Neuronal phosphoproteins. Mediators of signal transduction

Unlocking the Therapeutic Potential of Exosomes Derived From Nasal Olfactory Mucosal Mesenchymal Stem Cells: Restoring Synaptic Plasticity, Neurogenesis, and Neuroinflammation in Schizophrenia

BACKGROUND AND HYPOTHESIS

Schizophrenia (SCZ) is a multifaceted mental disorder marked by a spectrum of symptoms, including hallucinations, delusions, cognitive deficits, and negative symptoms. Its etiology involves intricate interactions between genetic and environmental factors, posing significant challenges for effective treatment. We hypothesized that intranasal administration of exosomes derived from nasal olfactory mucosal mesenchymal stem cells (OM-MSCs-exos) could alleviate SCZ-like behaviors in a murine model induced by methylazoxymethanol (MAM).

STUDY DESIGN

We conducted a comprehensive investigation to assess the impact of intranasally delivered OM-MSC-exos on SCZ-like behaviors in MAM-induced mice. This study encompassed behavioral assessments, neuroinflammatory markers, glial activation, synaptic protein expression, and neurogenesis within the hippocampus.

STUDY RESULTS

Our findings demonstrated that intranasal administration of OM-MSC-exos effectively ameliorated SCZ-like behaviors, specifically addressing social withdrawal and sensory gating deficits in the MAM-induced murine model. Furthermore, OM-MSC-exos intervention yielded a reduction in neuroinflammatory markers and a suppression of microglial activation within the hippocampus. Simultaneously, we observed an upregulation of key synaptic protein expression, including PSD95 and TH, the rate-limiting enzyme for dopamine biosynthesis.

CONCLUSIONS

Our study underscores the therapeutic potential of OM-MSC-exos in mitigating SCZ-like behavior. The OM-MSC-exos have the capacity to modulate glial cell activation, diminish neuroinflammation, and promote BDNF-associated synaptic plasticity and neurogenesis, thus ameliorating SCZ-like behaviors. In summary, intranasal administration of OM-MSC-exos offers a multifaceted approach to address SCZ mechanisms, promising innovative treatments for this intricate disorder.

Effect of Hyperbilirubinemia on Medial Olivocochlear System in Newborns

OBJECTIVES

To evaluate medial olivocochlear efferent system of babies with hyperbilirubinemia with normal auditory brain stem responses.

MATERIALS AND METHODS

This was a prospective study in a tertiary referral hospital. The study involved 40 hyperbilirubinemic and 44 healthy newborns. Cochlear and auditory activity of participants was evaluated by transient otoacoustic emissions (TOAEs) and brainstem auditory evoked response components (BAER). Medial olivocochlear (MOC) reflex was evoked with contralateral acoustic stimulation and recorded with TOAEs.

RESULTS

A comparison of the MOC reflex activity between two groups with Mann Whitney U test revealed that MOC reflex activity were significantly decreased in the hyberbilirubinemic group for both ears (p<.05). This difference was significant for all frequencies in both ears. There was no significant relation between total serum bilirubin level and MOC reflex activity.

CONCLUSION

Hyperbilirubinemic newborns had decreased MOC reflex activity. This may be indicative of future problems in speech discrimination and effective hearing in noisy background. Additional long cohort studies are needed to evaluate the clinical importance of MOC reflex measurements in this group. MOC reflex measurement has the potential to form part of the audiologic evaluation of newborns with hyperbilirubinemia in the future.

Auditory impairment in infants at risk for bilirubin-induced neurologic dysfunction

Classical and subtypes of kernicterus associated with bilirubin toxicity can be differentiated in part with physiological auditory measures that include auditory-evoked potentials and measures of cochlear integrity. The combination of these auditory measures suggests that bilirubin exposure results in auditory system damage initially at the level of the brainstem, progressing to the level of the VIII cranial nerve and then to greater neural centers. There is no evidence of neural damage at the level of the cochlea. Auditory neural damage from bilirubin toxicity ranges from neural timing deficits, including neural firing delays and dyssynchrony, to neural response reduction and even elimination of auditory neural responses. This condition is comprehensively described as auditory neuropathy spectrum disorder. Independent measures of cochlear function and auditory neural function up to the level of the brainstem can effectively diagnose auditory neural damage resulting from bilirubin neurotoxicity. Intervention, including cochlear implants can be effective.

Deletion of synapsins I and II genes alters the size of vesicular pools and rabphilin phosphorylation

Previous studies established that genetic deletion of synapsins, synaptic vesicle-associated phosphoproteins that regulate neurotransmitter release, decreases the number of synaptic vesicles in nerve terminals. To investigate whether these changes affect the release properties of the remaining synaptic vesicles, we used a radioactive labeling technique to measure release independently of the total number of synaptic vesicles. 3H-glutamate and 14C-gamma-amino-butyric-acid (GABA) release from isolated nerve terminals prepared from the neocortex of synapsins I and II double knock-out mice (DKO) was assayed and compared to wild-type preparations. Hyperosmotic shock-evoked 3H-glutamate was reduced by 20+/-3% from DKO nerve terminals and potassium depolarization-evoked glutamate release was also decreased by 28+/-2%. Surprisingly, sucrose or potassium depolarization-evoked release of 14C-GABA was increased by 32+/-4% and 29+/-5%, respectively. The basal efflux of both 3H-glutamate and 14C-GABA increased by 17+/-2% and 12+/-2% from DKO nerve terminals. As lack of synapsins I and II, major phosphoproteins of synaptic vesicles, may lead to deregulation of phosphorylation events, we compared phosphorylation state of another synaptic vesicle protein, rabphilin. In DKO nerve terminals, membrane-associated rabphilin level was reduced by approximately 0.28-fold, its phosphorylation at 234serine was increased by approximately 1.61-fold whereas cytosolic rabphilin levels showed both more dramatic reduction in abundance, approximately 16.5-fold, and increase in phosphorylation, approximately 4.8-fold. Collectively, these data suggest that deletion of major synapsin isoforms leads to (1) deregulation of basal neurotransmission causing "leaky" basal release, (2) changes in either the size or mobilization of releasable or reserve pools, and (3) a decrease in rabphilin abundance accompanied by an increase in basal phosphorylation of the remaining rabphilin.

Hyperbilirubinemia and kernicterus

This article describes new findings concerning the basic science of bilirubin neurotoxicity, new considerations of the definition of clinical kernicterus, and new and useful tools to diagnose kernicterus in older children, and discusses treatments for kernicterus beyond the newborn period and why proper diagnosis is important.

