Corina Bejar

Effect of rivastigmine on scopolamine-induced memory impairment in rats

The effect of rivastigmine on memory impairments induced in rats by scopolamine (0.5 mg/kg) was assessed in the Morris water maze and passive avoidance tests and compared with that of tacrine (2.5-17.7 mg/kg). Rivastigmine, (0.5-2.5 mg/kg) inhibited cholinesterase in the cortex and hippocampus by 21-60% and antagonised the deficits in working and reference memory. Tacrine (12.5 and 17.7 mg/kg) produced significantly less inhibition of cholinesterase in the hippocampus but more in the striatum than rivastigmine (0.75 and 1.5 mg/kg) and only antagonised the deficit in reference memory. Rivastigmine (1.5 and 2.5 mg/kg) or tacrine (12.5 mg/kg), injected immediately after completion of the acquisition trial in the passive avoidance test, antagonised the deficit induced by scopolamine (1 mg/kg) in memory retention. The inability of higher doses of the cholinesterase inhibitors to antagonise memory deficits induced by scopolamine may be related to excessive cholinergic stimulation in the central nervous system.

Intracerebroventricular injection of streptozotocin causes neurotoxicity to myelin that contributes to spatial memory deficits in rats

It has been reported that intracerebroventricular (icv) injection of streptozotocin (STZ) impairs spatial memory by disrupting glucose utilization through an insulin-dependent mechanism in the cerebral cortex and hippocampus. However, evidence of septal damage and microglosis induced by icv STZ suggested that its neurotoxic effects could contribute to the memory impairment. The present study examined the histopathological changes in adult rats following three icv STZ injections (0.25 mg into each lateral ventricle) and their effects on spatial memory in a Morris water maze task. STZ retarded acquisition of reference learning (progressive reduction in escape latency) and disrupted working memory (difference in escape latency between the two swims within a daily session). STZ caused selective injury to myelin and axons in the fornix and hippocampus in association with activation of microglia. The 3rd ventricle was enlarged by 100-150% because of a loss of ependymal cells and damage to hypothalamic periventricular myelin but the process involved in these changes is unclear. Our findings provide an alternative explanation for the decrease in glucose utilization in the hippocampus and cortex and the impairment of spatial memory induced by STZ. These could result from a disruption of the communication through myelinated axons in the fornix connecting the septum and the hippocampus, and through other myelinated axons adjacent to the ventricles. The selective damage to myelin may well result from oxidative stress.

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

Glial activation and oxidative-nitrative stress occur at an early stage in Alzheimers 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 (1mg/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.

Neuroprotective Effects of Novel Cholinesterase Inhibitors Derived from Rasagiline as Potential Anti-Alzheimer Drugs

Abstract: TV3326, (N‐propargyl‐(3R)‐aminoindan‐5‐yl‐ethyl, methyl carbamate) was prepared in order to combine the neuroprotective effects of rasagiline, a selective inhibitor of monoamine oxidase (MAO)‐B with the cholinesterase (ChE) inhibitory activity of rivastigmine as a potential treatment for Alzheimers disease. The study reported here examined the neuropotective effects of TV3326 against various insults in vitro and in vivo. TV3326 caused a dose related (10–500 μM) reduction in death induced in NGF differentiated rat pheochromocytoma (PC12) cells by 3–4 hour exposure to oxygen‐glucose deprivation. A single sc injection of TV3326 given five minutes after closed head injury in mice significantly reduced the cerebral edema, and accelerated the recovery of motor function and spatial memory several days later. Unilateral icv injection of streptozotocin (STZ) 1.5 mg in rats, caused specific damage to myelinated neurones in the fornix and corpus callosum accompanied by microgliosis. Three bilateral injections of STZ, 0.25 mg each, caused more widespread damage, and a marked impairment in spatial memory. Chronic oral treatment with TV3326 (75 μmols/kg) reduced the neuronal damage and microgliosis and almost completely prevented the memory impairment. The neuroprotective effect in PC12 cells may be due to a combination of ChE inhibition and antiapoptotic activity. The latter does not result from ChE inhibition. It is associated with the presence of the propargyl group, since it occurs with other propargylamines that do not inhibit MAO, but not with drugs that inhibit only ChE.

