Effect of calcium on the histochemical distribution and intensity of biogenic amine-containing neurons in the mouse brain

Regulation of blood pressure with calcium-dependent dopamine synthesizing system in the brain and its related phenomena

The effects of calcium on blood pressure regulation remain controversial. Although the mechanism by which calcium increases blood pressure when it is given intravenously and acutely has been elucidated, that by which calcium reduces blood pressure when it is supplemented chronically and slightly through daily diet is unclear. From a number of animal experiments concerning the effects of calcium on blood pressure, we believe that calcium ions have two separate roles in the regulation of blood pressure through both central and peripheral systems: (1) calcium ions reduce blood pressure through a central, calcium/calmodulin-dependent dopamine-synthesizing system and (2) calcium ions increase blood pressure through an intracellular, calcium-dependent mechanism in the peripheral vasculature. These concepts were applied to elucidate the mechanisms underlying hypertension in spontaneously hypertensive rats (SHR) and changes in blood pressure in other experimental animals, and the following conclusions were reached. The decrease of the serum calcium level in spontaneously hypertensive rats (SHR) causes a decrease in calcium/calmodulin-dependent dopamine synthesis in the brain. The subsequent low level of brain dopamine induces hypertension. The increase in susceptibility to epileptic convulsions and the occurrence of hypertension in epileptic mice (El mice) may be linked through a lowering of calcium-dependent dopamine synthesis in the brain, and epilepsy and hypertension may be associated. Exercise leads to increases in calcium-dependent dopamine synthesis in the brain, and the increased dopamine levels induce physiological changes, including a decrease in blood pressure. Cadmium which is not distinguished from calcium by calmodulin, activates calmodulin-dependent functions in the brain, and increased dopamine levels may decrease blood pressure. In this report, our studies are considered in light of reports from many other laboratories.

Enhanced depressor effect of centrally administered high-calcium solution in salt-loaded experimental hypertension

The depressor effect by oral calcium supplementation is known to be more pronounced in salt-dependent than in renin-dependent hypertension. This study was conducted to investigate the role of central calcium on two different pathophysiologic subtypes of experimental hypertension; (a) salt-dependent, deoxycorticosterone acetate-salt hypertensive rats (DOCA), and (b) renin-dependent, 2-kidney, 1 clip (2-K, 1C) hypertensive rats. In DOCA (n = 10), high-calcium solution (Ca+2, 65.2 mM, 10 microl) given centrally (i.c.v.) elicited a marked decrease in mean blood pressure (MBP; 170 +/- 4 to 138 +/- 5 mm Hg, p < 0.01) with a decrease in heart rate (HR; 390 +/- 18 to 344 +/- 17 beats/min, p < 0.05) lasting for 40 min. In 2-K, 1C (n = 10), high-Ca2+ i.c.v. showed a lesser decrease in MBP (178 +/- 4 to 171 +/- 5 mm Hg) and HR (419 +/- 10 to 395 +/- 12 beats/min) with shorter duration (for 20 min) than in DOCA. This significant depressor and bradycardic response to Ca2+ i.c.v. observed in DOCA was dose dependent at Ca2+ concentrations between 65.2 and 130.4 mM. In DOCA, high Ca2+ i.c.v. reduced the plasma noradrenaline (Nad) concentration significantly (479 +/- 81 to 319 +/- 62 pg/ml, p < 0.05). These results suggest that central Ca2+ plays a more important role in regulating sympathetic nerve activity and BP in salt-dependent than in renin-dependent experimental hypertension.

Centrally administered calcium increases the maximum vagal activation of baroreceptor reflex control of heart rate in spontaneously hypertensive rats