Role of efficient neurotransmitter release in barrel map development

Cortical maps are remarkably precise, with organized arrays of thalamocortical afferents (TCAs) that project into distinct neuronal modules. Here, we present evidence for the involvement of efficient neurotransmitter release in mouse cortical barrel map development using barrelless mice, a loss-of-function mutant of calcium/calmodulin-activated adenylyl cyclase I (AC1), and mice with a mutation in Rab3-interacting molecule 1alpha (RIM1alpha), an active zone protein that regulates neurotransmitter release. We demonstrate that release efficacy is substantially decreased in barrelless TCAs. We identify RIMs as important phosphorylation targets for AC1 in the presynaptic terminal. We further show that RIM1alpha mutant mice have reduced TCA neurotransmitter release efficacy and barrel map deficits, although not as severe as those found in barrelless mice. This supports the role of RIM proteins in mediating, in part, AC1 signaling in barrel map development. Finally, we present a model to show how inadequacies in presynaptic function can interfere with activity-dependent processes in neuronal circuit formation. These results demonstrate how efficient synaptic transmission mediated by AC1 function contributes to the development of cortical barrel maps.

Synaptic vesicle mobilization is regulated by distinct synapsin I phosphorylation pathways at different frequencies

During action potential firing, the rate of synapsin dissociation from synaptic vesicles and dispersion into axons controls the rate of vesicle availability for exocytosis at the plasma membrane. Here we show that synapsin Ia's dispersion rate tracks the synaptic vesicle pool turnover rate linearly over the range 5-20 Hz and that the molecular basis for this lies in regulation at both the calcium-calmodulin-dependent kinase (CaM kinase) and the mitogen-activated protein (MAP) kinase/calcineurin sites. Our results show that CaM kinase sites control vesicle mobilization at low stimulus frequency, while MAP kinase/calcineurin sites are critical at both lower and higher stimulus frequencies. Thus, multiple signaling pathways serve to allow synapsin's control of vesicle mobilization over different stimulus frequencies.

Decreased levels of ARPP-19 and PKA in brains of Down syndrome and Alzheimer's disease

ARPP-19 (cAMP-regulated phosphoprotein of Mr = 19,000) is a substrate for cAMP-dependent protein kinase (PKA). ARPP-19 is found in all brain regions but the function of ARPP-19 is not fully elucidated yet. We detected a downregulated sequence with 100% homology with ARPP-19 in temporal cortex of patients with Down syndrome (DS) as compared to controls, but not in Alzheimer's disease (AD) using differential displaypolymerase chain reaction (DD-PCR). We subsequently determined protein levels of ARPP-19 in temporal cortex and cerebellum by immunoblotting and observed significant reduction of ARPP-19 in DS (temporal cortex) and AD (cerebellum). We also observed decreased activities of PKA in DS (temporal cortex and cerebellum) and AD (temporal cortex). These findings suggest that decreased ARPP-19 along with decreased activities of PKA is involved in pathomechanisms of both neurodegenerative disorders. Furthermore, these findings provide first evidence for an impaired mechanism of cAMP-related signal transduction and phosphorylation in both dementing disorders.

Upregulation of synapsin IIa and IIb mRNAs in the paraventricular and supraoptic nuclei in chronic salt loaded and lactating rats

The effects of chronic salt loading (2% saline to drink for 5 and 10 days), gestation, lactation and adrenalectomy on the expression of synapsin IIa and IIb genes were examined in the rat paraventricular (PVN) and supraoptic nuclei (SON), using in situ hybridization histochemistry. In each control, synapsin IIa and IIb genes were moderately expressed in the magnocellular division of the PVN and SON, while few transcripts of synapsin IIa and IIb were observed in the parvocellular division of the PVN. Chronic salt loading, gestation on day 21 and lactation on day 10 caused significant increases in synapsin IIa and IIb transcripts in the magnocellular division of the PVN and SON, compared to each control. Although corticotropin-releasing hormone transcripts in the parvocellular division of the PVN were significantly increased in the adrenalectomized rats, no changes in the transcripts of synapsin IIa and IIb were observed throughout the PVN. These results suggest that physiological stimuli such as osmotic challenge and lactation potently increase synapsin IIa and IIb mRNAs in the magnocellular neurons of the PVN and SON.

A phospho-switch controls the dynamic association of synapsins with synaptic vesicles

Synapsins constitute a family of synaptic vesicle proteins essential for regulating neurotransmitter release. Only two domains are conserved in all synapsins: a short N-terminal A domain with a single phosphorylation site for cAMP-dependent protein kinase (PKA) and CaM Kinase I, and a large central C domain that binds ATP and may be enzymatic. We now demonstrate that synapsin phosphorylation in the A domain, at the only phosphorylation site shared by all synapsins, dissociates synapsins from synaptic vesicles. Furthermore, we show that the A domain binds phospholipids and is inhibited by phosphorylation. Our results suggest a novel mechanism by which proteins reversibly bind to membranes using a phosphorylation-dependent phospholipid-binding domain. The dynamic association of synapsins with synaptic vesicles correlates with their role in activity-dependent plasticity.

Homo- and heterodimerization of synapsins

In vertebrates, synapsins constitute a family of synaptic vesicle proteins encoded by three genes. Synapsins contain a central ATP-binding domain, the C-domain, that is highly homologous between synapsins and evolutionarily conserved in invertebrates. The crystal structure of the C-domain from synapsin I revealed that it constitutes a large (>300 amino acids), independently folded domain that forms a tight dimer with or without bound ATP. We now show that the C-domains of all synapsins form homodimers, and that in addition, C-domains from different synapsins associate into heterodimers. This conclusion is based on four findings: 1) in yeast two-hybrid screens with full-length synapsin IIa as a bait, the most frequently isolated prey cDNAs encoded the C-domain of synapsins; 2) quantitative yeast two-hybrid protein-protein binding assays demonstrated pairwise strong interactions between all synapsins; 3) immunoprecipitations from transfected COS cells confirmed that synapsin II heteromultimerizes with synapsins I and III in intact cells, and similar results were obtained with bacterial expression systems; and 4) quantification of the synapsin III level in synapsin I/II double knockout mice showed that the level of synapsin III is decreased by 50%, indicating that heteromultimerization of synapsin III with synapsins I or II occurs in vivo and is required for protein stabilization. These data suggest that synapsins coat the surface of synaptic vesicles as homo- and heterodimers in which the C-domains of the various subunits have distinct regulatory properties and are flanked by variable C-terminal sequences. The data also imply that synapsin III does not compensate for the loss of synapsins I and II in the double knockout mice.

