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SUMMARY1. The blocking action of adrenaline on the superior cervical ganglion of the rabbit was investigated with intracellular recording techniques.2. Adrenaline (10-5 M) blocked initiation of post-synaptic action potentials and decreased the amplitude of excitatory post-synaptic potentials (e.p.s.p.s), but did not hyperpolarize the post-synaptic membrane.3. The depressant action of adrenaline was antagonized by phenoxybenzamine and dihydroergotamine. 6. It was concluded that adrenaline blocks ganglionic transmission by acting at an alpha-adrenoceptive site in the presynaptic nerve terminals.

For high resolution positron emission tomographs based on scintillation detectors a fast, dense, and bright scintillator is required. A sample of a new scintillator, Lu 0 8 Y 0 2 AlO 3 :Ce (LuYAP) with a density of 7.7 g cm 3 and a scintillation decay time of 20 and 160 ns is compared with LSO and BGO crystals of the same size to estimate the potential of the crystal for high resolution PET detectors. Special attention was paid to use an application specific measurement setup with respect to high resolution PET. The light yield of the crystals using polished crystals as well as PTFE tape and BaSO 4 as reflector material and the temperature dependence of the light yield are measured using crystals of 2 2 10 mm 3 . At room temperature, the light yields of BGO : LuYAP : LSO are 1 : 1.5 : 4.5 with energy resolutions of 27.4% (BGO), 20% (LuYAP) and 15% (LSO), respectively. LuYAP shows an increase in light yield with increasing temperature whereas both BGO and LSO show a decrease.

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