Zipora Speiser

Studies with rasagiline, a MAO-B inhibitor, in experimental focal ischemia in the rat

Summary. Rasagiline, as the mesylate salt (TVP-1012), is a selective, potent, non-reversible MAO-B inhibitor of the propargylamine type. Current cellular and whole animal studies suggested a potential for neuroprotection by rasagiline. Rasagiline in repeat ip doses of 1–3 mg/kg within 16 h, or by sustained iv infusion to maintain a 3-h steady-state at corresponding levels, improved the outcome of permanent middle cerebral artery occlusion (MCAO) in the rat. In five independent studies using different protocols, rasagiline improved neurological severity score (NSS) with respect to saline from a high of 8.96 ± 2.18 (n = 94) at 24 h, and 7.64 ± 2.52 (n ± 49) at 48 h, to a low of 7.13 ± 2.32 (n = 88) at 24 h, and 4.99 ± 2.31 (n = 68) at 48 h. Under the same conditions, there was a decrease in the volume of necrotic brain region determined at 48 h by triphenyl tetrazolium chloride (TTC), from a high of 240 ± 66 (n = 54) to a low of 176 ± 77 mm3 (n = 55); and by MRI scan at 48 h, from a high of 297 ± 62 (n = 25), to a low of 209 ± 63 mm3 (n = 28). Improvement in NSS was more obvious at 48 h post MCAO, at the higher dose, when timing of drug administration was within the interval −30 min to 3 h from MCAO. A 3-h iv infusion of rasagiline caused a maximal reduction in infarct volume of about 49% of control. The (S)enantiomer of rasagiline TVP-1022, not a MAO inhibitor, was less effective, but still significantly different from saline, NSS at 48 h 5.6 ± 2.5 (n = 24) vs. 7.5 ± 2.5 (n = 24), infarct volume 200 ± 64 (n = 24) vs. 240 ± 55 mm3 (n = 24). Selegiline (n = 19) at corresponding ip doses was not different from saline. Dizocilpine decreased infarct volume from 277 ± 65 (n = 20) to 203 ± 52 mm3 (n = 21) but could not improve NSS at 24 or 48 h. In this model, rasagiline could have exerted a neuroprotective effect independent of MAO inhibition.

Changes in brain catecholamine turnover and receptor sensitivity induced by social deprivation in rats.

Catecholamine turnover was compared in two brain areas of rats housed under different social conditions. Rats reared in isolation for 6–8 weeks had a significantly lower noradrenaline turnover in the brainstem and lower noradrenaline and dopamine turnover in a brain segment comprising all other areas except the cerebellum, pineal gland, thalamus, and and subthalamus. In the open-field test, isolated rats were much more active than group-housed animals. Noradrenaline turnover increased in both brain areas of isolated rats but not in grouped animals after exposure to the open field. Hyperactivity was selectively reduced in isolated rats by chronic oral treatment with d-amphetamine, 5 mg/kg/24 h. It was also reduced 15 min after pretreatment with α-methyl-p-tyrosine 200 mg/kg. It is suggested that a prolonged period of reduced noradrenaline release may sensitise postsynaptic receptors in isolated rats. Hyperactivity appears to be associated with an increase in transmitter release onto sensitised receptors.

Hyperactivity in rats following postnatal anoxia

A model of hyperactive rats was produced by exposing pups to severe anoxia within 24 h following birth. These rats demonstrated augmented motor activity in ambulation, sniffing and rearing activities in an open field. Activity was significantly increased at 10 days of age, maximal at 20-25 days and returned to normal values around 6 weeks of age.

The effect of dl-propranolol, d-propranolol and practolol on the hyperactivity induced in rats by prolonged isolation

Exploratory behaviour in an open field situation was found to be greatly increased in rats, isolated for 6–8 weeks, when compared with grouphoused controls. Propanolol, dl- and d- and practolol, 0.2–0.5 mg/kg reduced hypermotility, sniffing and rearing in isolated rats without affecting behaviour of group-housed rats. 20 mg/kg dl-propanolol was needed to reduce exploratory behaviour of group housed rats. Chlorpromazine reduced activity of isolated rats at a dose of 0.1 mg/kg, and group housed rats at 0.5–1 mg/kg. The action of propranolol does not appear to result from central receptor blockade because of the almost equal activity of d- and dl-propranolol. Since practolol was also active in this test, the effect of these drugs also does not appear to result from general C.N.S. depression. It is suggested that these compounds may reduce hyperactivity by diminishing an excessive release of central catecholamines.

