Mechanically Matched Silicone Brain Implants Reduce Brain Foreign Body Response

Brain implants are increasingly used to treat neurological disorders and diseases. However, the brain foreign body response (FBR) elicited by implants affects neuro-electrical transduction and long-term reliability limiting their clinical adoption. The mismatch in Young's modulus between silicon implants (~180 GPa) and brain tissue (~1-30 kPa) exacerbates the FBR resulting in the development of flexible implants from polymers such as polyimide (~1.5-2.5 GPa). However, a stiffness mismatch of at least two orders of magnitude remains. Here, we introduce (i) the first mechanically matched brain implant (MMBI) made from silicone (~20 kPa), (ii) new microfabrication methods, and (iii) a novel dissolvable sugar shuttle to reliably implant MMBIs. MMBIs were fabricated via vacuum-assisted molding using sacrificial sugar molds and were then encased in sugar shuttles that dissolved within 2 min after insertion into rat brains. Sections of rat neocortex implanted with MMBIs, PDMS implants, and silicon implants were analyzed by immunohistochemistry 3 and 9-weeks post-implantation. MMBIs resulted in significantly higher neuronal density and lower FBR within 50 μm of the tissue-implant interface compared to PDMS and silicon implants suggesting that materials mechanically matched to brain further minimize the FBR and could contribute to better implant functionality and long-term reliability.

Development of the Neuro-Immune-Vascular Plexus in the Ventricular Zone of the Prenatal Rat Neocortex

Microglial cells make extensive contacts with neural precursor cells (NPCs) and affiliate with vasculature in the developing cerebral cortex. But how vasculature contributes to cortical histogenesis is not yet fully understood. To better understand functional roles of developing vasculature in the embryonic rat cerebral cortex, we investigated the temporal and spatial relationships between vessels, microglia, and NPCs in the ventricular zone. Our results show that endothelial cells in developing cortical vessels extend numerous fine processes that directly contact mitotic NPCs and microglia; that these processes protrude from vessel walls and are distinct from tip cell processes; and that microglia, NPCs, and vessels are highly interconnected near the ventricle. These findings demonstrate the complex environment in which NPCs are embedded in cortical proliferative zones and suggest that developing vasculature represents a source of signaling with the potential to broadly influence cortical development. In summary, cortical histogenesis arises from the interplay among NPCs, microglia, and developing vasculature. Thus, factors that impinge on any single component have the potential to change the trajectory of cortical development and increase susceptibility for altered neurodevelopmental outcomes.

Post-natal developmental changes in the composition of the rat neocortical N-glycome

Asparagine-linked glycosylation (N-glycosylation) plays a key role in many neurodevelopmental processes, including neural cell adhesion, neurite outgrowth and axon targeting. However, little is known about the dynamics of N-glycosylation during brain development and, in particular, how the N-glycome of the developing neocortex differs from that of the adult. The aim of this study, therefore, was to perform a thorough characterization of N-glycosylation in both the adult and neonatal rat neocortex in order to gain insights into the types of changes occurring in the N-glycome during neurodevelopment. To this end, we used hydrophilic interaction ultraperformance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry to compare the adult neocortical N-glycome with that of 24- and 48-h neonates. We report that the abundance of complex N-glycans is significantly lower in adults compared with neonates. Furthermore, the proportion of charged complex N-glycans is also greatly reduced. This decrease in the abundance of complex N-glycans is offset by a corresponding increase in the proportion of truncated and, to a lesser extent, hybrid N-glycans. Lastly, we report that although the proportion of oligomannose N-glycans remains constant at around 24%, the distribution of high-mannose subtypes shifts from predominantly large subtypes in neonates to smaller subtypes in the adult. In summary, our findings indicate that N-glycan synthesis in the rat neocortex is fundamentally different in neonates compared with adults with a general shift occurring from large, sialylated N-glycans towards smaller, neutral structures as neonates develop into adults, coupled with a parallel shift towards smaller oligomannose structures.

