Intracranial surgery. Mice (8 weeks old) were anesthetized with sodium pentobarbital (50 mg/kg, i.p.) and subjected to bilateral intracranial injection of IT solution [20 μg/ml anti-Tac(Fv)-PE38 in PBS containing 0.1% mouse serum albumin]. For targeting of cholinergic neurons in the MS/vDB and NBM, solution was injected into 12 sites (0.2 μl/site) and 6 sites (0.3 μl/site), respectively, through a glass micropipette that was stereotaxically introduced by using the coordinates from an atlas of the mouse brain52 . The anteroposterior, mediolateral and dorsoventral coordinates (mm) from bregma and dura were (1.1, ±0.1, −3.7), (1.1, ±0.1, −4.1), (0.8, ±0.1, −3.8), (0.8, ±0.3, −4.7), (0.6, ±0.1, −3.7), and (0.6, ±0.1, −4.2) for injection into the MS/vDB; and (−0.4, ±1.6, −3.7), (−0.7, ±1.8, −3.8), and (−0.9, ±2.0, −3.8) for injection into the NBM. Injection was carried out at a constant flow rate of 0.1 μl/min with a microinfusion pump, and the micropipette was left in situ for 2 min after each infusion.
Drug treatment. Donepezil hydrochloride (Sequoia Research Products Ltd.) and rivastigmine hydrogen tartrate (provided by Novartis Pharma AG, Basel, Switzerland) were dissolved into saline at a concentration of 0.2 or 0.4 mM. Mice received the intraperitoneal treatment of drug solution (2 or 4 μmol/kg) 30 min before the behavioural testing.
Histology. Fixed brains were cut into sections, and the sections were incubated with primary antibodies for GFP (rabbit, 1:2,000, Life Technologies), ChAT (mouse, 1:1,000, Millipore), parvalbumin (rabbit, 1:1000, Sigma-Aldrich), and then with fluorescein isothiocyanate-conjugated or biotinylated secondary antibodies. The immunoreactive signals were visualized by using a Vectastain Elite ABC kit. For double immunofluorescence histochemistry, the sections were incubated with anti-GFP and anti-ChAT antibodies, and then with species-specific secondary antibodies conjugated to Alexa488 (Molecular Probes) and Cy3 (Jackson ImmunoResearch). 4,6-Diamidino-2-phenylindole (DAPI, 1:1,000, Molecular Probes) was used to label nuclei. For cell counts, the number of immunopositive cells in each area was counted in the representative four sections through the MS/VDB or NBM (the anteroposterior coordinates from bregma: 1.3, 0.9, 0.7, and 0.5 mm for the MS/VDB; and −0.3, −0.5, −0.8, and −1.0 mm for the NBM), and the total number of immunopositive cells was calculated. Cresyl violet staining was processed to check for nonspecific damage on the brain tissue around the injection sites. For AChE staining, brain sections were rinsed in 0.1 M maleic acid buffer (pH = 6.0) and incubated for 10 min in 0.1 M maleic acid buffer containing 340 μM acetylthiocholine iodide, 50 μM sodium citrate, 30 μM cupric sulphate, and 5 μM potassium ferricyanide. To inhibit non-acetylcholinesterases, 10 nM ethopropazine was added to the solution. After the incubation, sections were washed with 50 mM Tris-HCl buffer (pH = 7.6) and soaked in 50 mM Tris-HCl buffer containing 620 nM cobalt chloride. Sections were then incubated for 7 min in 50 mM Tris-HCl buffer containing 190 μM diaminobenzidine, 0.003% H2O2, and 0.1% nickel ammonium sulphate.
Behavioural analysis. Adult naïve male mice were housed in standard lab Plexiglas cages (225 × 338 × 140 mm, length × width × height, four mice per cage) on a 12-h light/12-h dark cycle. The experiments were conducted during the light period. After the surgery, mice were given a 1-week recovery period, followed by the serial object exploration task32 (link) or one-trial object exploration task33 (link)34 (link). Different mice were used for the serial object exploration task, one-trial object recognition task, and the experiment with drug treatments. The open fields for these tasks were positioned in the centere of a room that had overhead lighting and contained various visual cues, including a computer, monitor, and shelves and posters on the wall. The animals’ behaviour was monitored using an overhead colour CCD camera (AVC-636SN; ITS, Co. Ltd.) connected to a digital video cassette recorder. During the tasks, the number of times the mouse snout made contact with an object (i.e., number of contacts) was manually counted. The counted data were confirmed by the video-recorded behaviour. The measurements of exploration were scored by an observer who was blinded to the animal groups and drug treatments.
For the serial object exploration task, a circular, polyvinylchloride open field (70-cm in diameter, 40-cm high) was used, and four positions in the open field were marked as north (N), south (S), east (E), and west (W) (see
For the one-trial object exploration task, a square, polyvinylchloride open field (35 × 35 cm and 30 cm high) was used (see
Statistical analysis. For statistical comparisons, the ANOVA and post hoc Bonferroni test were used with significance set at P < 0.05. All values were expressed as the mean ± s.e.m. of the data. Repeated ANOVA was used for the analysis of within-subjects design.