Development of inositol 1,4,5-trisphosphate 3-kinase immunoreactivity in cerebellar Purkinje cells in vivo and in vitro

Inositol trisphosphate 3-kinases: focus on immune and neuronal signaling

The localized control of second messenger levels sculpts dynamic and persistent changes in cell physiology and structure. Inositol trisphosphate [Ins(1,4,5)P(3)] 3-kinases (ITPKs) phosphorylate the intracellular second messenger Ins(1,4,5)P(3). These enzymes terminate the signal to release Ca(2+) from the endoplasmic reticulum and produce the messenger inositol tetrakisphosphate [Ins(1,3,4,5)P(4)]. Independent of their enzymatic activity, ITPKs regulate the microstructure of the actin cytoskeleton. The immune phenotypes of ITPK knockout mice raise new questions about how ITPKs control inositol phosphate lifetimes within spatial and temporal domains during lymphocyte maturation. The intense concentration of ITPK on actin inside the dendritic spines of pyramidal neurons suggests a role in signal integration and structural plasticity in the dendrite, and mice lacking neuronal ITPK exhibit memory deficits. Thus, the molecular and anatomical features of ITPKs allow them to regulate the spatiotemporal properties of intracellular signals, leading to the formation of persistent molecular memories.

Cerebellar long-term depression: characterization, signal transduction, and functional roles

Cerebellar Purkinje cells exhibit a unique type of synaptic plasticity, namely, long-term depression (LTD). When two inputs to a Purkinje cell, one from a climbing fiber and the other from a set of granule cell axons, are repeatedly associated, the input efficacy of the granule cell axons in exciting the Purkinje cell is persistently depressed. Section I of this review briefly describes the history of research around LTD, and section II specifies physiological characteristics of LTD. Sections III and IV then review the massive data accumulated during the past two decades, which have revealed complex networks of signal transduction underlying LTD. Section III deals with a variety of first messengers, receptors, ion channels, transporters, G proteins, and phospholipases. Section IV covers second messengers, protein kinases, phosphatases and other elements, eventually leading to inactivation of DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolone-propionate-selective glutamate receptors that mediate granule cell-to-Purkinje cell transmission. Section V defines roles of LTD in the light of the microcomplex concept of the cerebellum as functionally eliminating those synaptic connections associated with errors during repeated exercises, while preserving other connections leading to the successful execution of movements. Section VI examines the validity of this microcomplex concept based on the data collected from recent numerous studies of various forms of motor learning in ocular reflexes, eye-blink conditioning, posture, locomotion, and hand/arm movements. Section VII emphasizes the importance of integrating studies on LTD and learning and raises future possibilities of extending cerebellar research to reveal memory mechanisms of implicit learning in general.

Ontogeny of gene expression of inositol 1,4,5-trisphosphate receptor in the rat brain: high mRNA levels in the cerebellar Purkinje cells

The release of intracellular Ca, which is involved in many neuronal functions, is regulated by the second messenger inositol 1,4,5-trisphosphate (InsP3) interacting with specific receptor. The distribution of the mRNA coding for the recently cloned InsP3 receptor was studied in the developing rat brain using oligonucleotides derived from the rat cDNA sequence and in situ hybridization. The localizations of the mRNA in the postnatal brain were exactly superimposable to that previously reported in the adult [Mailleux et al., Neuroscience, 49 (1992)577-590]. Higher mRNA levels were consistently found in the adult neurons over their postnatal counterpart. Hybridization signal was first visible in the cerebellar Purkinje cells which express dramatically higher mRNA levels of the receptor than any other neurons in the brain. In conclusion, the levels of InsP3 receptor mRNA per neuron increased with synaptogenesis. This finding suggests the occurrence during this critical developmental period of a more complex regulation of Ca fluxes, perhaps requiring higher intraneuronal levels of InsP3 receptor.

Distribution of the neurons containing inositol 1,4,5-trisphosphate 3-kinase and its messenger RNA in the developing rat brain

As a result of its interaction with a specific receptor, inositol 1,4,5-trisphosphate (InsP3) mobilizes intracellular calcium. The metabolism of InsP3 is rather complex: InsP3 3-kinase produces Inositol 1,3,4,5-tetrakisphosphate (InsP4), a putative second messenger also involved in the intraneuronal calcium homeostasis. The distribution of the messenger RNA coding for the recently cloned InsP3 3-kinase was studied in the developing rat brain by using oligonucleotides derived from the rat cDNA sequence and in situ hybridization combined with Northern blot analysis. In addition, the locations of the enzyme were determined by immunohistochemistry in combination with Western blot analysis. By Northern blot and Western blot analyses on rat brain, the kinase was not detected in the embryo, was first found slightly at birth, and reached adult levels around 2-3 postnatal weeks. These findings were confirmed in the different positive regions by in situ hybridization conducted at the macroscopic level. At the cellular level, the mRNA was found exclusively in the neuronal populations previously demonstrated in the adult. The levels of transcripts per neuron were however higher in the adult than in the neonate brain. The enzyme mRNA could be detected first at postnatal day 0, (birth, P0) in the perikarya of the cerebellar Purkinje cells, followed at P4 by the hippocampal CA1 pyramidal cells and granule cells of the dentate gyrus and finally, at P9, by a majority of the neurons in the cortical layers II-III and V, especially in the frontal cortex and cingulate cortex; claustrum; caudate, putamen, accumbens, olfactory tubercle and calleja islets; anterior olfactory nucleus; taenia tecta; piriform piriform cortex; dorsolateral septum; bed nucleus stria terminalis; amygdala; hippocampal CA2-4 sectors and subiculum. By immunohistochemistry, the enzyme was initially found in the periphery of the cell bodies of the neonatal neurons; was progressively enriched in the developing dendritic arborization during the first postnatal weeks where it remained exclusively localized in the adult. In conclusion, in the developing brain, InsP3 3-kinase was first detected at birth, and thereafter its concentrations increased to reach adult levels around 2-3 postnatal weeks. At the cellular level, the kinase was exclusively found in the neurons. The small amounts of transcripts found per neuron in the neonate increase during synaptogenesis and the protein became progressively enriched in the developing dendritic arborization, where it is localized in the adult.

Developmental profile of inositol 1,4,5-trisphosphate 3-kinase in rat cerebellar cortex: light and electron microscopic immunohistochemical studies

Developmental expression and intracellular distribution of inositol 1,4,5-trisphosphate 3-kinase in the rat cerebellar cortex were studied immunohistochemically. Immunoreactivity appeared first at postnatal day 1 in the rostral region of the cerebellum and by day 15 had extended throughout the whole cerebellum, being localized in the Purkinje cell layer. Shortly after the expression of the enzyme in each Purkinje cell, the labelling showed a tendency to accumulate in the dendrites in a fine granular pattern. Electron microscopy revealed that immunoreactivity was present in the Purkinje dendritic trunks with accentuation in the distal segments during the early postnatal period, thereafter becoming concentrated in the dendritic spines at later developmental stages. Labelling was associated mainly with the plasmalemma, including the postsynaptic densities and open coated vesicles, and the subplasmalemmal vesicles of the smooth endoplasmic reticulum. Immunoreactivity was also evident in the perisomatic processes of immature Purkinje cells, which are transient projections synapsing with climbing fibers. In developing Purkinje axons, immunoreactivity was accentuated in the distal segments, associated with the plasmalemma and synaptic vesicles. These results suggest that inositol 1,4,5-trisphosphate 3-kinase is involved in the dendritic arborization and subsequent spine synaptogenesis of Purkinje cells, and that the developing presynaptic nerve endings of these cells are another functional site for the enzyme.