Effect of Ischemic Postconditioining on Change of Immunoreactivity Level to PECAM-1/CD31 in Rat Neocortex Structures after Global Brain Ischemia

Introduction. Ischemic postconditioning (IPostC) of the brain can be considered as a promising approach to limit reperfusion injury in the ischemic area of the brain. Objective – to study the effect of IPostC after global cerebral ischemia on the level of immunoreactivity to PECAM-1/CD31 in the structures of layers II, III and V of the neocortex of rats at different periods of the reperfusion period.Material and methods. In male Wistar rats, a 10-minute global cerebral ischemia was modeled followed by IPostC in the form of reperfusion-ischemia at 15sec/15sec. In the early (2 days) and late (7 days) reperfusion periods after damaging ischemia, the number of morphologically unchanged neurons and the level of immunoreactivity to PECAM-1/CD31 in the structures of layers II, III and V of the neocortex were estimated.Results. It is shown that the use of IPostC by 2 days of reperfusion contributed to the increase in the number of unchanged neurons in layers II and III of 25.8 and 28.2 % (P<0.05), which was not accompanied by changes in the level of immunoreactivity to PECAM-1/CD31, to 7 days of reperfusion there was an increase in the number of unchanged neurons in layers II, III and V of 19.2, 22,1, 21,4 % (P<0.05) was observed a decrease in the level of immunoreactivity to PECAM-1/CD31 in the structures of these layers of 27.4, 39.4, and 16.7 % (P<0.05), respectively, when compared with similar indicators in groups without the use of IPostC.Conlusions. In the mechanisms of physiological reaction formed in the application of ischemic postconditioning after cerebral ischemia and leading to the preservation of the number of unchanged neurons in the late reperfusion period involved PECAM-1/CD31, which suggests that the protective potential of the phenomenon is realized by possible inhibiting the migration of neutrophils, monocytes and lymphocytes and extravasation of leukocytes from the systemic blood flow into the damaged area of the brain, i.e. through suppression of inflammatory response.

Local axonal conduction delays underlie precise timing of a neural sequence

SUMMARYSequential activation of neurons has been observed during various behavioral and cognitive processes and is thought to play a critical role in their generation. Here, we studied a circuit in the songbird forebrain that drives the performance of adult courtship song. In this region, known as HVC, neurons are sequentially active with millisecond precision in relation to behavior. Using large-scale network models, we found that HVC sequences could only be accurately produced if sequentially active neurons were linked with long and heterogeneous axonal conduction delays. Although such latencies are often thought to be negligible in local microcircuits, we empirically determined that HVC interconnections were surprisingly slow, generating delays up to 22 ms. An analysis of anatomical reconstructions suggests that similar processes may also occur in rat neocortex, supporting the notion that axonal conduction delays can sculpt the dynamical repertoire of a range of local circuits.

Enhanced maturation of human stem cell derived interneurons by mTOR activation

SummaryThe use of stem cell derived neurons for cell-based therapies is limited by a protracted maturation. We present a novel approach for accelerating the post-mitotic maturation of human stem cell derived interneurons via the activation of mTOR signaling. Lox sites were placed within PTEN, a key mTOR inhibitor, in a cortical interneuron (CIn) reporter line. Following directed differentiation and purification by FACS, the CIns were exposed to Cre-expressing lentivirus, then transplanted into mouse neocortex or plated onto cultured rat neocortex. Input synaptogenesis and dendritogenesis was greatly enhanced in the PTEN-deleted CIns. Whole-cell recording of the PTEN-deleted CIns in slices of transplanted neocortex revealed multiple indices of enhanced maturation. Finally, we observed similar effects using transient, doxycycline-inducible activation of AKT. We thus present an inducible, reversible approach for accelerating the maturation of human stem cell derived CIns, and to study the influences of this disease-related signaling system in human neurons.