics the motoric symptoms of Huntington's disease

Huntingtons disease is a progressive neurodegenerative disorder associated with severe degeneration of basal ganglia neurons, especially the intrinsic neurons of the striatum, and characterized by involuntary abnormal choreiform movements and progressive dementia. With the discovery of the gene underlying HD, genetic therapy may be the next logical step towards finding a cure, but no such treatment is currently available. Animal models that closely mimic the neurobiological and clinical symptoms of the disease may offer an alternative approach for the development of new therapies. We report that systemic administration of 3-nitropropionic acid, an inhibitor of the mitochondrial citric acid cycle, results in a progressive locomotor deterioration resembling that of HD. We further demonstrate that manipulating the time course of 3-nitropropionic acid injections leads to sustained hyperactivity (early HD) or hypoactivity (advanced HD). These data suggest that this animal model can be used to test experimental treatments for HD across different stages of the disease.

Systemic 3-nitropropionic acid : behavioral deficits and striatal damage in adult rats

Previous animal studies have demonstrated that systemic administration of 3-nitropropionic acid (3-NP) leads to neuropathological changes similar to those seen in Huntingtons disease (HD). Recently, we reported hypoactivity in 6- and 10-week old rats treated with systemic 3-NP (IP, 10 mg/kg/day) once every 4 days for 28 days. Although these behavioral results seem to differ from the observed hyperactivity in most excitotoxic models of HD, 3-NP may provide a better model of juvenile onset and advanced HD. In the present study, older rats were similarly treated with 3-NP to further characterize the reported age dependency of striatal neuronal death caused by 3-NP. Hypoactivity was observed in 14- and 28-week old rats with the latter demonstrating more profound features. The present study also provided the first direct evidence of a 3-NP effect on passive avoidance behavior. Experimental and control animals showed no significant difference in daytime acquisition and retention of a passive avoidance task. However, when the retention tests were conducted during the night time (in contrast to previous daytime tests), 3-NP-treated animals exhibited significant retention deficits. In addition, the neuropathological effects of 3-NP were determined by Nissl, AChE and NADPH-diaphorase histochemistry. Metabolic activity was studied using cytochrome oxidase activity as an index. Results revealed striatal glial infiltration, loss of intrinsic striatal cholinergic neurons, but some sparing of large AChE positive neurons, minimal damage of NADPH-diaphorase-containing neurons, and very slight, if any, alterations in cytochrome oxidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Neural Transplantation as an Experimental Treatment Modality for Cerebral Ischemia

Cerebrovascular disease exemplifies the poor regenerative capacity of the CNS. While there are methods to prevent cerebral infarction, there is no effective therapy available to ameliorate the anatomical, neurochemical and behavioral deficits which follow cerebral ischemia. Focal and transient occlusion of the middle cerebral artery (MCA) in rodents has been reported to result in neuropathology similar to that seen in clinical cerebral ischemia. Using specific techniques, this MCA occlusion can result in a well-localized infarct of the striatum. This review article will provide data accumulated from animal studies using the MCA occlusion technique in rodents to examine whether neural transplantation can ameliorate behavioral and morphological deficits associated with cerebral infarction. Recent advances in neural transplantation as a treatment modality for neurodegenerative disorders such as Parkinsons disease, have revealed that fetal tissue transplantation may produce neurobehavioral recovery. Accordingly, fetal tissue transplantation may provide a potential therapy for cerebral infarction. Preliminary findings in rodents subjected to unilateral MCA occlusion, and subsequently transplanted with fetal striatal tissue into the infarcted striatum have produced encouraging results. Transplanted fetal tissue, assessed immunohistochemically, has been demonstrated to survive and integrate with the host tissue, and, more importantly, ameliorate the ischemia-related behavioral deficits, at least in the short term. Although, this review will focus primarily on cerebral ischemia, characterized by a localized CNS lesion within the striatum, it is envisioned that this baseline data may be extrapolated and applied to cerebral infarction in other brain areas.