Baroreceptor reflex control of heart rate (HR) was examined before and 15 min after intracerebroventricular infusion (i.c.v.) of 10 microliters of high-Ca2+ solution (Ca2+, 16.3 mM) in conscious spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). The slope of the individual regression line of the relation between reflex HR changes (delta HR) and changes in mean arterial pressure (delta MAP) produced by bolus injections of phenylephrine or sodium nitroprusside (delta HR/delta MAP; beats/min/ mm Hg) for bradycardia was significantly less in SHR (-0.60 +/- 0.30; n = 10) than in WKY (-1.78 +/- 0.27; n = 10; p < 0.01) at baseline. The slope increased in SHR during administration of high Ca2+ to -1.39 +/- 0.17 (p < 0.01) but not in WKY: In contrast, no significant changes were observed for the reflex tachycardia both in SHR (n = 7) and WKY (n = 10). Further, we analyzed sigmoidal MAP-HR reflex curves in SHR with i.c.v. of either high Ca2+ (n = 6) or artificial cerebrospinal fluid (aCSF; n = 5). Administration of high Ca2+ reduced the bradycardic plateau and increased HR range without changes in average gain. Our results suggest a modulatory role for central Ca2+ in the baroreceptor reflex control of HR in SHR.

Depressor effect of intraventricular administration of calcium on spontaneously hypertensive rats

The role of central Ca2+ in the regulation of blood pressure (BP) was investigated in conscious spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). Ten microliters of a high Ca2+ solution (Ca2+: 32.6 mM) administered intracerebroventricularly (i.c.v.) decreased the mean arterial pressure (MAP) for more than 20 min in SHR (n = 7, P < 0.005), while no change of MAP was observed in the WKY (n = 6). This depressor response to Ca2+ i.c.v. was dose-dependent at Ca2+ concentrations between 16.3 and 65.2 mM. We also investigated the effect of high Ca2+ i.c.v. in SHR after pretreatment with Ca2+ channel blockers, diltiazem (60 micrograms/10 microliters) or nisoldipine (4, 8, 16 and 32 micrograms/10 microliters), administered i.c.v., the autonomic ganglion blocker, hexamethonium (50 mg/kg), administered i.v. and alpha-methyl-p-tyrosine (100 and 400 micrograms/10 microliters) delivered i.c.v. Pretreatment with i.c.v. diltiazem (n = 8) or nisoldipine (n = 5 for 8 micrograms, n = 6 for 4, 16, 32 micrograms) abolished and/or blunted the decrease of MAP due to high Ca2+. Hexamethonium administered i.v. (n = 6) also canceled the depressor action of i.c.v. Ca2+. Pretreatment with 100 micrograms of i.c.v. alpha-methyl-p-tyrosine could not prevent the depressor action of i.c.v. Ca2+; however, 400 micrograms of alpha-methyl-p-tyrosine administered i.c.v. abolished the effect of i.c.v. Ca2+. Furthermore Ca2+ channel blockers administered i.c.v. in themselves increased MAP in SHR (P < 0.05). These results suggest that central Ca2+ is involved in the central regulation of BP in SHR. This effect may be mediated through changes in sympathetic activity.

Contribution of the central interaction between calcium and sodium to hemodynamic regulation in spontaneously hypertensive rats

The contribution of the central interaction between calcium and sodium to hemodynamic regulation was assessed in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats. The effect of a high calcium solution (Ca2+, 130 mg/dl, 10 microliters) infused into the cerebral ventricle (i.c.v.) on hemodynamic responses induced by a high sodium solution (Na+, 1,000 mEq/1, 10 microliters) i.c.v. and the mechanism by which high Ca2+ affects the hemodynamic responses induced by high Na+ i.c.v. were studied. High Na+ i.c.v. induced a pressor response with tachycardia in the SHRs, but induced a pressor response with reflex bradycardia in the WKYs. Prior treatment with high Ca2+ i.c.v. attenuated the pressor response induced by high Na+ i.c.v. (+55.6 +/- 4.4 to +33.1 +/- 3.2 mmHg, P < 0.01) and restored reflex bradycardia (+86.4 +/- 7.7 to -26.7 +/- 7.6 bpm, P < 0.01) in SHRs. Whereas prior treatment with high Ca2+ i.c.v. attenuated the pressor response (+35.7 +/- 2.0 to +22.2 +/- 4.0 mmHg, P < 0.05), it did not alter the degree of reflex bradycardia (-81.7 +/- 7.1 to -69.2 +/- 120 bpm, n.s.) in WKYs. Ganglionic blockade attenuated the pressor response (+56.9 +/- 3.5 to +42.9 +/- 2.3 mmHg, P < 0.05) and restored reflex bradycardia (+82.1 +/- 10.3 to -65.9 +/- 11.0 bpm, P < 0.01) in SHRs, whereas, inhibition of arginine vasopressin attenuated the pressor response without modification of the tachycardic response.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of convulsions on the rectification of central nervous system disorders in epileptic mice