Avanços em psicofarmacologia - mecanismos de ação de psicofármacos hoje

Desde o início da história da psicofarmacologia moderna, na década de 40, vários avanços foram obtidos na elucidação do mecanismo de ação dos compostos psicoativos. O artigo aborda tais avanços enfocando as principais técnicas utilizadas, desde o desenvolvimento das técnicas de mensuração de aminas por emissão de fluorescência e da técnica de ligação fármaco-receptor, até a incorporação de técnicas sofisticadas, tais como as moleculares, para o estudo das alterações pós-receptor, o uso de marcadores genéticos e técnicas de imagem (PET, SPECT). Espera-se que tais progressos levem à elucidação dos mecanismos de ação dos psicofármacos, permitindo o desenvolvimento de novas moléculas terapêuticas específicas para regular as alterações subjacentes aos transtornos psiquiátricos.

Immunohistochemical localization of calmodulin-dependent cyclic phosphodiesterase in the human brain

The amplification of cyclic nucleotide 'second messenger' signals within neurons is controlled by phosphodiesterases which are responsible for their degradation. Calmodulin-dependent phosphodiesterase (CaMPDE) is an abundant enzyme in brain which carries out this function. For the first time, we have localized CaMPDE in the normal human brain at various ages, using a mononoclonal antibody designated A6. This antibody was generated using standard techniques, purified, and applied to tissue sections. Autopsy specimens of human brain with no neuropathological abnormalities were selected representing a range of pre- and postnatal ages. Sections of various brain regions were evaluated for immunoreactivity, graded as nil, equivocal, or definite. We demonstrated definite CaMPDE immunohistochemical staining in neocortex, especially in neurons in layers 2 and 5. There was definite neuronal immunoreactivity in the hippocampus, and in the subiculum. The striatum had definite patchy neuronal staining. Definite terminal staining in the globus pallidus externa and substantia nigra pars reticulata outlined resident neurons, interpreted as axonal terminal staining. Cerebellar Purkinje cells showed definite immunoreactivity. In the developing brain, definite immunohistochemical staining was seen in the cerebellar external granular layer. The expression of CaMPDE in specific subsets of neurons suggests they may correlate with cells having dopaminergic innervation and/or high levels of neuronal integration.

In vitro generation of an active calmodulin-independent phosphodiesterase from brain calmodulin-dependent phosphodiesterase (PDE1A2) by m-calpain

In the present study we have shown that bovine brain 60-kDa calmodulin-dependent cyclic nucleotide phosphodiesterase isozyme (CaMPDE - PDE1A2) is proteolyzed by a Ca2+-dependent cysteine protease, m-calpain. The proteolysis of PDE1A2 by m-calpain results in its conversion to a totally calmodulin (CaM)-independent form accompanied by degradation of PDE1A2 into a 45-kDa catalytic fragment and a 15-kDa fragment. The activity of PDE1A2 is unaffected by the presence or absence of CaM during cleavage, suggesting that the interaction between CaM and PDE1A2 does not alter substrate recognition by calpain. Furthermore, we provide evidence, based on the studies of CaM overlay and phosphorylation, that the cleavage site is not present either in the CaM-binding domain or phosphorylation site. N-terminal sequence analysis of the 45-kDa fragment indicated that cleavage occurs between residues 126Gln and 127Ala, and eliminates the CaM-dependent activity of carboxy termini PDE1A2. The present findings suggest that limited proteolysis in the brain through calpains could be an alternate mechanism for activating CaMPDE(s) and for regulating intracellular levels of cAMP.

Conclusions and comments. Xth International Symposium on Cholinergic Mechanisms

Ancient medicine men of Egypt and Arabia employed, under another name, the cholinergic agents, as did the hunters, warriors and shamans of Africa and South America. An explosion of cholinergic science occurred in the last and the current century, and the ISCMs witnessed and catalyzed this progress. The Xth ISCM emphasized the molecular characteristics of the receptors, cholinesterase and of the system engaged in liberation of Ach.

Sympathetic neural response to immune signals involves nitric oxide: effects of exposure to alcohol in utero

In response to infection, inflammation, or injury, the neural-immune-endocrine networks are activated to restore or maintain stability in the internal environment. Disruption of any one of the functional components may impair the effectiveness of the immune response to challenges, and may consequently jeopardize the wellness of the host. Studies in the author's laboratory have shown that the normal activation of splenic sympathetic neurons in response to the endotoxin lipopolysaccharide, a tool frequently used to mimic infection or inflammation, does not occur in fetal alcohol-exposed (FAE) rats. The sympathetic innervation of lymphoid organs is considered an important immune modulator. Thus, the anomalous splenic sympathetic response may partly account for the impaired immunity associated with FAE. Although the underlying mechanism is far from clear, studies described in this report suggest that nitric oxide (NO), a gaseous free radical, is involved in the altered splenic sympathetic neural response to immune signals. The suggestion is supported by the following findings: (1) blockade of NO synthesis prevented the blunted sympathetic response to lipopolysaccharide or interleukin-1 in FAE rats, and (2) there was a further increase in NO formation in response to lipopolysaccharide in the FAE rats compared to their control cohorts. This was demonstrated by an augmented increase in the inducible NO synthase immunoreactivity in the spleen as well as in circulating levels of NO metabolites. It is suggested, therefore, that the altered splenic sympathetic response to immune signals involves excessive formation of NO that may account, at least in part, for the impaired immunity associated with FAE.

Splenic sympathetic response to endotoxin is blunted in the fetal alcohol-exposed rat: role of nitric oxide

This study was designed to test the hypothesis that nitric oxide (NO) mediates the blunted splenic sympathetic response to lipopolysaccharide (endotoxin) that occurs in young rats exposed to alcohol in utero (FAE). The subjects, 26-29-day-old rats, were progeny of pregnant dams fed an alcohol diet (35% of the calories were derived from ethanol) or their control and pair-fed (PFC) cohorts. We examined the effects of lipopolysaccharide (LPS) (0.5 mg/kg, i.p.) on splenic norepinephrine (NE) turnover, an index of sympathetic neural activity, splenic inducible NO synthase (iNOS) protein immunoreactivity, and NO metabolites nitrite/nitrate concentrations in plasma. In response to LPS, splenic NE turnover was increased by more than twofold in the PFC groups, but the increase did not occur in their FAE cohorts. The blockade of NOS with L-NAME (30 mg/kg, i.p.) reversed this difference. In both the PFC and FAE rats, basal levels of splenic iNOS protein immunoreactivity were equally barely detected and plasma NO metabolite levels were relatively low (25 microM in both groups). In response to LPS, however, iNOS protein displayed a marked increase in the PFC group and an even greater increase (by close to threefold) in the FAE rats. LPS also substantially increased plasma NO metabolite levels by close to eightfold in the control groups, but by 15-fold in their FAE cohorts compared to the basal levels. These findings support the hypothesis that in the FAE rat, an augmented NO formation accounts for the blunted sympathetic response to endotoxin.

