Synapse formation in the mouse olfactory bulb Quantitative studies

Abstract

A quantitative study of synapse formation in the mouse olfactory bulb has been carried out using serial sections. Volumetric synaptic density as well as absolute number of synapses per olfactory bulb for eight distinct synaptic types have been determined at 15 different ages, from the beginning of synapse formation at embryonic day 14 (E14) to postnatal day 44 (P44). Synapses are first found in appreciable numbers at E15 when both axo-dendritic and a few dendro-dendritic synapses occur in the presumptive glomerular layer. Initial synapse formation correlates closely with the reorientation of mitral cells from a primitive tangenital to a definitive radial direction. Synapse formation by mitral cell dendrites occurs after mitral cell axons have grown into the future olfactory cortical areas, either simultaneous with or before synapse formation by these axons. Virtually all synaptic types detected in adults have been found on the day of birth, consistent with the idea that olfaction is an important sensory modality for newborn mice. Volumeric density of a given synaptic type generally increases 50--100 times during development while the absolute number increases about 1,000 times. Synapses in glomeruli develop more precociously than those in the time of origin and differentiation of the principal postsynaptic elements of these two divisions (mitral cells and internal granule cells). Correlation of the time of synapse formation of various synaptic types with their putative excitary or inhibitory role determined in adult studies suggests that excitatory synapses generally form somewhat earlier, although throughout nearly all of synaptic development, both excitatory and inhibitory synapses are present. Reciprocal dendro-dendritic synapses in the external plexiform layer appear to have a special mode of formation. It is suggested that a granule-to-mitral dendro-dendritic synapse only forms next to an already existing mitral-to-granule synapse on the same gemmule.

Maternal ingestion of ortho-aminoacetophenone during gestation affects intake by offspring

“…The gustator) sensory system of the altricial rodents develops late in gestation though it is not fully functional until after parturition (20). Olfactory synapses are also present in appreciable numbers after gestational day 15, however, they too are not fully functional until after birth (13). Other stimuli were not tested, therefore, it is difficult to assess whether a decrease in sensitivity would be specific to OAP or a general reduction to similar stimuli.…”

Changes in the dendritic geometry of mouse superior cervical ganglion cells following postganglionic axotomy

“…A similar scenario has been suggested for normal development (see Jacobson, 1978). For example, in several systems, including rat superior cervical ganglia, axonal extension to targets precedes the growth and differentiation of dendrites (Hamburger and Keefe, 1944;Barron, 1948;Hinds and Hinds, 1976;Wise et al, 1979;Rubin, 1985;see, however, Landmesser and Pilar, 1974;Hughes and LaVelle, 1975;Oppenheim et al, 1978). Further evidence that supports this general view is that exogenous administration of NGF to neonatal rats enhances the complexity and length of dendritic arborizations and the rate of dendritic growth in the superior cervical ganglion (Snider, 1986, and unpublished observations).…”

Drosophilafragile X mental retardation protein developmentally regulates activity-dependent axon pruning

“…Research on Drosophila brain development has focused on the first 48 hours during pupal metamorphosis (Awasaki and Ito, 2004;Awasaki et al, 2006;Brown et al, 2006;Lee et al, 1999;Marin et al, 2005;Watts et al, 2004;Williams and Truman, 2005;Zheng et al, 2003), but less is known about the latter half of brain development. However, presumed roles for activity and FMRP coincide with this time of use-dependent process refinement (Boothe et al, 1979;Desai et al, 2002;Fox and Wong, 2005;Hinds and Hinds, 1976;Huttenlocher, 1979;Lund et al, 1977;Pan et al, 2004;Stern et al, 2001;Turrigiano and Nelson, 2004). To assay the temporal requirements for dFMRP during brain development versus maturity, we analyzed developmental time points beginning 60 hours after puparium formation (APF) and extending into the mature adult (9 days post-eclosion).…”