Sparing by Rasagiline (Tvp-1012) of Cholinergic Functions and Behavior in the Postnatal Anoxia Rat

Rasagiline (N-propargyl-1(R)aminoindan) is a selective and potent MAO-B inhibitor currently under development as the mesylate salt (TVP-1012) for the treatment of various neurologic disorders. Preliminary work in adult and senescent rats, either normal or hypoxia-lesioned, showed that chronic rasagiline treatment improved performance in memory and learning tasks, suggesting some beneficial effect on central cholinergic function. We have now used the postnatal anoxia-lesioned rat as a model of cholinergic dysfunction. In the neonatal rat, anoxia strongly affects the cholinergic system, which has not yet reached full maturation at this state of life. Rasagiline mesylate was administered from day 1 to completion of the study (day 60), first through nursing mother milk until weaning (day 21), then in drinking water, at the rate of 0.5 mg/kg/day. Drug access to the CNS was verified by analysis of MAO activity in brain (at 21 days). Treatment improved the juvenile hyperactivity syndrome associated with anoxia (at day 28). It improved performance in the passive avoidance test to normal control level (at day 40). It improved spatial memory performance in the Morris water maze to normal control level (at day 50). The untreated anoxia group failed in these tasks and was significantly inferior to either the normal control and rasagiline-treated anoxia groups. Determination of ChAT activity in the caudate and hippocampus of rats from each of these groups gave the following results (pmol ACh/mg protein/min). Caudate: normal control, 588 +/- 56; anoxia, 398 +/- 54; rasagiline-treated anoxia, 536 +/- 35. Hippocampus: normal control, 380 +/- 31; anoxia, 275 +/- 47; rasagiline-treated anoxia, 325 +/- 35. Results are mean +/- SD from each of seven to nine different donors in a group. Thus, improvement in memory and learning tasks of the rasagiline-treated anoxia group finds correspondence in the activity of the cholinergic marker ChAT in two brain regions that have prominent cholinergic innervation.

Rasagiline and its (S) enantiomer increase survival and prevent stroke in salt-loaded stroke-prone spontaneously hypertensive rats

Summary. The aim of this study was to determine whether chronic treatment with the selective MAO-B inhibitor rasagiline, N-propargyl-1-(R)-aminoindan (R-PAI), can prevent or delay stroke or improve its outcome in salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP). The S-enantiomer of rasagiline, S-PAI a much weaker MAO inhibitor was included in the study in order to expose a possible contribution from MAO inhibition to any beneficial effect by R-PAI. SHRSP were isolated, fed rat stroke prone diet and given 1% NaCl instead of water. Drugs were administered in the drinking fluid for 84 days. Rats were grouped as follows: (1) Untreated control; (2) R-PAI 1 mg/kg/day; (3) R-PAI 3 mg/kg/day; (4) S-PAI 3 mg/kg/day; (5) S-PAI 6 mg/kg/day. Survival, stroke frequency and neurological severity score following stroke were determined. R-PAI at 3 mg/kg/day significantly increased cumulative survival from 56.09 ± 1.77 days in the untreated to 73.6 ± 2.22 days in the R-PAI treated; S-PAI at 6 mg/kg/day to 78.61 ± 2.05 (censored at 84 days). In these groups stroke was delayed, its incidence was decreased and its outcome was less severe than in the control group. Proteinurea observed in the untreated rats and in both lower dose groups of R-PAI and S-PAI was absent in the higher dose groups of both drugs. Histological examination of the brains and kidneys showed that the effects on stroke and survival were associated with decreased infarcts and hemorrhages in the brains and decreased tubular nephropathy and glomerulopathy. The time-dependent rise in systolic blood pressure in the untreated rats was significantly attenuated only in the R-PAI group at 3 mg/kg/day but not in the S-PAI group. There were no significant effects on heart rate. MAO-B activity in the brain was 95% blocked by both doses of R-PAI but only 62% by S-PAI at 6 mg/kg/day. In salt-loaded SHRSP chronic therapy with either R-PAI or S-PAI prevented stroke and severe vascular lesions in the kidney. When stroke did occur its neurological outcome was less severe. The drugs were equipotent when they were given at a ratio of 1 : 2. The mechanism has yet to be elucidated. The differential effects of the drugs on blood pressure and MAO inhibition rule out either effect as the sole explanation.