Synapsin III, a novel synapsin with an unusual regulation by Ca2+

Synapsins I and II are synaptic vesicle proteins essential for normal Ca2+ regulation of neurotransmitter release. Synapsins are composed of combinations of common and variable sequences, with the central C-domain as the largest conserved domain. The C-domain is structurally homologous to ATPases, suggesting that synapsins function as ATP-dependent phosphotransfer enzymes. We have now identified an unanticipated third synapsin gene that is also expressed in brain. The product of this gene, synapsin IIIa, shares with synapsins Ia and IIa three conserved domains that are connected by variable sequences: the phosphorylated A-domain at the amino terminus, the large ATP-binding C-domain in the center, and the E-domain at the carboxyl terminus. Like other synapsins, synapsin IIIa binds ATP with high affinity and ADP with a lower affinity, consistent with a cycle of ATP binding and hydrolysis. ATP binding to the different synapsins is directly regulated by Ca2+ in a dramatically different fashion: Ca2+ activates ATP binding to synapsin I, has no effect on synapsin II, and inhibits synapsin III. Thus vertebrates express three distinct synapsins that utilize ATP but are specialized for different modes of direct Ca2+ regulation in synaptic function.

Synapsin I is structurally similar to ATP-utilizing enzymes

Synapsins are abundant synaptic vesicle proteins with an essential regulatory function in the nerve terminal. We determined the crystal structure of a fragment (synC) consisting of residues 110-420 of bovine synapsin I; synC coincides with the large middle domain (C-domain), the most conserved domain of synapsins. SynC molecules are folded into compact domains and form closely associated dimers. SynC monomers are strikingly similar in structure to a family of ATP-utilizing enzymes, which includes glutathione synthetase and D-alanine:D-alanine ligase. SynC binds ATP in a Ca2+-dependent manner. The crystal structure of synC in complex with ATPgammaS and Ca2+ explains the preference of synC for Ca2+ over Mg2+. Our results suggest that synapsins may also be ATP-utilizing enzymes.

Region-specific phosphorylation of rabphilin in mossy fiber nerve terminals of the hippocampus

In mossy fiber synapses of the CA3 region of the hippocampus, long-term potentiation (LTP) is induced presynaptically by activation of cAMP-dependent protein kinase A (PKA). Rab3A is a synaptic vesicle protein that regulates vesicle fusion and is essential for mossy fiber LTP. Rab3A probably acts via two effector proteins, rabphilin and RIM, of which rabphilin is an in vitro substrate for PKA. To test if rabphilin is phosphorylated in nerve terminals and if its PKA-dependent phosphorylation correlates with the PKA-dependent induction of LTP in mossy fiber terminals, we have studied the phosphorylation of rabphilin in synaptosomes isolated from the CA1 and CA3 regions of the hippocampus. Rabphilin was phosphorylated in both CA1 and CA3 synaptosomes. However, when we treated the CA1 and CA3 synaptosomes with forskolin (an agent that enhances PKA activity) or induced Ca2+ influx into synaptosomes with high K+, rabphilin phosphorylation was increased selectively in mossy fiber CA3 synaptosomes, but not in CA1 synaptosomes. In contrast, the phosphorylation of synapsin, studied as a control for the specificity of the region-specific phosphorylation of rabphilin, was augmented similarly by both treatments in CA1 and CA3 synaptosomes. These results reveal that the phosphorylation states of two synaptic substrates for PKA and CaM KII, rabphilin and synapsin, are regulated differentially in a region-specific manner, an unexpected finding because rabphilin and synapsin are similarly present in CA1 and CA3 synaptosomes and are colocalized on the same synaptic vesicles. The region-specific phosphorylation of rabphilin agrees well with the restricted induction of LTP by presynaptic PKA activation in mossy fiber, but not CA1, nerve terminals.

Brain-derived neurotrophic factor regulates maturation of the DARPP-32 phenotype in striatal medium spiny neurons: studies in vivo and in vitro

The medium spiny neuron is the predominant striatal neuronal subtype. The striatum, a participant in motor and cognitive functions, is a site of pathophysiology in prevalent neuropsychiatric diseases and is the target of many currently utilized pharmacologic agents. DARPP-32, a dopamine and cyclic AMP-regulated phosphoprotein, is a widely-used marker of mature striatal medium-sized neurons, but the molecules regulating DARPP-32 transcription have not been identified. We show that a null mutation in the mouse brain-derived neurotrophic factor gene leads to decreased DARPP-32 immunoreactivity in striatal medium spiny neurons at birth and postnatal day 10. Striatal DARPP-32 messenger RNA and protein are decreased relative to wild-type littermate controls. In densely plated (1 x 10(6) cells/cm2) primary cultures derived from the ganglionic eminences, addition of brain-derived neurotrophic factor (100 ng/ml) to defined media results in a greater than 3-fold increase in the number of DARPP-32-immunopositive cells after 12 h and greater than 4-fold (P<0.005) after 24 h. The increase in DARPP-32-immunopositivity is abolished by the addition of 2 microg/ml actinomycin D without a significant effect on cell viability. These data suggest that brain-derived neurotrophic factor directly or indirectly regulates DARPP-32 transcription in medium spiny neurons. This is the first demonstration of transcriptional regulation of DARPP-32, and the first evidence of a forebrain abnormality in a newborn neurotrophin "knockout" mouse.

