Enrike G. Argandoña

Effects of dark-rearing on the vascularization of the developmental rat visual cortex

Cerebral vascular density corresponds to metabolic demand, which increases in highly active areas. External inputs play an important role in the modeling and development of the visual cortex. Experience-mediated development is very active during the first postnatal month, when accurate simultaneous blood supply is needed to satisfy increased demand. We studied the development of visual cortex vascularization in relation to experience, comparing rats raised in darkness with rats raised in standard conditions. The parameters measured were cortical thickness, vascular density and number of perpendicular vessels, constituting the first stage of cortical vascular development. Vessels were stained using butyryl cholinesterase histochemistry, which labels some neurons and microvascularization (vessels from 5 to 50 microns). Animals from both groups were sampled at 0, 7, 14, 21 and 60 days postnatal. Vascularization of the brain starts with vertically oriented intracortical vascular trunks whose density decreases notably after birth in rats reared in standard laboratory conditions. The most striking finding of our work is the significantly lower decrease in the number of these vessels in dark-reared rats. Our results also show that cortex thickness and vessel density are significantly lower in dark-reared rats. These results suggest that the absence of visual stimuli retards the maturation of the visual cortex including its vascular bed.

Effects of Visual Experience on Vascular Endothelial Growth Factor Expression during the Postnatal Development of the Rat Visual Cortex

The development of the cortical vascular network depends on functional maturation. External inputs are an essential requirement in the modeling of the visual cortex, mainly during the critical period, when the functional and structural properties of visual cortical neurons are particularly susceptible to alterations. Vascular endothelial growth factor (VEGF) is the major angiogenic factor, a key signal in the induction of vessel growth. Our study focused on the role of visual stimuli on the development of the vascular pattern correlated with VEGF levels. Vascular density and the expression of VEGF were examined in the primary visual cortex of rats reared under different visual environments (dark rearing, dark-rearing in conditions of enriched environment, enriched environment, and laboratory standard conditions) during postnatal development (before, during, and after the critical period). Our results show a restricted VEGF cellular expression to astroglial cells. Quantitative differences appeared during the critical period: higher vascular density and VEGF protein levels were found in the enriched environment group; both dark-reared groups showed lower vascular density and VEGF levels, which means that enriched environment without the physical exercise component does not exert effects in dark-reared rats.

VEGFR-2 expression in brain injury : its distribution related to brain-blood barrier markers

Summary.VEGF is a major regulator of angiogenesis and vascular permeability in development and injury. The involvement of one of its receptors, Flk-1 in angiogenesis has been widely demonstrated, but few studies elucidate its role as a mediator of the BBB permeability and none displays its distribution following a cortical micronecrosis. A microvascular marker (LEA lectin), two BBB markers (EBA, GluT-1) and the VEGFR2 receptor were studied in adult rats after a minimal brain injury. Immunohistochemistry shows an increase of positive vessels, somata and processes around the micronecrosis from 6 to 72 hours after injury. Flk-1 was overexpressed mainly in endothelial cells, but also in astrocytes, neuronal somata and processes adjacent to the damage. This increase correlates to the lose of positivity for EBA. After injury, VEGFR-2 expression increases and its distribution corresponds to VEGF one. The whole system seems to play a role in the disruption of the BBB.

Influence of visual experience deprivation on the postnatal development of the microvascular bed in layer IV of the rat visual cortex.

Cerebral vascular density is correlated with metabolic demands, which increase in highly active brain areas. External inputs are an essential requirement in the modeling of the visual cortex. Experience-mediated development is very active during the first postnatal month, when congruous blood supply is needed. We studied the development of visual cortex vascularization in relation to experience, comparing rats raised in darkness with rats reared in normal conditions. Vascular density, vascular area and their ratio vs. neuronal density were calculated. Conventionally stained semi-thin sections were used to measure the vascular area by computer assisted morphometry. Animals from both groups were sampled at 14, 21, and 60 days postnatal (dpn). We found a significantly lower density of vessels and neurons as well as a smaller vascular area in dark-reared adult rats while no differences were founded at the other ages. Our results also show no differences between the ratio of vessels/neuron, and vascular area/neuron, between both groups. The absence of visual experience causes decrease of cortical activity which correlates with lower vessels density and vascular area, without their ratio/neuron being affected.

Enriched and Deprived Sensory Experience Induces Structural Changes and Rewires Connectivity during the Postnatal Development of the Brain

During postnatal development, sensory experience modulates cortical development, inducing numerous changes in all of the components of the cortex. Most of the cortical changes thus induced occur during the critical period, when the functional and structural properties of cortical neurons are particularly susceptible to alterations. Although the time course for experience-mediated sensory development is specific for each system, postnatal development acts as a whole, and if one cortical area is deprived of its normal sensory inputs during early stages, it will be reorganized by the nondeprived senses in a process of cross-modal plasticity that not only increases performance in the remaining senses when one is deprived, but also rewires the brain allowing the deprived cortex to process inputs from other senses and cortices, maintaining the modular configuration. This paper summarizes our current understanding of sensory systems development, focused specially in the visual system. It delineates sensory enhancement and sensory deprivation effects at both physiological and anatomical levels and describes the use of enriched environment as a tool to rewire loss of brain areas to enhance other active senses. Finally, strategies to apply restorative features in human-deprived senses are studied, discussing the beneficial and detrimental effects of cross-modal plasticity in prostheses and sensory substitution devices implantation.