The effects of postnatal anoxia on behaviour and on the muscarinic and beta-adrenergic receptors in the hippocampus of the developing rat

Exposure of rats to 25 min anoxia within 24 h following birth caused behavioural as well as biochemical changes during their development and maturity. Following postnatal anoxia, a significant increase in the concentration of the cholinergic muscarinic receptors in the hippocampus was noted at the early stages of development, between 6 and 20 days of age, but reached normal values at 40 days of age. However, at this age, significant increase in the concentration of beta-adrenergic receptors in the hippocampus was found, which remained significantly high during maturity and adulthood, as compared to controls. Rats submitted postnatally to anoxia exhibited hyperactivity in the open field which was maximal at 20-25 days of age and declined towards normal values at 40 days of age. At maturity, between 60 and 80 days of age, these rats showed poor performance in a complex 6-choice discrimination learning but not in simple differential conditioning. Possible correlations between the behavioural and biochemical findings are discussed.

Hypertension and neuronal degeneration in excised rat spinal cord studied by high-b value q-space diffusion magnetic resonance imaging

Hypertension is one of the major risk factors of stroke and vascular dementia (VaD). We used stroke prone spontaneous hypertensive rats (SPSHRs) as a model for neuronal degeneration frequently occurring in humans with vascular disease. Recently, high b value q-space diffusion-weighted imaging (DWI) was shown to be very sensitive to the pathophysiological state of the white matter. We studied the spinal cords of SPSHR rats ex vivo after the appearance of motor impairments using diffusion anisotropy and q-space diffusion imaging (measured at a high b value of up to 1 x 10(5) s/mm(2)). The diffusion anisotropy images computed from low b value data set (b(max) approximately 2500 s/mm(2)) showed a small but statistically significant decrease (approximately 12%, P < 0.05) in the diffusion anisotropy in the spinal cords of the SPSHR group as compared to control rats. However, more significant changes were found in the high b value q-space diffusion images. The q-space displacement values in the white matter of the SPSHR group were found to be higher by more than 70% (P < 0.002) than that of the control group. These observations concurred with electron microscopy (EM) that showed significant demyelination in the spinal cords of the SPSHR group. These results seem to indicate that high b value q-space DWI might be a sensitive method for following demyelination and axonal loss associated with vascular insults.

Reduction by propranolol of raised urinary output of MHPG in hyperactive rats

Prolonged isolation of rats resulted in hyperactivity in the open field and a significant increase in 24 hr urinary excretion of MHPG (3-methoxy-4-hydroxyphenylglycol). Exploratory activity of group-housed rats in open field was not associated with raised MHPG excretion, compared with that of rats remaining in home cages. Exposure of group-housed rats to 4 degrees C for 2 hr also increased urinary excretion of MHPG. Pretreatment of isolated rats with dl-, d-propranolol or practolol abolished hyperactivity of isolated rats and reduced MHPG output in these rats and in rats exposed to cold. dl-Propranolol did not reduce activity of group-housed rats in open field or their urinary excretion of MHPG. It is suggested that propranolol may have a selective inhibitory effect on stress-induced increases in noradrenaline turnover.

Behavioral differences in the developing rat following postnatal anoxia or postnatally injected AF-64A, a cholinergic neurotoxin

Rat pups were submitted postnatally to one of two procedures: a 25-min exposure to 100% nitrogen or an i.c.v. bilateral injection of AF-64A, 2 nmol contained in 1-microliter saline. Throughout further development of either group, their performance in passive and active avoidance tests and in amphetamine-induced stereotype behavior was followed and compared. Both groups exhibited hyperactivity which persisted until 42 days of age in the anoxia group and beyond 120 days in the AF-64A group. Both groups were equally inferior to controls in the passive avoidance test, but only the anoxia group was inferior to controls in the active avoidance test. Amphetamine-induced stereotype behavior was much less pronounced in the anoxia group relative to AF-64A-treated rats or to controls. The results suggest that the lesion induced by the neurotoxin is more specific and less widespread than the one caused by anoxia.