[3H] dynorphin binding to guinea pig and rat brain.

[3H] Dynorphin can be shown to bind to the brains of both rat and guinea pigs with approximately 50% specific binding. Characterization of the binding in terms of multiple opiate receptor types supports the kappa selectivity of dynorphin in guinea pig. However, in rat brain, a substantial proportion of the [3H] dynorphin binding is displaced by morphine, suggesting a mu as well as kappa component. Consequently, in rat, dynorphin may show effects at both mu and kappa receptors in vivo.