Synaptosomal protein kinase C subspecies: A. Dynamic changes in the hippocampus and cerebellar cortex concomitant with synaptogenesis

The Effect of Isosaponarin Derived from Wasabi Leaves on Glutamate Release in Rat Synaptosomes and Its Underlying Mechanism

Excessive glutamate release is known to be involved in the pathogenesis of neurological diseases, and suppression of glutamate release from nerve terminals is considered to be a treatment strategy. In this study, we investigated whether isosaponarin, a flavone glycoside isolated from wasabi leaves, could affect glutamate release in rat cerebral cortex nerve terminals (synaptosomes). The release of glutamate was evoked by the K⁺ channel blocker 4-aminopyridine (4-AP) and measured by an online enzyme-coupled fluorimetric assay. Isosaponarin produced a concentration-dependent inhibition of 4-AP-evoked glutamate release with a half-maximum inhibition of release value of 22 μM. The inhibition caused by isosaponarin was prevented by eliminating extracellular Ca²⁺ or by using bafilomycin A1, an inhibitor of synaptic vesicle exocytosis. Isosaponarin decreased intrasynaptosomal rises in Ca²⁺ levels that were induced by 4-AP, without affecting the synaptosomal membrane potential. The isosaponarin-induced inhibition of glutamate release was significantly prevented in synaptosomes that were pretreated with a combination of the calcium channel blockers ω-conotoxin GVIA (N-type) and ω-agatoxin IVA (P/Q-types). The protein kinase C (PKC) pan-inhibitor GF109203X and the Ca²⁺-dependent PKC inhibitor Go6976 abolished the inhibition of glutamate release by isosaponarin, while the Ca²⁺-independent PKC inhibitor rottlerin did not show any effect. The results from immunoblotting assays also showed that isosaponarin lowered PKC, PKCα, synaptosomal-associated protein of 25 kDa (SNAP-25), and myristoylated alanine-rich C-kinase substrate (MARCKS) phosphorylation induced by 4-AP. In addition, FM1-43-labeled synaptic vesicles in synaptosomes showed that treatment with isosaponarin resulted in an attenuation of the 4-AP-induced decrease in fluorescence intensity that is consistent with glutamate release. Transmission electron microscopy of synaptosomes also provided evidence that isosaponarin altered the number of synaptic vesicles. These results indicate that isosaponarin suppresses the Ca²⁺-dependent PKC/SNAP-25 and MARCKS pathways in synaptosomes, causing a decrease in the number of available synaptic vesicles, which inhibits vesicular glutamate release from synaptosomes.

Neuroprotective Role of the B Vitamins in the Modulation of the Central Glutamatergic Neurotransmission

BACKGROUND

Regulation of glutamate release is crucial for maintaining normal brain function, but excess glutamate release is implicated in many neuropathological conditions. Therefore, the minimum glutamate release from presynaptic nerve terminals is an important neuroprotective mechanism.

OBJECTIVE

In this mini-review, we analyze the three B vitamins, namely vitamin B2 (riboflavin), vitamin B6 (pyridoxine), and vitamin B12 (cyanocobalamin), that affect the 4-aminopyridine (4- AP)-evoked glutamate release from presynaptic nerve terminal in rat and discuss their neuroprotective role.

METHODS

In this study, the measurements include glutamate release, DiSC3(5), and Fura-2.

RESULTS

The riboflavin, pyridoxine, and cyanocobalamin produced significant inhibitory effects on 4-aminopyridine-evoked glutamate release from rat cerebrocortical nerve terminals (synaptosomes) in a dose-dependent relationship. These presynaptic inhibitory actions of glutamate release are attributed to inhibition of physiologic Ca2+-dependent vesicular exocytosis but not Ca2+-independent nonvesicular release. These effects also did not affect membrane excitability, while diminished cytosolic (Ca2+)c through a reduction of direct Ca2+ influx via Cav2.2 (N-type) and Cav2.1 (P/Q-type) Ca2+ channels, rather than through indirect Ca2+induced Ca2+ release from ryanodine-sensitive intracellular stores. Furthermore, their effects were attenuated by GF109203X and Ro318220, two protein kinase C (PKC) inhibitors, suggesting suppression of PKC activity. Taken together, these results suggest that riboflavin, pyridoxine, and cyanocobalamin inhibit presynaptic vesicular glutamate release from rat cerebrocortical synaptosomes, through the depression Ca2+ influx via voltage- dependent Cav2.2 (N-type) and Cav2.1 (P/Q-type) Ca2+ channels, and PKC signaling cascade.

CONCLUSION

Therefore, these B vitamins may reduce the strength of glutamatergic synaptic transmission and is of considerable importance as potential targets for therapeutic agents in glutamate- induced excitation-related diseases.

Potential Enzymatic Targets in Alzheimer's: A Comprehensive Review

Alzheimer's, a degenerative cause of the brain cells, is called as a progressive neurodegenerative disease and appears to have a heterogeneous etiology with main emphasis on amyloid-cascade and hyperphosphorylated tau-cascade hypotheses, that are directly linked with macromolecules called enzymes such as β- & γ-secretases, colinesterases, transglutaminases, and glycogen synthase kinase (GSK-3), cyclin-dependent kinase (cdk-5), microtubule affinity-regulating kinase (MARK). The catalytic activity of the above enzymes is the result of cognitive deficits, memory impairment and synaptic dysfunction and loss, and ultimately neuronal death. However, some other enzymes also lead to these dysfunctional events when reduced to their normal activities and levels in the brain, such as α- secretase, protein kinase C, phosphatases etc; metabolized to neurotransmitters, enzymes like monoamine oxidase (MAO), catechol-O-methyltransferase (COMT) etc. or these abnormalities can occur when enzymes act by other mechanisms such as phosphodiesterase reduces brain nucleotides (cGMP and cAMP) levels, phospholipase A2: PLA2 is associated with reactive oxygen species (ROS) production etc. On therapeutic fronts, several significant clinical trials are underway by targeting different enzymes for development of new therapeutics to treat Alzheimer's, such as inhibitors for β-secretase, GSK-3, MAO, phosphodiesterase, PLA2, cholinesterases etc, modulators of α- & γ-secretase activities and activators for protein kinase C, sirtuins etc. The last decades have perceived an increasing focus on findings and search for new putative and novel enzymatic targets for Alzheimer's. Here, we review the functions, pathological roles, and worth of almost all the Alzheimer's associated enzymes that address to therapeutic strategies and preventive approaches for treatment of Alzheimer's.

