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 then removed, and the syringe pump was turned on for approximately 30 sec to ensure that fluid still flowed through the microinjector. The guide cannulae were plugged with small handmade stainless steel stylets. Animals were put inside operant chambers immediately after this procedure.
