Elsevier

Neuropharmacology

Volume 52, Issue 3, March 2007, Pages 836-843
Neuropharmacology

Ladostigil prevents gliosis, oxidative–nitrative stress and memory deficits induced by intracerebroventricular injection of streptozotocin in rats

https://doi.org/10.1016/j.neuropharm.2006.10.005Get rights and content

Abstract

Glial activation and oxidative–nitrative stress occur at an early stage in Alzheimer's disease (AD). In a rat model of AD, deficits in cerebral glucose utilization and memory were seen 3–4 weeks after intracerebroventricular (icv) injection of streptozotocin (STZ). This study examined whether icv STZ induced glial activation and oxidative–nitrative stress preceded the memory deficits and whether they could be prevented by ladostigil a novel drug, a cholinesterase and monoamine oxidase inhibitor with neuroprotective activity. One week after STZ injection activated microglia and astrocytes were seen in the cortex, around the cannula penetration area, in the hippocampal CA1 region, corpus callosum, medial and lateral septum. The activated astrocytes showed a significant increase in nitrotyrosine immunoreactivity, a measure of oxidative–nitrative stress. Only 3 weeks later were deficits in episodic (object recognition test) and spatial memory (place recognition) seen in STZ-injected rats. Daily oral administrations of ladostigil (1 mg/kg) for 1 week, before and after STZ prevented the glial changes, increase in nitrotyrosine immunoreactivity and memory deficits. Taken together the data support the role of glial activation and oxidative–nitrative stress in discrete brain areas in the aetiology of memory deficits and indicate a potential mechanism for their prevention by drug treatment.

Introduction

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline and widespread loss of neurons and their synapses in the cerebral cortex and hippocampus (Katzman, 1986). In AD and other age-related neurodegenerative conditions recruitment and activation of microglia and astrocytes occur before pathological and clinical signs of the disease (Mrak and Griffin, 2005, Strohmeyer and Rogers, 2001). Activated microglia and astrocytes can release cytokines, reactive oxygen species (ROS) and nitric oxide (NO) that may contribute to the memory deficits (Tuppo and Arias, 2005). Glial changes also play a role in the cognitive decline that occurs during normal human aging even in the absence of overt neuron loss (Morgan et al., 1999, Nichols et al., 1993).

In a detailed histological examination of the brain after intracerebroventricular (icv) injection of streptozotocin (STZ) in rats we found that microglial activation occurs in discrete areas (Shoham et al., 2003). icv STZ was originally given to mimic the decrement in cerebral glucose metabolism (Duelli et al., 1994) seen in the early stages of AD (Arnaiz et al., 2001). While parenteral injection of STZ induces diabetes, by damaging pancreatic beta cells possibly through the generation of ROS (Takasu et al., 1991), STZ has no effect on blood sugar when given icv (Mayer et al., 1990), but decreases glucose utilization in discrete areas of the cortex and hippocampus (Duelli et al., 1994). It also damages the septohippocampal system (Prickaerts et al., 1999), and increases brain levels of malondialdehyde, an indirect measure of oxidative stress (Sharma and Gupta, 2001). Memory deficits are seen 3–8 weeks later, particularly after three icv injections of STZ (Lannert and Hoyer, 1998) and can be reduced by chronic treatment with antioxidants, melatonin and resveratrol (Sharma and Gupta, 2001, Sharma and Gupta, 2002), supporting a role of ROS in their aetiology.

Ladostigil (TV3326, N-propargyl-(3R)-aminoindan-5-yl-ethyl methyl carbamate, hemitartrate) is currently being developed as a treatment for AD (Weinstock et al., 2003). It was designed to combine the cholinesterase (ChE) inhibitory activity of rivastigmine with the neuroprotective actions of rasagiline, a monoamine oxidase (MAO-B) inhibitor which slows the progression of Parkinson's disease (Olanow, 2006). Rasagiline protects against the sequelae of head injury in rats (Huang et al., 1999) and prevents cytotoxicity in cultured neuronal cells induced by ROS and NO and by serum deprivation (Youdim and Weinstock, 2001). Since the neuroprotective effect is shared by similar concentrations of its S-enantiomer (TV1022) and by ladostigil that are 100–1000-fold less potent as MAO-B inhibitors, it is unlikely to result from MAO inhibition.

The aims of the present study were twofold: (a) to detect and quantify glial changes and oxidative–nitrative stress in discrete regions in the cortex and hippocampus 1 week after a single icv injection of STZ, before neuronal damage and memory deficits occur; (b) to determine whether chronic treatment with ladostigil can prevent the glial changes and subsequent memory deficits induced by icv STZ.

Some of these data were presented at a meeting of the Israel Society for Neuroscience, December 2005 (Weinstock et al., 2005).

Section snippets

Animals

The study was performed on male Sprague–Dawley rats (Harlan, Jerusalem) weighing 320–340 g, aged four months, according to the guidelines of the University Committee for Institutional Animal Care and based on those of the National Institutes of Health, USA. The rats were housed for 1 week prior to surgery in the Animal House at an ambient temperature of 21 ± 1 °C and a 12 h diurnal light cycle (lights on at 07:00 h).

Experimental protocol

Ninety-four rats were anesthetised by an intraperitoneal injection of Equithesin 0.3 

Glial changes induced by icv STZ in vicinity of cannula penetration site

In the motor and cingulate cortex around the cannula penetration site three zones of gliosis could be distinguished seven days after icv STZ. Zone (i) contained microglia that resembled macrophages, with round shaped soma devoid of processes, but was almost free of astrocytes; zone (ii) had activated microglia with polymorphic shaped soma and a variety of fibrous processes and activated astrocytes with elongated processes but no soma; zone (iii) had resident microglia resembling those in the

Discussion

The major new finding in this study is that icv injection in rats of STZ induced reactive gliosis and oxidative–nitrative stress before the induction of memory deficits. The reactive gliosis involved microglia and astrocytes in the cingulate and motor cortex around the area of cannula penetration, CA1 region of the hippocampus, and in the corpus callosum, medial and lateral septum close to the lateral ventricle. Oxidative–nitrative stress was present in the form of NT immunoreactivity in

Acknowledgement

The authors wish to thank Teva Pharmaceuticals Ltd for financial support and for performing the measurements of monoamine oxidase activity. The funding source had no direct or indirect role in collecting analyzing or interpreting the data, writing the paper or deciding to submit it for publication.

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