Despite the advancement of pharmaceutical and biomechanical therapeutic interventions, spinal cord injury (SCI) remains a disease without a cure. The cellular-molecular footprint of SCI suggests that the trauma is a multi-factorial event; one that requires a multi-active intervention to improve outcome. The pathophysiology of SCI begins immediately and extends for months. It is carried out by signaling mechanisms in central nervous system (CNS) cells (neuronal, astroglial, oligodendroglial and microglial) and by cells that infiltrate the CNS after blood-brain barrier rupture. The signaling events between the multiple cells continue through time, creating a non-permissive environment for neuronal survival and impeding sensory and motor recovery after SCI. The progression of the initial lesion into rostro-caudal penumbras alters neuro-glial homeostasis, leading to neurotransmitter imbalances, activation of aberrant sprouting processes, axonal and neuronal degeneration affecting the transmission of tactile and noxious stimulus.
In addition to the loss of motor function, approximately 60% of SCI patients suffer from neuropathic pain, a process caused mostly by the spontaneous activation of spinothalamic neurons leading to pain transmission. Previous findings suggest biological sex influences the outcome after SCI (females recover better than males). Estrogen receptors (ERs) activation exert neuroprotection after CNS trauma, but the long-term use of estrogenic hormones should be managed carefully due to the excessive trophic activity (among others). Tamoxifen (TAM), a selective estrogen receptor modulator, may be used to activate ERs and exploit their neuro and glio-protective activity. Patients often arrive at the clinic hours after the trauma, suggesting that therapeutic interventions should evaluate the therapeutic window after SCI.
A gap of knowledge exists on the time-dependent nature of SCI as a multi-factorial event that biological sex differences affect the outcome and the effects of therapy delay in male and female. The objective of this study was to investigate the spatio-temporal mechanisms activated by TAM (associated to neuronal, astroglial and oligodendrocytes), the therapeutic window available to administer treatment and the effects of biological sex on locomotor recovery and allodynia after SCI. The general hypothesis of this study is that TAM will exert neuro and glio-protection by reducing secondary damage, favoring locomotor recovery and reducing pain development after SCI in a clinically-relevant therapeutic window. To test this, we used the MACSIS impactor to exert a moderate contusion to male and female rats, followed by TAM administration immediately or in a window of 6, 12 or 24 hrs after SCI. The animals were sacrificed at 2, 7, 14, 28 and 35 days post-injury (DPI) to study mechanisms of secondary damage. We studied the cellular mechanisms by Western blot, immunofluorescence, and histology. Locomotor recovery was evaluated weekly, until 35 DPI while allodynia development was evaluated during the chronic stages (21–35 DPI).
Our results demonstrate that TAM exerts sex and time-dependent effects after SCI. Spatio-temporal response mechanisms were similar between male and female rats (TAM reduced chronic astrogliosis, increased white matter spared tissue and increased neuronal survival). Female rats exhibited a therapeutic window of 24 hrs, while male exhibited a reduced window of 6 hrs. TAM reduced mechanical allodynia at 28 DPI in female rats, and this response was sex-specific. The glutamate transporters EAAT-1 and EAAT-2 were differentially expressed in male and female rats with no significant changes after SCI or upon TAM treatment. Female (sham or SCI) showed significantly higher levels of EAAT-1 while male (sham or SCI) showed significantly higher levels of EAAT-2 when compared to female. The observed behavioral (allodynia) response was not related to changes in glutamatergic transporters (EAAT-1 or EAAT-2) expression or alterations in peptidergic/non-peptidergic fiber sprouting into deeper laminae (IB4 and cGRP-α immunoreactivity). These findings suggest a potential role of TAM as a therapeutic intervention after SCI due to its neuroprotective and glio-protective effects favoring locomotor recovery in a clinically relevant window, without enhancing allodynia development after SCI.
|Advisor:||Gonzalez, Jorge D. Miranda|
|Commitee:||Escobales Alicea, Nelson, Garcίa Arrarás, José E., Rosa Molinar, Eduardo, Segarra Marrero, Annabell C.|
|School:||University of Puerto Rico Medical Sciences (Puerto Rico)|
|School Location:||United States -- Puerto Rico|
|Source:||DAI-B 79/10(E), Dissertation Abstracts International|
|Subjects:||Molecular biology, Neurosciences, Physiology|
|Keywords:||Chronic pain, Estrogen receptors, Selective estrogen receptor modulators, Sex differences, Spinal cord injury, Therapeutic window|
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