# Sexual dimorphism of the ventral premammillary nucleus of the rat: stereological evaluation

## TL;DR

This study finds sex differences in the number and size of neurons in the ventral premammillary nucleus of rats, which may relate to sex-specific behaviors like aggression and reproduction.

## Contribution

The study provides the first stereological analysis of sexual dimorphism in the PMv, revealing sex differences in neuronal number and volume.

## Key findings

- Male rats have more neurons and larger neurons in the PMv than females.
- Female rats show increased neuronal volume during estrus compared to diestrus.
- No sexual dimorphism was found in overall PMv volume or neuronal density.

## Abstract

The ventral premammillary nucleus (PMv), situated within the ventrobasal hypothalamus, is sensitive to steroid hormones and is involved in pheromone-responsive circuits. It maintains robust connections with sexually dimorphic nuclei both within and beyond the hypothalamus. Investigations over the past 15 years have suggested the role of the PMv in integrating environmental cues from conspecifics with internal states, thereby facilitating appropriate physiological and behavioral responses during reproductive and agonistic interactions. Neurochemical evidence indicates sexual dimorphism in the PMv of rats; however, comprehensive structural analyses are lacking.

After perfusing and processing the brains of male and female rats during the estrus and diestrus phases, we applied stereological methodology in the PMv.

Males presented significantly greater neuronal volume and quantity than females did across both cycling phases. Neuronal volume in females was notably greater during estrus than during diestrus. However, no dimorphism was detected in overall volume, neuronal density, volume occupied by neurons, or neuropils.

Given its role as a nexus between nutritional status and reproductive physiology, as well as its involvement in modulating agonistic behavior, including maternal aggression, structural disparities in the PMv between males and females may reflect divergent functional roles, contributing to sex-specific strategies in reproduction and aggression.

The ventral premammillary nucleus (PMv) is a hypothalamic nucleus known to influence both agonistic and reproductive behaviors.

We conducted a stereological analysis to explore the presence of sexual dimorphism within the PMv.

Our findings indicate that neither the overall volume nor the neuronal density of the PMv exhibits sexual dimorphism. Similarly, the volume occupied by neurons and the neuropil do not differ significantly between sexes.

However, male rats possess a greater number of neurons in the PMv, and these neurons exhibit a larger volume compared to female rats in both estrus and diestrus phases.

Female rats in estrus presented a greater neuronal somatic volume in the PMv than those in diestrus.

These observed sexual dimorphisms in the PMv, along with their hormonal modulation, may reflect the nucleus’s involvement in sex-specific behaviors, such as aggression and reproduction.