Sexual dimorphism in the human olfactory bulb: females have more neurons and glial cells than males

PLoS One. 2014 Nov 5;9(11):e111733. doi: 10.1371/journal.pone.0111733. eCollection 2014.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Cell Count
  • Female
  • Humans
  • Male
  • Middle Aged
  • Neuroglia / cytology
  • Neurons / cytology
  • Olfactory Bulb / anatomy & histology
  • Olfactory Bulb / cytology*
  • Organ Size
  • Sex Characteristics*
  • Sex Factors

Grant support

The following Brazilian institutions contributed with research grants of different types, as well as fellowships of different categories to students who participated on the work. The grants are not unified as in the American system, so the total number of formal “grants” totalize something like 30 or so. This is why they cannot be listed by their protocol numbers in each agency. (1) Conselho Nacional de Desenvolvimento Científico e Tecnológico (R. Lent) (www.cnpq.br). (2) Instituto Nacional de Ciência e Tecnologia em Neurociência Translacional (R. Lent). (3) Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (R. Lent, A.V. Oliveira-Pinto) (www.capes.gov.br). (4) Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (R. Lent) (www.faperj.br). (5) Fundação de Amparo à Pesquisa do Estado de São Paulo (Lea T. Grinberg, C. Pasqualucci, W. Jacob-Filho) (www.fapesp.br). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.