Microinjectors were made according to Mark et al. (2006). A silica glass tube (0.15 mm o.d. × 0.037 mm i.d.; Polymicro Tech Inc.) was fitted into a 26-gauge stainless steel shaft and extended 1.5 mm beyond the shaft. Thus, the silica tip reached the ventral coordinate of -7.5 mm into the LDTg. Silica minimized tissue damage and served to preload the drug prior to the injection. The other end of the silica and the 26-ga shaft were press-fit into PE20 tubing (6 cm long) which was loaded with drug. This PE 20 tubing was connected to a longer piece of PE 20 tubing that was filled with water and connected to a 10 ul gas-tight glass syringe (Hamilton; Fisher, St. Louis, MO). The gas-tight syringe was loaded onto a syringe pump (Razel; Braintree Inc., Braintree, MA) that delivered fluid into the brain at a constant rate. 100 nl of the fluid was infused over a 30-sec period. The microinjector was left in the brain for another 30-sec period after delivery of the fluid to allow for fluid diffusion. Microinjectors were
