Physical training decreases susceptibility to pilocarpine-induced seizures in the injured rat brain

Epilepsy Associated Depression: An Update on Current Scenario, Suggested Mechanisms, and Opportunities

Depression is one of the most frequent psychiatric comorbidities associated with epilepsy having a major impact on the patient's quality of life. Several screening tools are available to identify and follow up psychiatric disorders in epilepsy. Out of various psychiatric disorders, people with epilepsy (PWE) are at greater risk of developing depression. This bidirectional relationship further hinders pharmacotherapy of comorbid depression in PWE as some antiepileptic drugs (AEDs) worsen associated depression and coadministration of existing antidepressants (ADs) to alleviate comorbid depression has been reported to worsen seizures. Selective serotonin reuptake inhibitors (SSRIs) and selective serotonin and norepinephrine reuptake inhibitors (SNRIs) are first choice of ADs and are considered safe in PWE, but there are no high-quality evidences. Similar to observations in people with depression, PWE also showed pharmacoresistant to available SSRI/SNRIs, which further complicates the disease prognosis. Randomized double-blind placebo-controlled clinical trials are necessary to report efficacy and safety of available ADs in PWE. We should also move beyond ADs, and therefore, we reviewed common pathological mechanisms such as neuroinflammation, dysregulated hypothalamus pituitary adrenal (HPA) axis, altered neurogenesis, and altered tryptophan metabolism responsible for coexistent relationship of epilepsy and depression. Based on these common pertinent pathways involved in the genesis of epilepsy and depression, we suggested novel targets and therapeutic approaches for safe management of comorbid depression in epilepsy.

Impacts of exercise intervention on various diseases in rats

BACKGROUND

Exercise is considered as an important intervention for treatment and prevention of several diseases, such as osteoarthritis, obesity, hypertension, and Alzheimer's disease. This review summarizes decadal exercise intervention studies with various rat models across 6 major systems to provide a better understanding of the mechanisms behind the effects that exercise brought.

METHODS

PubMed was utilized as the data source. To collect research articles, we used the following terms to create the search: (exercise [Title] OR physical activity [Title] OR training [Title]) AND (rats [Title/Abstract] OR rat [Title/Abstract] OR rattus [Title/Abstract]). To best cover targeted studies, publication dates were limited to "within 11 years." The exercise intervention methods used for different diseases were sorted according to the mode, frequency, and intensity of exercise.

RESULTS

The collected articles were categorized into studies related to 6 systems or disease types: motor system (17 articles), metabolic system (110 articles), cardiocerebral vascular system (171 articles), nervous system (71 articles), urinary system (2 articles), and cancer (21 articles). Our review found that, for different diseases, exercise intervention mostly had a positive effect. However, the most powerful effect was achieved by using a specific mode of exercise that addressed the characteristics of the disease.

CONCLUSION

As a model animal, rats not only provide a convenient resource for studying human diseases but also provide the possibility for exploring the molecular mechanisms of exercise intervention on diseases. This review also aims to provide exercise intervention frameworks and optimal exercise dose recommendations for further human exercise intervention research.

Post-Traumatic Epilepsy and Seizure Susceptibility in Rat Models of Penetrating and Closed-Head Brain Injury

Traumatic brain injury (TBI) carries a risk of developing post-traumatic epilepsy (PTE). Currently, animal models that replicate clinical PTE (delayed spontaneous and recurrent seizures) are limited, which hinders pre-clinical research. In this study, we used two rat models of penetrating ballistic-like brain injury (PBBI) and closed-head injury (CHI) to induce spontaneous seizures and also measure changes in seizure susceptibility. In the PBBI model, two trajectories (frontal and lateral) and two injury severities for each trajectory, were evaluated. In the CHI model, a single projectile impact to the dorsal/lateral region of the head was tested. Continuous video-electroencephalographic (EEG) recordings were collected for 10 days at 1 or 6 month(s) post-injury. After EEG recording, all rats were given a sub-convulsant dose of pentylenetetrazole (PTZ) to challenge the seizure susceptibility. The video-EEG recording did not detect PTE following the PBBI. Only one CHI rat demonstrated persistent and recurrent non-convulsive seizures detected at 6 months post-injury. However, after PTZ challenge, 50-100% of the animals across different TBI groups experienced seizures. Seizure susceptibility increased over time from 1 to 6 months post-injury across the majority of TBI groups. Injury severity effects were not apparent within the PBBI model, but were evident between PBBI and CHI models. These results demonstrated the difficulties in detecting delayed spontaneous post-traumatic seizures even in a high-risk model of penetrating brain injury. The PTZ-induced increase in seizure susceptibility indicated the existence of vulnerable risk of epileptogenesis following TBI, which may be considered as an alternative research tool for pre-clinical studies of PTE.