Abnormal behavior in epileptic mice (El mice) may be rectified after convulsive seizures. This mechanism was investigated behaviorally through measurements of ethanol-induced sleeping time and locomotor activity, as well as immunohistochemically using a microphotometry system. Decreased ethanol-induced sleeping time and increased ethanol-dependent locomotor activity in El mice as compared to ddY mice (the mother strain of El mice) were rectified by convulsions as well as the intraventricular (IVT) administration of CaCl2, dopamine, or serotonin. Also, the lower dopamine levels in the neostriatum and nucleus accumbens septi in El mice as compared to ddY mice were improved by convulsions as well as the IVT administration of CaCl2. We have previously observed that a lower level of serum calcium in El mice causes a decrease in central biogenic amine synthesis through a calmodulin-dependent system. This may increase the susceptibility to epileptic convulsions and induce abnormal behavior. Combining the present results with our previous observations, we suggest that the convulsions in El mice will be induced when the balance of physiological functions is lost, as may be seen when the biogenic amine syntheses are decreased. The serum calcium level in El mice is increased by convulsions, and an elevated serum calcium level enhances brain biogenic amine synthesis through a calmodulin-dependent system. Subsequently, biogenic amines rectify physiological disorders in El mice.

Multiple analysis of tyrosine hydroxylase and calmodulin distributions in the forebrain of the rat using a microphotometry system

Immunohistochemical distributions of tyrosine hydroxylase and calmodulin in the rat forebrain were analyzed quantitatively to confirm our previous results that the activities of central catecholamine-synthesizing enzymes are regulated by a calcium-calmodulin-dependent system. The adjacent slices of adult rat brain were stained immunohistochemically for tyrosine hydroxylase and for calmodulin, and the distributions and amounts of these proteins were measured by a fluorescence microphotometry system that was developed in our laboratory. Immunohistochemical fluorescence intensity was measured stepwise at 40 microns intervals through a 6 microns phi (on the slice) pin hole. Each stained brain slice was divided into approximately 100,000 areas, and measured for fluorescence intensity and displayed two- and three-dimensionally. Immunoreactive staining of tyrosine hydroxylase and calmodulin was observed in almost all areas of the brain, but its intensity varied. The relatively high levels of calmodulin could be observed in brain regions with high levels of tyrosine hydroxylase distribution, though high levels of tyrosine hydroxylase could not always be observed in brain regions where high levels of calmodulin were distributed. In the present study, high levels of tyrosine hydroxylase and calmodulin were distributed in the nucleus accumbens septi and the lateral part of the neostriatum regions in which the amount of dopamine was increased by the intraventricular administration of calcium. These findings suggest that the synthesis of central catecholamines is regulated by a calcium-calmodulin-dependent system.

Effect of intraventricular administration of calcium on the lowering of brain dopamine level in epileptic mice

Dopamine (DA) levels in the various brain regions of epileptic mice (El mice) were compared immunohistochemically with those in ddY mice (the mother strain of El mice) using a fluorescence microphotometry system. The fluorescence intensities of DA in the neostriatum and nucleus accumbens septi in El mice were approximately 11-15% (P less than 0.01) and 13% (P less than 0.01) lower than in ddY mice. On the other hand, the lower DA amounts in these regions of El mice were improved by intraventricular administration of CaCl2 (10 mumol/kg). The brain regions in which the amount of DA was increased by calcium were areas where high levels of calmodulin and tyrosine hydroxylase are distributed. This finding reconfirmed our previous report that the biogenic amine level disorder in El mice was related to a calcium ion level disorder through a central calcium-calmodulin-dependent biogenic amine-synthesizing mechanism, and this might increase their susceptibility to epileptic convulsions.