Postnatal ontogeny of striatal-enriched protein tyrosine phosphatase (STEP) in rat striatum

The present study was undertaken to examine developmental change in expression of striatal-enriched protein tyrosine phosphatase (STEP) in the postnatal striatum of rats. For this purpose, immunohistochemical staining and transimmunoblotting analyses were carried out using a cDNA-generated polyclonal antibody to the STEP with a molecular weight of 46 kDa. Immunostaining showed that in neonatal striatum STEP-immunoreactivity was found in discrete patches composed of many immature cells, which corresponded to the tyrosine hydroxylase-immunopositive "dopamine islands." With development there was an increase in staining intensity and in the number of positively reacting cells. By 4 weeks postnatally, STEP-immunoreactivity was almost homogeneously distributed throughout the striatum, as was seen at the adult stage. Immunoblotting analysis showed that STEP protein expression abruptly increased from 2 to 4 weeks postnatally when it reached the adult level. These findings suggest that STEP is involved in development and maturation of the striatal neurons.

Cholinergic neurotransmission and synaptic plasticity concerning memory processing

The brain is able to change the synaptic strength in response to stimuli that leave a memory trace. Long-term potentiation (LTP) and long-term depression (LTD) are forms of activity-dependent synaptic plasticity proposed to underlie memory. The induction of LTP appears mediated by glutamate acting on AMPA and then on NMDA receptors. Cholinergic muscarinic agonists facilitate learning and memory. Acetylcholine depolarizes pyramidal neurons, reduces inhibition, upregulates NMDA channels and activates the phosphoinositide cascade. Postsynaptic Ca2+ rises and stimulates Ca-dependent PK, promoting synaptic changes. Electroencephalographic desynchronization and hippocampal theta rhythm are related to learning and memory, are inducible by cholinergic agonists and elicited by hippocampal cholinergic terminals. Their loss results in memory deficits. Hence, cholinergic pathways may act synergically with glutamatergic transmission, regulating and leading to synaptic plasticity. The stimulation that induces plasticity in vivo has not been established. The patterns for LTP/LTD induction in vitro may be due to the loss of ascending cholinergic inputs. As a rat explores pyramidal cells fire bursts that could be relevant to plasticity.

Ca2+/calmodulin system: participation in the progesterone-induced facilitation of lordosis behavior in the ovariectomized estrogen-primed rat

We studied the effect some drugs that participate in the Ca2+/ calmodulin system have on the progesterone (P) facilitation of lordosis behavior in ovariectomized estradiol (E2) primed rats. We injected rats 44 h after E2 priming with 2 mg P together with various dosages of one of the following compounds: pentobarbital, trifluoperazine (TPZ), promethazine (PMZ), Chlorpromazine (CPZ), haloperidol (HAL), pimozide (PIM), and verapamil (VER). Then 4 h after treatment, animals were tested for sexual behavior, expressed as the lordosis quotient (LQ). All drugs at 4 mg/kg or higher inhibited lordosis, but only HAL, PIM, and VER were active at 1 mg/kg. The maximum level of activity was shown by PIM, although at the dose of 8 mg/kg no statistical differences were found between this compound and TPZ or HAL. Pentobarbital (25 mg/kg) showed no significant difference from saline-treated controls. The activity of the tested drugs on the facilitation of sexual behavior appears to be related to their efficiency as inhibitors of calmodulin (CaM)-dependent phosphodiesterase and as ligands for the Ca(2+)-CaM complex.

ARPP-21: murine gene structure and promoter identification of a neuronal phosphoprotein enriched in the limbic striatum

ARPP-21 (cAMP-regulated phosphoprotein, Mr = 21,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis) is a phosphoprotein highly enriched in concentration in the neurons of the limbic striatum. It is likely a third messenger in the intracellular cascade of events following neuronal stimulation by first-messenger activators of the adenylate cyclase system, including dopamine via the D1 receptor. ARPP-21 expression is restricted to telencephalic post-mitotic, post-migrational neurons, and its precise pattern of temporal and spatial expression makes it an attractive candidate for the study of transcriptional regulation of neuronal maturation. To define genomic regions likely to contain functional promoter elements, we isolated the murine ARPP-21 gene. Primer extension and T2 RNase protection analyses identified multiple transcription start sites, but 1.3 kb of 5'-flanking DNA revealed few consensus transcription factor binding sequences. A series of transient transfection assays in clonal cell lines which do not express ARPP-21 identified a basal promoter active in both neuronal and non-neuronal lines. Expression in all lines was decreased by the inclusion of regions further upstream, and extinguished by the inclusion of the first intron. Further analyses are likely to reveal cell specific regulatory sequences.

Immunocytochemical localization of the striatal enriched protein tyrosine phosphatase in the rat striatum: a light and electron microscopic study with a complementary DNA-generated polyclonal antibody

The present study concerns the immunocytochemical localization of the striatal enriched protein tyrosine phosphatase in the rat striatum. A novel molecular biology technique allowed us to produce a complementary DNA-generated polyclonal antibody raised against the non-catalytic domain of the striatal enriched protein tyrosine phosphatase, which selectively recognized the striatal enriched protein tyrosine phosphatase protein with 46,000 mol. wt on western blots. Immunocytochemical analysis with the specific antibody revealed strong striatal enriched protein tyrosine phosphatase immunoreactivity in the striatum. Light microscopy showed striatal striatal enriched protein tyrosine phosphatase-immunopositive neurons to be of medium size (mean diameter of 14.4 microns), and to comprise approximately 80% of the total neuronal population in the striatum. These cells had round, triangular or polygonal cell bodies with relatively little cytoplasm. Nerve fibers stained positively for striatal enriched protein tyrosine phosphatase were also present in the globus pallidus and the substantia nigra, and the nigral labeling on the ipsilateral side almost disappeared subsequent to cerebral hemitransection, suggesting these immunolabeled structures to be striatal projections. Double-immunofluorescence analysis demonstrated separate populations of striatal enriched protein tyrosine phosphatase-positive cells and neurons stained for parvalbumin. Also, ultrastructural study showed that the striatal enriched protein tyrosine phosphatase-positive neurons (n = 50) possessed no nuclear indentations or intranuclear inclusions. Thus, most striatal striatal enriched protein tyrosine phosphatase-positive neurons were thought to be of the medium-sized spinous type. At the light microscopic level, stained striatal neurons exhibited striatal enriched protein tyrosine phosphatase immunolabeling in their somata, dendrites and axonal processes, but not in their nuclei. Electron microscopic observation showed strong striatal enriched protein tyrosine phosphatase-immunoreactivity on the inner surface of the plasmalemma, on the outer surfaces of mitochondria and on microtubules, particularly of dendrites. A heavy deposit of immunoreaction product was also present on postsynaptic densities in labeled dendrites, while a light deposit was seen on the synaptic vesicles of nerve terminals. The characteristic distribution profile of striatal enriched protein tyrosine phosphatase suggested that the enzyme may play a role in a variety of functional properties of striatal neurons, especially in postsynaptic signaling processes and in regulation of microtubular functions. On the basis of the present findings, we propose the following conclusions: (i) a protein tyrosine phosphorylation system regulated by striatal enriched protein tyrosine phosphatase is involved in certain specialized cellular processes (e.g. signal transduction cascades) of medium-sized spinous neurons distinct from those of other neuronal subsets in the striatum; (ii) a striatal medium spiny neuron is characterized by its expression of striatal enriched protein tyrosine phosphatase and, therefore, the enzyme is useful for detection of the distinct subset of striatal cells or for tracing their axonal projection fibers in the basal ganglia.

