Effects of serine on morphine-dependent mice

Single doses of serine (250 mg/kg i.p.) failed to elevate central glycine in mice (1 h after injection), or to compensate for losses caused by implantation of morphine base (70 mg/animal), and reduced the jumping response to nalorphine (100 mg/kg i.p.). In contrast, sustained treatment with 250-mg/kg doses of serine at 24-hour intervals produced increases in brain and medullar glycine (1 h after 4th injection: 46-50% in normal, 39-75% in morphine-dependent mice, and enhanced the jumping response (40% over controls).