Cortical hemorrhage‐associated neurological deficits and tissue damage in mice are ameliorated by therapeutic treatment with nicotine

Intracerebral hemorrhage (ICH) is associated with diverse sets of neurological symptoms and prognosis, depending on the site of bleeding. Relative rate of hemorrhage occurring in the cerebral cortex (lobar hemorrhage) has been increasing, but there is no report on effective pharmacotherapeutic approaches for cortical hemorrhage either in preclinical or clinical studies. The present study aimed to establish an experimental model of cortical hemorrhage in mice for evaluation of effects of therapeutic drug candidates. Type VII collagenase at 0.015 U, injected into the parietal cortex, induced hemorrhage expanding into the whole layer of the posterior parts of the sensorimotor cortex in male C57BL/6 mice. Mice with ICH under these conditions exhibited significant motor deficits as revealed by beam‐walking test. Daily administration of nicotine (1 and 2 mg/kg), with the first injection given at 3 hr after induction of ICH, improved motor performance of mice in a dose‐dependent manner, although nicotine did not alter the volume of hematoma. Immunohistochemical examinations revealed that the number of neurons was drastically decreased within the hematoma region. Nicotine at 2 mg/kg partially but significantly increased the number of remaining neurons within the hematoma at 3 days after induction of ICH. ICH also resulted in inflammatory activation of microglia/macrophages in the perihematoma region, and nicotine (1 and 2 mg/kg) significantly attenuated the increase of microglia. These results suggest that nicotine can provide a therapeutic effect on cortical hemorrhage, possibly via its neuroprotective and anti‐inflammatory actions. © 2017 Wiley Periodicals, Inc.     

Neuroarchitecture of the central complex of the desert locust: Tangential neurons

The central complex (CX) comprises a group of midline neuropils in the insect brain, consisting of the protocerebral bridge (PB), the upper (CBU) and lower division (CBL) of the central body and a pair of globular noduli. It receives prominent input from the visual system and plays a major role in spatial orientation of the animals. Vertical slices and horizontal layers of the CX are formed by columnar, tangential, and pontine neurons. While pontine and columnar neurons have been analyzed in detail, especially in the fruit fly and desert locust, understanding of the organization of tangential cells is still rudimentary. As a basis for future functional studies, we have studied the morphologies of tangential neurons of the CX of the desert locust Schistocerca gregaria. Intracellular dye injections revealed 43 different types of tangential neuron, 8 of the PB, 5 of the CBL, 24 of the CBU, 2 of the noduli, and 4 innervating multiple substructures. Cell bodies of these neurons were located in 11 different clusters in the cell body rind. Judging from the presence of fine versus beaded terminals, the vast majority of these neurons provide input into the CX, especially from the lateral complex (LX), the superior protocerebrum, the posterior slope, and other surrounding brain areas, but not directly from the mushroom bodies. Connections are largely subunit- and partly layer-specific. No direct connections were found between the CBU and the CBL. Instead, both subdivisions are connected in parallel with the PB and distinct layers of the noduli.     

Reelin activates the small GTPase TC10 and VAMP7 to promote neurite outgrowth and regeneration of dorsal root ganglia (DRG) neurons

Axonal outgrowth is a fundamental process during the development of central (CNS) and peripheral (PNS) nervous system as well as in nerve regeneration and requires accurate axonal navigation and extension to the correct target. These events need proper coordination between membrane trafficking and cytoskeletal rearrangements and are under the control of the small GTPases of the Rho family, among other molecules. Reelin, a relevant protein for CNS development and synaptic function in the adult, is also present in the PNS. Upon sciatic nerve damage, Reelin expression increases and, on the other hand, mice deficient in Reelin exhibit an impaired nerve regeneration. However, the mechanism(s) involved the Reelin‐dependent axonal growth is still poorly understood. In this work, we present evidence showing that Reelin stimulates dorsal root ganglia (DRG) regeneration after axotomy. Moreover, dissociated DRG neurons express the Reelin receptor Apolipoprotein E‐receptor 2 and also require the presence of TC10 to develop their axons. TC10 is a Rho GTPase that promotes neurite outgrowth through the exocytic fusion of vesicles at the growth cone. Here, we demonstrate for the first time that Reelin controls TC10 activation in DRG neurons. Besides, we confirmed that the known CNS Reelin target Cdc42 is also activated in DRG and controls TC10 activity. Finally, in the process of membrane addition, we found that Reelin stimulates the fusion of membrane carriers containing the v‐SNARE protein VAMP7 in vesicles that contain TC10. Altogether, our work shows a new role of Reelin in PNS, opening the option of therapeutic interventions to improve the regeneration process.     

