S. Eliash

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.

Role of adrenergic neurone blockade in the hypotensive action of propranolol

1 Propranolol, in doses of 25–100 μg/kg, blocks contractions of the nictitating membrane to nerve stimulation but not to injected noradrenaline. 2 This adrenergic neurone blocking action of propranolol is antagonized by amphetamine. 3 It is also reversed by raising the dose of propranolol to amounts exceeding 0·5 mg/kg. 4 Still larger amounts potentiate the responses of the nictitating membrane to both submaximal stimulation of the cervical sympathetic nerve and to injected noradrenaline. 5 The (+) isomer of propranolol produced adrenergic nerve blockade and some degree of hypotension without blocking cardiac β‐adrenoceptors. 6 The relevance of adrenergic neurone blockade to the hypotensive effect of propranolol is discussed.

The muscarinic cholinergic receptors in the posterior hypothalamus of hypertensive and normotensive rats

The density of [3H]quinuclidin-3-yl benzilate ([3H]QNB) binding sites in the posterior hypothalamus was determined in spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats at the ages of 1, 3, 11 and 50 weeks. In SHR, even at the early age of 1 week which is prehypertensive, the values obtained were 1.5 times greater than those of age-matched WKY rats. The values of the equilibrium dissociation constant (KD) did not differ between SHR and WKY rats of the same age. In the pons medulla, however, the density of [3H]QNB binding sites was not different between the two strains of rats of matching age. Isolation-induced hypertension in adult Wistar rats and an increase in the density of [3H]QNB binding sites in the posterior hypothalamus were observed to arise concomitantly. A hypothesis is offered whereby a relative increase in ACh receptor sites in the posterior hypothalamus is a primary cause of hypertension in the models considered.

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.

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.

Neuroprotective effect of rasagiline, a monoamine oxidase-B inhibitor, on spontaneous cell degeneration in a rat model.

Summary.Spontaneously hypertensive rats (SHR) pathologically elevate blood pressure with age. This elevation is accompanied by specific neuronal degeneration in the hypothalamus and enlargement of the lateral ventricles. The aim of this study was to assess the neuroprotective effect of the monoamine oxidase B (MAO-B) inhibitor, rasagiline on paraventricular (PVN) hypothalamic degeneration in SHR. The S-enantiomer of rasagiline, S-PAI, a much weaker MAO inhibitor, and two antihypertensive drugs, captopril and hydralazine were also tested. Normotensive Wistar Kyoto (WKY) rats served as controls. One month-old SHR or WKY rats were treated daily for 3–4 months. Systolic blood pressure was recorded, parvocellular vasopressin (VP) immunopositive cells were counted and the area of the third ventricle measured. In saline-treated SHR, blood pressure rose significantly and the number of VP parvocellular cells was reduced by about 60% relative to WKY. Rasagiline, 1 mg/kg/day, reduced PVN neuronal cell death in SHR up to 112% relative to saline-treated SHR; 0.3 mg/kg/day exerted a smaller but significant effect. These actions were accompanied by parallel reductions in systolic blood pressure. Captoril, hydralazine and S-PAI did not prevent death of VP neurons. In SHR, the volume of the third ventricle was about double that of WKY. Rasagiline significantly prevented this ventricular dilation. These results indicate than rasagiline protects from cell death in an in vivo animal model in a dose-dependant manner and could be of use as a neuroprotector in the central nervous system.

Neurodegeneration in thiamine deficient rats? A longitudinal MRI study

Selective neurodegeneration accompanied by mitochondrial dysfunction characterizes neurodegenerative disorders such as Alzheimers and Parkinsons diseases. Thiamine deficiency (TD) in rats is a model for the study of cellular and molecular mechanisms that lead to selective neuronal loss caused by chronic oxidative deficits. Neurodegeneration in TD-rats develops over a period of 12 to 14 days and can be partially reversed by thiamine administration. The aim of this study was to characterize the in-vivo progression of neurodegeneration and the neuronal rescue processes in TD using T(2) magnetic resonance mapping and diffusion tensor imaging (DTI). Each rat was scanned prior to TD induction (day 0), before the appearance of neurological symptoms (day 10), during the symptomatic stage (days 12 and 14) and during the recuperation period (days 31 and 87). Time-dependent lesions were revealed mainly in the thalamus and the inferior colliculi. Early decrease in the fractional anisotropy (FA) was found on day 10 in the inferior colliculi and to a lesser degree in the thalamus, while the earliest detectable changes in the T(2) parameter occurred only on day 12. FA values in the thalamus remained significantly low after thiamine restoration, suggesting irreversible disarrangement and replacement of neuronal structures. While T(2) values in the frontal cortex demonstrated no lesions, FA values significantly increased on days 14 and 31. An enlargement of the lateral ventricles was observed and persevered during the recovery period. This longitudinal MRI study demonstrated that in TD MRI can detect neurodegeneration and neuronal recovery. DTI is more sensitive than T(2) mapping in the early detection of TD lesions.

