The synaptic organization of the sexually dimorphic nucleus of the preopticarea(SDN-POA)of male and female rats were examined with electron micro-scope.The results indicated that the synaptic pattern of SDN-POA showedsignificant sexual dimorphism:1.The numbers of total and shaft synapses whichoccupied the vast majority of total synapse were 2 times greater in male than infemale.2.The number of spine synapse of the female was 4.6 times greater thanthat of the male.3.In female,either the numbers of spine synapse with clear andmixed synaptic vesicles or the numbers of symmetrical and asymmetrical spinesynapses were markedly higher than in male.In contrast,the ratio of Gray Ⅱ toGray Ⅰ was 2.4 times larger in male than in female.4.The number of shaft synapsewith clear vesicle was greater in male than in female.In both sexes,however,thesignificant difference in the number of shaft synapse with mixed vesicle was notfound.5.There was no significant sexual difference in the number of asymmetricalshaft synapse,while the number of symmetrical shaft synapse was 2.7 times greaterin male than in female.

The cytoarchitecture of the sexually dimorphic nucleus of the preoptic area(SDN-POA)of male and female rats was studied with Nissl stain and rapid Golgimethod under light microscope.The results were as follows:1.The volume of theSDN-POA of the male was markedly 3.1 times larger than that of the female.2.In both sexes,the cell density of the SDN-POA significantly increased as comparedwith that of the surrounding,while the sexual difference of the cell density withinthe SDN-POA was not found.3.There was marked male-female difference in theneu(?)onal organization of the nucleus,in which the number of large cells was signi-ficantly greater in males than in females.4.In males,dendritic trees principallyoriented in dorsolateral,ventrolateral and medial directions.In contrast,dendritictrees in females mainly oriented in dorsal and ventromedial directions.5.The meantotal length of the dendritic tree was larger in males than in females and the dis-tribution of the dendritic tree showed sexual difference in the X axis but not in theY axis.6.The number of the dendritic spine was 2.1 times greater in females thanin males.