Central dopamine-synthesis regulation by the calcium-calmodulin-dependent system

The effects of the intraventricular (IVT) administration of calcium on the amount of dopamine (DA) in various regions of the mouse brain were analyzed immunohistochemically by using a microphotometry system. The DA levels in the nucleus accumbens and the lateral part of the neostriatum were increased by approximately 45% (p less than 0.01) and 25-35% (p less than 0.01), respectively, by the IVT administration of CaCl2 (10 mumol/kg). It was also found that this effect was abolished by the calmodulin antagonist, W-7 (4.2 micrograms/mouse, IVT). The brain regions in which the amount of DA was increased by calcium were areas where high levels of calmodulin and tyrosine hydroxylase are distributed. These findings suggest that the synthesis of central DA is regulated by calcium through a calmodulin-dependent system.

The mechanism by which calcium reduces blood pressure

The mechanism by which exogenous calcium reduces blood pressure was investigated. The verapamil (300 micrograms/kg i.v.)-induced decrease of the mean arterial pressure in the conscious rat was prolonged by 400% by pretreatment with CaCl2 (300 mumol/kg i.v.). This ability of calcium to enhance the effect of verapamil was decreased by i.c.v. injection of EDTA (10 nmol/kg). In light of our previous reports, these results suggest that i.v. calcium reduces blood pressure by a central calcium-calmodulin-dependent mechanism.

1H-NMR studies of calmodulin: the modifying effect of W-7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide) on the calcium-induced conformational changes of calmodulin

The effect of W-7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide), a calmodulin antagonist, on the calcium-bound conformation of calmodulin was studied by 1H-NMR at 400 MHz. W-7 affected the resonances of Ile-27, Phe-68, Phe-92, Ile-100, His-107 and Val-142. The resonances of Met-71, Met-72, Met-76, Phe-89 and Phe-141 may be affected by W-7. These findings suggest that W-7 binds to hydrophobic amino acid residues, which almost occur in calcium-binding sites II, III and IV or their vicinity. The effect of W-7 on the structure of calmodulin was similar to that of other drugs, trifluoperazine, D600 and oxmetidine. Thus, those residues in the high-field methyl region, the methionine methyl region and the phenylalanine aromatic region of calmodulin, which were similarly affected by all four drugs, may be important at the interface for binding of calmodulin to the regulatory sites on target enzymes.

Effect of intraventricular administration of calcium and calmodulin antagonist on the blood pressure in the rat

The effect of intraventricular administration of calcium on the mean arterial pressure in the conscious rat was investigated. Biphasic changes of blood pressure, fugitive rapid increment during the first 3 min and gradual lengthy decrement during the next 60 min were observed by the administration of CaCl2 (30 mumol/kg). Both these changes were significant as compared with the control level. On the other hand, the biphasic response of blood pressure by CaCl2 was abolished by the administration of calmodulin antagonist, W-7, or catecholamine synthesizing enzyme inhibitor, alpha-methyltyrosine. These results are discussed on the basis of our calcium-calmodulin-dependent biogenic amine-synthesizing mechanism.

The relationship between metal ion levels and biogenic amine levels in epileptic mice

The metabolism of various metal ions and biogenic amines in El mice, an inbred mutant strain susceptible to epilepsy, was investigated as a possible model for seizure mechanism. Serum Na, P, Ca, Mg, Fe and Zn levels in El mice were lower than those in ddY mice, the mother strain of El mice. Conversely, bone Ca, P, Na, Mg and Zn levels in El mice were higher than those in ddY mice. The results obtained by chemical analysis are consistent with radiographic observations. Possible mechanisms for the lower serum metal ion levels seen in El mice include a decrease in availability of these ions from bone. The dopamine (DA) level in El mouse brain was 15% lower than in ddY mice but could be raised by intraventricular administration of CaCl2. This result was supported a decreased ethanol-induced sleeping time in El as compared to ddY mice, with 'normalization' occurring after intraventricular administration of Da or CaCl2. The biogenic amine levels disorder in El mice is discussed on the basis of our pharmacological observation that biogenic amine synthesis is regulated by divalent cations via a calmodulin-dependent system. Our results suggest that the disorders of metal ion metabolism could be a mechanism for epileptic convulsions in El mice.