Effects of DAGO on the rodent hippocampal evoked potentials using different perfusion solutions

Opioid receptor agonists exert excitatory effects in the hippocampus by inhibiting GABA release. We report that the y-opioid agonist, DAGO, increases the amplitude of the population spikes (PS) measured in the stratum pyramidal of the CAI cell layer in mouse and rat hippocampal slices perfused with an artificial cerebrospinal fluid (ACSF), but not when perfused in Krebs solution. The GABAA agonist, 3-APS, induces inhibitory responses when perfused in either ACSF or Krebs. Also, the field excitatory postsynaptic potentials (EPSP) measured on stratum radiatum do not differ when the slice is perfused with either ACSF or Krebs. The increase in the amplitude of the PS induced by DAGO is not obtained when perfused in a modified ACSF whose concentration of MgSOl was lowered to its concentration in the Krebs solution (from 2.4 mM to 1.2 mM). Thus, changes in the concentration of MgSOl seem to be responsible for the different responses induced by DAGO.