Effects of 5-hydroxytryptophan on extracellular serotonin in the spinal cord of rats with experimental allergic encephalomyelitis

Hormones in experimental autoimmune encephalomyelitis (EAE) animal models

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) in which activated immune cells attack the CNS and cause inflammation and demyelination. While the etiology of MS is still largely unknown, the interaction between hormones and the immune system plays a role in disease progression, but the mechanisms by which this occurs are incompletely understood. Several in vitro and in vivo experimental, but also clinical studies, have addressed the possible role of the endocrine system in susceptibility and severity of autoimmune diseases. Although there are several demyelinating models, experimental autoimmune encephalomyelitis (EAE) is the oldest and most commonly used model for MS in laboratory animals which enables researchers to translate their findings from EAE into human. Evidences imply that there is great heterogeneity in the susceptibility to the induction, the method of induction, and the response to various immunological or pharmacological interventions, which led to conflicting results on the role of specific hormones in the EAE model. In this review, we address the role of endocrine system in EAE model to provide a comprehensive view and a better understanding of the interactions between the endocrine and the immune systems in various models of EAE, to open up a ground for further detailed studies in this field by considering and comparing the results and models used in previous studies.

Administration of the 5-hydroxytryptamine(1A) receptor antagonist WAY100635 suppresses acute experimental allergic encephalomyelitis in Lewis rats

Experimental allergic encephalomyelitis (EAE) is a T-cell inflammatory disease of the central nervous system (CNS) widely considered as an animal model of multiple sclerosis. In Lewis rats, myelin basic protein-complete Freund's adjuvant (MBP-CFA)-induced EAE is an acute monophasic disease from which animals recover fully. In our experiments, daily treatment (since day 1 after MBP-CFA inoculation) with the 5-hydroxytryptamine((1A)) (5-HT(1A)) receptor agonist (R)-(+)-8-hydroxy-2-(Dipropylamino)-tetralin (R(+)-8-OH-DPAT) resulted in a dose-related enhancement of neurological and histological signs in EAE-induced rats. This effect of R(+)-8-OH-DPAT was reduced by the co-administration of the 5-HT(1A) receptor antagonist (N-[2-(4-[2-mehoxyphenil]-1-piperazinyl)-ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY100635) at the peak of the acute disease. Moreover, treatment with WAY100635 since inoculation resulted in a delayed onset of the first clinical signs, milder disease and earlier regression of neurological signs along with a decrease in inflammation in the CNS.

Serotonergic neuronal sprouting as a potential mechanism of recovery in multiple sclerosis

Experimental allergic encephalomyelitis (EAE) is widely considered as an animal model of multiple sclerosis (MS). Damage to the bulbospinal serotonergic (5-HT) neurons occurs in the early paralytic stages of EAE in rats with the severity of neurologic signs corresponding to spinal serotonergic depletion. Neurologic recovery of EAE rats is associated with reestablishment of spinal 5-HT transmission possibly through sprouting of undamaged axons and nerve terminals. Damage to the bulbospinal serotonergic fibers also occurs in patients with MS (as reflected by reduced lumbar CSF 5-HIAA levels) and may contribute to several manifestations of the disease including autonomic dysregulation, sensory symptoms (i.e., paresthesias, pain) and motor symptoms (weakness, spasticity, clonus). Spinal serotonergic neuronal sprouting with regeneration of 5-HT nerve terminals may also occur in the early stages of MS and may be associated with spontaneous remission of MS symptoms following an acute relapse. Sprouting of serotonergic neurons may also explain the disparity in MS between the extent of demyelinating plaques and clinical signs of the disease. The chronic course of MS may be associated with progressive axonal degenerative changes with reduction of serotonergic nerve terminals and loss of their sprouting capability. It is proposed that the beneficial effects of treatment with AC pulsed electromagnetic fields on the symptoms and course of the disease in patients with chronic progressive MS may be related in part to renewed sprouting of serotonergic neurons.

Prazosin suppresses development of axonal damage in rats inoculated for experimental allergic encephalomyelitis

The effectiveness of the alpha 1-adrenergic antagonist prazosin for preventing monoaminergic axonal damage in the spinal cords of rats that were inoculated for experimental allergic encephalomyelitis (EAE) was assessed using immunohistochemistry. Prazosin injections (2 mg, i.p.) given twice daily from day 7 to day 15 postinoculation significantly reduced paralysis, spinal cord inflammation and monoaminergic axonal damage compared to saline injections. A close positive correlation between severity of inflammation and severity of axonal damage was found for both prazosin- and saline-treated rats that were inoculated for EAE. These findings confirmed previous observations of suppression of the development of clinical signs of EAE by prazosin treatment and supported the hypothesis that some factor associated with spinal cord inflammation may be responsible for the bulbospinal monoaminergic axonal damage that occurs during EAE.