Local cerebral glucose utilization and local cerebral blood flow in conscious rats after administration of flunarizine

Heterogeneous brain distribution of bumetanide following systemic administration in rats

Bumetanide is used widely as a tool and off-label treatment to inhibit the Na-K-2Cl cotransporter NKCC1 in the brain and thereby to normalize intra-neuronal chloride levels in several brain disorders. However, following systemic administration, bumetanide only poorly penetrates into the brain parenchyma and does not reach levels sufficient to inhibit NKCC1. The low brain penetration is a consequence of both the high ionization rate and plasma protein binding, which restrict brain entry by passive diffusion, and of brain efflux transport. In previous studies, bumetanide was determined in the whole brain or a few brain regions, such as the hippocampus. However, the blood-brain barrier and its efflux transporters are heterogeneous across brain regions, so it cannot be excluded that bumetanide reaches sufficiently high brain levels for NKCC1 inhibition in some discrete brain areas. Here, bumetanide was determined in 14 brain regions following i.v. administration of 10 mg/kg in rats. Because bumetanide is much more rapidly eliminated by rats than humans, its metabolism was reduced by pretreatment with piperonyl butoxide. Significant, up to 5-fold differences in regional bumetanide levels were determined with the highest levels in the midbrain and olfactory bulb and the lowest levels in the striatum and amygdala. Brain:plasma ratios ranged between 0.004 (amygdala) and 0.022 (olfactory bulb). Regional brain levels were significantly correlated with local cerebral blood flow. However, regional bumetanide levels were far below the IC50 (2.4 μM) determined previously for rat NKCC1. Thus, these data further substantiate that the reported effects of bumetanide in rodent models of brain disorders are not related to NKCC1 inhibition in the brain.

Flunarizine enhances functional recovery following sciatic nerve crush lesion in rats

We have used the rat sciatic nerve crush (SNC) injury model to assess the neuroprotective effects of flunarizine (FNZ), a calcium channel antagonist and a vasodilator. The animals were treated with FNZ for various durations following SNC (0.33 mg/kg per day, i.p). Employing the physical disector method, we quantitated the rates of neuron loss in the dorsal root ganglion and spinal cord and protective effects of FNZ. FNZ treatment following SNC reduced neuron loss up to 86.6 and 82.5% in DRG sensory and spinal cord motor neurons, respectively. Functional recovery following SNC with or without FNZ treatment was assessed using the measurements of the total, 1-5 and 2-4-toe spread to quantitate percentage relative toe spread in relation to the respective controls. FNZ provided a superior return of function, i.e. near absolute recovery of both sensory and motor functions in 4 weeks, which is consistent with its neuroprotective effects.

Effects of a new diphenylpiperazine calcium antagonist, KB-2796, on cerebral ischemic neuronal damage in rats

1. The effects of KB-2796, a new diphenylpiperazine calcium antagonist, on the mitochondrial dysfunction and energy metabolism deficits were examined in the ischemic rat brain. 2. KB-2796 (30 mg/kg, p.o.), administered 60 min prior to decapitation, improved the reduced respiratory activity of mitochondria obtained from rat brain 5 min after decapitative ischemia. 3. KB-2796 (30 mg/kg, p.o.), administered 60 min prior to ischemic insult, improved both the reductions in pyruvate and ATP and prevented increases in the lactate/pyruvate ratio induced by 30-min forebrain ischemia in rats with 4-vessel occlusion (4-VO). 4. The effect of KB-2796 on local cerebral glucose utilization (LCGU) was examined by a quantitative autoradiographic 2-[14C]deoxyglucose method in normal and 4-VO rats. 5. Postischemic LCGU measured 24 hr after reperfusion in the forebrain, in particular in the cortex, thalamus, geniculate body, hippocampus, caudate-putamen, nucleus accumbens, colliculus, and corpus callosum, was below the normal control value. 6. KB-2796 (1 mg/kg, i.v.), administered 1 min prior to the injection of 2-[14C]deoxyglucose, improved the reductions in LCGU that were produced by cerebral ischemia in the cortex, thalamus, geniculate body, caudate-putamen, nucleus accumbens and substantia nigra, but did not affect LCGU in normal rats. 7. These findings suggest that KB-2796 minimized the deficits in brain energy metabolism produced by ischemia; this agent may therefore be a valuable therapeutic drug in cerebrovascular-related disorders.