Mosaic organization of calcineurin immunoreactivity in the adult cat striatum

Calcineurin is a Ca2+/calmodulin-regulated protein phosphatase which is thought to play an essential role in the intracellular Ca(2+)-signal transduction. The present study showed that calcineurin immunolabeling was differentially concentrated in the two distinct compartments showing a mosaic-like pattern in the adult cat striatum. The compartment of heightened calcineurin immunolabeling corresponded to the extrastriosomal matrix visualized by calbindin-D28K immunostaining. Under the light microscope, striatal neurons appeared to be less strongly immunoreactive for calcineurin in the striosomes than in the matrix compartment. These findings suggest that the novel striatal compartments may differ in the intracellular Ca(2+)-signaling cascade associated with protein dephosphorylation.

Ca/calmodulin-dependent kinase II inhibitor KN62 attenuates glutamate release by inhibiting voltage-dependent Ca(2+)-channels

The effect of KN62 (1-[N,O-bis(5-isoquinolinesulphonyl)-N -methyl-L-tyrosyl]-4-phenylpiperazine), a putative inhibitor of Ca/calmodulin-dependent kinase II (Ca/CaM-K II), on glutamate release from isolated nerve-terminals (synaptosomes) was examined. The drug caused a potent inhibition of KCl- and 4-aminopyridine-evoked glutamate release from isolated nerve-terminals (synaptosomes). Examination of the effect of the inhibitor on Ca(2+)-influx revealed that the diminution of glutamate release could be attributed to a decrease in cytosolic Ca. A direct effect of KN62 on synaptosomal Ca(2+)-channels was confirmed in experiments where Ba, which does not support CaM-dependent processes, was used in place of Ca. Additionally, whole-cell patch-clamping of cerebellar granule neurones directly demonstrated inhibition of Ca-currents by KN62. We therefore suggest that, in cellular systems, conclusions based on the use of KN62 as a Ca/CaM-K II blocker may be ambiguous and should be viewed with caution unless the effect of the drug on Ca-influx has also been quantified. The effect of KN62 on Ca(2+)-influx appears to be specific to slowly-or non-inactivating conductances, and therefore presents KN62 as a potentially useful tool in this context.

Functional identification of histamine H3-receptors in the human heart

Norepinephrine release contributes to ischemic cardiac dysfunction and arrhythmias. Because activation of histamine H3-receptors inhibits norepinephrine release, we searched for the presence of H3-receptors directly in sympathetic nerve endings (cardiac synaptosomes) isolated from surgical specimens of human atria. Norepinephrine was released by depolarization with K+. The presence of H3-receptors was ascertained because the selective H3-receptor agonists (R) alpha-methylhistamine and imetit reduced norepinephrine release, and the specific H3-receptor antagonist thioperamide blocked this effect. Norepinephrine release was exocytotic, since it was inhibited by the N-type Ca(2+)-channel blocker omega-conotoxin and the protein kinase C inhibitor Ro31-8220. Functional relevance of these H3-receptors was obtained by showing that transmural electrical stimulation of sympathetic nerve endings in human atrial tissue increased contractility, an effect blocked by propranolol and attenuated in a concentration-dependent manner by (R) alpha-methylhistamine. Also, thioperamide antagonized the effect of (R) alpha-methylhistamine. Our findings are the first demonstration that H3-receptors are present in sympathetic nerve endings in the human heart, where they modulate adrenergic responses by inhibiting norepinephrine release. Since myocardial ischemia causes intracardiac histamine release, H3-receptor-induced attenuation of sympathetic neurotransmission may be clinically relevant.

The synaptic vesicle cycle: a cascade of protein-protein interactions

The synaptic vesicle cycle at the nerve terminal consists of vesicle exocytosis with neurotransmitter release, endocytosis of empty vesicles, and regeneration of fresh vesicles. Of all cellular transport pathways, the synaptic vesicle cycle is the fastest and the most tightly regulated. A convergence of results now allows formulation of molecular models for key steps of the cycle. These developments may form the basis for a mechanistic understanding of higher neural function.

Passive avoidance learning induced change in GAP43 phosphorylation in day-old chicks

Day-old chicks trained on a single trial passive discriminated avoidance task demonstrated a significant increase in in vitro phosphorylation of a 50 kDa protein in P2M fractions of total forebrain. The increase occurred 30 min posttraining, at a time when previous reports suggest that mechanisms for triggering protein synthesis-dependent long-term memory consolidation are activated. These changes in phosphorylation rates were accompanied by a substantial enhancement of total kinase activity. Immunoblotting studies with monoclonal anti-GAP43 antibody indicate that this protein is GAP43. These results contradict previous reports of a decrease in in vitro GAP43 phosphorylation following the same learning paradigm. A number of procedural differences may account for this discrepancy. The results suggest that changes in the phosphorylation state may be associated with mechanisms triggering long-term memory consolidation.

Endogenous phosphorylation of a 61,000 dalton hippocampal protein increases following traumatic brain injury

Acute biochemical consequences of moderate traumatic brain injury (TBI) include activation of kinases, including protein kinase C (PKC). To determine the possible consequences of PKC activation at the substrate level, we have examined protein phosphorylation patterns 1 h following injury. Although the phosphorylation of most proteins remained unchanged following injury, we observed a significant increase in the phosphorylation of a 61,000 dalton protein (TBI61) in injured rat hippocampus (121% higher than sham control) in vitro. TBI61 phosphorylation could be enhanced by phosphatidyl serine and diacylglycerol or by addition of exogenous PKC. In addition, TBI61 phosphorylation was inhibited by the PKC inhibitor, staurosporine, suggesting further that this protein may be a PKC substrate. These data suggest that TBI increases the phosphorylation of a 61 kD hippocampal protein in vitro. Increases in the protein level and activity of PKC could contribute to this increased phosphorylation.

