Sexual Stimulation Increases the Survival of New Cells in the Accessory Olfactory Bulb of the Male Rat.

Nancy M Unda,Wendy Portillo,Rebeca Corona,Raúl G Paredes

doi:10.3389/fnins.2016.00065

Abstract

Sexual behavior in rodents is modulated by the olfactory system. The olfactory bulb (OB) is a structure that undergoes continues neurogenesis in adulthood. We have previously shown that 15 days after males rats pace the sexual interaction and ejaculate 1 or 3 times, there is an increase in the density of new cells that reach the accessory olfactory bulb (AOB). The aim of the present study was to evaluate if sexual behavior in male rats increases the density of new neurons that survive 45 days after sexual behavior in the AOB and in the main OB (MOB). Male rats were randomly divided in four groups: (1) Control (Ctr), males without sexual interaction; (2) Exposed (Exp), males only exposed to a sexually receptive female; (3) No pacing (NP), males that mated in conditions in which the female paced the sexual interaction; (4) One ejaculation (1E), males that paced the sexual interaction with a receptive female and ejaculated once; and (5) Three ejaculations (3E), males that paced the sexual interaction and were allowed to ejaculate three times. All males were injected with the DNA synthesis marker 5-bromo-2-deoxyuridine (BrdU), and were tested in one of the above conditions. 45 days later they were sacrificed, and the OBs were processed to identify new cells and evaluate if they had differentiated into neurons. Our data indicate that males that ejaculated three times showed an increase in the density of new cells that survive in the posterior part of the granular cell layer of the AOB and have more new neurons that the control group. However, no significant differences were found in the percentage of new cells that differentiate into neurons. No significant increase in the density of new cells was observed in the MOB. Our data show that pacing the sexual interaction until three ejaculations increases the density of new cells and neurons in the granular layer of the AOB, confirming that sexual behavior induces long-lasting plastic changes in the OB.

Highlights

In rodents, the olfactory system regulates neuroendocrine and reproductive functions, allowing animals to recognize conspecifics and to determine gender and hormonal condition (Tirindelli et al, 2009)
Since we only found significant differences in the density of new cells that survive in the granular cell layer (GrL) of the accessory olfactory bulb (AOB), we evaluated if sexual behavior increased the density and percentage of new cells that differentiate into neurons in the 3E group in comparison to the control group
Our data reveal that those males that ejaculated three times pacing the sexual interaction show an increase in the density of new cells and neurons that survive in the granular cell layer (GrL) of the posterior accessory olfactory bulb

Summary

Introduction

The olfactory system regulates neuroendocrine and reproductive functions, allowing animals to recognize conspecifics and to determine gender and hormonal condition (Tirindelli et al, 2009). The main (MOS) and the accessory olfactory system (AOS) process odorants. The odorants are detected by the olfactory neurons that extend axons to the glomeruli. Sexual Behavior Increases Neurogenesis and synapse onto dendrites of the mitral and periglomerular cells. The dendrites of periglomerular cells form reciprocal dendrodendritic synapses with dendrites of mitral cells. Granular interneurons modulate the activity of the mitral neurons, establishing microcircuits in the olfactory bulb (Murphy et al, 2005). Mitral cells of the main olfactory bulb (MOB) send their axons through the lateral olfactory tract to central regions in the brain such as the anterior olfactory nucleus, cortical and medialanterior amygdala (AMG), olfactory tuberculus, piriform, and entorhinal cortex (Baum and Kelliher, 2009; Sosulski et al, 2011; Baum and Cherry, 2015)

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