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However, a subset of these cells remains undifferentiated, scattered throughout all CNS regions, and are recruited in response to demyelinating insults . Demyelination slows down the conduction of electrical impulses along the nerves and leads to the interruption or loss of function. MS is a chronic, inflammatory, demyelinating disease of the CNS with secondary axonal damage and loss.
Some antiepileptic drugs, namely phenytoin, phenobarbital, carbamazepine, oxcarbazepine, and eslicarbazepine, are known to decrease free testosterone androgen levels in males and can cause potential side effects due to hypogonadism . This data highlights the potential protective effects of androgens in demyelinating disorders. This male predominance, particularly among those with testosterone deficiency, has sparked research into the potential role of androgens in PD pathogenesis and as a therapeutic target. A deeper understanding of the mechanisms involved in neuroplasticity could guide therapeutic interventions with androgens such as testosterone replacement therapy (TRT) in neurological recovery in neurodegenerative diseases. The relationship between androgens and brain development highlights the need to understand their role in neuroplasticity. The primary function of androgens involves reproduction and the development of secondary sexual characters. This article explores the intricate relationship between androgens, androgen receptors, and the central nervous system.
Conversely, inhibiting BDNF-AS upregulates BDNF mRNA, activates BDNF-mediated signaling pathways, increases BDNF protein levels, suppresses neuronal apoptosis, and promotes neuronal outgrowth and differentiation. BDNF exon IV expression also seems capable of further stimulating its own expression through TrkB activation. Through a protein signaling cascade requiring Erk, CaM KII/IV, PI3K, and PLC, NMDA receptor activation is capable of triggering BDNF exon IV transcription.
Dysfunction in these neurotransmitter systems can lead to sexual dysfunction and changes in sexual behaviour. Neurotransmitters play essential roles in sexual behaviour by influencing mood, motivation, and arousal. Dopamine, for example, increases motivation and pleasure, which can lead to more frequent and intense sexual activity. Some antidepressants that increase serotonin levels, such as Selective Serotonin Reuptake Inhibitors (SSRIs), can also decrease sexual desire and position . High dopamine levels can increase sexual stimulation and lead to more intense sexual experiences .
There was also a marked increase in the relapse rate during the first three months after delivery, after the drop in sex steroid levels . These observations suggest that differences in circulating sex hormones could play a role in its development. Interestingly, the enzyme 5 alpha-reductase, involved in the metabolism of testosterone to its more potent form dihydro-testosterone, is mainly concentrated in the white matter. However, more in-depth studies and comparisons between species are needed to better define this concept. Therefore, immediate and active therapeutic interventions that inhibit the loss of oligodendrocytes may be crucial to promote remyelination. However, whether spared mature oligodendrocytes contribute to remyelination remains a topic of debate.
Unlike myelination, carried out during development, for which a close association exists between axon diameter and myelin thickness, the thickness of the myelin sheath during remyelination is independent of the diameter of the axon. Rapid remyelination is important to restore metabolic support to the axon, to prevent axon degeneration and subsequent neurological disability, and also to reconstruct the nodes of Ranvier, where are located the voltage-dependent sodium channels necessary for saltatory conduction . In agreement with this concept, most OPCs generated during the early postnatal period, when the greater part of CNS myelination takes place, differentiate into mature and myelinating oligodendrocytes. The knowledge of this process is of major importance as spontaneous regeneration of myelin (also called "remyelination") following demyelinating events taking place in the adult CNS. The inflammatory process is driven by a T-cell-mediated immune reaction that leads to attacks against both the myelin sheaths and the oligodendrocytes. For example, in MS, the loss of this communication due to oligodendrocyte death and demyelination leads to a considerable degeneration of axons and astrocytic gliosis 47,48.
Interestingly, neuroactive steroids, such as DHP or 3α-diol are able to counteract these effects. This neuroactive steroid and also 17β-estradiol promote a faster return to normal values of sciatic function index and increase the number of myelinated fibers and fiber diameters after nerve crush injury in rats and mice . As previously mentioned, neuroactive steroids such as PROG and DHP, increase gene expression of P0 after nerve transection . These effects of PROG and its derivatives seem to be a peculiarity of this class of neuroactive steroids because neither T nor its derivatives were able to influence the morphological parameters analyzed in these experiments 15,20. Indeed, as discussed below, neuroactive steroids act as protective agents in different experimental models of peripheral neuropathy.
Moreover, larger cohort sizes and multiple routes of administration in addition to transdermal testosterone gels should be explored. Moreover, treatment of EAE mice with 5α-DHT resulted in improved clinical scores, and reduced spinal cord gliosis and inflammation . The differences in cytokine production between males and females could be due to a testosterone-induced shift in the immune system toward Th2 immunity. Interestingly, MENT is not a substrate for the 5α-reductase enzymes and thus does not stimulate the growth of the prostate, a possible concern with androgen therapy. Complete androgen insensitivity is referred to as Tfm (for testicular feminization mutation) and affected individuals are males with a feminine appearance, internal and poorly developed testicles. The discovery of an AR mutation in mice in 1970 by Lyon and Hawkes provided an excellent model for the study of CAIS.