On the Run for Hippocampal Plasticity

Accumulating research in rodents and humans indicates that exercise benefits brain function and may prevent or delay onset of neurodegenerative conditions. In particular, exercise modifies the structure and function of the hippocampus, a brain area important for learning and memory. This review addresses the central and peripheral mechanisms underlying the beneficial effects of exercise on the hippocampus. We focus on running-induced changes in adult hippocampal neurogenesis, neural circuitry, neurotrophins, synaptic plasticity, neurotransmitters, and vasculature. The role of peripheral factors in hippocampal plasticity is also highlighted. We discuss recent evidence that systemic factors released from peripheral organs such as muscle (myokines), liver (hepatokines), and adipose tissue (adipokines) during exercise contribute to hippocampal neurotrophin and neurogenesis levels, and memory function. A comprehensive understanding of the body-brain axis is needed to elucidate how exercise improves hippocampal plasticity and cognition.

Inflammation in the developing rat modulates astroglial reactivity to seizures in the mature brain

Astrocytes participate in neuronal development and excitability, and produce factors enhancing or suppressing inflammatory processes occurring due to neurodegenerative diseases, such as epilepsy. Seizures, in turn, trigger the release of inflammatory mediators, causing structural and functional changes in the brain. Therefore, it appears reasonable to determine whether generalized inflammation at developmental periods can affect astrocyte reactivity to epileptic seizures occurring in the adult brain. Lipopolysaccharide (LPS) was injected in 6- or 30-day-old rats (P6 or P30, respectively). At the age of 2 months, seizures were induced, and pilocarpine and morphological changes of astrocytes located within the hippocampal formation were assessed. Additionally, expression of glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), aquaporin 4 (AQP4), and inwardly rectifying potassium channel Kir 4.1 (Kir4.1) was determined using Western blots. The animal group given LPS on P6 displayed maximal susceptibility to pilocarpine-induced seizures, significantly higher than the group that received LPS on P30. In the immunohistologically examined hippocampal formation, the GFAP-immunoreactive area was not affected by LPS alone. However, it was reduced following seizures in naïve controls but not in LPS-pretreated rats. Increases in the ramification of astrocytic processes were detected only in adult rats given LPS on P30, not on P6. Seizures abolished the effects. Following seizures, the process ramification showed no significant change in the two LPS-treated rat groups, whereas it was significantly reduced in the dentate gyrus of LPS-untreated controls. Glial fibrillary acidic protein (GFAP) expression showed no changes induced with LPS alone and rose slightly after seizures. AQP4 content was lower in rats given LPS on P6 and was seizure-resistant in the two LPS-treated groups, contrary to a decrease in untreated controls. GS expression was not affected by LPS treatments and was reduced after seizures without an intergroup difference. Kir4.1 underwent highly significant increases in all groups experiencing seizures, but LPS alone had no effect. It can be concluded that the generalized inflammatory status led to some important changes in astrocytes reflected, in part at least by permanent modifications of their morphology and molecular profile. Moreover, the previously experienced inflammation prevented the cells from much stronger changes in response to seizures observed in adult untreated controls. The obtained results point to a link between the activation of astrocytes by transient systemic inflammation occurring during the developmental period and their subsequent reactivity to seizures, which may play an important role in the functional features of the brain, including its susceptibility to seizures.

CB1 receptor antagonism prevents long-term hyperexcitability after head injury by regulation of dynorphin-KOR system and mGluR5 in rat hippocampus

Both endocannabinoids and dynorphin are feedback messengers in nervous system that act at the presynaptic nerve terminal to inhibit transmitter release. Many studies showed the cannabinoid-opioid cross-modulation in antinociception, hypothermia, sedation and reward. The aim of this study was to assess the influence of early application of cannabinoid type 1 (CB1) receptor antagonism SR141716A after brain injury on dynorphin-κ opioid receptor (KOR) system and the expression of metabotropic glutamate receptors (mGluRs) in a rat model of fluid percussion injury (FPI). Firstly, seizure latency induced by pentylenetetrazole was significantly prolonged 6 weeks after brain injury in group of SR141716A treatment. Then, PCR and western blot showed that SR141716A inhibited the long-term up-regulation of CB1 receptors in hippocampus. However, SR141716A resulted in long-term potentiation of dynorphin release and did not influence the up-regulation of KOR in hippocampus after brain injury. Furthermore, SR141716A reverse the overexpression of mGluR5 in the late stage of brain injury. We propose that during the induction of epileptogenesis after brain injury, early application of CB1 receptor antagonism could prevent long-term hyperexcitability by up-regulation of dynorphin-KOR system and prevention of mGluR5 induced epileptogenesis in hippocampus.