A morphometric study of the preoptic area of the guinea pig.

The aim of the study was to provide the topography and morphometric characteristics of the preoptic area (POA) of the guinea pig. The study was carried out on the brains of sexually mature guinea pigs of both sexes. A uniform procedure was followed in the study of the paraffin-embedded brain tissue blocks of males and females. The blocks were cut in the coronal plane into 50 mm sections and stained according to the Nissl method. The guinea pig POA consists of four parts: the medial preoptic area (MPA), lateral preoptic area (LPA), periventricular preoptic nucleus (PPN), and median preoptic nucleus (MPN). The topography and general structure of POA parts are similar in males and females. However, the PPNa cells of females are more intensely stained and are more densely packed than the PPNa cells of males. For morphometric analysis, the MPA and LPA as well as PPN and MPN were considered respectively as uniform structures, namely MPA-LPA and PPN-MPN. The statistical analysis showed that the volume of the PPN-MPN was larger in males than in females, whereas the MPA-LPA volume did not differ between the sexes. Moreover, the numerical density and the total number of neurons were statistically larger in males than in females in both the MPA-LPA and PPN-MPN. The parameters describing POA neurons were larger for MPA-LPA neurons in comparison with the PPN-MPN neurons. However, in this respect no sex differences were observed in both studied complexes.