Bryostatin Effects on Cognitive Function and PKCɛ in Alzheimer's Disease Phase IIa and Expanded Access Trials

Bryostatin 1, a potent activator of protein kinase C epsilon (PKCɛ), has been shown to reverse synaptic loss and facilitate synaptic maturation in animal models of Alzheimer’s disease (AD), Fragile X, stroke, and other neurological disorders. In a single-dose (25 μg/m²) randomized double-blind Phase IIa clinical trial, bryostatin levels reached a maximum at 1-2 h after the start of infusion. In close parallel with peak blood levels of bryostatin, an increase of PBMC PKCɛ was measured (p = 0.0185) within 1 h from the onset of infusion. Of 9 patients with a clinical diagnosis of AD, of which 6 received drug and 3 received vehicle within a double-blind protocol, bryostatin increased the Mini-Mental State Examination (MMSE) score by +1.83±0.70 unit at 3 h versus –1.00±1.53 unit for placebo. Bryostatin was well tolerated in these AD patients and no drug-related adverse events were reported. The 25 μg/m² administered dose was based on prior clinical experience with three Expanded Access advanced AD patients treated with bryostatin, in which return of major functions such as swallowing, vocalization, and word recognition were noted. In one Expanded Access patient trial, elevated PKCɛ levels closely tracked cognitive benefits in the first 24 weeks as measured by MMSE and ADCS-ADL psychometrics. Pre-clinical mouse studies showed effective activation of PKCɛ and increased levels of BDNF and PSD-95. Together, these Phase IIa, Expanded Access, and pre-clinical results provide initial encouragement for bryostatin 1 as a potential treatment for AD.

Ontogeny of biochemical, morphological and functional parameters of synaptogenesis in primary cultures of rat hippocampal and cortical neurons

Background

Synaptogenesis is a critical neurodevelopmental process whereby pre- and postsynaptic neurons form apposed sites of contact specialized for chemical neurotransmission. Many neurodevelopmental disorders are thought to reflect altered patterns of synaptic connectivity, including imbalances between excitatory and inhibitory synapses. Developing rapid throughput approaches for assessing synaptogenesis will facilitate toxicologic and drug screening studies of neurodevelopmental disorders. The current study describes the use of high-content imaging to quantify the ontogeny of excitatory and inhibitory synapses using in vitro models of neurodevelopment. These data are compared to biochemical and functional measures of synaptogenesis.

Results

The ontogenetic patterns of synapse formation were compared between primary rodent hippocampal and cortical neurons over 28 days in vitro (DIV). As determined by ELISA, the increase in synaptophysin expression levels as cultures matured was similar between hippocampal and cortical cultures. High-content imaging of immunoreactivity of excitatory and inhibitory synaptic biomarkers demonstrated an overall greater number of synapses in hippocampal relative to cortical neurons with marked differences in the pattern of inhibitory synapse development between these two neuronal cell types. Functional assays revealed that both the mean firing rates and mean bursting rates were significantly increased in cortical cultures relative to hippocampal cultures. This difference may reflect decreased inhibitory synaptic tone in cortical versus hippocampal cultures.

Conclusions

These data demonstrate differences and similarities in the ontogeny of synaptogenesis between hippocampal and cortical neurons, depending on the biological level examined. Assessment of synaptophysin protein levels by ELISA showed a general increase in synapse formation in both cell types with increasing time in culture, while high-content imaging was able to delineate cell type-dependent differences in formation of excitatory versus inhibitory synapses. The functional significance of differences in the balance of excitatory to inhibitory synapses was confirmed by the assessment of network activity using microelectrode arrays. These results suggest that high-content imaging and microelectrode arrays provide complementary approaches for quantitative assessment of synaptogenesis, which should provide a robust readout of toxicologic and pharmacologic effects on this critical neurodevelopmental event.

Synaptic localization of growth-associated protein 43 in cultured hippocampal neurons during synaptogenesis

Growth-associated protein 43 (GAP-43), a novel axonal phosphoprotein, is originally identified as a growth-cone-specific protein of developing neurons in vitro. The expression of GAP-43 is also shown to be up-regulated concomitant with increased synaptic plasticity in the brains in vivo, but how GAP-43 is concerned with synaptic plasticity is not well understood. In the present study, therefore, we aimed to elucidate subcellular localization of GAP-43 as culture development of rat hippocampal neurons. Western blotting showed that the expression of GAP-43 in the cerebral and hippocampal tissues was prominently high at postnatal days 14 and 21 or the active period of synaptogenesis. Double-labelling immunohistochemistry with an axonal marker Tau revealed that the immunoreactivity of GAP-43 was seen throughout axons of cultured hippocampal neurons but stronger at axonal puncta of developing neurons than axonal processes. Double-labelling immunohistochemistry with presynaptic terminal markers of synapsin and synaptotagmin revealed that the immunoreactivity of GAP-43 was observed mostly at weak synapsin- and synaptotagmin-positive puncta rather than strong ones. The quantitative analysis of immunofluorescent intensity showed a clear inverse correlation between GAP-43 and either synapsin or synaptotagmin expression. These data indicate that GAP-43 is highly expressed at immature growing axonal terminals and its expression is decreased along with the maturation of synaptogenesis.

σ-1 Receptor agonist SKF10047 inhibits glutamate release in rat cerebral cortex nerve endings

σ-1 Receptors are expressed in the brain, and their activation has been shown to prevent neuronal death associated with glutamate toxicity. This study investigates the possible mechanism and effect of [2S-(2α,6α,11R*]-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazocin-8-ol (SKF10047), a σ-1 receptor agonist, on endogenous glutamate release in the nerve terminals of rat cerebral cortex. Results show that SKF10047 inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP), and the σ-1 receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047) blocked this phenomenon. The effects of SKF10047 on the evoked glutamate release were prevented by the chelating extracellular Ca²⁺ions and the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor DL-threo-β-benzyl-oxyaspartate did not have any effect on the action of SKF10047. SKF10047 decreased the depolarization-induced increase in the cytosolic free Ca²⁺ concentration ([Ca²⁺](C)), but did not alter 4-AP-mediated depolarization. Furthermore, the effects of SKF10047 on evoked glutamate release were prevented by blocking the Ca(v)2.2 (N-type) and Ca(v)2.1 (P/Q-type) channels, but not by blocking the ryanodine receptors or the mitochondrial Na⁺/Ca²⁺ exchange. In addition, conventional protein kinase C (PKC) inhibitors abolished the SKF10047 effect on 4-AP-evoked glutamate release. Western blot analyses showed that SKF10047 decreased the 4-AP-induced phosphorylation of PKC and PKCα. These results show that σ-1 receptor activation inhibits glutamate release from rat cortical nerve terminals. This effect is linked to a decrease in [Ca²⁺](C) caused by Ca²⁺ entry through presynaptic voltage-dependent Ca²⁺ channels and the suppression of the PKC signaling cascade.

Pyridoxine inhibits depolarization-evoked glutamate release in nerve terminals from rat cerebral cortex: a possible neuroprotective mechanism?