Attenuation of cholinergic analgesia by nifedipine

Nociception was tested in mice receiving oxotremorine or physostigmine either after the dihydropyridine calcium channel blocker nifedipine or the non-calcium antagonist vasodilator hydralazine. Nifedipine did not change the reaction time to thermal stimulation (tail-flick test), but attenuated the prolonging action on tail-flick latencies exerted by the two cholinomimetic agents. Hydralazine had no effect alone nor modified the action of cholinomimetics. The results suggest that attenuation of cholinergic analgesia by nifedipine might be related to not yet defined neuronal changes produced by calcium channel blockade, but changes in the pharmacokinetics of oxotremorine and physostigmine cannot be ruled out.

Facilitation of shuttle-box avoidance behaviour in mice treated with nifedipine in combination with amphetamine

The dihydropyridine calcium channel antagonist nifedipine, tested in mice of CD-1, C57BL/6 and DBA/2 strains, at doses of 2.5, 5 and 10 mg/kg IP, had no significant effect on shuttle-box avoidance acquisition. Nifedipine also failed to affect performance retention in CD-1 mice subjected to a one-trial passive avoidance task (step-through). While ineffective alone, nifedipine strongly enhanced the shuttle-box avoidance facilitating action of amphetamine (1 and 2 mg/kg IP) in low performing CD-1 mice. The results indicate that although calcium channel blockers do not affect learning in avoidance paradigms in normal animals, they can interfere with the effects of other centrally acting drugs. Calcium antagonists might interfere with neuronal changes induced by amphetamine, but at present it is difficult to explain the strong avoidance facilitation produced by combinations of nifedipine and amphetamine. A possibility that the action of nifedipine on cerebral circulation is involved in the amphetamine-nifedipine interaction cannot be excluded.

Effect of flunarizine on electroencephalogram recovery and brain temperature in gerbils after brain ischemia

BACKGROUND AND PURPOSE

This study was designed to determine whether flunarizine enhances the rate of brain recovery as measured by electroencephalography after cerebral ischemia and whether these effects are attributable to changes in brain temperature.

METHODS

Male gerbils (n = 81) were treated with either 10 mg/kg flunarizine or its vehicle, beta-cyclodextrin, intraperitoneally, 60 minutes before bilateral carotid occlusion of either 4 or 6 minutes' duration. The electroencephalogram was continuously recorded in the preischemic, ischemic, and postischemic stages of the experiment and rated for the time necessary for the return of 4-6, 7-10, and 11-15 Hz activity. In a second set of experiments, intracerebral temperature was monitored for 60 minutes before ischemia, during 10 minutes of carotid occlusion, and for 60 minutes after ischemia.

RESULTS

Flunarizine pretreatment resulted in significantly more rapid return of electroencephalographic activity in each of the three frequency categories monitored when compared with those animals pretreated with vehicle alone (p less than 0.001). Flunarizine had no effect on brain temperature before, during, or up to 60 minutes after termination of ischemia.

CONCLUSIONS

Flunarizine, which has been of efficacy in reducing neuronal death, mortality, and functional impairment when administered after ischemic insults, may have prophylactic value in accelerating brain recovery from ischemia, but does not have this effect as a result of altered brain temperature.

HA1077, a novel calcium antagonistic antivasospasm drug, increases both cerebral blood flow and glucose metabolism in conscious rats

The effects of a novel calcium antagonistic antivasospasm drug, HA1077, on local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were studied in 33 anatomically discrete regions of the brain in conscious rats, using the quantitative autoradiographic [14C]iodoantipyrine and [14C]2-deoxyglucose techniques. HA1077 was infused i.v. over a 30-min period (1 or 3 mg/kg). HA1077 significantly increased LCBF in 9 of 33 sites in rats given 1 mg/kg, and in 14 of 33 sites in rats given 3 mg/kg compared to the control group given vehicle. Significant increases in LCGU were also noted in 16 of 33 sites in rats given 3 mg/kg. HA1077 increased both cerebral blood flow and glucose metabolism in conscious rats.

