Experimental design to study age-dependent vulnerability of the striatum to mutant huntingtin (Htt).

<p>Young (3 week old) and old (15 month old) rats were injected with a lentiviral vector encoding the 171 N-terminal amino acids of mutant huntingtin with 82 polyglutamine repeats (Htt171-82Q), the corresponding wild-type fragment with 18 polyglutamine repeats (Htt171-18Q) or the reporter protein β-Galactosidase (β-Gal). In the first experiment (<i>A</i>), young and old rats received a stereotaxic injection of lentiviral vectors (2 µl, 200 ng/µl of p24) encoding β-Gal (left striatum) or Htt-171-82Q (right striatum). Histological evaluation was carried out 4 weeks after infection to determine the effects of aging on the expression of β-Gal and Htt171-82Q. In a second experiment (<i>B</i>), the actual degeneration produced by Htt171-82Q was characterized at a later time point after infection. Animals were injected with lentiviral vectors (4 µl, 200 ng/µl of p24) encoding β-Gal mixed with lentiviral vectors encoding either Htt171-82Q or Htt171-18Q. Histological characterization of the striatum consisting of an assessment of DARPP-32, EM48, and β-Gal immunoreactivity and activity was carried out 12 weeks post-infection. Unbiased stereological count of β-Gal-positive neurons were used to compare Htt-171-82Q toxicity with that of Htt171-18Q. Analysis of β-Gal levels in neurons in the Htt171-18Q-expressing striatum permitted the verification of the effect of age on transgene promoter (PGK) efficiency.