Hyperactivity and hypoactivity in a rat model of Huntington's disease: the systemic 3-nitropropionic acid model

The present study proposes the use of systemic 3-nitropropionic acid (3-NP) treatment in rats as a model of Huntingtons disease (HD). The systemic 3-NP model involves chronic injection of low dose intraperitoneal (i.p.) injections of 3-NP to rats once every 4 days over a period of time. Evidence from our experimental studies suggests that manipulating the number of injections can result in either increased nocturnal spontaneous locomotor activity (hyperactivity) or nocturnal akinesia (hypoactivity) [1]. For example, two injections of 3-NP (using the treatment of one injection every 4 days) result in hyperactivity, while four injections or more of 3-NP lead to hypoactivity [1]. The locomotor activity is recorded by Digiscan locomotor activity monitors [11]. The observation of these two types of locomotor activity is unique since no excitotoxin model has replicated a two-stage progression of a HD-like behavioral alteration. Most studies using excitotoxins like quinolinic acid (QA) and kainic acid (KA) have only reproduced the hyperactivity stage [4,5,7]. With the systemic 3-NP model, investigations into at least two stages of the disease are made possible. This allows for better assessment of intervention strategies such as neural transplants across different stages of the disease. The systemic 3-NP rat model is believed to be an improved animal model of HD.

Intrastriatal 3-nitropropionic acid : a behavioral assessment

Systemic injections of 3-nitropropionic acid (3-NP) in Sprague-Dawley rats have led to (1) hypoactivity that resembles juvenile onset and advanced Huntingtons disease (HD), and (2) impairment in contextual retention of passive avoidance. Since it has been established that 3-NP exerts its primary effects in the striatum, we selected intrastriatal injections to more thoroughly understand the direct behavioral effects of 3-NP. Each 14-week old rat received bilateral intrastriatal injections of one of the following: 500 and 750 nmol of 3-NP or vehicle (0.9% saline). At seven days following surgery, the animals were tested for spontaneous locomotor behavior and passive avoidance behavior. Results revealed deficits in both locomotor activity and passive avoidance learning. The animals injected with 500 and 750 nmol of 3-NP were significantly hypoactive compared with control animals. Similarly, the 2 groups of animals were severely impaired in the retention of passive avoidance compared with control. The 3 groups, however, did not differ in their acquisition of this learning task. Macroscopic analyses of brains of these animals revealed that 500 and 750 nmol of 3-NP caused severe loss of neuronal cell bodies and marked glial infiltration in the medial aspect of the striatum. Larger lesions showed a necrotic cavity at the injection site. In comparison with systemic administration of 3-NP, intrastriatal injections resulted in more profound hypoactivity, greater loss of passive avoidance retention, and more severe striatal damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P containing polymer implants protect against striatal excitotoxicity

The present study examined whether substance P (Sub P) could protect against quinolinic acid (QA)-induced lesions of the striatum, as measured by a loss of striatal D1 dopamine receptors. Sub P was extruded into Evac polymer rods for slow release. One 4 mm rod segment was implanted unilaterally into the striatum of each rat. One week later, animals received a striatal injection of QA (50, 75 or 100 nmol/microliters) medial to the implanted rod. Controls received QA alone. Three weeks later, there was a dose-dependent loss of D1 receptors following QA. Sub P rods protected the striatum from QA-induced D1 receptor loss at this time. These results support the neuroprotection role of Sub P on excitotoxicity.

Human Fetal Striatal Transplantation in an Excitotoxic Lesioned Model of Huntington's Disease

Transplantation of fetal neural tissue into the adult brain was initially investigated to examine the developmental and regenerative capacity of the nervous systern.l2 Intrastriatal transplantation has been a major focus of neural transplantation research because of the well-characterized anatomy of the normal striatum (or caudate-putamen). With many chemically identified types of striatal neurons and fiber systems, their reaction upon lesioning and transplantation could provide essential information about factors regulating, for instance, neuronal survival and differentiation. Apart from this initial goal of investigating CNS development and plasticity, neural grafting has been demonstrated to ameliorate the functional deficits induced by various brain lesions. Accordingly, it was suggested that neural grafting might be an appropriate treatment for various neurodegenerative di~0rders. l~

Implications of Neurological Rehabilitation for Advancing Intracerebral Transplantation

Neurological rehabilitation involves the systematic presentation of environmental stimuli and challenges that enable the patient to learn strategies for minimizing their disabilities. Rehabilitation therapy of transplant recipients may be an important factor in enhancing the efficacy of the transplanted organ or tissue to promote functional recovery. Laboratory research and clinical trials on neural transplantation, as an experimental treatment for neurological disorders (e.g., Parkinsons disease, Huntingtons disease, and cerebral ischemia), have focused primarily on devising effective surgical implantation strategies with little attention devoted to the interaction between environmental factors and restorative neurosurgery. Exercise training as part of neurological rehabilitation may be an important factor for neural transplantation therapy for Parkinsons disease. Rehabilitation providers are particularly well placed to provide the environment and the support to optimize the behavioral functioning of neural transplant patients in learning to use the new grafted tissue.