Postnatal development of the Ammon's horn (CA1 and CA3 fields). A karyometric and topographic study

We have performed a karyometric study of the pyramidal neurons of CA1 and CA3 fields of the Ammon's horn, in male mice aged from the 5th to the 190th postnatal day. Nuclear sizes were measured with the aid of a Magiscan Analysis System, used in an interactive form, in both superficial and deep layers of the stratum pyramidal in those fields. The measurements were made at three different topographic levels: rostral; intermediate; and caudal, to detect any possible difference related to the topography of the neuron in the same field. We have found that both CA1 and CA3 fields are correlated in the postnatal development of their nuclear pyramidal sizes and that all topographic levels of the hippocampus reach their highest karyometric sizes at the 10th-15th postnatal day. Caudal levels show higher karyometric values than the other levels and some differences between neurons of the superficial and deep layers of both fields are also described here and analysed in relation to the different ontogenetic gradients of these cells.