Nimodipine enhances spontaneous activity of hippocampal pyramidal neurons in aging rabbits at a dose that facilitates associative learning

The functional activity of hippocampal neurons is strongly correlated with behavioral performance in a vertebrate model learning system, rabbit eyeblink conditioning. Using this system, we have previously shown that (a) complete removal of the hippocampus blocks acquisition of the conditioned response; (b) a calcium-dependent postsynaptic afterhyperpolarization is reduced in pyramidal cells recorded intracellularly in hippocampal slices taken from conditioned rabbits; and (c) nimodipine, a 1,4-dihydropyridine calcium-channel antagonist, facilitates acquisition of the conditioned response in aging rabbits. Although calcium-channel antagonists directly block neuronal calcium currents in vitro, they also alter cerebral blood flow in vivo. Thus, the effects of nimodipine on hippocampal neuronal activity in awake animals were examined, with controls for cerebrovascular changes. A total of 457 pyramidal cells and 160 theta cells were studied. During infusion of nimodipine, pyramidal cell firing activity was enhanced and theta interneuron activity was suppressed at all doses tested in aging animals. This effect was rapidly reversed when infusion of the drug ceased. The greatest enhancement of neuronal firing was seen at the most behaviorally effective dose of nimodipine. The enhancement of pyramidal cell firing was age-dependent, with greater increases in firing activity seen in aging than in young animals, but with a similar dose-dependent pattern of effects in the two age groups. Two other calcium-channel antagonists, nifedipine and flunarizine, did not significantly alter spontaneous firing rates of hippocampal neurons. A calcium-channel agonist, BAY-K-8644, produced less easily interpretable results. BAY-K-8644 enhanced interneuron activity at one dose, but enhanced pyramidal cell activity at a dose one log unit higher. The calcium-channel agonist's enhancement of pyramidal cell activity at the highest dose was sustained up to 1 h after drug infusion. Nimodipine's enhancement of the activity of hippocampal pyramidal cells is consistent with the hypothesis that these neurons, which play a necessary role in some forms of learning, may mediate the calcium-channel antagonist's behavioral effects.

Effects of antihypertensive drugs on experimental cerebral ischemia in spontaneously hypertensive rats

The effects of antihypertensive drugs on ischemic cerebral damage were investigated using the bilateral carotid artery occlusion (BCAO) model in SHR. Oral budralazine and nifedipine, at doses that increased cerebral blood flow (CBF) in SHR in our previous study (Tanaka, S. et al., Folia Pharmacol, Japan, 87, 1986), significantly improved cerebral energy failure after the BCAO, but prazosin which does not increase CBF had no effect on the energy failure. These results suggest that the amelioration by these antihypertensive drugs of the energy failure after the BCAO results from its CBF-increasing effects in SHR.

Flunarizine. A reappraisal of its pharmacological properties and therapeutic use in neurological disorders

Flunarizine is a class IV calcium antagonist with a pharmacological profile which suggests its therapeutic potential in a number of neurological and cerebrovascular disorders. It is an effective prophylactic treatment for common or classic migraine in children and adults, and it appears at least as effective as a number of other agents which act by different pharmacological mechanisms, including pizotifen (pizotyline), cinnarizine, methysergide, nimodipine, metoprolol, propranolol, aspirin and cyclandelate. Flunarizine is also effective in reducing the frequency of seizures, when used as an 'add-on' treatment, in some patients with partial or generalised epilepsy resistant to maximal therapy with a combination of several conventional antiepileptic drugs. Placebo-controlled studies show that flunarizine is effective in the treatment of vertigo and associated symptoms of either peripheral or central origin, and in the treatment of cerebrovascular insufficiency where psychological symptoms, rather than vertigo, are the primary symptoms. In the treatment of vertigo, flunarizine appears at least as effective as cinnarizine and more effective than nicergoline, betahistine dichlorhydrate, pentoxifylline (oxpentifylline) and vincamine. Flunarizine therefore is useful in the prophylaxis of migraine, an effective treatment for vertigo and a worthwhile alternative as 'add-on' therapy in patients with epilepsy resistant to conventional drugs.

Effects of flunarizine on postischemic blood flow, energy metabolism and neuronal damage in the rat brain

The effects of flunarizine on local cerebral blood flow, cortical energy metabolism and neuronal necrosis were evaluated in a rat model of forebrain ischemia. The application of flunarizine (2 X 40 mg/kg p.o.) at 24 and 4 h before ischemia accelerated the restoration of cortical high-energy phosphates during early post-ischemic recirculation and also increased the flow in cortical but not in hippocampal areas. Neuronal necrosis was reduced in the hippocampal CA 1 sector but unchanged in the cortex. It is concluded that flunarizine reduces ischemic damage mainly via a direct effect on brain tissue.