Sexual dimorphism in the human olfactory bulb: females have more neurons and glial cells than males.
Sex differences in the human olfactory function reportedly exist for olfactory sensitivity, odorant identification and memory, and tasks in which odors are rated based on psychological features such as familiarity, intensity, pleasantness, and others. Which might be the neural bases for these behavioral differences? The number of cells in olfactory regions, and especially the number of neurons, may represent a more accurate indicator of the neural machinery than volume or weight, but besides gross volume measures of the human olfactory bulb, no systematic study of sex differences in the absolute number of cells has yet been undertaken. In this work, we investigate a possible sexual dimorphism in the olfactory bulb, by quantifying postmortem material from 7 men and 11 women (ages 55-94 years) with the isotropic fractionator, an unbiased and accurate method to estimate absolute cell numbers in brain regions. Female bulbs weighed 0.132 g in average, while male bulbs weighed 0.137 g, a non-significant difference; however, the total number of cells was 16.2 million in females, and 9.2 million in males, a significant difference of 43.2%. The number of neurons in females reached 6.9 million, being no more than 3.5 million in males, a difference of 49.3%. The number of non-neuronal cells also proved higher in women than in men: 9.3 million and 5.7 million, respectively, a significant difference of 38.7%. The same differences remained when corrected for mass. Results demonstrate a sex-related difference in the absolute number of total, neuronal and non-neuronal cells, favoring women by 40-50%. It is conceivable that these differences in quantitative cellularity may have functional impact, albeit difficult to infer how exactly this would be, without knowing the specific circuits cells make. However, the reported advantage of women as compared to men may stimulate future work on sex dimorphism of synaptic microcircuitry in the olfactory bulb.
Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Ana V
AV
Oliveira-Pinto
Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Raquel M
RM
Santos
Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Renan A
RA
Coutinho
Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Lays M
LM
Oliveira
Aging Brain Study Group, University of São Paulo Medical School, São Paulo, Brazil; Brain Institute, Hospital Israelita Albert Einstein, São Paulo, Brazil.
Gláucia B
GB
Santos
Aging Brain Study Group, University of São Paulo Medical School, São Paulo, Brazil; Brain Institute, Hospital Israelita Albert Einstein, São Paulo, Brazil.
Ana T L
AT
Alho
Aging Brain Study Group, University of São Paulo Medical School, São Paulo, Brazil.
Renata E P
RE
Leite
Aging Brain Study Group, University of São Paulo Medical School, São Paulo, Brazil; Discipline of Geriatrics, University of São Paulo Medical School, São Paulo, Brazil.
José M
JM
Farfel
Aging Brain Study Group, University of São Paulo Medical School, São Paulo, Brazil; Discipline of Geriatrics, University of São Paulo Medical School, São Paulo, Brazil.
Claudia K
CK
Suemoto
Aging Brain Study Group, University of São Paulo Medical School, São Paulo, Brazil; Department of Neurology and Pathology, University of California San Francisco, San Francisco, United States of America.
Lea T
LT
Grinberg
Aging Brain Study Group, University of São Paulo Medical School, São Paulo, Brazil.
Carlos A
CA
Pasqualucci
Aging Brain Study Group, University of São Paulo Medical School, São Paulo, Brazil; Discipline of Geriatrics, University of São Paulo Medical School, São Paulo, Brazil.
Wilson
W
Jacob-Filho
Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; National Institute of Translational Neuroscience, Ministry of Science and Technology, São Paulo, Brazil.
Roberto
R
Lent
D000368:Aged; D000369:Aged, 80 and over; D002452:Cell Count; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009457:Neuroglia / Q000166:cytology; D009474:Neurons / Q000166:cytology; D009830:Olfactory Bulb / Q000033:anatomy & histology / Q000166:cytology*; D009929:Organ Size; D012727:Sex Characteristics; D012737:Sex Factors