Effect of nitecapone and clorgyline, given intracerebro-ventricularly on L-dopa metabolism in the rat brain

Treatment of spinal cord injury by transplantation of cells via cerebrospinal fluid

It is very important to probe into the axonal regeneration and functional recovery of central nervous system (CNS) after implantation of cells into cerebrospinal fluid (CSF) for spinal cord injury (SCI). Transplantation of cells via CSF poses great potentials for SCI in clinic. Studies on administration of cells via CSF indicate that the method is safe and convenient. The method is more suitable to treating multiple lesions of the CNS since it does not produce open lesions. However, there are disputes over its promotion effects on axonal regeneration and functional recovery of spinal cord after injury; and some questions, such as the mechanisms of functional recovery of spinal cord, the proper time window of cell transplantation, and cell types of transplantation, still need to be handled. This review summarized the method of cell transplantation via CSF for treatment of SCI.

The role of physicochemical properties of entacapone and tolcapone on their efficacy during local intrastriatal administration

Aqueous solubility, apparent partition coefficient (logPapp) and catechol-O-methyltransferase (COMT, EC 2.1.1.6) inhibiting potency of entacapone and tolcapone were compared in vitro. Both drugs (at 10 and 100 microM) were also delivered directly into rat striatum via a microdialysis probe. Extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) concentrations were measured to evaluate the inhibition of striatal COMT in vivo. Although entacapone had 15-fold better aqueous solubility than tolcapone at pH 7.4, also tolcapone had sufficient aqueous solubility to remain in solution at 100 microM. The logPapp of tolcapone was higher than that reported for entacapone in the pH range from 5.0 to 7.4. Entacapone and tolcapone inhibited equally rat striatal COMT in vitro with Ki values of 1.86 and 2.50 nM, respectively. Both drugs had similar outflow from the microdialysis probe in vitro. Perfusion of 100 microM entacapone increased significantly extracellular DOPAC levels compared to the control group. Both entacapone and tolcapone (at 10 and 100 microM) decreased significantly HVA levels, but entacapone was significantly more effective than tolcapone at 100 microM. In conclusion, entacapone and tolcapone are equally potent COMT inhibitors against rat striatal COMT in vitro. After local intrastriatal administration, entacapone appeared to inhibit COMT faster and more effectively than the more lipophilic tolcapone. Thus, intrastriatal administration led to opposite results compared to those reported in the brain after systemic administration. The present results also suggest that the local distribution of entacapone and tolcapone differ when the drugs are delivered directly into the brain.

Dissemination and proliferation of neural stem cells on the spinal cord by injection into the fourth ventricle of the rat: a method for cell transplantation

We examined the distribution of hippocampus-derived neural stem cells on the spinal cord surface for up to 3 weeks following injection through the fourth ventricle. The injected cells were disseminated as tiny spots on the pia mater of the spinal cord and proliferated into large cell-clusters. On both the dorsal and ventral side, cell clusters increased in number rapidly up to 5 days after injection and thereafter decreased gradually due to the coalition of neighbouring clusters. Concomitantly, individual cell clusters continuously increased in size, occupying almost 50% of the spinal cord surface. Cell attachment was usually found around blood vessels, along which cells invaded into the spinal cord. In the injured site, cells migrated into the lesion and were integrated into the spinal cord tissue, some of which had differentiated into astrocytes 1-2 weeks after injection. BrdU-uptake experiments demonstrated that the transplanted cells proliferated within the host cerebrospinal fluid. These results indicate that application of neural stem cells through the ventricle is an effective method to disseminate cells all over the spinal cord and that they can migrate and be integrated into the injured spinal cord.

New method for transplantation of neurosphere cells into injured spinal cord through cerebrospinal fluid in rat

Here we report a novel method of supplying cultured neurosphere cells to the injured spinal cord, by injection of cells into the cerebrospinal fluid (CSF) through the fourth ventricle or cisterna magna. Hippocampus-derived neurosphere cells, isolated from a transgenic rat fetus expressing green fluorescent protein, were transplanted into the CSF of a rat with spinal cord injury. It was found that injected cells were extensively transported by CSF within the subarachnoidal space, and survived as clusters on the pial surface of the spinal cord. The most notable finding was that a large number of injected cells migrated into the lesion site and integrated into the injured spinal cord tissues.

Effect of intracerebral 6-nitronoradrenaline, an endogenous catechol-O-methyltransferase (COMT) inhibitor, on striatal dopamine metabolism in anaesthetised rats

