Spinal paralysis and catalepsy induced by intrathecal injection of opioid agonists

The intrathecal administration of high (1.05 mumol) doses of D-Ala2-Met5-enkephalinamide (DAMA), D-Ala2-Leu5-enkephalinamide (DADLE), Try-D-Thr-Gly-Phe-Leu-Thr, MR2034-TA, dextrorphan tartrate, U50,488H, levorphanol tartrate, methadone hydrochloride, and 1-methyl-4-phenyl-4-propionoxypiperidine induced spinal hypokinesia. The first 5 of these compounds caused spinal paralysis, whereas the other compounds and lower doses of the first 4 induced waxy catalepsy that was restricted to the hindquarters of rats. The paralysis induced by DAMA was not reversible by IT injections of 50 micrograms naltrexone, indicating, together with the paralytic effects of dextrorphan, that traditional opiate receptors are not involved in this behavioral effect. The spinal catalepsy induced by 0.26 mumol of DAMA was prevented by IT pretreatment with 10 micrograms of naltrexone. In view of this finding and the observation that spinal catalepsy can be induced by agonists of all opiate receptor classes, it seems likely that spinal catalepsy is produced by activation of specific opiate receptors, although the subtype remains to be established.