A marked surge of luteinizing hormone (LH) occurs daily at 18.00 h in oestrogen-treated ovariectomized rats maintained under regular lighting from 06.00 to 20.00 h. The administration of p-chlorophenylalanine (PCPA),p-chloramphetamine or 5,6-dihydroxytryptamine in treatments designed to cause a severe depletion of brain serotonin abolished this daily surge. Synthesis of serotonin may be temporarily restored in PCPA-treated animals by the administration of the serotonin precursor, 5-hydroxytryptophan. The effectiveness with which restoration of synthesis resulted in restoration of the LH surge varied according to the time at which the precursor was administered, the optimal time being 10.00 h. The results suggest that there is an essential, permissive function performed by serotonin in the production of the LH surge and that this function occurs during a critical period.

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PREVENTION OF BEDSORES BRITISH 55L MEDICAL JOURNAL Observations over a period of six months show that it is at least as effective as the usual method. The saving in nursing time and labour justifies its continued use. The cost of treatment is low. Further trials are in progress.

Ovariectomized rats in which less than 7% of the suprachiasmatic nuclei had been spared by bilateral radiofrequency lesions were distinguishable from those with greater than 40% of the nuclei by their consistent failure to show the oestrogen-induced daily surge of LH, either with or without pharmacological manipulations of serotonin (5-HT), and also by their loss of the normal rhythmicity of drinking. Minor damage to structures adjacent to the suprachiasmatic nuclei was similar in both groups. The identical facility with which electrical stimulation of the preoptic area induced LH release in the two groups of animals suggested that they were not characterized by different degrees of damage to the preopticotuberal pathway. These results are considered in relation to evidence indicating that the suprachiasmatic nuclei represent the densest concentration of 5-HT terminals in the forebrain and also the site of a mechanism involved in the generation of circadian rhythms.