Neuroanatomy and sex differences of the lordosis-inhibiting system in the lateral septum

Abstract

Female sexual behavior in rodents, termed lordosis, is controlled by facilitatory and inhibitory systems in the brain. It has been well demonstrated that a neural pathway from the ventromedial hypothalamic nucleus (VMN) to the midbrain central gray (MCG) is essential for facilitatory regulation of lordosis. The neural pathway from the arcuate nucleus to the VMN, via the medial preoptic nucleus, in female rats mediates transient suppression of lordosis, until female sexual receptivity is induced. In addition to this pathway, other regions are involved in inhibitory regulation of lordosis in female rats. The lordosis-inhibiting systems exist not only in the female brain but also in the male brain. The systems contribute to suppression of heterotypical sexual behavior in male rats, although they have the potential ability to display lordosis. The lateral septum (LS) exerts an inhibitory influence on lordosis in both female and male rats. This review focuses on the neuroanatomy and sex differences of the lordosis-inhibiting system in the LS. The LS functionally and anatomically links to the MCG to exert suppression of lordosis. Neurons of the intermediate part of the LS (LSi) serve as lordosis-inhibiting neurons and project axons to the MCG. The LSi-MCG neural connection is sexually dimorphic, and formation of the male-like LSi-MCG neural connection is affected by aromatized testosterone originating from the testes in the postnatal period. The sexually dimorphic LSi-MCG neural connection may reflect the morphological basis of sex differences in the inhibitory regulation of lordosis in rats.

The lateral septum mediates kinship behavior in the rat

“…One interesting and related hypothesis is a role for endogenous opioids in social attachment behavior 34,35 . The intermediate lateral septum receives input from the leuenkephalin fibers of the hypothalamus and the medial amygdala 17 and forms output to areas relevant for social and sexual behaviors such as the lordosis reflex in the periaqueductal gray 36 . We suggest that the lateral septum is not only a substrate for pair bonding, as previously shown 37 , but that it also plays a key role in kin-affiliation as indicated by the present study and human imaging studies 18,19 .…”

Ascending Control of Arousal and Motivation: Role of Nucleus Incertus and its Peptide Neuromodulators in Behavioural Responses to Stress

“…In addition to the mnemonic roles of the hippocampus and theta rhythm, this circuit also functions to modulate interrelated emotional and social behaviour. For example, the lateral septum is an essential negative regulator of lordosis/sociosexual and anxiety‐like behaviour , which is also strongly modulated by the ventral hippocampus . Recent studies also indicate that a specific subclass of interneurones in the prefrontal cortex, which is a primary NI input area and receives moderate NI projections, mediate changes in female sociosexual behaviour in response to oxytocin .…”

Medial preoptic area in mice is capable of mediating sexually dimorphic behaviors regardless of gender

“…The medial preoptic area (mPOA) of the hypothalamus is a central node in a conserved neural network that regulates social behaviors and social reward 16 – 20 , and is anatomically sexually dimorphic in many species, including humans 21 – 23 . The mPOA expresses at high levels gonadal steroid hormone receptors that regulate sexually differentiation 8 , 18 and connects to other sexually dimorphic brain areas 4 , 24 – 27 . Indeed, neuronal numbers or densities 7 , 28 – 31 , synaptic organizations 32 – 34 , distributions of innervating fibers 35 , 36 , and gene expression patterns 8 in the mPOA are all found to be sexually dimorphic.…”