Synapse formation and morphological differentiation of neuron types in embryonic rat dentate gyrus explants in vitro

The hNT Human Neuronal Cell Line Survives and Migrates into Rat Retina

The present studies were undertaken to determine if hNT cells can survive in the vitreous of the eye and migrate into the retina. The hNT neuronal cell line represents a uniform source of human tissue that may be of use in retinal grafts. hNT cells stored in liquid nitrogen were thawed and labeled with the fluorescent dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine Perchlorate (DiI). Thirty thousand cells in 1 μL were injected epiretinally in rat. At survival times of 3, 14, 28, or 56 days, retinal sections were examined quantitatively by epifluorescence to reveal DiI-labeled cells. hNT cells survived in the vitreous at all time points without evidence of vascularization. At 3 days, essentially no hNT cells were found in deep retina, and only very few were attached to retina. At days 14, 28, and 56, hNT cells were found to cluster on the vitreal/retinal interface, and in deeper layers. The clusters of hNT cells took on the shape of a funnel at 14 days, and inverted funnel at 28 days, and by 56 days, populated the photoreceptor layer as a stratum. It is possible that hNT cells took on the morphology and function of photoreceptors. These results suggest that hNT cells injected epiretinally survive in the vitreous at least 56 days, migrate to the retinal/vitreous interface, and may migrate through the retina. This system permits the independent and quantitative evaluation of survival and migratory trophic responses. © 1998 Elsevier Science Inc.

Medullary serotonin defects and respiratory dysfunction in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that occurs during sleep and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. It is the leading cause of postneonatal mortality in the developed world. The cause of SIDS is unknown, but is postulated to involve impairment of brainstem-mediated homeostatic control. Extensive evidence from animal studies indicates that serotonin (5-HT) neurons in the medulla oblongata play a role in the regulation of multiple aspects of respiratory and autonomic function. A subset of SIDS infants have several abnormalities in medullary markers of 5-HT function and genetic polymorphisms impacting the 5-HT system, informing the hypothesis that SIDS results from a defect in 5-HT brainstem-mediated control of respiratory (and autonomic) regulation. Here we review the evidence from postmortem human studies and animal studies to support this hypothesis and discuss how the pathogenesis of SIDS is likely to originate in utero during fetal development.

Regulated expression of ?2B adrenoceptor during development

There are three subtypes of alpha2 adrenoceptor, i.e., alpha2A, alpha2B, and alpha2C, mediating the specific effect of epinephrine and norepinephrine in various tissues by means of G protein-coupled signal transduction pathways. In an attempt to delineate the regulatory mechanism of the alpha2B receptor subtype (encoded by subtype gene Adra2b) expression in the central nervous system (CNS), we have established transgenic (Tg) mice lines in which the transgene (NN-lacZ) was composed of the promoter region of Adra2b (NcoI fragment, 4.7 kb immediately upstream from receptor coding region) and a reporter gene lacZ (encoding beta-galactosidase). The selective expression of alpha2B in brain as indexed by beta-galactosidase, under the direction of this promoter region, may be traced in situ by using X-gal staining. The expression pattern of Adra2b-NN-lacZ in CNS of Tg mice during development was examined. The temporal course of examination was from gestation day 9.5 (E9.5) to postnatal day 28 (P28). Significant X-gal staining was detected in the dorsal root ganglion and cranial nerves V and VII at E12.5. By E18.5, expression was noted in the cerebral cortex, anterior olfactory nucleus, hypothalamus, brainstem, and cerebellar Purkinje cells, among others, and persisted through postnatal development. Adra2b-NN-directed reporter expression was detected in the hippocampal dentate gyrus first at P4. The temporal course of expression up to P28 in this area is in accordance with the developmental profiles of granule neurons of dentate gyrus. From P7 on, transgene expression was detected in additional brain areas, including the septum and thalamus. The expression correlates well with the noradrenergic innervations as evidenced by colocalization by using tyrosine hydroxylase or dopamine-beta-hydroxylase immunocytochemistry.

Maturation of glutamatergic neurotransmission in dentate gyrus granule cells

We studied the development of glutamatergic neurotransmission in dentate gyrus granule cells (GCs) in hippocampal slices from 5 to 12-day-old rats. The active postnatal neuronogenesis in dentate permits GCs with staggered birthdates to be studied in situ in a single preparation. We recorded evoked responses to medial perforant path stimulation using visually-guided whole-cell patch clamping to select immature GCs, and biocytin filling to correlate electrophysiologic responses with maturational stage. Even within this immature cell population we found four distinct electrophysiologic patterns. Type 1 cells had no glutamatergic current; Type 2 cells had only N-methyl-D-aspartate receptor (NMDA) current; Type 3 cells had both NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) current although the NMDA component could be isolated at low stimulus intensity (NMDA threshold<AMPA threshold); Type 4 cells had both AMPA and NMDA currents with NMDA threshold>/=AMPA threshold. Type 1 cells were least mature, and Type 4 cells most mature as assessed by cell properties, dendritic arborization, and penetration of dendrites into the molecular layer. Thus NMDA-mediated currents predominate early in GC development as is consistent with their role in processes that determine dentate architecture - neuronal migration, dendritic outgrowth and regression, and synapse stabilization. By analogy with 'silent synapses' (i.e. synapses that contain only NMDA receptors), Type 2 cells are candidate 'silent cells' that may undergo activity-dependent acquisition of functional fast-conducting AMPA receptors with maturation.

Chronic fluoxetine administration to juvenile rats prevents age-associated dendritic spine proliferation in hippocampus

The density of dendritic spines, the postsynaptic sites of most excitatory synapses, increases during the first 2 postnatal months in rat hippocampus. Significant alterations in hippocampal levels of serotonin and norepinephrine impact synaptic development during this time period. In the present study, dendritic spine density was studied in the hippocampus (CA1) and dentate gyrus of juvenile rats acutely and chronically exposed to antidepressant drugs that act on serotonin and norepinephrine. One group of 21-day-old rats was given a single injection of a serotonin specific re-uptake inhibitor (fluoxetine or fluvoxamine), a norepinephrine-specific re-uptake inhibitor (desipramine), or saline and killed after 24 h. A second group of rats was injected daily, beginning on postnatal day (PN) 21, for 3 weeks. This group was further subdivided into rats that were killed 1 day or 21 days after the last injection. Golgi analysis showed that a single injection of fluvoxamine produced a significant increase in dendritic spine density in stratum radiatum of CA1 and in the dentate gyrus. Further, acute treatment with all three antidepressants increased the total length of secondary dendrites in CA1, with fluoxetine and desipramine increasing the number of secondary dendrites as well. In fluoxetine-treated animals killed on days 42 or 62 (1 or 21 days post-treatment, respectively), dendritic spine density remained at levels present in CA1 at 21 days. These results show that acute antidepressant treatment can impact dendritic length and spine density, and raise the possibility that chronic fluoxetine treatment arrests spine development into young adulthood.