Conclusion
The major finding of the study was that intrastriatal silica-dopamine implants reversed the rotational asymmetry induced by apomorphine, a dopamine agonist, in hemiparkinsonian rats. No dyskinesias or other motor abnormalities were observed in animals implanted with silica or silica-dopamine.
Methods
Several samples were prepared by varying the wt% of dopamine added during the hydrolysis of tetraethyl orthosilicate. The silica-dopamine reservoirs were characterized by N(2) adsorption, scanning and transmission electron microscopy, and Fourier transform infrared spectroscopy. The in vitro release profiles were determined using ultraviolet visible absorbance spectroscopy. The textural analyses showed a maximum value for the surface area of 620 m(2)/g nanostructured silica materials. The stability of dopamine in the silica network was confirmed by infrared and (13)C-nuclear magnetic resonance spectroscopy. The reservoirs were evaluated by means of apomorphine-induced rotation behavior in hemiparkisonian rats.
Results
The in vitro dopamine delivery profiles indicate two regimes of release, a fast and sustained dopamine delivery was observed up to 24 hours, and after this time the rate of delivery became constant. Histologic analysis of formalin-fixed brains performed 24-32 weeks after reservoir implantation revealed that silica-dopamine implants had a reddish-brown color, suggesting the presence of oxidized dopamine, likely caused by the fixation procedure, while implants without dopamine were always translucent.