Pyridoxine (vitamin B(6)) protects neurons against neurotoxicity. An excessive release of glutamate is widely considered to be one of the molecular mechanisms of neuronal damage in several neurological diseases. We investigated whether pyridoxine affected glutamate release in rat cerebral cortex nerve terminals (synaptosomes). Pyridoxine inhibited the release of glutamate that was evoked by exposing synaptosomes to the K(+) channel blocker 4-aminopyridine (4-AP), and this phenomenon was concentration-dependent. Inhibition of glutamate release by pyridoxine was prevented by the vesicular transporter inhibitor bafilomycin A1, or by chelating intraterminal Ca(2+), but was insensitive to DL-threo-beta-benzyl-oxyaspartate, a glutamate transporter inhibitor. Pyridoxine did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization. Examination of the effect of pyridoxine on cytosolic [Ca(2+)] revealed that diminution of glutamate release could be attributed to a reduction in voltage-dependent Ca(2+) influx. Consistent with this, the pyridoxine-mediated inhibition of glutamate release was completely prevented by blocking the N- and P/Q-type Ca(2+) channels, but not by blocking intracellular Ca(2+) release or Na(+)/Ca(2+) exchange. Furthermore, the pyridoxine effect on 4-AP-evoked glutamate release was abolished by the protein kinase C (PKC) inhibitors bisindolylmaleimide I (GF109203X) or bisindolylmaleimide IX (Ro318220), and pyridoxine significantly decreased the 4-AP-induced phosphorylation of PKC, PKCalpha, and myristoylated alanine-rich C kinase substrate. Together, these results suggest that pyridoxine inhibits glutamate release from rat cortical synaptosomes, through the suppression of presynaptic voltage-dependent Ca(2+) entry and PKC activity.

The signal-induced phospholipid degradation cascade and protein kinase C activation

Acting in synergy with diacylglycerol, unsaturated free fatty acids such as arachidonic, oleic, linoleic, linolenic and docosahexaenoic acids dramatically activate some members of the protein kinase C family at the basal level of Ca2+ concentration. It is plausible that phospholipase C and phospholipase A2, and possibly phospholipase D as well, are involved in the activation of protein kinase C. Presumably, this enzyme activation is integrated into the signal-induced membrane phospholipid degradation cascade, prolonging the activation of protein kinase C. The sustained activity of this enzyme appears to be of importance for long-term cellular responses such as development of neuronal plasticity and gene activation.

BDNF occludes GABABreceptor-mediated inhibition of GABA release in rat hippocampal CA1 pyramidal neurons

During the development of the rat hippocampus, both gamma-aminobutyric acid (GABA)(B) autoreceptors and brain-derived neurotrophic factor (BDNF) play important roles in the formation of GABAergic synapses as well as in the GABA(A) receptor-mediated transmissions. While a number of studies have reported rapid effects of BDNF on GABA(A) receptor-mediated responses, the interactions between GABA(B) autoreceptors and BDNF are less clear. Using conventional whole-cell patch-clamp recordings, we demonstrated here that BDNF significantly occludes baclofen-induced suppression of GABA(A) receptor-mediated transmissions in each of the preparations including hippocampal slices prepared from P14 rats, hippocampal CA1 pyramidal neurons isolated from P14 and P21 rats, and cultured hippocampal pyramidal neurons. This effect of BDNF was rapid and reversible, and was mediated via the activation of presynaptic TrkB receptor tyrosine kinases, and subsequent activation of phospholipase C and protein kinase C. On the contrary, in hippocampal CA1 pyramidal neurons isolated from P7 rats, BDNF failed to occlude the GABA(B) receptor-mediated inhibition of GABA release. Thus, the ability of BDNF to occlude the GABA(B) receptor-mediated inhibition of GABA release develops between P7 and P14. This demonstrates a novel aspect of the effects of BDNF on inhibitory transmissions in rat hippocampus, which may have some functional roles in the induction of developmental plasticity and/or pathophysiology of epilepsy.

Development- and activity-dependent regulation of SNAP-25 phosphorylation in rat brain

Synaptosomal-associated protein of 25kDa (SNAP-25), a member of the SNARE proteins essential for neurotransmitter release, is phosphorylated at Ser(187) in PC12 cells and in the rat brain in a protein kinase C-dependent manner. It remains unclear how the phosphorylation of SNAP-25 is regulated during development and by neuronal activity. We studied the mode of SNAP-25 phosphorylation at Ser(187) in the rat brain using an anti-phosphorylated SNAP-25 antibody. Both the expression and phosphorylation of SNAP-25 increased remarkably during the early postnatal period, but their onsets were quite different. SNAP-25 expression was detected as early as embryonic Day 18, whereas the phosphorylation of SNAP-25 could not be detected until postnatal Day 4. A delay in the onset of phosphorylation was also observed in cultured rat hippocampal neurons. The phosphorylation of SNAP-25 was regulated in a neuronal activity-dependent manner and, in the rat hippocampus, decreased by introducing seizures with kainic acid. These results clearly indicated that the phosphorylation of SNAP-25 at Ser(187) is regulated in development- and neuronal activity-dependent manners, and is likely to play important roles in higher brain functions.

Identification of adrenoceptor subtype-mediated changes in the density of synapses in the rat visual cortex

Both serotonin and noradrenaline affect synapse formation and maintenance in the CNS. Although we previously demonstrated that serotonin regulates synaptic density via activation of serotonin(2A) receptor, it was still unclear which receptor subtype mediates the function of noradrenaline. In the present study we tried to identify the noradrenaline receptor (adrenoceptor) subtype, which could regulate the density of synapses in the rat visual cortex. Selective antagonists and/or agonists of adrenoceptor subtypes were administered to six weeks old rats. Changes in the density of axodendritic synapses were quantitatively examined in lamina I, where noradrenaline rather than serotonin is known to regulate the density of synapses. The alpha1 adrenoceptor antagonists (prazosin and 2-{[b-(4-hydroxyphenyl)ethyl]aminomethyl}-1-tetralone) decreased the number of synapses in a dose-dependent manner. In contrast, administrations of the alpha1-agonist (methoxamine) increased the density of synapses. The beta1 adrenoceptor antagonist (atenolol) had no effect on the density of synapses. The alpha2-antagonist (rauwolscine) increased synaptic density, whereas the beta2-antagonist (ICI-118,551) decreased synaptic density. Simultaneous treatments with the alpha1-antagonist and alpha1-agonist caused the alpha1-agonist to competitively block the effect of the alpha1-antagonist and recover the density of synapses to the control values. In addition, the alpha1-antagonist/agonist appeared to show a reverse effect on the changes in synaptic density following alpha2- or beta2-antagonist treatment by acting via the alpha1 receptor. Moreover, decreased synaptic density when a selective noradrenergic neurotoxin (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine) was counterbalanced by the alpha1-agonist. These data suggest that noradrenaline regulates the density of synapses in the rat visual cortex primarily via the alpha1 receptor subtype. Both serotonin(2A) and alpha1 receptors are known to couple with phospholipase C, which has been shown to increase intracellular calcium. It may help us to understand the underlying mechanisms for synaptic plasticity in the CNS.

