Hypothesis :

•The more prevalent populations of neurons in the male, those

with a single nucleolus, will be stimulated in response to

female vaginal secretions

Sex differences in pheromonal stimulation of

neuronal subtypes in the hamster MPN mag

HOLLY RICHENDRFER AND JENNIFER SWANN

Biol. Sci., Lehigh Univ., Bethlehem, PA 18015

Introduction• Hamsters rely solely on pheromonal cues to mate

• The magnocellular division of the medial preoptic nucleus

(MPN mag) (figure 1A) plays a critical role in male

copulatory behavior. Lesions of this area eliminate male

sex behavior.

• The MPN mag integrates chemosensory and hormonal

information; only the MPN mag of the male is stimulated

in response to female pheromones

• Using a stereological approach to analyze cresyl violet

(CV) stained sections we found that the MPN mag is

sexually dimorphic in neuronal type by p30. The male

MPN mag has more neurons with a single nucleolus;

females have more with multiple nucleoli

Methods• Male and female hamsters, 60 days old were exposed to

FHVS for one hour before perfusion with 4%

paraformaldehyde, postfixed, sectioned in 40 um on a

microtome, mounted onto slides and immunolabeled with

EGR-1 then counterstained with CV. This was performed

in order to show neuronal type differences (figure 1B).

• Stereologic analysis - The MPN mag was outlined and

the number of cells stimulated with EGR-1 (with nova red

chromagen) were counted and put into two groups based

upon neuronal morphology

• Differences were determined using multiple analysis of

variance.

Results•The neurons that are stimulated in the male that contain a single nucleolus are almost double the number of

neurons that contain multiple nucleoli and these distributions are different from the other three groups (fig 3). The

distribution of four different sets of neurons is similar in females given FHVS compared to female controls.

Conclusion•The MPN mag of the male contains both types of stimulated neurons whereas the female does not (Fig 2),

suggesting both types play a role in male typical sexual behavior

•Our current results confirm previous findings in which the MPN mag of the female is not stimulated

•There may be other factors involved that promote sex specific regulation of sex behavior in the MPN mag

•

Results

Figure 2: Males exposed to FHVS had more neurons with a single

nucleolus stimulated (*p<.001) than any other group. Males exposed to

FHVS had more multiple nucleoli neurons stimulated than both unexposed

males and females (**p=.012 and p=.001 respectively), but not compared

to FHVS treated females (p=.085).

Figure 1: A) Schematic diagram of MPN mag within the medial preoptic area. B/C) EGR-1 immunolabeling (in

red) and cresyl violet counterstain reveals neurons with both a b)single nucleolus and c) multiple nucleoli

MPN mag

A

P 43

B C

A

Figure 3: The number

of single or multiple

nucleoli neurons

expressing EGR-1 in

males and females after

exposure to FHVS or

clean swabs (control)

relative to the total

number of neurons with

single or multiple

nucleoli (total neuron

numbers taken from

Richendrfer and

Swann, 2010). The

whole pie chart

represents total number

of neurons in males and

females.