Exorhodopsin and melanopsin systems in the pineal complex and brain at early developmental stages of Atlantic halibut (Hippoglossus hippoglossus)

The complexity of the nonvisual photoreception systems in teleosts has just started to be appreciated, with colocalization of multiple photoreceptor types with unresolved functions. Here we describe an intricate expression pattern of melanopsins in early life stages of the marine flat fish Atlantic halibut (Hippoglossus hippoglossus), a period when the unpigmented brain is directly exposed to environmental photons. We show a refined and extensive expression of melanopsins in the halibut brain already at the time of hatching, long before the eyes are functional. We detect melanopsin in the habenula, suprachiasmatic nucleus, dorsal thalamus, and lateral tubular nucleus of first feeding larvae, suggesting conserved functions of the melanopsins in marine teleosts. The complex expression of melanopsins already at larval stages indicates the importance of nonvisual photoreception early in development. Most strikingly, we detect expression of both exorhodopsin and melanopsin in the pineal complex of halibut larvae. Double‐fluorescence labeling showed that two clusters of melanopsin‐positive cells are located lateral to the central rosette of exorhodopsin‐positive cells. The localization of different photopigments in the pineal complex suggests that two parallel photoreceptor systems may be active. Furthermore, the dispersed melanopsin‐positive cells in the spinal cord of halibut larvae at the time of hatching may be primary sensory cells or interneurons representing the first example of dispersed high‐order photoreceptor cells. The appearance of nonvisual opsins early in the development of halibut provides an alternative model for studying the evolution and functional significance of nonvisual opsins. J. Comp. Neurol. 522:4003–4022, 2014. © 2014 Wiley Periodicals, Inc.     

Target‐ and input‐dependent organization of AMPA and NMDA receptors in synaptic connections of the cochlear nucleus

We examined the synaptic structure, quantity, and distribution of α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA)‐ and N‐methyl‐D‐aspartate (NMDA)‐type glutamate receptors (AMPARs and NMDARs, respectively) in rat cochlear nuclei by a highly sensitive freeze‐fracture replica labeling technique. Four excitatory synapses formed by two distinct inputs, auditory nerve (AN) and parallel fibers (PF), on different cell types were analyzed. These excitatory synapse types included AN synapses on bushy cells (AN‐BC synapses) and fusiform cells (AN‐FC synapses) and PF synapses on FC (PF‐FC synapses) and cartwheel cell spines (PF‐CwC synapses). Immunogold labeling revealed differences in synaptic structure as well as AMPAR and NMDAR number and/or density in both AN and PF synapses, indicating a target‐dependent organization. The immunogold receptor labeling also identified differences in the synaptic organization of FCs based on AN or PF connections, indicating an input‐dependent organization in FCs. Among the four excitatory synapse types, the AN‐BC synapses were the smallest and had the most densely packed intramembrane particles (IMPs), whereas the PF‐CwC synapses were the largest and had sparsely packed IMPs. All four synapse types showed positive correlations between the IMP‐cluster area and the AMPAR number, indicating a common intrasynapse‐type relationship for glutamatergic synapses. Immunogold particles for AMPARs were distributed over the entire area of individual AN synapses; PF synapses often showed synaptic areas devoid of labeling. The gold‐labeling for NMDARs occurred in a mosaic fashion, with less positive correlations between the IMP‐cluster area and the NMDAR number. Our observations reveal target‐ and input‐dependent features in the structure, number, and organization of AMPARs and NMDARs in AN and PF synapses. J. Comp. Neurol. 522:4023–4042, 2014. © 2014 Wiley Periodicals, Inc.     

Rat subthalamic nucleus and zona incerta share extensively overlapped representations of cortical functional territories

The subthalamic nucleus (STN) and the zona incerta (ZI) are two major structures of the subthalamus. The STN has strong connections between the basal ganglia and related nuclei. The ZI has strong connections between brainstem reticular nuclei, sensory nuclei, and nonspecific thalamic nuclei. Both the STN and ZI receive heavy projections from a subgroup of layer V neurons in the cerebral cortex. The major goal of this study was to investigate the following two questions about the cortico‐subthalamic projections using the lentivirus anterograde tracing method in the rat: 1) whether cortical projections to the STN and ZI have independent functional organizations or a global organization encompassing the entire subthalamus as a whole; and 2) how the cortical functional zones are represented in the subthalamus. This study revealed that the subthalamus receives heavy projections from the motor and sensory cortices, that the cortico‐subthalamic projections have a large‐scale functional organization that encompasses both the STN and two subdivisions of the ZI, and that the group of cortical axons that originate from a particular area of the cortex sequentially innervate and form separate terminal fields in the STN and ZI. The terminal zones formed by different cortical functional areas have highly overlapped and fuzzy borders, as do the somatotopic representations of the sensorimotor cortex in the subthalamus. The present study suggests that the layer V neurons in the wide areas of the sensorimotor cortex simultaneously control STN and ZI neurons. Together with other known afferent and efferent connections, possible new functionality of the STN and ZI is discussed. J. Comp. Neurol. 522:4043–4056, 2014. © 2014 Wiley Periodicals, Inc.     

