Differential behavioral syndrome evoked in the rats after multiple doses of SSRI fluoxetine with selective MAO inhibitors rasagiline or selegiline

This study investigated whether rasagiline and selegiline (MAO-B inhibitors) induce serotonin syndrome in fluoxetine-treated rats. Rats received rasagiline (0.1, 0.5, 2.0 mg/kg), or selegiline (0.8, 4.0, 16.0 mg/kg) (doses reflecting the clinical ratio of 1:8 base) in drinking water for 28 days. During the last 21 days, they received injections of fluoxetine 10 mg/kg (controls received water only, then saline injections; a fluoxetine only group received water only then fluoxetine). Serotonin syndrome was assessed using neurological severity score (NSS), food intake and weight gain. Mean NSS significantly increased, and weight and food consumption significantly decreased in rats receiving fluoxetine alone compared with controls. Selegiline 16 mg/kg but not rasagiline (regardless of dose) exacerbated these effects. We concluded that selegiline's amphetamine-like metabolites may increase synaptic cathecholamines and possibly serotonin, aggravating fluoxetine's effect. Rasagiline is devoid of this effect and may therefore be safer for use with serotonergic drugs in parkinsonian patients.

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

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.

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

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.

Nonlinear dynamics applied to blood pressure control

Hypertension is a very frequent disease, known to trigger a range of severe cardiovascular problems. The elucidation of its pathophysiology requires investigation of the mechanisms responsible for the maintenance of blood pressure in the normal system, and their possible failure in hypertension. Some of these control mechanisms display nonlinear features, indicating that the blood pressure signal might be characterized by nonlinear dynamics. Our aim was thus to investigate the nonlinear properties of the blood pressure signal under normal conditions, and in a cardiovascular system prone to hypertension. Blood pressure was investigated in young spontaneously hypertensive rats (SHR), versus their age-matched normotensive progenitors (WKY). The correlation dimension was computed as quantification of blood pressure control complexity. The parameters required for the calculation procedure of the correlation dimension were carefully determined. The results were tested with surrogate data statistics. assuming linear autocorrelated Gaussian noise as the null hypothesis. Non-integer correlation dimension values were found in both strains, with lower values for SHR than for WKY, in particular following alpha-blockade. In all cases, a statistically significant difference was found between the real and surrogate data. These results show that the nonlinear dynamics parameter D, can be used to detect differences in BP control between prehypertensive SHR and WKY rats as early as 6-7 weeks after birth.

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

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 1-3mg/kg within 16h, 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 24h, and 7.64 +/- 2.52 (n +/- 49) at 48h, to a low of 7.13 +/- 2.32 (n = 88) at 24h, and 4.99 +/- 2.31 (n = 68) at 48h. Under the same conditions, there was a decrease in the volume of necrotic brain region determined at 48h by triphenyl tetrazolium chloride (TTC), from a high of 240 +/- 66 (n = 54) to a low of 176 +/- 77 mm(3) (n = 55); and by MRI scan at 48h, from a high of 297 +/- 62 (n = 25), to a low of 209 +/- 63 mm(3) (n = 28). Improvement in NSS was more obvious at 48h 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 48h 5.6 +/- 2.5 (n = 24) vs. 7.5 +/- 2.5 (n = 24), infarct volume 200 +/- 64 (n = 24) vs. 240 +/- 55 mm(3) (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 +/- 52mm(3) (n = 21) but could not improve NSS at 24 or 48h. In this model, rasagiline could have exerted a neuroprotective effect independent of MAO inhibition.

Computer-controlled heart rate increase by isoproterenol infusion: mathematical modeling of the system

The purpose of this study was mathematical modeling of the heart rate (HR) response to isoproterenol (Iso) infusion. We developed a computerized system for the controlled increase of HR by Iso, based on a modified proportional-integral controller. HR was measured in conscious, freely moving rats. We found that the steady-state HR can be described as a hyperbolic power function of the steady-state Iso flow rate. This dependence was coupled with a first-order difference equation to form a pharmacodynamic model that reliably describes the relationship between HR and Iso flow for any arbitrary form of Iso flow function. In simulation studies, we showed that the model continued to follow the HR curve from real-time experiments far beyond the initial "learning interval" from which its parameters were calculated. Our results suggest that the predictive ability and the simplicity of calculating the parameters render this pharmacodynamic model appropriate for use within future advanced, model-based, adaptive control systems and as a part of larger cardiovascular models.

