A Stereological Estimation of Total Neuron Number and Volume of the Hippocampus at One and Seven Day-Old Chicks

Abstract

Hippocampal complex of the avian brain is one of the most studied brain regions in recent years. This structure is thought to be homologous to mammalian hippocampus and have an important role in spatial memory. Connection patterns between the avian hippocampus and other brain regions strongly support the idea of homology between mammalian and avian hippocampal complexes. Total neuron number of chick hippocampus in different ages was estimated using optical fractionator counting method. Animals were separated into two groups as one day- and seven day-old chicks. The mean total number of nerve cells in the right hippocampi of one day-old and seven day-old chicks was estimated as 783 310 ± 12 749 and 760 028 ± 12 256 respectively. The difference between two groups was not statistically significant (p > 0.05). The mean total volume of hippocampi of chicks was estimated by Cavalieri's principle and it was found to be 2.48 ± 0.08 mm3 for one day-old chicks and 2.80 ± 0.04 mm3 for seven day-old chicks. The difference between these volume values was statistically significant (p < 0.01). Although the difference in total neuron numbers between two groups was not raised statistically significant level, decreasing cell number with age might be depend on the destruction of unneeded nerve cells with aging. The increased volume in seven day-old group may be associated with enlargement due to several reasons during development.