Numbers of neurons and astroglial cells in the suprachiasmatic nucleus of male and female rats.

The suprachiasmatic nucleus (SCN) of male and female rats contains about 180,000 neurons per mm3 tissue. As the volume of the SCN (unilaterally) does not exceed 0.064 mm3 in the present preparation it is assumed to contain between 11,000 and 12,000 neurons. The astroglia: neuron ratio is approximately 1:3. The number of neurons and glial cells were obtained by a new approach measuring the areal density of the nuclei on micrographs and their mean volume from three-dimensionally reconstructed nuclei in serial thick sections. Neuronal nuclei tend to be smaller in SCN of male rats, but contain relatively more nucleoli than neuronal nuclei in SCN of female rats.