The diastolic decay constant in spontaneously hypertensive rats versus WKY rats as an indicator for vasomotor control

This research uses the diastolic decay constant (tau) to investigate the short term mechanism responsible for vasomotor control, mainly the alpha-sympathetic control system. Previous studies have shown that vasomotor control is altered in spontaneously hypertensive rats (SHR) preceding the phase of overt hypertension. The diastolic decay, according to the two element Windkessel model, displays an exponential shape with a decay constant, tau, depending on both the vascular resistance and the compliance. In our experiments, we used tau to characterize vasomotor activity and its control in the normotensive rats as well as in the spontaneously hypertensive rats (SHR) prone to hypertension. The beat to beat value of tau was evaluated from a continuous arterial blood pressure (ABP) signal, measured in the tail artery of the conscious, unrestrained rat. Four months old prehypertensive SHR were compared to their age matched normotensive controls (WKY). To study vasomotor regulation, we computed gains and delay times by investigating the compensatory response in tau to changes in mean ABP (MBP). These parameters are expected in the short term to be neurally controlled by the sympathetic system, mainly alpha-sympathetic. Our set of experiments consisted of changing MBP by performing successive injections in bolus of increasing doses of the vasoconstrictor angiotensin II. This procedure was repeated under double cardiac autonomic blockade of the vagal and beta 1 = sympathetic limbs. Our results show that, under baseline conditions, the absolute gain and delay times of tau are reduced in SHR compared to WKY. Double cardiac blockade decreases the absolute gain in both strains, while abolishing the baseline strain differences. These results reinforce our assumption that, in SHR, the alpha-sympathetic system is in a basic state of excitation even prior to the onset of overt hypertension and therefore reacting with reduced sensitivity (lower gain) to changes in MBP.

Nonlinear analysis of BP signal. Can it detect malfunctions in BP control?

In the present study, our aim was to evaluate the applicability of the nonlinear technique to the investigation of cardiovascular control. We applied an approach known as the "surrogate data method" to test for nonlinear components in the blood pressure (BP) signal. Our results strongly indicate that there are nonlinear components in the BP time series taken from a Wistar-Kyoto rat (WKY), suggesting that the use of nonlinear methods may provide new information about the BP control system. We developed a procedure appropriate for the stable and reliable calculation of the Grassberger-Procaccia correlation dimension (D) of the arterial BP signal. The saturation value D was 5.48 +/- 0.30 for the WKY group and 5.92 +/- 0.26 for the spontaneously hypertensive rat (SHR) group, with P < 0.001. We also found that in the WKY group D displays a significant response to complete alpha 1 blockade and bleeding, whereas no response is observed in the SHR group. These results imply that differences in the control mechanisms may be detected by the nonlinear dynamics approach both under baseline conditions and when interfering with cardiovascular control.

Effect of haemorrhage on the power of low frequency blood pressure fluctuations in young spontaneously hypertensive rats

1. Before the onset of hypertension low frequency (0.04-0.1 Hz) MAP fluctuations are reduced in SHR when compared to WKY. We studied the effect of haemorrhage under alpha1 blockade or angiotensin converting enzyme inhibition (CEI) on the power spectra (PS) of each strain. 2. MAP was recorded from the caudal artery in conscious, 1 month old SHR and WKY. Three groups of rats were studied. Group 1, acute 2 mL haemorrhage; groups 2 and 3, injection of prazosin (0.25-2.5 mg/kg) or captopril (0.5-4 mg/kg), followed by haemorrhage, as in group 1. The PS was divided into 3 frequency bands, 0.004-0.04, 0.04-0.07 and 0.07-0.1 Hz. 3. In SHR, although the baseline MAP levels were similar to those of WKY, the PS was significantly damped in each of the 3 frequency bands. 4. Haemorrhage induced a similar MAP fall in both strains accompanied by an increase in the slow MAP fluctuations. However, in SHR the PS response was significantly greater than in WKY. The biggest response was in the slowest (0.004-0.04 Hz) frequency band, 8.7 +/- 1.7 vs 1.5 +/- 0.4 times baseline levels, respectively. 5. The difference between the two strains in the PS response to haemorrhage was eliminated by alpha1 blockade. The exaggerated response observed in haemorrhaged, unblocked SHR was reduced in the 3 frequency bands. 6. Captopril reduced the PS response to haemorrhage in SHR to the level observed in WKY in all 3 frequency bands. 7. The enhanced amplification of the MAP fluctuations in haemorrhaged SHR may indicate that SHR requires greater recruitment of control mechanisms than WKY to maintain MAP at a similar level to WKY.