6-Nitronoradrenaline, a bioactive compound recently identified in the brain, is known to inhibit catechol-O-methyltransferase. To study its effect on dopamine metabolism, it was administered into rat striatum via a microdialysis probe. Other nitrated catechols (6-nitrodopamine, 6-nitro-DOPAC and 5-nitro-HVA) were studied for comparison. Tolcapone, a selective catechol-O-methyltransferase inhibitor, was used as a positive reference compound. Both 6-nitronoradrenaline and tolcapone increased striatal extracellular dopamine levels during the perfusion (at 100 microM concentration but not at 10 microM) and decreased the efflux of homovanillic acid. Tolcapone, but not other nitrated catechols, increased 3,4-dihydroxyphenylacetic acid efflux. None of the compounds inhibited MAO-B activity at 100 microM or lower. At 1 mM, 6-nitrodopamine inhibited MAO-B by 60%. Compared to tolcapone, other nitrated catechols were very weak COMT inhibitors in vitro. Neither tolcapone nor 6-nitronoradrenaline modified the metabolism of L-dopa which was given peripherally. In binding studies, both 6-nitronoradrenaline and other nitrocatechols failed to affect the dopamine transporter even at high micromolar concentrations. In conclusion, exogenous 6-nitronoradrenaline can act as a COMT inhibitor in the striatum and elevate striatal dopamine levels without inhibiting dopamine reuptake. Whether endogenous 6-nitronoradrenaline can be formed also in vivo in the striatum and act as a regulator of dopaminergic tone remains to be determined.

In vivo dynamics and distribution of intracerebroventricularly administered gadodiamide, visualized by magnetic resonance imaging

Direct injections into the cerebroventricles have been extensively utilized in neurophysiological studies. Mapping the distribution of injectate after intracerebroventricular injection has been made only by post mortem analysis, and the dynamic distribution of injectate within the brain has not been well characterized. In this report, we apply contrast-enhanced magnetic resonance imaging to study the pharmacokinetics and extent of non-ionic gadodiamide transport into brain tissue in vivo after intracerebroventricular administration. The results indicate that intracerebroventricular injectate travels quickly throughout the ventricular system from the lateral ventricular site of injection to the fourth ventricle and foramina of Luschka and Magendie within 2 min. After this, the signal intensity begins to increase in the periventricular and paraventricular brain parenchyma. Contrast enhancement is visible 2 mm into the brain tissue from the ventricles. Quantitative analysis of the data shows that the transport of gadodiamide across the ependymal layer that lines the cerebrospinal fluid space characterized a rate constant of 0.066+/-0.017 min(-1). These results provide a better understanding of chemical transport and diffusion following direct injection into the cerebroventricles. They provide information on the in vivo dynamics of injectate after intracerebroventricular administration, and show that contrast enhanced magnetic resonance imaging may be used to more precisely define the target sites of chemicals after intracerebroventricular administration into the brain.

Comparison of two new inhibitors of catechol O-methylation on striatal dopamine metabolism: a microdialysis study in rats

1. Effects of two new inhibitors of catechol O-methylation (CGP 28014 and entacapone; 30 mg kg-1, i.p.) were compared by means of brain microdialysis in rats treated with L-3,4-dihydroxyphenylalanine (L-dopa)/carbidopa (50/50 mg kg-1, i.p., respectively) or saline. 2. In saline-treated rats, CGP 28014 maximally (max) increased striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) effluxes by 41% and 49%, respectively, whereas homovanillic acid (HVA) levels were decreased by 71%. 3. In the presence of L-dopa/carbidopa, a peripherally active inhibitor of catechol O-methyltransferase (COMT) entacapone had a short-lasting increasing effect on L-dopa efflux. Compared to the effects of L-dopa/carbidopa alone 3-O-methyldopa (3-OMD) levels were effectively reduced (max 79%) by entacapone, but not by CGP 28014. 4. Entacapone, in contrast to CGP 28014, increased striatal dopamine efflux (max 492% of that after L-dopa/carbidopa alone). Also DOPAC levels were increased by entacapone (255% at 180 min), but not significantly by CGP 28014 (159% at 180 min). 5. Both compounds initially decreased HVA efflux. The effect of CGP 18014 was longer-lasting. By the end of the measurement, entacapone even increased HVA levels (max 259%). 6. Our results demonstrate that entacapone is a peripheral COMT inhibitor and support the view that CGP 18014 is mainly a centrally acting inhibitor of O-methylation.

Modulation of rat brain endogenous dopamine metabolism by new inhibitors of catechol O-methyltransferase

The extraneuronal and intraneuronal metabolism of rat brain endogenous dopamine was stimulated by amphetamine (5 mg/kg) and pimozide (2 mg/kg), respectively. Additional metabolic effects of two inhibitors of catechol O-methyltransferase (entacapone and tolcapone (both 30 mg/kg)) and a putative central uptake2 inhibitor (CGP 28014 (30 mg/kg)) were assessed. Amphetamine increased striatal dopamine and 3-methoxytyramine and decreased 3,4-dihydroxyphenylacetic acid (DOPAC) levels. The latter two effects were reversed by tolcapone and CGP 28014, but not by entacapone. Tolcapone, CGP 28014 and even entacapone decreased striatal homovanillic acid (HVA) levels. Pimozide-induced striatal DOPAC levels were further increased by tolcapone and CGP 28014. Both substances also decreased striatal HVA levels. Striatal 3-methoxytyramine levels were significantly lowered only by tolcapone. Our results show that enhanced central dopamine metabolism is modified by the inhibition of catechol O-methyltransferase even in the absence of L-3,4-dihydroxyphenylalanine (L-DOPA). The results also suggest that the mechanism of action of CGP 28014 may be other than true inhibition of catechol O-methyltransferase.