Cellular localization of type II Ca2+/calmodulin-dependent protein kinase in the rat basal ganglia and intrastriatal grafts derived from fetal striatal primordia, in comparison with that of Ca2+/calmodulin-regulated protein phosphatase, calcineurin

We investigated immunohistochemically the cellular localization of multifunctional type II Ca2+/calmodulin-dependent protein kinase in the rat basal ganglia and intrastriatal grafts derived from fetal striatal primordia, in comparison with that of calcineurin, a reliable marker for striatal medium-sized spinous neurons. The type II Ca2+/calmodulin-dependent protein kinase-positive neurons were of medium size, with a mean diameter of 16.1 +/- microns (average +/- S.D., n = 72, range 13.6-18.3 microns) and comprised approximately 70% of the total neuronal population in the striatum. Light microscopy showed that the type II Ca2+/calmodulin-dependent protein kinase-positive cells had round, triangular or polygonal cell bodies with relatively little cytoplasm. Analysis of serial sections showed that type II Ca2+/calmodulin-dependent protein kinase and calcineurin immunoreactivities were co-localized in the striatal neurons examined with a similar distribution pattern. Type II Ca2+/calmodulin-dependent protein kinase-positive cells were always immunoreactive for calcineurin and cells negative for type II Ca2+/calmodulin-dependent protein kinase showed no apparent calcineurin immunoreactivity. Type II Ca2+/calmodulin-dependent protein kinase-positive nerve fibers in the globus pallidus and substantia nigra almost disappeared following striatal ischemic injury produced by transient middle cerebral artery occlusion and cerebral hemitransection, respectively, suggesting that these immunopositive fibers were striatal projections. Thus, most type II Ca2+/calmodulin-dependent protein kinase-positive neurons in the rat striatum are considered to be of the medium-sized spinous type. Type II Ca2+/calmodulin-dependent protein kinase or calcineurin immunoreactivity was also observed in a large number of neurons in transplants derived from fetal striatal primordia grafted into striatal ischemic lesions. In addition, type II Ca2+/calmodulin-dependent protein kinase- or calcineurin-immunoreactive nerve fibers appeared in the deafferented globus pallidus of the host rats, suggesting that the striatopallidal pathway was reformed by striatal projection neurons of the transplants. This finding may also indicate that Ca2+/calmodulin-regulated enzymes are useful for tracing striatal projection fibers as endogenous marker proteins.

Cyclic AMP-regulated AChR assembly is independent of AChR subunit phosphorylation by PKA

Forskolin treatment of cells expressing Torpedo acetylcholine receptors leads to enhanced assembly efficiency of subunits, which correlates with increased phosphorylation of the gamma subunit. To determine the role of the two potential protein kinase A sites of the gamma subunit in receptor assembly, cell lines expressing different mutant receptors were established. Mouse fibroblast cell lines stably expressing wild-type Torpedo acetylcholine receptor alpha, beta, delta subunits plus one of three gamma subunit mutations (S353A, S354A, or S353,354A) were established to identify the protein kinase A phosphorylation sites of gamma in vivo, and to determine if increased phosphorylation of the gamma subunit leads to enhanced expression of receptors. We found that both serines (353, 354) in gamma are phosphorylated in vivo by protein kinase A, however, phosphorylation of either or both of these sites does not lead to increased assembly efficiency. We established a cell line expressing alpha, beta, and gamma(S353,354A) subunits only (no delta), and found that the presence of delta (or its phosphorylation) is also not necessary for the observed stimulation by forskolin. alpha beta gamma, alpha gamma, and beta gamma associations were stimulated by forskolin but alpha beta and alpha delta interactions were not. These data imply that the presence of gamma is necessary for forskolin action. We postulate that forskolin may stimulate acetylcholine receptor expression through a cellular protein that is involved in the folding and/or assembly of protein complexes, and that forskolin may regulate the action of such a protein through phosphorylation.

Neostriatal mosaic and type II Ca2+/calmodulin-dependent protein kinase: an immunohistochemical study on the adult rat striatum

The present immunohistochemical study is concerned with the expression of type II Ca2+/calmodulin-dependent protein kinase (CaM-kinase II), which is supposed to play an essential role in the intracellular Ca2+ signal transduction, in the striatum of adult rats. CaM-kinase II immunoreactivity was differentially concentrated in irregularly shaped compartments within the nucleus in a mosaic-like fashion. The compartment of heightened CaM-kinase II-immunolabeling corresponded to the extrastriosomal matrix visualized by calbindin-D28k-immunostaining. Light microscopic observation showed neurons immunoreactive for CaM-kinase II to be less densely distributed in the striosomes than in the matrix compartment. The present data suggest that these two striatal compartments may differ in an intracellular Ca(2+)-signaling process associated with protein phosphorylation.

Interferon-alpha, beta and tumor necrosis factor-alpha enhance the frequency of miniature end-plate potentials at rat neuromuscular junction

The effects of the two cytokines, rat interferon-alpha, beta and human tumor necrosis factor-alpha, were studied at the rat neuromuscular junction by using classical electrophysiological techniques. Both cytokines in a similar way at concentrations of 2,000 and 35,000 U/ml, respectively, increased transiently and with a relatively long delay (15 to 25 min) the frequency of miniature endplate potentials. The observed effects may be related to complex second messenger mechanisms and contribute to modulation and plasticity of neurotransmission.