Vascular Endothelial Growth Factor and Other Angioglioneurins: Key Molecules in Brain Development and Restoration

Angioneurines are a family of molecules that include vascular growth factors such as VEGF, neurotrophins such as BDNF, IGF-I, and Erythropoietin, among others. They affect both neural and vascular processes. Due to the fact that all of them act over glia, we propose the term angioglioneurins to name them. They play a key role in the neurogliovascular unit that represents the functional core maintaining BBB. Although delivery to CNS is still an unsolved problem nowadays, exogenous angioglioneurin administration represents a promising therapeutic strategy for many neurological pathologies due to their neurotrophic and neurogenic role. In brains, VEGF is produced by neurons and astrocytes in different stages and situation, binding to tyrosine kinase receptors and also to neuropilin family. This fact reinforces its key role in the cross talk between neural and vascular development and activity. Angioglioneurins described in this report might become an important therapeutic resource in CNS restoration, especially in pathologies as stroke or traumatic brain injury.

Combination of intracortically administered VEGF and environmental enrichment enhances brain protection in developing rats.

Postnatal development of the visual cortex is modulated by experience, especially during the critical period. In rats, a stable neuronal population is only acquired after this relatively prolonged period. Vascular endothelial growth factor (VEGF) is the most important angiogenic factor and also has strong neuroprotective, neurotrophic and neurogenic properties. Similar effects have been described for rearing in enriched environments. Our aim is to investigate the vascular and neuronal effects of combining VEGF infusion and environmental enrichment on the visual cortex during the initial days of the critical period. Results showed that a small percentage of Cleaved Caspase-3 positive cells colocalized with neuronal markers. The lesion produced by the cannula implantation resulted in decreased vascular, neuronal and Caspase-3 positive cell densities. Rearing under enriched environment was unable to reverse these effects in any group, whereas VEGF infusion alone partially corrected those effects. A higher effectiveness was reached by combining both the procedures, the most effective combination being when enriched-environment rearing was introduced only after minipump implantation. In addition to the angiogenic effect of VEGF, applied strategies also had synergic neuroprotective effects, and the combination of the two strategies had more remarkable effects than those achieved by each strategy applied individually.

VEGF reverts the cognitive impairment induced by a focal traumatic brain injury during the development of rats raised under environmental enrichment

The role of VEGF in the nervous system is extensive; apart from its angiogenic effect, VEGF has been described as a neuroprotective, neurotrophic and neurogenic molecule. Similar effects have been described for enriched environment (EE). Moreover, both VEGF and EE have been related to improved spatial memory. Our aim was to investigate the neurovascular and cognitive effects of intracerebrally-administered VEGF and enriched environment during the critical period of the rat visual cortex development. Results showed that VEGF infusion as well as enriched environment induced neurovascular and cognitive effects in developing rats. VEGF administration produced an enhancement during the learning process of enriched animals and acted as an angiogenic factor both in primary visual cortex (V1) and dentate gyrus (DG) in order to counteract minipump implantation-induced damage. This fact revealed that DG vascularization is critical for normal learning. In contrast to this enriched environment acted on the neuronal density of the DG and V1 cortex, and results showed learning enhancement only in non-operated rats. In conclusion, VEGF administration only has effects if damage is observed due to injury. Once control values were reached, no further effects appeared, showing a ceiling effect. Our results strongly support that in addition to neurogenesis, vascularization plays a pivotal role for learning and memory.

Vascular endothelial growth factor: adaptive changes in the neuroglialvascular unit.

Brain postnatal development is modulated by adaptation and experience. Experience-mediated changes increase neuronal activity leading to increased metabolic demands that involve adaptive changes including ones at the microvascular network. Therefore, vascular environment plays a key role in central nervous system (CNS) development and function in health and disease. Trophic factors are crucial in CNS development and cell survival in adults. They participate in protection and proliferation of neuronal, glial and endothelial cells. Among the most important molecules are: the proangiogenic vascular endothelial growth factor (VEGF), the neurotrophin brain derived neurotrophic factor (BDNF), insulin growth factor (IGF-I) and the glycoprotein erythropoietin (EPO). We propose the term angioglioneurins to define molecules acting on the three components of the neurogliovascular unit. We have previously reported the effects of environmental modifications on the three components of the neurogliovascular unit during the postnatal development. We have also described the main role played by VEGF in the experience-induced postnatal changes. Angioglioneurin administration, alone or in combination with other neuroprotective strategies such as environmental enrichment, has been proposed as a non-invasive therapeutic strategy against several CNS diseases.

Activation of cannabinoid system in anterior cingulate cortex and orbitofrontal cortex modulates cost-benefit decision making

Despite the evidence for altered decision making in cannabis abusers, the role of the cannabinoid system in decision-making circuits has not been studied. Here, we examined the effects of cannabinoid modulation during cost-benefit decision making in the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC), key brain areas involved in decision making. We trained different groups of rats in a delay-based and an effort-based form of cost-benefit T-maze decision-making task. During test days, the rats received local injections of either vehicle or ACEA, a cannabinoid type-1 receptor (CB1R) agonist in the ACC or OFC. We measured spontaneous locomotor activity following the same treatments and characterized CB1Rs localization on different neuronal populations within these regions using immunohistochemistry. We showed that CB1R activation in the ACC impaired decision making such that rats were less willing to invest physical effort to gain high reward. Similarly, CB1R activation in the OFC induced impulsive pattern of choice such that rats preferred small immediate rewards to large delayed rewards. Control tasks ensured that the effects were specific for differential cost-benefit tasks. Furthermore, we characterized widespread colocalizations of CB1Rs on GABAergic axonal ends but few colocalizations on glutamatergic, dopaminergic, and serotonergic neuronal ends. These results provide first direct evidence that the cannabinoid system plays a critical role in regulating cost-benefit decision making in the ACC and OFC and implicate cannabinoid modulation of synaptic ends of predominantly interneurons and to a lesser degree other neuronal populations in these two frontal regions.