Autoradiographic visualization of kappa opioid receptors with labelled dynorphins in guinea pig brain

The distribution of kappa opioid receptors in guinea pig brain was measured by in vitro receptor autoradiography using [3H]dynorphin A1-9, [3H]dynorphin A1-8 and [3H]bremazocine as ligands. The sites labelled by the two dynorphins had identical, heterogeneous distributions in brain sections. High levels of kappa receptors were seen in striatum, claustrum, nucleus accumbens and laminae V and VI of the cerebral cortex. The substantia nigra and superior colliculus also had high dynorphin binding levels. The [3H]dynorphin autoradiographs were closely similar to those obtained using [3H]bremazocine in the presence of mu and delta receptor displacers. It is concluded that tritiated dynorphin A fragments can be used for autoradiographic studies of kappa opioid receptors in brain.