Stability of neuron number in the ageing mouse paraventricular nucleus.

The number of neurons in the paraventricular nucleus was estimated in brains from male mice aged 6, 25, 28 and 31 months. There was no significant variation with age in neuron number (mean 2715). At all ages most neurons were parvocellular neurons and the neurosecretory magnocellular neurons made up only 10% of the total. There was no significant variation in neuronal nuclear diameter (mean 9.4 microns) with age. The nuclear diameter of both parvocellular and magnocellular neurons was identical. The difference in size between the two types of neurons was due to the difference in volume of their perikarya.