Brain-derived neurotrophic factor (BDNF) (20 ng/ml) significantly enhanced the growth of the somata of GABA-immunoreactive neurones in primary cultures of hippocampal neurones from postnatal rats after only 24h. Whole-cell patch-clamp experiments showed an increase in spontaneous synaptic activity between neurones with time in culture. After 10 days in culture, 90% of neurones sampled in control cultures showed spontaneous synaptic activity, whereas in cultures treated with BDNF, 100% of neurones had synaptic inputs after only 6 days. This difference in spontaneous activity was not due to the lack of synaptic inputs as KCl-induced synaptic activity was equally effective in BDNF and control cultures. These experiments demonstrate the rapid rate at which BDNF can promote neuronal growth and also show that BDNF can promote long term synaptic activity.

1Hippocampal slices have been used to assess the sensitivity of the CNS to adenosine and yaminobutyric acid (GABA) in diabetes. The effects of adenosine, 2-chloroadenosine, GABA, muscimol and baclofen were studied on orthodromic synaptic potentials recorded in the CAl region of slices taken from normal rats or animals made diabetic by the injection of streptozotocin. 2 In diabetic animals the sensitivity to adenosine was increased 4 fold compared with normal rats. The potency of 2-chloroadenosine was unchanged. 3 The nucleoside transport inhibitor, hydroxynitrobenzylthioinosine (HNBTI), increased the potency of adenosine in slices from normal rats but not in slices from diabetic rats. 4 No change was observed in the potency of GABA or muscimol, although a small but significant decrease was detected in the ECM value for baclofen.5 Treatment of diabetic animals with insulin restored the potency of adenosine to control levels. 6 It is concluded that the diabetic state is accompanied by substantial changes of adenosine sensitivity due to the loss of nucleoside uptake processes. Secondary neurochemical changes followingfrom this in human diabetic patients may contribute to the reported behavioural changes.

1. Using the whole-cell variation of the patch-clamp technique to record from mammalian NG108-15 cells, we have studied the ligand-gated ion channel current activated by a high concentration (100 /uM) of local pressure-applied 5-hydroxytryptamine (5-HT). The response was induced at intervals of at least 90-120 s, which allowed the receptor to fully recover between activations.2. The rapid inward current induced by pressure-applied 5-HT was reproducibly inhibited by the superfusion of low concentrations of 5-HT which evoked little or no detectable inward current alone (0 01-0 3 uM). This inhibitory effect was most likely to be due to a direct action on the 5-HT3 receptor as it could be recorded using intracellular solutions with or without adenosine triphosphate (ATP) and guanosine triphosphate (GTP). 3. The maximum inhibitory effect of a given concentration of 5-HT was not dependent on its superfusion time but on the number of activations of the receptor by pressure-applied 5-HT. This activation dependence was clearly evident, since the first inward current in the presence of 0 1 /M 5-HT was often unaffected in amplitude. 4. The inhibitory effect of 5-HT was evident at holding potentials of +60 and -60 mV; with the calcium chelator BAPTA in the recording pipette and with the nominal removal of extracellular calcium and magnesium ions.5. The inhibitory effect was concentration dependent, with 50% inhibition of the inward current amplitude occurring at -50 nM 5-HT. The slope factor of the inhibition curve was 1-3. The effect was mimicked by two other 5-HT3 receptor agonists, 2-methyl-5-HT and m-chlorophenylbiguanide (mCPBG) which gave 50% inhibition at -600 nm and 20 nM, respectively. These values are similar to the affinity values for these ligands determined in radioligand binding assays. 6. The 5-HT3 receptor 'antagonists' (+)-tubocurarine and quipazine (both at 3 nM) reduced the inward current amplitude by -50 %. The rate of onset of the inhibitory effect of bath-applied 5-HT was slowed in the presence of (+)-tubocurarine but not in the presence of quipazine. This difference might be explained by the agonist properties seen only with quipazine. 7. The inhibition of the 5-HT3 receptor mediated inward current by low concentrations of bath-applied 5-HT3 receptor agonists is compatible with the cyclic model of receptor activation and desensitization. We conclude that we have been studying the high-affinity binding of agonists to the desensitized form of the 5-HT3 receptor.

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