The History of Discovery of Adult Neurogenesis

Generation of a Dcx-CreERT2 knock-in mouse for genetic manipulation of newborn neurons

A wide variety of CreERT2 driver lines are available for genetic manipulation of adult-born neurons in the mouse brain. These tools have been instrumental in studying fate potential, migration, circuit integration, and morphology of the stem cells supporting lifelong neurogenesis. Despite a wealth of tools, genetic manipulation of adult-born neurons for circuit and behavioral studies has been limited by poor specificity of many driver lines targeting early progenitor cells and by the inaccessibility of lines selective for later stages of neuronal maturation. We sought to address these limitations by creating a new CreERT2 driver line targeted to the endogenous mouse doublecortin locus as a marker of fate-specified neuroblasts and immature neurons. Our new model places a T2A-CreERT2 cassette immediately downstream of the Dcx coding sequence on the X chromosome, allowing expression of both Dcx and CreERT2 proteins in the endogenous spatiotemporal pattern for this gene. We demonstrate that the new mouse line drives expression of a Cre-dependent reporter throughout the brain in neonatal mice and in known neurogenic niches of adult animals. The line has been deposited with the Jackson Laboratory and should provide an accessible tool for studies targeting fate-restricted neuronal precursors.

Hyperbaric Oxygenation Prevents Loss of Immature Neurons in the Adult Hippocampal Dentate Gyrus Following Brain Injury

A growing body of evidence suggests that hyperbaric oxygenation (HBO) may affect the activity of adult neural stem cells (NSCs). Since the role of NSCs in recovery from brain injury is still unclear, the purpose of this study was to investigate the effects of sensorimotor cortex ablation (SCA) and HBO treatment (HBOT) on the processes of neurogenesis in the adult dentate gyrus (DG), a region of the hippocampus that is the site of adult neurogenesis. Ten-week-old Wistar rats were divided into groups: Control (C, intact animals), Sham control (S, animals that underwent the surgical procedure without opening the skull), SCA (animals in whom the right sensorimotor cortex was removed via suction ablation), and SCA + HBO (operated animals that passed HBOT). HBOT protocol: pressure applied at 2.5 absolute atmospheres for 60 min, once daily for 10 days. Using immunohistochemistry and double immunofluorescence labeling, we show that SCA causes significant loss of neurons in the DG. Newborn neurons in the subgranular zone (SGZ), inner-third, and partially mid-third of the granule cell layer are predominantly affected by SCA. HBOT decreases the SCA-caused loss of immature neurons, prevents reduction of dendritic arborization, and increases proliferation of progenitor cells. Our results suggest a protective effect of HBO by reducing the vulnerability of immature neurons in the adult DG to SCA injury.

Postnatal Neurogenesis Beyond Rodents: the Groundbreaking Research of Joseph Altman and Gopal Das

An integral component of neural ontogeny and plasticity is the ongoing generation of new neurons from precursor cells throughout the lifespan in virtually all animals with a nervous system. In mammals, postnatal neurogenesis has been documented in the cerebellum, olfactory bulb, hippocampus, striatum, substantia nigra, hypothalamus, and amygdala. Germinal centers of new neuron production in the adult brain have been identified in the neuroepithelium of the subventricular zone and the dentate gyrus. One of the earliest lines of evidence gathered came from studies on the production of cerebellar microneurons in the external germinal layer of rodents and carnivores in the 1960s and 1970s. The undeniable pioneer of that research was the insightful developmental neurobiologist Joseph Altman (1925-2016). This Cerebellar Classic is devoted to the groundbreaking work of Altman and his graduate student and, subsequently, fellow faculty member, Gopal Das (1933-1991), on postnatal neurogenesis using tritiated thymidine autoradiography to tag newly formed neurons in the cerebellum of cats. Perseverant to their ideas and patiently working in West Lafayette (Indiana), they were the founders of two fields that brought about paradigm shifts and led to an explosive growth in brain research: adult neurogenesis and neural tissue transplantation.

Nerve density in cancer: Less is better

The density of nerves in cancer is emerging as a relevant clinical parameter for patient survival. Nerves in the tumor microenvironment have been associated with poor survival and recurrence, particularly if involved in perineural invasion. However, usually only a few nerves inside a tumor are affected by perineural invasion, while most nerves are not. Mechanistic studies have shown nerve-secreted factors promote tumor growth and invasion thereby making tumors more aggressive. Therefore, the overall number of nerves in the tumor microenvironment should be more representative of the nerve-tumor biological interaction than perineural invasion. This review summarizes the available clinical information about nerve density as a measure of clinical outcome in cancer and explores the mechanisms underlying nerve density in cancer, specifically, neurogenesis, axonogenesis, and neurotropism.