Lamina-selective changes in the density of synapses following perturbation of monoamines and acetylcholine in the rat medial prefrontal cortex

The rat medial prefrontal cortex is known to have diverse brain functions such as learning and memory, attention, and behavioral flexibility. Although these functions are affected by monoamines (dopamine (DA), noradrenaline (NA) and serotonin (5-HT)) and acetylcholine (ACh), the detailed mechanisms remain unclear. These neuromodulators also have effects on synapse formation and maintenance, and regulate plasticity in the central nervous system (CNS). To clarify the effects of these neuromodulators on changes in the density of synapses in the rat medial prefrontal cortex, we separately administered a D1- or D2-antagonist, NA neurotoxin, 5-HT synthetic inhibitor, or muscarinic ACh antagonist for 1 week, and counted the number of synapses on electron microscopic photographs taken from the prelimbic area of the medial prefrontal cortex. The density of synapses in lamina I was regulated by DA via D1-like receptors, and that in laminae II/III was decreased by depletion of NA or ACh. However, 5-HT did not have a regulatory effect on the synaptic density throughout the layers in this brain region. The data in this study and our previous studies indicate that there are appreciable regional differences in the magnitude of biogenic amine-mediated synaptic plasticity in the rat CNS. These neuromodulators may have a trophic-like effect on the selected neuronal circuit to maintain synaptic contacts in the rat CNS. The synaptic density in the medial prefrontal cortex regulated by monoamines and ACh could be important not only for synaptic plasticity in this region but also for pharmacotherapeutic drug treatment.

PKC-independent inhibition of glutamate exocytosis by arachidonic acid in rat cerebrocortical synaptosomes

In rat cerebrocortical synaptosomes, the addition of 4 beta-phorbol dibutyrate (4 beta-PDBu) and arachidonic acid enhances and decreases, respectively, the glutamate release evoked by 4-aminopyridine. Pretreatment of synaptosomes with 12-O-tetradecanoylphorbol 13-acetate (TPA) or pre-incubation with staurosporine, prevent the stimulatory effect of 4 beta-PDBu, but are without effect on the inhibitory action of arachidonic acid. Moreover, methyl arachidonate, which is not effective as a PKC activator, also strongly inhibits glutamate exocytosis. These results suggest that PKC is not involved in the inhibition of glutamate release by arachidonic acid.

Learning behaviour and cerebral protein kinase C, antioxidant status, lipid composition in senescence-accelerated mouse: influence of a phosphatidylcholine-vitamin B12 diet

Our objective was to determine whether dietary supplementation with phosphatidylcholine (PC) plus vitamin B12 could afford beneficial effects on biochemical and biophysical events in the brain of senescence-accelerated mouse (SAM) substrain SAMP8. We measured learning behaviour, hippocampal protein kinase C (PKC) activity, cerebral antioxidant status, phospholipid composition and fatty acid composition in 6-month-old SAMP8 and in age-matched controls (SAM substrain SAMR1). In comparison with SAMR1, SAMP8 showed a significant elevation in total grading score of senescence and a significant decline in acquisition SAMP8 had a lower hippocampal PKC activity and cerebral PKC-beta mRNA abundance than SAMR1. SAMP8 had increased cerebral lipid peroxide levels and proportion of sphingomyelin, and a lower proportion of 20 : 4n-6 and 22 : 6n-3 in cerebral phosphtidylethanolamine than SAMR1. SAMP8 fed the PC combined with vitamin B12 diet had an increased PKC activity and a higher proportion of 22 : 6n-3 than SAMP8 fed the control diet. These results indicate the potential benefit of PC combined with vitamin B12 as a dietary supplement.

Protein phosphatase 2B inhibitors mimic the action of arachidonic acid and prolong the facilitation of glutamate release by group I mGlu receptors

We have addressed the role of arachidonic acid in the facilitation of glutamate release by group I metabotropic glutamate (mGlu) receptors. The activation of these receptors with the specific agonist 3,5-dihydroxyphenylglycine (DHPG) failed to enhance the cumulative Ca(2+)-dependent release of glutamate evoked by a 5 min depolarization with 4-aminopyridine, in the absence but not in the presence of arachidonic acid. However, DHPG, in the absence of arachidonic acid, transiently enhanced diacylglycerol levels, transiently potentiated 4AP-evoked depolarization, and significantly enhanced the fast but not the slow component of glutamate release observed after prolonged stimulations of nerve terminals. Further evidence that DHPG was able to initiate release facilitation in the absence of arachidonic acid was obtained in experiments where the protein phosphatase 2B (cyclosporine A and cypermethrine) but not protein phosphatase 1 or 2A inhibitors (okadaic acid and calyculin A) facilited glutamate release to a maximal extent comparable to that induced by arachidonic acid. We conclude that an active protein phosphatase 2B (calcineurin) dephosphorylates the presynaptic target/s responsible for facilitation of glutamate release.

Gender influences the effect of perinatal copper deficiency on cerebellar PKC gamma content

Change in cerebellar protein kinase C gamma (PKCgamma) content caused by perinatal copper (Cu) deficiency was determined in 22-day old rats. The offspring of dams with low Cu intake during gestation and lactation exhibited signs characteristic of Cu deficiency including anemia, greater than 90% reduction in liver Cu concentration, and undetectable serum ceruloplasmin. In addition, brain Cu concentrations were reduced 80%. No differences in the signs of Cu deficiency were observed between female and male offspring. However, cerebellar PKCgamma content was reduced 54% (P < 0.05, Tukey's test) in female offspring but only 18% (P > 0.05) in male offspring. Following 6 weeks of Cu supplementation, brain Cu concentrations remained depressed in female and male rats that experienced perinatal Cu deficiency, but cerebellar PKCgamma content was completely restored to control levels. Postnatal expression of PKCgamma in the cerebellum coincides with and regulates cerebellar maturation. The results of the present study indicate perinatal Cu deficiency may impair cerebellar maturation to a greater extent in females than in males. However, it is not clear whether suppression of PKCgamma by perinatal Cu deficiency produces permanent neuropathology in the cerebellum because the effects were reversed by Cu supplementation.

Proline-rich synapse-associated protein-1/cortactin binding protein 1 (ProSAP1/CortBP1) is a PDZ-domain protein highly enriched in the postsynaptic density

The postsynaptic density (PSD) is crucially involved in the structural and functional organization of the postsynaptic neurotransmitter reception apparatus. Using antisera against rat brain synaptic junctional protein preparations, we isolated cDNAs coding for proline-rich synapse-associated protein-1 (ProSAP1), a PDZ-domain protein. This protein was found to be identical to the recently described cortactin-binding protein-1 (CortBP1). Homology screening identified a related protein, ProSAP2. Specific antisera raised against a C-terminal fusion construct and a central part of ProSAP1 detect a cluster of immunoreactive bands of 180 kDa in the particulate fraction of rat brain homogenates that copurify with the PSD fraction. Transcripts and immunoreactivity are widely distributed in the brain and are upregulated during the period of synapse formation in the brain. In addition, two short N-terminal insertions are detected; they are differentially regulated during brain development. Confocal microscopy of hippocampal neurons showed that ProSAP1 is predominantly localized in synapses, and immunoelectron microscopy in situ revealed a strong association with PSDs of hippocampal excitatory synapses. The accumulation of ProSAP1 at synaptic structures was analyzed in the developing cerebral cortex. During early postnatal development, strong immunoreactivity is detectable in neurites and somata, whereas from postnatal day 10 (P10) onward a punctate staining is observed. At the ultrastructural level, the immunoreactivity accumulates at developing PSDs starting from P8. Both interaction with the actin-binding protein cortactin and early appearance at postsynaptic sites suggest that ProSAP1/CortBP1 may be involved in the assembly of the PSD during neuronal differentiation.

