Introduction 5HT role as a differentiation signal in the development of

Brain Research 883 2000 1–14 www.elsevier.com locate bres Research report Neuroglial interactions in a model of para-chlorophenylalanine- induced serotonin depletion ´ ´ Alberto Javier Ramos, Patricia Tagliaferro, Ester Marıa Lopez, Jorge Pecci Saavedra, Alicia Brusco ´ Instituto de Biologıa Celular y Neurociencia ‘‘Prof. Eduardo De Robertis’’, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155 1121, Buenos Aires, Argentina Accepted 15 August 2000 Abstract Serotonin 5HT is involved in the development and plasticity of the CNS through the release of S-100b, a glial trophic factor which stabilizes synapses and neuronal cytoskeleton and promotes neuronal development. S-100b is released from glial cells after activation of glial 5HT receptors. We present in this paper the effects upon neurons and glia of a 5HT depletion induced by 14 days of treatment with 1A para-chlorophenylalanine PCPA in adult rats. S-100b, 5HT, 5HT-transporter 5HT-T and neurofilaments Nf-200 and Nf-68 expressions were studied by immunohistochemistry and image analysis in striatum, hippocampus, parietal and frontal cortex. Immediately after ending PCPA treatment we found increased intracellular S-100b immunoreactivity in glial cells, reduced 5HT immunolabelling, reduced density of 5HT-T, Nf-200 and Nf-68 fibers and morphological alterations in neuronal cytoskeleton. One week after PCPA treatment S-100b immunoreactivity decreased towards control levels, 5HT was normalized in dorsal raphe nucleus, but not in innervation areas; 5HT-T, Nf-200 and Nf-68 fiber densities increased but some neuronal cytoskeletal alterations were still present in striatum. Two weeks after PCPA treatment S-100b had returned to control levels in most studied regions; 5HT immunoreactivity was normalized, meanwhile 5HT-T, Nf-200 and Nf-68 fiber densities increased reaching values over the control level. We propose that S-100b could be accumulated in glial cells during the 5HT depletion period, to be released once 5HT levels have recovered. Neuronal cytoskeletal alterations and reduced fiber density may be the expression of decreased extracellular availability of S-100b. Conversely, increased 5HT-T, Nf-200 and Nf-68 expressions, once S-100b is normalized, may be the biological response to the growth factor release.  2000 Elsevier Science B.V. All rights reserved. Theme : Development and regeneration Topic : Neurotrophic factors: biological effects Keywords : Serotonin; Parachlorophenylalanine; Neurotrophic factor; S-100b; Neurofilament; Serotonin transporter

1. Introduction 5HT role as a differentiation signal in the development of

the central nervous system CNS. This hypothesis is Serotoninergic neurons located in the brainstem project supported by several facts: i 5HT is the classical to cortical and subcortical brain regions through a network neurotransmitter expressed in the early brain development, of fibers with dense branching. Terminal fibers containing prior to finishing synaptogenesis and before reaching the serotonin 5HT present a broad distribution at synaptic as complete stabilization of neurotransmission systems and it well as non-synaptic sites, raising the hypothesis of seems to promote neuronal growth [26,28]; ii neuronal another role for this amine, besides neurotransmission. differentiation in specific regions correlates with the arrival The early expression of 5HT in the brain development of 5HT axons [27]; iii a depletion of 5HT in pregnant was the starting evidence [26,27] for the hypothesis of the rats [26] or during the synaptogenesis [34] leads to decreased brain development. In the adult brain, 5HT plays a role in neuronal and glial Corresponding author. Correspondence address: Rivera Indarte 132 plasticity. It has been reported that a 5HT depletion 1ro ‘‘A’’, 1406, Buenos Aires, Argentina. Fax: 154-11-4941-5618. E-mail address : hbruscofmed.uba.ar A. Brusco. produces significant glial reaction [11,47], increases nitric 0006-8993 00 – see front matter  2000 Elsevier Science B.V. All rights reserved. P I I : S 0 0 0 6 - 8 9 9 3 0 0 0 2 8 6 2 - 6 2 A oxide synthase NOS activity [48] and reduces MAP-2 neurite growth see [20,23] for review and 200-kDa and synaptophysin immunoreactivities [5]. In addition, neurofilaments Nf-200 which are characteristic of mature 5HT is involved in the regulation of hippocampal and axons see [40] for review. Specific morphology of 5HT subventricular neurogenesis in the adult brain [6]. 5HT’s fibers has been studied by 5HT transporter 5HT-T role in the development and plasticity of CNS seems to be immunostaining. Recovery of 5HT has been followed by mediated by the stimulation of glial 5HT receptors that 5HT immunoreactivity 5HT-IR in the dorsal raphe 1A cause S-100b protein release [51]. S-100b is a growth nucleus DRN and innervation areas. factor that derives from glial cells. S-100b has important effects on axonal growth of 5HT neurons [2,3,33], partici- pates in neurite extension in 5HT innervated areas [24,39],

2. Materials and methods