Corticosterone mediates some but not other behavioural changes induced by prenatal stress in rats.

The effect of daily varied stress from days 13–21 of gestation in Wistar rats was investigated by tests of learning and memory and anxiogenic behaviour in the 60‐day‐old offspring of both sexes. Prenatal stress decreased the anogenital distance in males at 1 day of age. Anxiogenic behaviour in the elevated plus maze was seen in prenatally‐stressed rats of both genders. There was no significant gender difference in the rate of spatial learning in the Morris water maze but prenatal stress only slowed that of males. In the object recognition test with an inter‐trial interval of 40 min, females but not males, discriminated between a familiar and novel object. Prenatal stress did not affect object discrimination in females but feminised that in males. Maternal adrenalectomy with replacement of basal corticosterone levels in the drinking fluid prevented all of the above effects of prenatal stress in the offspring. To mimic the peak corticosterone levels and time course of elevation in response to stress, corticosterone (3 mg/kg) was injected twice (0 and 30 min) on days 13–16 and once on days 17–20 of gestation to adrenalectomised mothers. This treatment re‐instated anxiogenic behaviour similar to that induced by prenatal stress, indicating that it is mediated by exposure of the foetal brain to raised levels of corticosterone. However, steroid administration to adrenalectomised dams did not decrease anogenital distance, feminise object recognition memory or slow spatial learning in their male offspring. The findings indicate that other adrenal hormones are necessary to induce these effects of prenatal stress.

cDNA gene expression profile of rat hippocampus after chronic treatment with antidepressant drugs.

Summary.  Background. Chronic antidepressant treatment causes alterations in several hippocampal genes, which participate in neuronal plasticity. However the full picture of their mechanism of action is not known. The advent of genomics enables to identify a broader mechanism of action and identify novel targets for antidepressant development. Methods. The present study examined the cDNA microarray gene expression profile in the hippocampus induced by chronic antidepressant treatment, in rats exposed to the forced swim test. Animals were treated for 2 weeks with moclobemide, clorgyline and amitriptyline. Results. The three antidepressants significantly reduced immobility in the forced swim test and initiated significant homologous changes in gene expressions. These include up regulation of cAMP response element binding protein and down regulation of corticotrophin releasing hormone. Other gene changes noted were those related to neuropeptides, neurogenesis and synaptogenesis, including synaptophysin and neogenin. Some 89 genes were changed by at least 2 drugs, out of which 53 were changed oppositely by forced swim test. Confirmation of gene changes, have come from real time RT-PCR. Conclusions. A significant number and homology in gene expression were observed with the three antidepressants. Many of the genes were associated with neurogenesis and synaptogenesis, including synaptophysin and neogenin.

Gender differences in the effect of rivastigmine on brain cholinesterase activity and cognitive function in rats

This study compared the effect of rivastigmine on cholinesterase (ChE) activity in different brain regions, heart, skeletal muscle and plasma and on the cognitive impairment induced by scopolamine (0.5 mg/kg) in male and female rats. Rats were injected s.c. with saline or rivastigmine (0.75-2.5 mg/kg) or physostigmine (0.05 mg/kg) and killed 30-120 min later. Amelioration of scopolamine-induced memory deficits by rivastigmine (0.75 mg/kg) was assessed in the Morris water maze. There were no gender differences in spatial memory or basal ChE activity in the brain or other organs. Rivastigmine (0.75 and 1.5 mg/kg) and physostigmine (0.05 mg/kg) caused significantly greater ChE inhibition in females than in males (P<0.01) in the cerebral cortex, hippocampus and striatum, but not in the periphery 30 and 60 min after injection. Rivastigmine was also more effective in antagonising the scopolamine-induced spatial memory impairment in female than in male rats. Ovariectomy did not affect the degree of enzyme inhibition by rivastigmine in any brain area. Orchidectomy completely abolished the difference in enzyme inhibition. It is concluded that a testicular hormone suppresses the effect of rivastigmine, by reducing the amount of drug reaching the brain or its interaction with ChE.