Evidence that M1 muscarinic receptors enhance noradrenaline release in mouse atria by activating protein kinase C

1. The M1 selective muscarinic agonist, McNeil A 343, enhanced the electrically evoked release of noradrenaline from postganglionic sympathetic nerves in mouse atria. This has been found previously to be due to activation of muscarinic receptors of the M1 subtype, probably located on sympathetic nerve terminals. The present study investigated the signal transduction mechanisms involved in the release-enhancing effects of McNeil A 343. The release of noradrenaline from mouse atria was assessed by measuring the electrically-induced (3 Hz, 60 s) outflow of radioactivity from atria which had been pre-incubated with [3H]-noradrenaline. 2. 8-Bromo cyclic AMP in the presence of IBMX was used to enhance maximally S-I noradrenaline release through cyclic AMP-dependent mechanisms. However, the facilitatory effect of McNeil A 343 (10 microM) was not different from the effect in the absence of these drugs, suggesting that McNeil A 343 enhances noradrenaline release independently of the cyclic AMP system. Furthermore, the release-enhancing effect of McNeil A 343 (10 microM) on noradrenaline release was also not altered by the 5-lipoxygenase inhibitor, BW A4C. 3. The facilitatory effect of McNeil A 343 was not altered in the presence of drugs (trifluoperazine, W7, and calmidazolium) which inhibit calmodulin-dependent processes, suggesting that the mechanisms of action of McNeil A 343 does not depend on calmodulin. 4. It was considered likely that the facilitatory effect of McNeil A 343 on noradrenaline release may be due to activation of protein kinase C, since activators of protein kinase C enhance noradrenaline release. The facilitatory effect of McNeil A 343 was abolished by the non-selective protein kinase C inhibitor,K-252a. To investigate further the involvement of protein kinase C, mouse atria were chronically incubated (9-O h) with the protein kinase C activator, 4 beta-phorbol dibutyrate (1.0 microM) in order to down-regulate protein kinase C activity. In protein kinase C-down-regulated atria, the facilitatory effect of McNeil A 343 (30 microM) was abolished. Incubation with 4 alpha-phorbol dibutyrate which does not affect protein kinase C did not reduce the facilitatory effect of McNeil A 343. This provides evidence that activation of protein kinase C is involved in the signal transduction process of McNeil A 343.

Probing modifications of the neuronal cytoskeleton

The prominent death of central neurons in Alzheimer's and Parkinson's is reflected by changes in cell shape and by the formation of characteristic cytoskeletal inclusions (neurofibrillary tangles, Lewy bodies). This review focuses on the biology of neurofilaments and microtubule-associated proteins and identifies changes that can occur to these elements from basic and clinical research perspectives. Attention is directed at certain advances in neurobiology that have been especially integral to the identification of epitope domains, protein isoforms, and posttranslational (phosphorylation) events related to the composition, development, and structure of the common cytoskeletal modifications. Recently, a number of experimental strategies have emerged to simulate the aberrant changes in neurodegenerative disorders and gain insight into possible molecular events that contribute to alterations of the cytoskeleton. Descriptions of specific systems used to induce modifications are presented. In particular, unique neural transplantation methods in animals have been used to probe possible molecular and cellular conditions concerned with abnormal cytoskeletal changes in neurons.

Electrotransfer of fixed phosphoproteins from pieces of dried polyacrylamide gel to small disks of nitrocellulose, nylon or polyvinylidene difluoride

A simple method for the transfer of 32P-labeled proteins from dried polyacrylamide gels to small disks of nitrocellulose, nylon or polyvinylidene difluoride (PVDF) is described. Gel pieces containing the desired phosphoprotein are rehydrated in buffer containing sodium dodecyl sulfate (SDS) and sealed in agarose in a glass tube over a supporting gel of polyacrylamide. Protein is transferred upwards through a discontinuous density gradient of SDS-buffer and methanol to a disk of membrane sealed to the mouth of the tube with dialysis membrane. The method allows the concentration of a phosphoprotein present in several gel pieces to a single disk of immobilized membrane. Recovery of phosphoprotein was at least as good as obtained with conventional electroblotting. Application of the method to the analysis of the phosphoamino acid content of the astrocyte marker, glial fibrillary acidic protein, is described.

ZNC(C)PR affects developmental changes of P46 phosphorylation in rat hippocampus

Protein phosphorylation has been suggested to be correlated with brain development and with the molecular mechanism of behavioral effects of neuropeptides. The present study reports in vitro endogenous phosphorylation of P46, a membrane-associated protein that is changed during development of the rat hippocampus. This study indicated that the degree of endogenous phosphorylation may be correlated with the establishment of synaptic connections. Interestingly, P46 was proved to be identical to a well-known growth-associated protein B-50/GAP-43 in its identical apparent molecular weight, isoelectric point, phosphorylation dependence, and the cross immunoreaction of monoclonal anti-B-50/GAP-43 antibody and P46. Moreover, neonatal administration of neuropeptide ZNC(C)PR could facilitate the developmental progress of P46 endogenous phosphorylation. It is suggested that the changes in P46 phosphorylation could be involved in the cellular mechanism of ZNC(C)PR behavioral effects on learning.

Calcitonin gene-related peptide potentiates synaptic responses at developing neuromuscular junction

Protein phosphorylation is important in synaptic transmission and plasticity. At the neuromuscular junction, phosphorylation of acetylcholine (ACh) receptor-channels increases the rate of agonist-induced channel desensitization. In contrast, potentiation of ACh channel activity through protein phosphorylation has not been described. We report here that calcitonin gene-related peptide (CGRP), a neuropeptide present at presynaptic motor nerve terminals, enhances the postsynaptic response at developing neuromuscular junctions by increasing the burst duration of embryonic ACh channels. The effect of CGRP on these ACh channels is mimicked by dibutyryl-cyclic AMP and by cAMP-dependent protein kinase (PKA) and prevented by a specific peptide inhibitor of PKA. Moreover, postsynaptic inhibition of PKA reduced the amplitude and decay time of spontaneous synaptic currents, suggesting that endogenous CGRP may act as a potentiating factor during the early phase of synaptogenesis.

Evidence for the existence of cAMP-dependent protein kinase phosphorylation system associated with specific phosphoproteins in stable microtubules from rat cerebral cortex

Cyclic AMP is a second messenger by which different extracellular signals are transduced into biological responses. Within the cell, most of the effects of cAMP are mediated through the cAMP protein kinase which appears to be localized in specific compartments of the cell near to their substrate proteins. In the present study, we have investigated the possible association of cAMP-dependent protein kinase, its substrate proteins and RII binding proteins in stable microtubules from rat cerebral cortex. The results show that in this fraction there is a cAMP binding protein of 52-54 kDa. This cAMP receptor is in the inactive holoenzyme form, since the addition of cAMP (5 microM) induces an increase in the endogenous phosphorylation of different stable microtubules polypeptides, which is completely inhibited in the presence of a specific protein kinase inhibitor (PKI 5-24 1 microM). Interestingly, overlay binding assay reveals that beside MAP2, 32P/R II is able to bind stable microtubule proteins of M(r) 150 and 75 kDa which, according to their electrophoretic mobility, can also be endogenous substrates for the enzyme. We conclude that cAMP-dependent phosphorylation system is indeed associated with stable microtubules from rat cerebral cortex.