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.

The antihypertensive effect of ethylcholine aziridinium (AF64A), a cholinergic neurotoxin, in spontaneously hypertensive rats, following administration into the posterior hypothalamus

The aim of this study was to ascertain whether drug-induced cholinergic hypofunction in the posterior hypothalamus would affect the development and the maintenance of hypertension in hypertensive rats. Spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats were treated with AF64A, a neurotoxin which can irreversibly inhibit cholinergic transmission in vivo. AF64A or saline was injected bilaterally into the posterior hypothalamus of rats of two age groups: normotensive one month-old rats whose blood pressure was subsequently measured at the age of three months and hypertensive three month-old rats, whose blood pressure was measured four weeks later. In both age groups there was a significant fall in mean arterial blood pressure in SHR but not WKY rats. In SHR injected at the age of one month, there was a fall of at least 15.9 mm Hg, while in the rats injected at the age of three months there was a fall of 14.3 mm Hg. Heart rate in either strain was not affected. When AF64A was injected into the anterior hypothalamus of one month-old SHR, no antihypertensive effect was observed in these rats at the age of three months. These results show that cholinergic stimulation in the posterior hypothalamus may play a role in both the development and maintenance of hypertension in SHR.

Hemodynamic regulation in SHR: investigation by spectral analysis

This work is based on the premise that hypertension in the spontaneously hypertensive rat (SHR) is a consequence of an imbalance in autonomic cardiovascular control. Spontaneous, instantaneous fluctuations in heart rate (HR) and arterial blood pressure (ABP) were studied by spectral analysis in age-matched groups of SHR and normotensive Wistar-Kyoto (WKY) rats. Continuous recordings of ABP and HR made in conscious, unrestrained, young 1-, 2-, 3-, and 6-mo-old rats show that power spectra of HR fluctuations were similar in both strains, whereas ABP fluctuations were significantly different in the low, presumably vasomotor frequency range being reduced in SHR as compared with age-matched WKY rats. In 1-mo-old rats, the difference between strains became smaller with urethan anesthesia and disappeared with spinalization, suggesting that it might have originated in some disparity between the strains at the level of the central nervous system. Low doses of phentolamine elicited a fall in low-frequency ABP fluctuations of WKY but a rise in SHR, whereas larger doses produced a fall in the power of both. In SHR, reduction in the power spectrum of ABP fluctuations in the presence of unaltered HR fluctuations may indicate an impaired control of sympathetic drive to resistance vessels compared with WKY. Note that in young SHR, hypertension also cannot be detected by conventional measurement. Fluctuations in ABP in WKY may reflect an optimal level of sympathetic activity; reduction in fluctuations may be associated with an increase or decrease in sympathetic activity at the vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Prevention by drugs of tachyphylaxis at nicotinic receptors in the cat superior cervical ganglion in situ

A new compound, AF3 (4-ethyl-6-oxa-1-azatricyclo)4.2.2.02,7)dodecan-5-one), and its 4-phenyl analogue, AF6, embodying the structural elements of acetylcholine in a highly rigid framework, were shown to evoke nicotine-like responses in the nictitating membrane (NM) and blood pressure when applied to the superior cervical ganglion in anaesthetized cats. In this respect, their equiactive molar ratio was (nicotine : 1),20-30. However, at doses that were too low to evoke any response, AF3 appeared to potentiate the responses to nicotine or tetra-methylammonium (TMA) by preventing or abolishing tachyphylaxis to the two latter drugs, the effect being dose-dependent with AF3. DMPP which produces much less tachyphylaxis, or preganglionic nerve stimulation, was little or not potentiated in presence of AF3. It is proposed that potentiation to nicotine or TMA occurs following occupancy by AF3 of a regulatory subsite, thereby preventing further access to it by nicotine or TMA. In this respect, AF3 plays the role of a "neutral" molecule.

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.

Role of adrenergic neurone blockade in the hypotensive action of propranolol

1. Propranolol, in doses of 25-100 mug/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 beta-adrenoceptors.6. The relevance of adrenergic neurone blockade to the hypotensive effect of propranolol is discussed.