Hippocampal neuron number is unchanged 1 year after fractionated whole-brain irradiation at middle age.
OBJECTIVE
To determine whether hippocampal neurons are lost 12 months after middle-aged rats received a fractionated course of whole-brain irradiation (WBI) that is expected to be biologically equivalent to the regimens used clinically in the treatment of brain tumors.


METHODS
Twelve-month-old Fischer 344 X Brown Norway male rats were divided into WBI and control (CON) groups (n = 6 per group). Anesthetized WBI rats received 45 Gy of (137)Cs gamma rays delivered as 9 5-Gy fractions twice per week for 4.5 weeks. Control rats were anesthetized but not irradiated. Twelve months after WBI completion, all rats were anesthetized and perfused with paraformaldehyde, and hippocampal sections were immunostained with the neuron-specific antibody NeuN. Using unbiased stereology, total neuron number and the volume of the neuronal and neuropil layers were determined in the dentate gyrus, CA3, and CA1 subregions of hippocampus.


RESULTS
No differences in tissue integrity or neuron distribution were observed between the WBI and CON groups. Moreover, quantitative analysis demonstrated that neither total neuron number nor the volume of neuronal or neuropil layers differed between the two groups for any subregion.


CONCLUSIONS
Impairment on a hippocampal-dependent learning and memory test occurs 1 year after fractionated WBI at middle age. The same WBI regimen, however, does not lead to a loss of neurons or a reduction in the volume of hippocampus.
Shi
Lei
L
Department of Neurobiology and Anatomy, Wake Forest University Health Sciences, Winston-Salem, NC 27157-1010, USA. lshi@wfubmc.edu
Molina
Doris P
DP
Robbins
Michael E
ME
Wheeler
Kenneth T
KT
Brunso-Bechtold
Judy K
JK
D000367:Age Factors; D000818:Animals; D002452:Cell Count; D002587:Cesium Isotopes; D016371:Cranial Irradiation / Q000379:methods*; D018891:Dentate Gyrus / Q000166:cytology / Q000528:radiation effects; D019583:Dose Fractionation, Radiation; D006624:Hippocampus / Q000166:cytology / Q000528:radiation effects*; D008297:Male; D009474:Neurons / Q000166:cytology / Q000528:radiation effects*; D011897:Random Allocation; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
D002587:Cesium Isotopes