Objective     To establish stereological methods for the quantitative studies of neurons and synapses in the hippocampus.     Methods     After five 18-month female Long-Evans rats were anesthesized

one of the two hemispheres was sampled randomly after fixatio

n with paraformaldehyde perfusion

and then embedded in paraffin blocks. Serial coronal sections in thickness of 14 μm were cut. The sections were uniformly and randomly sampled from the consecutive sections through hippocampus according to the principles of systematic

uniform and random sampling. One series of sections were stained for Nissl substance for the quantification of neuron number

and another series of sections were stained for the quantification of synaptophysin-positive bouton number. The number of neurons in CA

1

and DG and the number of synaptophysin-positive boutons in CA

1

CA

1

sr

DGiml

and DGoml were estimated with the unbiased stereological technique

the optical fractionator.     Results     The total number of the neurons in CA

1

and DG was 3.17×10

5

±2.23×10

4

and 1.70×10

6

±1.87×10

5

respectively. The total number of the synapses in CA

1

CA

1

sr

DGiml

and DGoml was 1.04×10

8

±5.39×10

6

4.36×10

7

±3.78×10

6

1.87×10

7

±1.81×10

6

and 4.48×10

7

±7.29×10

5

respectively.     Conclusion     Our established methods can quantitatively study the neuron and synapse changes during hippocampal formation in normal aging process and in various neurodegenerative diseases.