The distribution of intrahippocampal projections arising from the CA3 region of the rat hippocampus was investigated using in vitro and in vivo methods. In the in vitro hippocampal slice preparation, single CA3 pyramidal cells were intracellularly labeled with horseradish peroxidase (HRP), and the three-dimensional organization of the axonal plexus was analyzed by using a computer-aided digitizing system. As many as eight primary collaterals originated from the principal axon of CA3 pyramidal cells and these commonly bifurcated further and innervated stratum oriens and stratum radiatum of CA3 and CA1. Within the 400 microns slice, the summed length of all visible collaterals per neuron ranged from 2.6 mm to approximately 12.5 mm. While the CA3 principal axon tended to be relatively smooth, the axonal collaterals bore numerous varicosities that electron microscopy confirmed to be presynaptic boutons. These varicosities occurred, on average, once every 7 microns of collateral length. The distribution of axonal collaterals differed depending on the location of the parent pyramidal cell. Only rarely could CA3 collaterals be followed in the slice to their terminations within CA1. To study the topographic organization of CA3 projections both to other levels of CA3 and to CA1, the anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into various transverse and septotemporal levels of CA3. Immunohistochemical visualization of the lectin was conducted in dissected and "extended" hippocampi to facilitate analysis of the topographic distribution of projections along the long or septotemporal axis. Projections from all portions of CA3 reached widespread regions of CA3, CA2, and CA1, but only a few fibers entered the subicular complex and there were no projections to the entorhinal cortex. There were also some CA3 and CA2 projections to the hilus of the dentate gyrus, but these did not enter the granule cell or molecular layers. The CA3 projections to CA1 were organized according to several distinctive and consistent gradients that can generally be summarized as follows. 1. CA3 cells located close to the dentate gyrus (proximal CA3), while projecting both septally and temporally, tended to project more heavily to levels of CA1 located septal to the injection site. CA3 cells located closer to CA1, in contrast, projected more heavily to levels of CA1 located temporally to the injection site. 2. At, or close to, the septotemporal level of the injection, cells located proximally in CA3 gave rise to collaterals that tended to terminate more superficially in stratum radiatum than did those arising from mid and distal levels of CA3.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuregulin-1 (NRG1), a regulator of neural development, has been shown to regulate neurotransmission at excitatory synapses. Although ErbB4, a key NRG1 receptor, is expressed in glutamic acid decarboxylase (GAD)-positive neurons, little is known about its role in GABAergic transmission. We show that ErbB4 is localized at GABAergic terminals of the prefrontal cortex. Our data indicate a role of NRG1, both endogenous and exogenous, in regulation of GABAergic transmission. This effect was blocked by inhibition or mutation of ErbB4, suggesting the involvement of ErbB4. Together, these results indicate that NRG1 regulates GABAergic transmission via presynaptic ErbB4 receptors, identifying a novel function of NRG1. Because both NRG1 and ErbB4 have emerged as susceptibility genes of schizophrenia, these observations may suggest a mechanism for abnormal GABAergic neurotransmission in this disorder.

The neuregulins (NRGs) are a family of multipotent epidermal-growth-factor-like (EGF-like) factors that arise from splice variants of a single gene. They influence the growth, differentiation, survival and fate of several cell types. We have now discovered a set of new neuregulin-like growth factors, which we call neuregulin-2 (NRG-2): these are encoded by their own gene and exhibit a distinct expression pattern in adult brain and developing heart. Like NRG-1, the EGF-like domain of the new ligands binds to both the ErbB3- and ErbB4-receptor tyrosine kinases. However, NRG-2 stimulates different ErbB-receptor tyrosine-phosphorylation profiles from NRG-1. Our results indicate that NRG-1 and NRG-2 mediate distinct biological processes by acting at different sites in tissues and eliciting different biochemical responses in cells.

We grafted human spinal cord-derived neural progenitor cells (NPCs) into sites of cervical spinal cord injury in rhesus monkeys (Macaca mulatta). Under three-drug immunosuppression, grafts survived at least 9 months postinjury and expressed both neuronal and glial markers. Monkey axons regenerated into grafts and formed synapses. Hundreds of thousands of human axons extended out from grafts through monkey white matter and synapsed in distal gray matter. Grafts gradually matured over 9 months and improved forelimb function beginning several months after grafting. These findings in a 'preclinical trial' support translation of NPC graft therapy to humans with the objective of reconstituting both a neuronal and glial milieu in the site of spinal cord injury.

Appropriate development of nervous system connectivity involves a variety of processes, including neuronal life-and-death decisions, differentiation, axon guidance and migration, and synaptogenesis. Although these activities likely require specialized signaling events, few substrates unique to these neurotrophic functions have been identified. Here we describe the cloning of ankyrin repeat-rich membrane spanning (ARMS), which encodes a novel downstream target of neurotrophin and ephrin receptor tyrosine kinases, Trk and Eph, respectively. The amino acid sequence of ARMS is highly conserved from nematode to human, suggesting an evolutionarily conserved role for this protein. The ARMS protein consists of 1715 amino acids containing four putative transmembrane domains, multiple ankyrin repeats, a sterile alpha motif domain, and a potential PDZ-binding motif. In the rat, ARMS is specifically expressed in the developing nervous system and in highly plastic areas of the adult brain, regions enriched in Trks and Eph receptors. ARMS can physically associate with TrkA and p75 neurotrophin receptors. Moreover, endogenous ARMS protein is tyrosine phosphorylated after neurotrophin treatment of pheochromocytoma 12 cells and primary hippocampal neurons or ephrin B treatment of NG108-15 cells, demonstrating that ARMS is a downstream target for both neurotrophin and ephrin receptors.