Localization and characterization of val‐opsin isoform‐expressing cells in the brain of adult zebrafish

In addition to vision, light information is used to regulate a range of animal physiology. Such nonimage‐forming functions of light are mediated by nonvisual photoreceptors expressed in distinct neurons in the retina and the brain in most vertebrates. A nonvisual photoreceptor vertebrate ancient long opsin (VAL‐opsin) possesses two functional isoforms in the zebrafish, encoded by valopa and valopb, which has received little attention. To delineate the neurochemical identities of valop cells and to test for colocalization of the valop isoforms, we used in situ hybridization to characterize the expression of the valop genes along with that of neurotransmitters and a neuropeptide known to be present at the sites of valop expression. Double labeling showed that the thalamic valop population coexpresses valopa and valopb. All the thalamic valop cells overlapped with a GABAergic cell mass that continues from the anterior nucleus to the intercalated thalamic nucleus. A novel valopa cell population found in the superior raphe was serotonergic in nature. A valopb cell population in the Edinger‐Westphal nucleus was identified as containing thyrotropin‐releasing hormone. Valopb cells localized in the hindbrain intermediate reticular formation were noncholinergic in nature (nonmotorneurons). Thus, the presence of valop cell populations in different brain regions with coexpression of neurotransmitters and neuropeptides and the colocalization of valop isoforms in the thalamic cell population indicate regulatory and functional complexity of VAL‐opsin in the brain of the zebrafish. J. Comp. Neurol. 522:3847–3860, 2014. © 2014 Wiley Periodicals, Inc.     

Topographic specializations in the retinal ganglion cell layer of Australian passerines

Thornbills, honeyeaters, and silvereyes represent an abundant group of Australian passerines, whose diversity in niche differentiation suggests a pivotal role for vision. Using stereological methods and retinal wholemounts, we studied the topographic distribution of neurons in the ganglion cell layer of insectivorous, nectarivorous, and frugivorous species occupying terrestrial and arboreal microhabitats. All species studied have a central convexiclivate fovea (peak densities from 130,000 to 160,000 cells/mm²), which is shallow in the terrestrial/insectivorous yellow‐rumped thornbill and deep in the arboreal/nectarivorous honeyeaters and frugivorous silvereye. Surrounding the fovea, neuronal densities in the ganglion cell layer form a broadly ovoid and asymmetric plateau in the yellow‐rumped thornbill and a more restricted, circular and symmetric plateau in the other species. These differences in the plateau organization may reflect specific needs to locate food on the ground or among dense vegetation. We also found a temporal area (peak densities from 43,000 to 54,000 cells/mm²) across species, which increases spatial resolution in the frontal visual field and assists with foraging. Using microtubule‐associated protein 2 (MAP2) immunohistochemistry, we detected a higher concentration of giant ganglion cells forming an area gigantocellularis in the temporal retina of all species. Giant ganglion cell densities also form a horizontal streak in all species, except in the yellow‐rumped thornbill, which has an unusual increase toward the retinal periphery. In the yellow‐rumped thornbill and silvereye, giant ganglion cells also peak in the nasal retina. We suggest that these topographic variations afford differential sampling of motion signals for the detection of predators. J. Comp. Neurol. 522:3609–3628, 2014. © 2014 Wiley Periodicals, Inc.     

Climbing fiber projections in relation to zebrin stripes in the ventral uvula in pigeons

The cerebellum consists of sagittally oriented zones that are delineated by afferent input, Purkinje cell response properties, and the expression of molecular markers such as zebrin II (ZII). ZII is heterogeneously expressed in Purkinje cells such that there are parasagittal stripes of high expression (ZII+) interdigitated with stripes of little or no expression (ZII?). In pigeons, folium IXcd consists of seven pairs of ZII+/? stripes denoted P1+/? (medial) to P7+/? (lateral). In the present study we examined the climbing fiber input to the medial half of folium IXcd, the ventral uvula, which spans the medial two stripe pairs (P1+/? to P2+/?). Purkinje cells in the ventral uvula respond to patterns of optic flow resulting from self‐motion through the environment along translational axes and their climbing fibers originate in the lateral half of the medial column in the inferior olive (mcIO). Using anterograde injections into this region of the mcIO, we found the following topographic relationship: climbing fibers from the caudal lateral mcIO were located in P1+ and medial P1? ZII stripes; climbing fibers from the rostral lateral mcIO were located in lateral P2+ and P2? ZII stripes, and climbing fibers from the middle lateral mcIO were located in lateral P1? and medial P2+ ZII stripes. These data complement our previous findings showing a topographic relationship between Purkinje cell responses to optic flow visual stimuli and ZII stripes. Taken together, we suggest that a ZII+/? stripe pair may represent a functional unit in the pigeon vestibulocerebellum. J. Comp. Neurol. 522:3629–3643, 2014. © 2014 Wiley Periodicals, Inc.