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1. Using tritiated ligands [H-3]DADLE, [H-3]DAGO, [H-3]EKC and [H-3]Bremazocine, we have demonstrated the presence of delta, mu and kappa sites in brain membranes from jerboa (Jaculus orientalis), a desert rodent and a true hibernator.

2. A comparative study was realized in the case of the induced hibernating state, indicating a reduction of binding capacities during the hibernation state.

3. Using radioimmunoassay, the endogenous pentapeptide methionine-enkephalin (Met-enk) was evaluated in different areas of jerboa brain in comparison with the effect of induced hibernation on the level of Met-enk.

4. A thermodynamic analysis of the effect of temperature on the binding of opioids, indicates that the hibernating and the active state are energetically different. DELTAG-degrees, DELTAH-degrees and DELTAS-degrees were calculated. A break of the Van’t Hoff plot was observed in the active state at 15-degrees-C, indicating a possible transition state of membranous phospholipids and/or proteins.

5. The role of phospholipids was studied, using the effect of phospholipase A2 and membrane reconstitution. Phospholipids play a key role in the opioid binding.