Protein kinase C modulates ventilatory patterning in the developing rat

Protein kinase C (PKC) mediates important components of signal transduction pathways underlying neuronal excitability and modulates respiratory timing mechanisms in adult rats. To determine ventilatory effects of systemic PKC inhibition during development, whole-body plethysmographic recordings were conducted in 2-3-d (n = 11), 5-6-d (n = 19), 10-12-d (n = 14), and 20-21-d-old (n = 14) rat pups after treatment with vehicle and Ro 32-0432 (100 mg/kg, intraperitoneally). Ro 32-0432 decreased minute ventilation (V E) by 51.0 +/- 5.5% (mean +/- SEM) in youngest pups (p < 0.01) but only 19.1 +/- 6.8% in 20-21-d-old pups (p < 0.01). V E decreases were always due to frequency reductions with tidal volume (VT) remaining unaffected. Respiratory rate decreases primarily resulted from marked expiratory time (TE) prolongations being more pronounced in 2-3-d-old (115.5 +/- 28.9%) compared with 20-21-d old (36.6 +/- 10.9%; p < 0.002 analysis of variance [ANOVA] ). Expression of the PKC isoforms alpha, beta, gamma, delta, iota, and mu was further examined in brainstem and cortex by immunoblotting and revealed different patterns with postnatal age and location. We conclude that endogenous PKC inhibition elicits age-dependent ventilatory reductions which primarily affect timing mechanisms rather than changes in volume drive. This effect on ventilation abates with increasing postnatal age suggesting that the neural substrate mediating overall respiratory output may be more critically dependent on PKC activity in the immature animal.

Protein kinase C: a physiological mediator of enhanced transmitter output

Protein kinase C (PKC), activated by either diacylglycerol and/or arachidonic acid, through the activation of presynaptic receptors or nerve or nerve depolarization is involved is involved in the enhancement of transmitter release from many neural types. This facilities is most likely mediated by the phosphorylation of proteins involved in vesicle dynamics although a role for ion channels cannot be ruled out. PKC is not fundamental to the release process but rather has a modulatory role of PKC is to help maintain transmitter output during prolonged or elevated levels of activation and this seems to parallel suggestions that PKC is involved in the movement of reserve pools of vesicles into release-study sites. presynaptic facilitatory actions mediated by PKC are also involved in integrated modulatory functions such as long term potentiation, again where it elevates or maintains transmitter output. Although studies have tried to identify specific roles for various PKC isoforms, the actions of phorbol esters in elevators transmitter release do not fit with known potencies on individual isoforms and lit suggests that PKC may be located at an intraneuronal location which is difficult to access for lipophilic phorbol esters and further work is required in this area.

Selective up-regulation of protein kinase C epsilon in granule cells after kainic acid-induced seizures in rat

Kainate-induced seizure activity causes persistent changes in the hippocampus that include synaptic reorganization and functional changes in the mossy fibers. Using in situ hybridization histochemistry, the expression of PKC alpha, PKC beta, PKC gamma, PKC delta and PKC epsilon mRNAs was investigated in the hippocampus of adult rats following seizures induced by a s.c. injection of kainic acid. In CA1 and CA3, we found a significant decrease in PKC gamma mRNA 1 day after kainic acid which persisted for a 2nd day in CA1. None of the other PKC isoform mRNAs were altered in CA1 or CA3. In granule cells, a significant up-regulation specific to PKC epsilon mRNA was observed. One week after kainic acid administration, a marked increase in PKC epsilon immunoreactivity was found that persisted 2 months after kainic acid administration. PKC epsilon immunoreactivity was found associated with mossy fibers projecting to the hilus of the dentate gyrus and to the stratum lucidum of the CA3 field and presumably with the newly sprouted mossy fibers projecting to the supragranular layer. These data provide the first evidence for a long-lasting increase of the PKC epsilon in the axons of granule cells caused by kainate-induced seizures and suggest that PKC epsilon may be involved in the functional and/or structural modifications of granule cells that occur after limbic seizures.

Protein kinase C in synaptic plasticity: changes in the in situ phosphorylation state of identified pre- and postsynaptic substrates

1. Long-term potentiation and its counterpart long-term depression are two forms of activity dependent synaptic plasticity, in which protein kinases and protein phosphatases are essential. 2. B-50/GAP-43 and RC3/neurogranin are two defined neuronal PKC substrates with different synaptic localization. B-50/GAP-43 is a presynaptic protein and RC3/neurogranin is only found at the postsynaptic site. Measuring their phosphorylation state in hippocampal slices, allows us to simultaneously monitor changes in pre- and postsynaptic PKC mediated phosphorylation. 3. Induction of LTP in the CA1 field of the hippocampus is accompanied with an increase in the in situ phosphorylation of both B-50/GAP-43 and RC3/neurogranin, during narrow, partially overlapping, time windows. 4. Pharmacological data show that mGluR stimulation results in an increase in the in situ phosphorylation of B-50/GAP-43 and RC3/neurogranin.

Spinocerebellar mossy fiber terminal topography in the NR2C/PKC gamma double mutant cerebellum

The spatiotemporal expression patterns of the NR2C subunit of the NMDA receptor and PKC gamma isoform during cerebellar development suggests that both proteins are involved in the molecular mechanisms of synaptogenesis. However, the topographic distribution of WGA-HRP labeled spinocerebellar mossy fiber terminals in NR2C/PKC gamma double mutants (n = 4) appears similar to controls (n = 3). While the results do not rule out a role for NR2C receptor subunits and the PKC gamma isoform in cerebellar synaptogenesis, they indicate that neither is necessary for the formation or maintenance of normal spinocerebellar mossy fiber afferent maps.