Prenatal stress diminishes gender differences in behavior and in expression of hippocampal synaptic genes and proteins in rats.

The study determined whether there were gender differences in the expression of hippocampal genes in adult rats in association with dissimilarity in their behavior, and how these were affected by prenatal stress. Pregnant Wistar rats were subjected to varied stress once daily on days 14–20 of gestation. Adult female offspring of control rats showed significantly less anxiogenic behavior in the elevated plus maze and better discrimination between a novel and familiar object than males in the object recognition test. These gender differences in behavior were markedly attenuated by prenatal stress. Using Affymetrix DNA chip technology on hippocampal extracts prepared from littermates of the offspring used for behavioral tests, we found that 1,680 genes were differentially expressed in control males and females. The gender difference in gene expression was decreased to 11% (191 genes) by prenatal stress. In both sexes, processes like the translational machinery, mitochondrial activity, and cation transport were downregulated compared to controls, but there was a greater suppression of genes involved in vesicle trafficking, regulation of synaptic plasticity, and neurogenesis in females than in males. This was compensated by a higher expression of other components of vesicle trafficking, microtubule‐based processes, and neurite development. Prenatal stress decreased the expression of 19 Rab proteins in females and five Rabs in males, but a compensatory increase of Rab partner proteins and effectors only occurred in females. Exposure to stress decreased the expression of synaptic proteins, synaptophysin, and synaptopodin in prenatally stressed males and females and increased those of PSD‐95 and NR1 subunit of the N‐methyl‐D‐aspartic acid (NMDA) glutamate receptor only in females. The study provides an unbiased view of key genes and proteins that act as gender dependent molecular sensors. The disruption of their expression by adverse early life stress may explain the alterations that occur in behavior.

Ladostigil prevents age-related glial activation and spatial memory deficits in rats.

Oxidative stress and glial activation occur in the aging brain. Ladostigil is a new monoamine oxidase (MAO) and acetylcholinesterase (AChE) inhibitor designed for the treatment of Alzheimers disease. It has neuroprotective and antioxidant activities in cellular models at much lower concentrations than those inhibiting MAO or AChE. When ladostigil (1mg/kg/day) was given for 6 months to 16-month-old rats it prevented the age-related increase in activated astrocytes and microglia in several hippocampal and white matter regions and increased proNGF immunoreactivity in the hippocampus towards the levels in young rats. Ladostigil also prevented the age-related reduction in cortical AChE activity and the increase in butyrylcholinesterase activity in the hippocampus, in association with the reduction in gliosis. The immunological and enzymatic changes in aged rats were associated with improved spatial memory. Ladostigil treatment had no effect on memory, glial or proNGF immunoreactivity in young rats. Early treatment with ladostigil could slow disease progression in conditions like Alzheimers disease in which oxidative stress and inflammatory processes are present.

Ladostigil, a novel multifunctional drug for the treatment of dementia co-morbid with depression

Ladostigil is a novel drug that inhibits acetyl and butyrylcholinesterase, and monoamine oxidase (MAO) A and B selectively in the brain. It reverses memory deficits induced by chronic inhibition of cortical cytochrome oxidase in rats and has anxiolytic and antidepressant-like activity in prenatally-stressed rats. Ladostigil also prevents oxidative-nitrative stress induced in astrocytes in the hippocampal CA1 region following icv injection of STZ in rats which also impairs their episodic memory. The unique combination of ChE and MAO enzyme inhibition combined with neuroprotection makes ladostigil a potentially useful drug for the treatment of dementia in subjects that also have extrapyramidal dysfunction and depression.