A method to perform direct transcutaneous intrathecal injection in rats

This work describes a method for performing direct intrathecal (i.t.) injections in rats without introducing a spinal catheter. Its ease of use in awake animals yields rapid and reproducible results with no sign of motor impairment. The quality of each injection was ensured by the observation of an injection-induced tail-flick. A 10-microL injection of methylene blue was well localized yielding a very limited diffusion along the spinal cord. The method was validated by demonstrating that morphine (i.t.) had a marked antinociceptive effect and that naloxone (i.t.) blocked the effect of systemic (s.c.) morphine in mononeuropathic rat.