Neurogranin in the development of the rat telencephalon

We have used a novel antibody to map the distribution of the protein kinase C substrate protein RC3/neurogranin during the development of the rat telencephalon. Neurogranin appearance in the rat brain is biphasic: it shows an early stage of anatomically restricted, low-intensity expression, and a juvenile stage of anatomically widespread, high-intensity expression. Most of the structures that express neurogranin during development conserve it in the adult stage. Neurogranin expression starts on embryonic day 18 in two different sites-the amygdalar primordium and in the piriform cortex-and is confined to these structures until the first postnatal day (P1). On P1, neurogranin expression increases dramatically in intensity, and appears in the olfactory cortex, isocortex, subiculum and hippocampus. In the striatum, expression starts on P1 and extends to the caudoputamen and parts of the globus pallidus and septum. Particularly complex patterns of labelling can be seen in the amygdala and cerebral cortex. Cortical layers showing early expression are the presumptive layers 4 and 5 in the somatosensory cortex, and layers 2 and 5 in the anterior cingulate and agranular insular cortices. Immunoreactivity is found mostly in cell bodies during the early and juvenile stages, but by the end of the first postnatal week it starts being more apparent in the neuropil. This phenomenon probably reflects the intracellular translocation of neurogranin to distal parts of the dendrites and dendritic spines. This process culminates by the end of the second postnatal week, when the adult pattern is reached. According to the timing and anatomy of its distribution, expression of neurogranin seems to be independently regulated in each telencephalic region by specific signalling mechanisms. It is proposed, on this basis, that neurogranin could be implicated in neuronal differentiation and synaptogenesis during telencephalic development.

Increased protein kinase C isoform gamma in the hippocampus of pentylenetetrazol-induced chemoshocked mouse

Protein kinase C (PKC) activity, Western blot analysis of PKC alpha, -beta and -gamma, endogenous substrate protein phosphorylation and Western blot analysis of neuromodulin were studied in the cortex, striatum, hippocampus and cerebellum of mouse brain after pentylenetetrazol-induced chemoshock. The PKC isozymes and endogenous substrates in the crude cytosolic and membrane fractions of these four brain regions were partially purified by DE-52 columns eluted with buffer containing 100 or 200 mM KCl. Almost the same PKC activity in the cortex, striatum, hippocampus and cerebellum was found. This kinase activity was increased in the membrane fractions of hippocampus from chemoshocked mice, while that in other brain regions was not changed. On further analysis by immunoblotting, this increased activity was found to be due to the increase of PKC gamma isozyme. The in vitro phosphorylation of neuromodulin was also found to be increased in the hippocampus of chemoshocked mice, while the level of neuromodulin was not changed after chemoshock. Therefore, an increase of PKC gamma alone, but not neuromodulin, in the hippocampus contributed to the increased phosphorylation of this substrate in chemoshocked mice.

Presynaptic receptors and the control of glutamate exocytosis

When a typical glutamate-containing neurone fires, an action potential is propagated down the branching axon through more than a thousand varicosities. At each of these release sites the probability that a synaptic vesicle will be exocytosed into the synaptic cleft is individually controlled by means of presynaptic receptors: autoreceptors responding by positive or negative feedback to previously released transmitter, or heteroreceptors under the influence of other neurotransmitters or modulators. The simplest system in which to investigate presynaptic modulation is the isolated nerve terminal or synaptosome; studies with this preparation have revealed a complex interplay of signal-transduction pathways.

Expression of alpha-, beta-, and gamma-subspecies of protein kinase C in the motor neurons in the embryonic and postnatal rat spinal cord

Using polyclonal antibodies against alpha-, beta- and gamma-subspecies of protein kinase C, developmental changes in expression of these subspecies in the motor neurons in the rat cervical spinal cord were immunohistochemically investigated. On embryonic day-12, the motor neurons began to differentiate from undifferentiated neuroepithelial cells. On embryonic day-13, they began to express weak immunoreactivity for alpha- and beta-protein kinase C and slightly more evident immunoreactivity for gamma-protein kinase C. Immunoreactivity for protein kinase C in these neurons gradually became stronger, as the development progressed. Between embryonic day-18 and postnatal day-7, the motor neurons showed distinct immunoreactivity in the nucleus, perikaryal cytoplasm, axon and dendrites. At these stages, distribution and intensity of immunoreactivity for alpha-, beta- and gamma-protein kinase C were very similar. Thereafter, the expression of this enzyme in the nucleus gradually declined, while in the other structures, expression of each subspecies changed independently. On postnatal day-28 and 35, expression of beta-protein kinase C in the axons was stronger than that of alpha- and gamma-protein kinase C, and immunoreactivity for gamma-protein kinase C in the perikaryal cytoplasm and dendrites was slightly weaker than that for alpha- and beta-protein kinase C. Expression of this enzyme in the motor neurons at these stages was almost the same as in the adult animal. Electron microscopically, immunoreactivity for protein kinase C was randomly distributed in the nucleus, and in the perikaryal cytoplasm, often near the cisterns of the endoplasmic reticulum. Expression of protein kinase C in the growing axons was quite different from that in the mature axons. In the dendrites, immunoreactivity for protein kinase C was distributed randomly in the cytoplasm and at the postsynaptic densities. These findings suggest that protein kinase C might regulate not only the neural functions, but also several aspects of the differentiation process in the motor neurons.

The use of null mutant mice to study complex learning and memory processes

A number of neural substrates have been proposed to mediate complex learning and memory processes in mammalian organisms. One strategy for testing the involvement of a particular gene in learning and memory is to create a mouse line with a null mutation in that gene. Recently, embryonic stem cell-based gene-targeted homologous recombination techniques have been employed to create a number of such mutant mouse lines that do not express interesting candidate genes. These animals have been examined for impairments in several complex learning paradigms which are known to depend on the integrity of the hippocampus. In this review several complex learning and memory paradigms are described, the techniques to create null mutants are reviewed, and the results of recent studies with null mutants are described. Finally, the limitations for interpretation of behavioral data using null mutants are discussed.

Tissue-specific developmental regulation of protein kinase C isoforms

The limited amount of available information regarding the developmental control of protein kinase C (PKC) isoform expression restricts our understanding of the role of these enzymes in normal physiology. Accordingly, this study investigated PKC isoform expression in selected tissues from fetal, neonatal, and adult rats. PKC beta immunoreactivity was prominent in brain tissue, whereas the expression of PKC alpha, PKC delta, PKC epsilon, and PKC zeta was found to be widespread. Although no developmental change in any PKC isoform was evident in liver, striking tissue-specific age-dependent differences in PKC isoform abundance were noted in other tissues. For example, age-dependent increases in PKC alpha, PKC beta, and PKC delta in brain contrasted with age-dependent decreases in PKC alpha and PKC delta in lung, kidney, and heart. Immunoreactivity for PKC epsilon was abundant in all fetal/neonatal tissues; PKC epsilon was detected in the adult brain, heart, and liver, but not the adult kidney and lung. Finally, PKC zeta was more abundant in fetal/neonatal than in adult brain, lung, kidney, and heart. These results indicate that the fetal/neonatal lung, kidney, and heart are enriched in PKC zeta, PKC alpha, PKC delta, and PKC epsilon, relative to the adult tissues. These age-dependent variations in the abundance of individual isoforms of PKC may critically influence tissue responsiveness to external stimuli. Moreover, the finding that PKC zeta is particularly abundant in fetal tissues as well as the liver, the only tissue included in this study which retains regenerative capacity in the adult animal, is consistent with the notion that PKC zeta may play a role in cell proliferation.

