Hypertrophy of the ageing rat medial preoptic nucleus

The medial preoptic nucleus (MPN) Flays an essential role in the coordinati on of behaviours and physiological responses necessary for reproduction Sin ce ageing is associated with a progressive deterioration of reproductive fu nctions we have explored the possibility that changes in the structural org anization of the MPN might be implicated in this process. Thus, we have est imated the volume of the MPN, and the total number and size of its neurons, using stereological methods, and quantitatively evaluated the dendritic tr ees of MPN neurons in Golgi-impregnated material. Male and female rats, age d 6, 24 and 30 months, were independently analysed. No cell loss was observ ed in aged rats of both sexes. However, the volume of the MPN and the somat ic size of its neurons were remarkably enlarged in aged rats. No significan t age-related changes in the size or shape of the dendritic trees or in den dritic spine density were found. To evaluate whether the changes observed i n aged rats could be ascribed to an altered interaction between gonadal ste roids and steroid-sensitive neurons, we have additionally estimated the tot al number of MPN neurons immunoreactive for the estrogen receptor-alpha. No significant age-related variations were detected. The age effects upon the MPN were more marked in females than in males and, consequently, the sexua l dimorphisms in neuronal size and in the number of estrogen receptor-immun oreactive neurons were blunted in aged rats.