In fact, adding progesterone to the culture medium accelerated the myelination of axons and its effect involved PR, as it was no longer observed in cerebellar slices prepared from PR knockout mice . A study by Caruso et al. showed increased levels of pregnenolone and decreased levels of 5α-dihydroprogesterone (5α-DHP), 5α-dihydrotestosterone (5α-DHT) and estradiol in the cerebrospinal fluid of adult men with Relapse Remitting (RR) MS . Importantly, sex-specific neurosteroid synthesis and signaling in the brain may also play a significant role in MS. In men with MS, estrogen synthesis and ERβ signaling are induced, whereas in females with MS, progesterone synthesis and PR signaling are upregulated . Mechanisms by which progesterone and testosterone act on oligodendrocyte lineage development and myelination. Importantly, many steroid receptors have been implicated in neurological, neurodegenerative, and psychiatric diseases, including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, schizophrenia and MS 70,72,78,79,80,81,82. Glial cells in the demyelinating lesions appear to be the primary site of expression of steroidogenic enzymes and steroid receptors 85,87. These neuroactive steroids (S) either derived from the systemic circulation or produced locally in the brain, bind and dissociate nuclear receptors (SR) from HSPs (heat shock proteins). The term "neuroactive steroid" corresponds to a functional concept and refers to natural hormonal steroids, produced by the nervous system or the peripheral glands, and to synthetic steroids, that modify the activity of neural cells. The reciprocal communication between axons and oligodendrocytes is very important and its deficiency leads to neurological diseases. Different glycolipids such as galactocerebroside, galactosulfatide and ganglioside are also contained in the myelin bilayer 27,43. The quantitatively most significant lipids in myelin are cholesterol, galactosylceramide and ethanolamine plasmalogen. Myelination accelerates nerve conduction 20 to 100 times compared to non-myelinated axons of the same diameter, without occupying much space 38,39. Any disruption or dysfunction in this pathway can lead to sexual problems, such as erectile dysfunction, premature ejaculation, or inhibited sexual desire . When sexual stimuli are detected, the brain’s limbic system, including the hypothalamus and amygdala, is activated. The process begins with the brain’s processing of sexual stimuli, which can be visual, auditory, or tactile . Dysfunction in any of these regions can lead to sexual dysfunction or changes in sexual behaviour. The prefrontal cortex plays a role in decision-making and regulating sexual behaviour. The insula plays a role in processing bodily sensations and emotions, including those related to sexual arousal and orgasm. Overall, the sexual brain is a complex and fascinating area of study that continues to yield new insights into human sexuality and behaviour. The neurotransmitters dopamine, serotonin, and norepinephrine are also important in sexual function, as they affect mood, motivation, and arousal . Other areas of the brain, such as the amygdala, prefrontal cortex, and insula, are also involved in processing sexual stimuli and generating sexual responses . Overall, this comprehensive review provides a valuable synthesis of current knowledge on the sexual brain, offering insights into the neurobiological mechanisms underlying human sexual response. Finally, the review acknowledges the importance of societal and cultural factors in shaping sexual behaviour and the brain’s response to sexual stimuli. Moreover, the review examines the influence of sexual orientation on the neural processing of sexual stimuli, emphasizing the differentiation between romantic love and sexual desire in the brain. Estrogen also plays a role in the regulation of the menstrual cycle and the maintenance of reproductive health. It is responsible for developing secondary sexual characteristics in males, such as body hair and muscle mass. The parasympathetic nervous system is responsible for promoting sexual arousal and maintaining erections in men. These systems work together to regulate physiological responses to sexual stimuli, such as changes in heart rate, blood pressure, and respiration. These regions are responsible for processing emotions and motivation, including sexual desire.