Excitatory amino acid-, except 1S,3R-ACPD, induced transient high stimulation of phosphoinositide metabolism during hippocampal neuron development

Rat hippocampal neurons in culture extended their neurites until day 5 in vitro (DIV). Then, the mean neuritic length slightly decreased. Excitatory amino acid (EAA)-elicited inositol phosphate (IP) formation increased from 0.5 to 2 DIV, reached a plateau between 2 and 4-5 DIV, and then gradually decreased until 10 DIV. This decrease was likely not due to neuronal death. This developmental pattern was observed for N-methyl-D-aspartate, kainate, glutamate, ibotenate and quisqualate (QA). Interestingly, the 1S,3R-aminocyclopentane dicarboxylate (1S,3R-ACPD) response slightly increased during neuronal culture development. At 3 DIV, the ionotropic antagonists 6,7-dinitro-quinoxalin-2,3-dion and D-2-amino-5-phosphonopentanoate efficiently blocked N-methyl-D-aspartate and kainate-elicited IP formation, and partially inhibited glutamate and ibotenate responses. QA and 1S,3R-ACPD responses were not affected, suggesting a metabotropic action for these two compounds. Furthermore, QA and 1S,3R-ACPD potencies significantly increased between 3 and 10 DIV. The transient high activity periods induced by EAA, except for 1S,3R-ACPD, are not observed for norepinephrine, carbachol and potassium chloride responses. Taken together, these data suggest that: (i) QA and 1S,3R-ACPD can act on two different glutamate metabotropic receptors subtypes during development; and (ii) the EAA-induced transient peaks of IP stimulation, which are specific with respect to other neuroactive substances profiles, could be involved in the development of hippocampal neurons. Indeed, these transient high activities take place when the neuritic length regularly increases in vitro.

Synergistic activation by cis-fatty acid and diacylglycerol of protein kinase C and protein phosphorylation in hippocampal slices

cis-Unsaturated fatty acid, which activates protein kinase C in vitro, stimulates protein phosphorylation in intact hippocampal slices. Two protein bands (44,000 and 47,000 mol. wt) are particularly sensitive to cis-fatty acid and are phosphorylated in a dose- and time-dependent manner. The cis-fatty acid-stimulated protein phosphorylation can be further potentiated with diacylglycerol or 12-O-tetradecanoylphorbol 13-acetate. Several lines of evidence indicate that the cis-fatty acid-stimulated phosphorylation of these proteins is mediated by protein kinase C. First, the cis-fatty acid effect is mimicked by other protein kinase C activators such as diacylglycerol. Second, the stimulation of the phosphorylation by these activators can be blocked by staurosporine, which potently inhibits protein kinase C. Third, a concomitant application of cis-fatty acid and diacylglycerol or 12-O-tetradecanoylphorbol 13-acetate enhances the 44,000 and 47,000 mol. wt phosphorylation in a synergistic manner, which is a novel activation mode for protein kinase C. Fourth, they can be phosphorylated by purified protein kinase C (type III: alpha). Moreover, the synergistic activation of purified protein kinase C by cis-fatty acid and diacylglycerol leads to a drastic increase in the phosphorylation of these two protein bands. Two-dimensional gel electrophoresis and immunoblot analysis revealed that they are both acidic proteins. The 47,000 mol. wt band consists of two protein components; one is found to be F1/growth-associated protein-43 (pI = 4.5), and the other 47,000 mol, wt protein has broad pI ranging from 4.6 to 4.9. The 44,000 mol. wt component is a major phosphoprotein with pI of 4.8-5.1. Our results strongly indicate that cis-fatty acid can act as a regulator of endogenous protein kinase C in concert with diacylglycerol, and stimulate protein phosphorylation of its substrates such as F1/growth-associated protein-43 in the hippocampus.

Developmental changes in the expression of alpha-, beta- and gamma-subspecies of protein kinase C at synapses in the ventral horn of the embryonic and postnatal rat spinal cord

Developmental changes in expression of alpha-, beta- and gamma-subspecies of protein kinase C (PKC) at synapses in the ventral horn of the rat spinal cord were immunocytochemically investigated. On embryonic day 15, a few synapses were found in the ventral horn, and they gradually increased in number until postnatal day 21 or 28. During the embryonic period, immunoreactivity (IR) for all three subspecies was demonstrated in both the pre- and postsynaptic regions. In the former, IR was detected mainly along the outer surface of the synaptic vesicles, and in the latter, along the postsynaptic membranes. At these stages, synapses were morphologically immature, having a faint postsynaptic density and a few round synaptic vesicles. After birth, IR for PKCs at the postsynaptic densities became stronger, but gradually disappeared in most of the presynaptic regions. In adult, IR for PKCs was detected only at the postsynaptic densities. At the later postnatal stages, the synapses were fully mature, having a thick postsynaptic density, a great number of synaptic vesicles and a distinct synaptic cleft as those in adult animals. In addition, the developmental changes in expression of these subspecies of PKC in the presynaptic regions were quite different. These findings suggest that the increase in expression of PKC at postsynaptic densities might be closely related with the development of synaptic functions, and also that each subspecies of PKC may take part in different aspects of synaptogenesis.

Protein kinase C activity, translocation, and conventional isoforms in aging rat brain

Protein kinase C was studied in various brain areas in aging Wistar rats. Histone-directed kinase activity from the cortex, hippocampus and cerebellum did not change with aging. Using purified protein B-50 as a substrate, between 3 and 8 months a decrease in in vitro phosphorylation was detected in the membrane fraction of the cortex but after this age values remained stable. In hippocampal membranes, B-50 phosphorylation was increased in aged rats. PKC translocation was impaired in aged rats in both the cortex and the hippocampus. PKC alpha and beta mRNA decreased in the cortex between 3 and 8 months with no further decline in aged animals. Hippocampal mRNA for calcium-dependent PKC isoforms was not modified during aging, as assessed by Northern and in situ hybridization. Western blot analysis revealed a change in PKC gamma protein only, which was increased in hippocampal membranes from aged rats. The data indicate that the key PKC function that is impaired in aged rats is enzyme translocation irrespective of the brain area investigated.

Cyanide induces protein kinase C translocation: blockade by NMDA antagonists

Activation and translocation of protein kinase C (PKC) during KCN-induced histotoxic hypoxia was studied in rat brain slices prepared from cerebellum, hippocampus, and cortex. Treatment with 1-10 mM KCN produced a significant increase in PKC translocation and enzyme activity in the particulate fraction of cerebellar and hippocampal slices. In cortical slices, PKC activity was not affected by cyanide treatment. The membrane-associated PKC activity reached a maximum 30 minutes after incubation with KCN and remained elevated up to 60 minutes in both the hippocampus and cerebellum. Pretreatment with MK-801 and APV, specific NMDA receptor antagonists, blocked the cyanide-stimulated translocation in the hippocampus and cerebellum, whereas CNQX, an AMPA/kainate receptor antagonist, did not alter the response. These results demonstrate that cyanide stimulates PKC activation and translocation from the cytosol to membranes in select brain areas and NMDA receptor activation mediates this process.

