We report the distinct cellular distribution in the human cerebellar cortex of the mammalian mt1 (Mel1a) and MT2 (Mel1b) (1) melatonin receptor subtypes. Specific binding of the non-selective radioligand 2-[125I]iodomelatonin to the outer molecular layer was significantly higher than to the granule cell layer. Melatonin receptor subtype expression was assessed by in situ hybridization using selective and specific digoxigenin-labeled antisense oligonucleotide probes. This is the first demonstration of MT2 melatonin receptor mRNA expression in human cerebellar Bergmann glia and astrocytes. On the other hand, the mt1 melatonin receptor mRNA was expressed in both basket-stellate cells and granule cells. We conclude that mt1 and MT2 melatonin receptors are heterogeneously expressed in human cerebellar cortex.

SUMMARY1. Putrescine has been implicated in modulating cytoplasmic calcium concentration and is correlated with selective neuronal vulnerability in cerebral ischaemia. In order to determine whether putrescine modulates voltage-activated calcium channels, whole-cell and single channel patch clamp experiments were performed with NIE-115 mouse neuroblastoma cells.2. L-type calcium channel currents showed a 34 + 21 % increase (n = 6 cells) during external application of 1 mm putrescine. There was no change in the kinetics of the current and no shift in the current-voltage relationship along the voltage axis.3. T-type calcium channel currents were not affected by 1 mM putrescine. 4. The effect of putrescine on single L-type calcium channels was studied using the cell-attached configuration of the patch clamp technique. Putrescine (5 mM) applied to the bathing solution, but not present in the pipette, caused an increase in open time of the single channel current without changing the conductance of the channel. In 345 depolarizing steps compiled from three cells, the number of channel openings longer than 3 ms increased from six to seventy-six, and the number of channel openings longer than 9 ms increased from zero to twenty-seven. This single channel study supports the hypothesis that putrescine acts on the L-type channel from the inside of the cell.5. External application of 1 mm spermine and 1 mm spermidine had no effect on T-and L-type calcium channels. Thus, the effect of putrescine is probably not mediated by the higher polyamines.6. In order to test whether the effect of putrescine is mediated by a second messenger, specific protein kinase C and cyclic AMP-dependent protein kinase inhibitors, staurosporine and KT5720, respectively, were applied prior to putrescine. When cells were preconditioned with 200 nm staurosporine, the increase of the Ltype calcium current by 1 mm putrescine was inhibited. By contrast, 200 nM KT5720 did not inhibit the putrescine effect. Therefore, the increase of L-type channel currents by putrescine may be mediated by protein kinase C but not the cyclic AMPdependent protein kinase. MS 1220 M. D. HERMAN, E. REUVENY AND T. NARAHASHI 7. The putrescine-induced enhancement of the L-type calcium channel activity may play an important role in calcium-induced neurotoxicity.

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It is sometimes difficult to apply the headframes of stereotactic systems in awake patients who are lethargic or demented or in patients who are very sensitive to the discomfort of local anesthestic injection. A device for external stabilization of the stereotactic system during its application to the head is described. This device, a modification of the Somi brace, is easy to apply, allows for adjustment of the base ring in all planes and provides sufficient stability even in obtunded or uncooperative patients. This device simplifies and makes more precise the application of the stereotactic headframe and may be of considerable utility in stereotactic surgery.