The study of protein function in neurons has been hindered by the lack of highly efficient, nontoxic methods of inducing RNA interference in such cells. Here we show that application of synthetic small interfering RNA (siRNA) linked to the vector peptide Penetratin1 results in rapid, highly efficient uptake of siRNA by entire populations of cultured primary mammalian hippocampal and sympathetic neurons. This treatment leads to specific knock-down of targeted proteins within hours without the toxicity associated with transfection. In contrast to current methods, our technique permits study of protein function across entire populations with minimal disturbance of complex cellular networks. Using this technique, we found that protein knock-down (evident after 6 hr) precedes any decrease in targeted message (evident after 24 hr), suggesting an early, translational repression by perfectly targeted siRNAs.

The prechiasmatic SAH model seems to be the most suitable for study of the sequelae after SAH; it produces a significant decrease in CBF, an acceptable mortality rate, and substantial pathological lesions, with high reproducibility. The CBF reduction is predominantly dependent on the amount of subarachnoid blood.

A new experimental model of subarachnoid hemorrhage (SAH) in rats is described. A needle was stereotaxically placed in the prechiasmatic cistern and 300, 250 or 200 microl of blood was injected manually, keeping the intracranial pressure (ICP) at the mean arterial blood pressure (MABP) level. An acceptable mortality was observed only after injection of 200 microl of blood. In this group, MABP and ICP increased immediately after SAH, but soon approached baseline levels. The subarachnoid blood was mainly distributed in the basal cisternal system and its estimated volume was about 95% of the amount injected. This new model resembles clinical SAH, is very reproducible, easy to use and seems to be a suitable model for studies of the pathophysiology of SAH.

Subarachnoid hemorrhage resulted in delayed cell death in a large proportion, but not all, of the surviving animals. The acute CBF decrease was related to the degree of subsequent cell death. These findings indicated the relevance of apoptotic-like pathways. There appears to be a temporal therapeutic window during which adequate treatment might reduce the final damage following SAH.

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