Components of neurite outgrowth that determine neuronal cytoarchitecture: Influence of calcium and the growth substrate

Abstract

The present study examined the cellular mechanisms underlying the generation of neuroarchitecture. Identified Helisoma neurons in isolated cell culture normally require factors present in brain-conditioned medium (CM) in order to display the different components of neurite outgrowth (sprouting, elongation, branching, and growth cone motility), which ultimately determine their overall architecture. We report here that cell calcium and cell-substrate interactions can play quite specific roles in the regulation of these different components of neuronal outgrowth. CM-induced neurite outgrowth was inhibited by calcium ionophore A23187. In the absence of CM the calcium channel blocker La3+ (10 microM) reduced intracellular calcium levels and induced neurite sprouting and elongation; growth cone motility and branching were greatly reduced in the La3+-induced neurites. Neurons plated into an environment containing La3+ and a fibronectin substrate exhibited all of the components of neuronal outgrowth normally seen in response to CM. Fibronectin alone had little outgrowth-promoting activity. Neurite elongation rates and branching were increased by exposure to La3+ in neurons on either a CM or fibronectin substrate. The neurons growing on CM or fibronectin whose outgrowth was accelerated by La3+ elaborated neuritic arbors that differed from those of neurons grown in response to CM; differences were seen in neurite length, area of outgrowth, branching frequency, and varicosity numbers. Taken together, these results indicate that 1) calcium and the growth substrate can exert specific effects on neurite sprouting, elongation, growth cone motility, and branching; 2) appropriate levels of activation of these two systems can elicit neurite outgrowth that closely resembles that induced by endogenous growth factors; 3) both the differential expression of the separate components of outgrowth and the kinetics of outgrowth determine a neuron's morphology.

Axonal regeneration of an identified Helisoma neuron depends on the site of axotomy

“…For example, buccal neuron 5 of Helisoma regenerates its single axon in situ even after detachment of its full length (Cohan et al, 1983(Cohan et al, , 1987Kruk and Bulloch, unpublished observation). Helisoma buccal neurons 5 and 19 extend neurites when cultured in vitro, under appropriate conditions (Wong et al, 1981), with all their original processes removed (Wong et al, 1984;Cohan et al, 1985;Haydon et al, 1985;Mattson et al, 1988;Cohan, 1990). Analogous results were obtained from other related pulmonate species (Geletyuk, 1977;Wong et al, 1983;Ridgway et al, 1991).…”

Hippocampal growth cone responses to focally applied electric fields

“…In slightly older cultures, for example, glutamate receptors coupled to Ca2+ entry were found on dendritic growth cones and not on axonal growth cones (Mattson et al, 1988a). Also, various reagents affecting intracellular calcium, protein kinase C, and CAMP all produced greater responses in dendritic growth cones than in axonal growth cones (Mattson, Guthrie, and Kater, 1988b). Thus, any of these messenger systems may be the cause for the observed dendritic orientation and lack of axonal orientation.…”

Effects of Prenatal Testosterone on Sexual Behavior, Reproductive Morphology and LH Secretion in the Female Rat

“…Specifically, prenatal glucocorticoids along with T (or its metabolites) have been implicated in regulating calbindin levels within the medial basal hypothalamic and preoptic area [Lephart et al, 1997]. Intracellular calcium levels appear to be in volved in neuronal development, maturation, and surviv al [Mattson, 1988[Mattson, , 1992, These potential factors repre sent a putative complex mechanism for neural develop ment. Therefore, several important mechanism(s) need to be studied such as the relationship(s) between perinatal T exposure, the regulation of enzymes which metabolize T (i.e.…”