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Abstract
The effects of the sulfated octapeptide of cholecystokinin (CCK8-S), the non-sulfated
homolog (CCK8-NS) as well as the C-terminal di-, tri- and tetrapeptidic fragments
(respectively CCK2, CCK3 and CCK4) were studied in vitro in rat hippocampal slices
by extracellular recording of the spontaneous action potential discharge frequency
of neurons located in the CA1 stratum pyramidalis. Bath-applied CCK8-S concentration-dependently
increased the action potential discharge frequency of hippocampal CA1-neurons in concentrations
ranging from 0.05 to above 1 microM. Both CCK8-NS and CCK4 exhibited reversible and
concentration-dependent excitatory effects. They were 4 and 10 times less potent than
CCK8-S, respectively, as concentrations of 2 microM CCK8-NS and 5 microM CCK4 were
needed to evoke the same excitation as that induced for a given neuron by 0.5 microM
CCK8-S. In contrast, none of the shorter fragments (CCK2 and CCK3) were effective
in altering spontaneous discharge of CCK8-S-sensitive neurons even at concentrations
of 100 microM. The pharmacologic profile of the excitatory response observed in the
rat hippocampus follows the same pattern as the binding profile observed on brain
membrane preparations. It is therefore concluded that the CCK receptors involved in
this response seem to be related more to the 'central'- or B-type CCK receptors rather
than to the 'peripheral'- or A-type CCK receptors.