Alterations of protein kinase C isozyme and substrate proteins in mouse brain after electroconvulsive seizures

Protein kinase C (PKC) activity, Western blot analysis of PKC alpha, beta, gamma, epsilon and zeta with isozyme-specific antibodies, endogenous substrate protein phosphorylation, and Western blot analysis of neuromodulin, were studied in mouse brain after repeated electroconvulsive shock. The PKC isozymes and endogenous substrates in the crude cytosolic and membrane fractions were partially purified on DE-52 columns eluted with buffer containing 100 or 200 mM KCl. The kinase activity assayed by phosphorylation of exogenous histone was increased in the 200 mM KCl eluates of both the cytosol and membrane fractions from electroshocked mice. Further analysis by immunoblotting demonstrated that this increased activity was due to an increase in the PKC gamma isozyme. The level of the novel type isozymes, epsilon and zeta, was not altered in electroshocked mice. An in vitro phosphorylation study showed that the endogenous substrate, 17 kDa neurogranin, was mostly eluted by 100 mM KCl. In contrast, the 43 kDa neuromodulin only appeared in the 200 mM KCl eluate, according to autoradiography, SDS-PAGE and Western blot analysis; its level was found to be increased in the membrane fraction of electroshocked mice, as demonstrated by in vitro phosphorylation studies. Therefore, an increase in both PKC gamma and neuromodulin contributed to the increased phosphorylation of neuromodulin during electroshock seizure.

Pentylenetetrazole-induced chemoshock affects protein kinase C and substrate proteins in mouse brain

Protein kinase C (PKC) activity, western blot analysis of PKC alpha, beta, gamma, epsilon, and zeta by isozyme-specific antibodies, and in vitro phosphorylation of endogenous substrate proteins were studied in the mice brain after pentylenetetrazole-induced chemoshock. The PKC isozymes and endogenous substrates in the crude cytosolic and membrane fractions were partially purified by DE-52 columns eluted with buffer A containing 100 or 200 mM KCl. This method consistently separates cytosolic and membrane proteins and various PKC isoforms. The 100 mM KCl eluates from DE-52 columns contain more PKC alpha and beta in both cytosol and membrane than the 200 mM KCl eluates, whereas PKC gamma, epsilon, and zeta appear in equal amounts in these two eluates. The kinase activity assayed by phosphorylation of exogenous histone was increased in the chemoshocked mice in both the cytosol and membrane of 200 mM KCl eluates. In further analysis by immunoblotting, this increased activity was found to be due to the increase in content of PKC gamma isozyme. As for novel-type epsilon and zeta isozymes, they were not altered in the chemoshocked mice. From autoradiography, the endogenous substrate 17-kDa neurogranin, which was shown below 21 kDa, was mostly eluted by 100 mM KCl from the DE-52 column, whereas 43-kDa neuromodulin, which was also demonstrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, only appeared in the 200 mM KCl eluates. The in vitro phosphorylation of neuromodulin was found to be increased in the chemoshocked mice. Therefore, the increased phosphorylation of neuromodulin and increased content of the PKC gamma isoform were involved in the pentylenetetrazole-induced chemoshock.

Protein kinase C delta- and epsilon-subspecies in rat central nervous tissue; differential distribution and phorbol ester-induced redistribution in synaptosomes

Distribution of the delta- and epsilon-subspecies of protein kinase C (PKC) in rat central nervous tissues was semiquantitated by an immunoblot analysis. The epsilon-subspecies, which is expressed predominantly in the brain, was abundant in hippocampus and cerebral cortex among rat brain areas, whereas the delta-subspecies, which is expressed ubiquitously in many tissues, showed no significant difference among tissue areas tested. Unlike other subspecies, the delta-subspecies was primarily associated with particulate fractions. Subcellular fractionation analysis revealed that both the epsilon- and delta-subspecies were enriched in the synaptosomal P2 fraction. Treatment with 12-O-tetradecanoyl-phorbol 13-acetate (TPA) induced translocation of the epsilon-subspecies from cytosolic fraction to membrane fraction. In contrast, upon treatment with TPA, the delta-subspecies normally bound to membrane fraction was released into cytosol.

Lithium decreases membrane-associated protein kinase C in hippocampus: selectivity for the alpha isozyme

We investigated the effects of lithium on alterations in the amount and distribution of protein kinase C (PKC) in discrete areas of rat brain by using [3H]phorbol 12,13-dibutyrate quantitative autoradiography as well as western blotting. Chronic administration of lithium resulted in a significant decrease in membrane-associated PKC in several hippocampal structures, most notably the subiculum and the CA1 region. In contrast, only modest changes in [3H]phorbol 12,13-dibutyrate binding were observed in the various other cortical and subcortical structures examined. Immunoblotting using monoclonal anti-PKC antibodies revealed an isozyme-specific 30% decrease in hippocampal membrane-associated PKC alpha, in the absence of any changes in the labeling of either the beta (I/II) or gamma isozymes. These changes were observed only after chronic (4 week) treatment with lithium, and not after acute (5 days) treatment, suggesting potential clinical relevance. Given the critical role of PKC in regulating neuronal signal transduction, lithium's effects on PKC in the limbic system represent an attractive molecular mechanism for its efficacy in treating both poles of manic-depressive illness. In addition, the decreased hippocampal membrane-associated PKC observed in the present study offers a possible explanation for lithium-induced memory impairment.

Immunocytochemical localization of alpha-, beta I-, beta II- and gamma-subspecies of protein kinase C in the motor and premotor cortices of the rhesus monkey

We obtained evidence for the localization of alpha-, beta I-, beta II- and gamma-subspecies of protein kinase C (PKC) in the monkey motor and premotor cortices (Brodmann's areas 4 and 6). In Brodmann's area 4, the immunoreactivity for the alpha-PKC was present in horizontal and round cells in the layers I and II, and small pyramidal cells in layer III and also in the glial cells in subcortical white matter. The alpha-PKC immunopositive glial cells contained GFAP-immunoreactive product. The beta I-PKC immunoreactivity was present in the round cells in layer I and in the pyramidal cells in the layer V, including Betz cells. The beta II-PKC immunoreactivity was observed as small dots in perikarya of the small and medium-sized pyramidal cells in layers II, III, V and VI, but not in layer I. The gamma-PKC immunoreactive cell bodies were observed in layers II, III and VI, and most of the immunoreactive cells were pyramidal. Intense gamma-PKC immunoreactivity was found in the neuropils of layers I and II. Similar distributions of four PKC subspecies were seen in Brodmann's area 6, except that beta I-PKC immunoreactive Betz cells were not present. The unique localization of PKC subspecies suggested that each PKC subspecies was involved in the specific function in motor and premotor cortices of the rhesus monkey.