Insight into blood-pressure control in SHR via the response to acute hemorrhage: a spectral analysis approach

In this study we investigated, by means of the spectral analysis approach, the possible alterations in the activity of the pressor-control mechanisms in relation to the development of essential hypertension. Since the maintenance of controlled arterial blood pressure (ABP) levels is achieved by a continuously fluctuating control system, instantaneous ABP varies continuously in direct correlation with the activation of various control branches. The power spectrum of ABP fluctuations thus provides a quantitative measure of the activity of the various controlling mechanisms. Two strains of rats, Spontaneously Hypertensive Rats (SHR) and Wistar-Kyoto normotensive rats (WKY), were subjected to acute hemorrhage, a procedure known to trigger a strong response, of both the neural (autonomic nervous system) and the hormonal (renin-angiotensin and vasopressin) systems. ABP was continuously recorded from the caudal artery in conscious, 1-month-old SHR and WKY. Three groups of rats were studied. Group 1, acute 2-ml hemorrhage; Groups 2, injection of prazosin (2.5 mg/kg) or Group 3, captopril (4 mg/kg), each followed by bleeding as in the group 1. Spectral analysis of ABP fluctuations was performed on time traces of 20 min duration. The low-frequency part of the power spectrum was analyzed. Three frequency bands were investigated: 0.004-0.04 Hz, 0.04-0.07 Hz and 0.07-0.1 Hz. In SHR, although the baseline mean ABP levels were similar to those of WKY, ABP fluctuations were significantly dampened in SHR in each of the three frequency ranges. Hemorrhage induced, in both strains, a similar fall in mean ABP accompanied by an increase in the slow ABP fluctuations. However, in SHR, the response was significantly greater that that of WKY. The steepest response was observed in the slowest, 0.004-0.04 Hz frequency band, 8.7 +/- 1.7 vs. 1.5 +/- 0.4 times the baseline levels. However, this intense increase in power after hemorrhage brought the two strains to similar levels. The difference in the response to bleeding was eliminated, in the three frequency ranges, by alpha 1 blockade. Captopril reduced the response to bleeding in SHR, to the level observed in WKY in all three frequency bands. Spectral analysis of the spontaneous oscillations in ABP unmasks abnormalities which conventional blood pressure measurements cannot detect in 1-month-old, still normotensive SHR. It thus, provides a tool to study the dynamics of the abnormalities which precede the development of hypertension. Bleeding amplifies the malfunction observed in SHR under baseline conditions, since the mean ABP levels were similar in both strains before and after bleeding, SHR seem to retain the ability to respond to a fall in blood volume by requiring a greater recruitment of the control mechanisms than WKY.

Neuroprotection by rasagiline in thiamine deficient rats.

Thiamine deficiency (TD) in rats is a model of chronic impairment of oxidative metabolism leading to neuronal loss. TD rats exhibit neuropathological, behavioral and cognitive abnormalities. The aim of this study was to use this syndrome to assess the neuroprotective potential of drugs in a whole animal model. TD was produced in rats using the following protocol: thiamine deficient diet, daily injections of the central thiamine antagonist, pyrithiamine (0.5 mg/kg), and the test drugs, the selective monoamine oxidase (MAO) B inhibitors, rasagiline (1 or 3 mg/kg/day) and selegiline (2.4 or 8 mg/kg/day). Normal rats and untreated TD rats served as controls. Upon the appearance of neurological symptoms, the TD protocol was suspended, rats were transferred to a regular diet, pyrithiamine and test drug injections were terminated and rats were injected with 3 daily doses of thiamine (100 mg/kg). Neuroprotective potential was assessed by: general behavioral observations, cognitive testing using the Morris water maze and histopathological examination of the brains. Rasagiline but not selegiline significantly delayed the onset and severity of the neurological symptoms of TD. In the Morris water maze, TD-untreated rats displayed severe cognitive impairment while rasagiline-treated rats were similar to control rats and significantly different from TD-untreated rats. The effects were dose related. Selegiline treatment had no significant protective effect. TD-untreated brains displayed extensive gliotic and necrotic lesions mainly in the thalamus and posterior collicular nucleus, which were significantly reduced in the rasagiline-treated TD rats. These findings demonstrate significant neuroprotection by rasagiline with possible implications for clinical neurodegenerative disorders.

Factors influencing the adrenergic neurone blocking action of propranolol

1 The reversal by propranolol of its own adrenergic neurone blocking effect in the cat can be prevented by cutting the splanchnic nerves or by ligating the adrenal veins. 2 In the absence of secretion from the adrenal medulla the nerve blocking action of propranolol is more complete, but can still be reversed by repeated injections or a constant infusion of adrenaline. 3 Prior treatment with adrenaline or noradrenaline also prevents the development of the blocking action of propranolol in the cat and in the isolated guinea‐pig vas deferens. 4 It is suggested that in the cat, propranolol stimulates the release of catecholamines from the adrenal medulla which antagonize its nerve blocking effect.