An interview with Michael Barresi

Michael Barresi is Professor of Biological Sciences at Smith College, Northampton, MA, USA, where he uses the zebrafish to understand central nervous system development. Michael is also Program Director of the ‘Student Scientists’ outreach project and has made significant contributions to teaching developmental biology, including being co-author and illustrator of the textbook Developmental Biology, producing developmental documentaries and starting the Online Developmental Teaching Forums. He was awarded the 2021 Viktor Hamburger Outstanding Educator Prize from the Society of Developmental Biology (SDB). We caught up with Michael over Teams to hear more about his career and love of learning.

Therapeutic effects of Lacosamide in a rat model of traumatic brain injury: A histological, biochemical and electroencephalography monitoring study

OBJECTIVE

Traumatic Brain Injury (TBI) is a major cause of death and disability worldwide, especially in children and young adults. TBI can be classified based on severity, mechanism or other features. Inflammation, apoptosis, oxidative stress, and ischemia are some of the important pathophys-iological mechanisms underlying neuronal loss after TBI. Lacosamide (LCM) is an anticonvulsant compound approved for the adjunctive treatment of partial-onset seizures and neuropathic pain. This study aimed to investigate possible neuroprotective effects of LCM in a rat model of TBI.

MATERIAL AND METHODS

Twenty-eight adult male, Wistar albino rats were used. The rats were divided into 4 groups. Group 1 was the control group (n=7). Group 2 was the trauma group (n=7) where rats were treated with 100 mg/kg saline intraperitoneally (IP) twice a day. Groups 3 and 4, rats were treated with 6 (group 3, n=7) or 20 (group 4, n=7) mg/kg Lacosamide IP twice a day. For each group, brain samples were collected 72 hours after injury. Brain samples and blood were evaluated with histopathological and biochemical methods. In addition, electroencephalograpy monitoring results were compared.

RESULTS

The immunoreactivity of both iNOS and eNOS (oxidative stress markers) were decreased with LCM treatment compared to trauma group. The results were statistically significant (***P<0.001). The treatments of low (56,17±9,69) and high-dose LCM (43,91±9,09) were decreased the distribution of HIF-1α compared to trauma group (P<0.01). The number of apoptotic cells were decreased with LCM treatment the difference between the trauma group and 20mg/kg LCM treated group (9,55±1,02) was statistically significant (***P<0.001). Malondialdehyde level was reduced with LCM treatment. MDA level was significantly higher in trauma group compared to LCM treated groups (***P<0.001). The level of Superoxide dismutase in the trauma group was 1,86 U/ml, whereas it was 36,85 U/ml in 20mg/kg LCM treated group (***P<0.001). Delta strength of EEG in 20mg/kg LCM treated group were similar to control group values after LCM treatment.

CONCLUSION

No existing study has produced results suggesting that different doses of LCM has therapeutic effect against TBI, using EEG recording in addition to histological and biochemical evaluations in rats.

Docosahexaenoic and Arachidonic Acids as Neuroprotective Nutrients throughout the Life Cycle

The role of docosahexaenoic acid (DHA) and arachidonic acid (AA) in neurogenesis and brain development throughout the life cycle is fundamental. DHA and AA are long-chain polyunsaturated fatty acids (LCPUFA) vital for many human physiological processes, such as signaling pathways, gene expression, structure and function of membranes, among others. DHA and AA are deposited into the lipids of cell membranes that form the gray matter representing approximately 25% of the total content of brain fatty acids. Both fatty acids have effects on neuronal growth and differentiation through the modulation of the physical properties of neuronal membranes, signal transduction associated with G proteins, and gene expression. DHA and AA have a relevant role in neuroprotection against neurodegenerative pathologies such as Alzheimer's disease and Parkinson's disease, which are associated with characteristic pathological expressions as mitochondrial dysfunction, neuroinflammation, and oxidative stress. The present review analyzes the neuroprotective role of DHA and AA in the extreme stages of life, emphasizing the importance of these LCPUFA during the first year of life and in the developing/prevention of neurodegenerative diseases associated with aging.