Biomedical subjects

G Hertting

Publications and source records attributed to G Hertting.

At least 55 records · Page 3Linked to original sources

PubMed1991

Regulation and glucocorticoid-independent induction of lipocortin I in cultured astrocytes.

Stimulation of prostaglandin (PG) release in rat astroglial cultures by various substances, including phorbol esters, melittin, or extracellular ATP, has been reported recently. It is shown here that glucocorticoids (GCs) reduced both basal and stimulated PGD2 release. Hydrocortisone, however, did not inhibit ATP-, calcium ionophore A23187-, or tetradecanoyl phorbol acetate (TPA)-stimulated arachidonic acid release, and only TPA stimulations were affected by dexamethasone. GC-mediated inhibition of PGD2 release thus appeared to exclude regulation at the phospholipase A2 (PLA2) level. Therefore, the effects of GCs on the synthesis of lipocortin I (LC I), a potent, physiological inhibitor of PLA2, were studied in more detail. Dexamethasone was not able to enhance de novo synthesis of LC I in freshly seeded cultures and failed to increase LC I synthesis in 2-3-week-old cultures. It is surprising that LC I was the major LC synthesized in those cultures, and marked amounts accumulated with culture time, reaching plateau levels at approximately day 10. In contrast, LC I was barely detectable in vivo. This tonic inhibition of PLA2 is the most likely explanation for unsuccessful attempts to evoke PG release in astrocyte cultures by various physiological stimuli. GC receptor antagonists (progesterone and RU 38486) given throughout culture time reduced LC I accumulation and simultaneously increased PGD2 release. Nonetheless, a substantial production of LC I persisted in the presence of antagonists. Therefore, LC I induction did not seem to involve GC receptor activation. This was confirmed in serum- and GC-free brain cell aggregate cultures. Here also a marked accumulation of LC I was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Long-term survival of intrastriatal dopaminergic grafts: modulation of acetylcholine release by graft-derived dopamine.

The nigrostriatal dopaminergic system of rats was unilaterally lesioned with 6-hydroxydopamine. Part of the animals was grafted 2 weeks later with fetal dopaminergic cells on the lesioned side; untreated rats of the same strain served as controls. Both 3 and 12-14 months after surgery the striatal dopamine (DA) content and the in vivo rotational response following injection of D-amphetamine showed significant changes in grafted as compared to lesioned animals. At 12-14 months after transplantation, the electrically evoked release of tritiated DA and acetylcholine (ACh) in slices (preincubated with [3H]DA or [3H]choline, respectively) of striata of intact, lesioned, or grafted animals was also investigated. Electrical field stimulation of striatal slices of the lesioned side did not evoke any significant [3H]DA overflow, whereas a marked [3H]DA release was observed in slices of grafted and control striata. Moreover, both DL-amphetamine (3 microM) and nomifensine (10 microM) strongly enhanced basal 3H outflow in these slices. Electrically evoked [3H]ACh release was significantly reduced in slices from all striatal tissues by 0.01 microM apomorphine. In slices from denervated striata a clearcut hypersensitivity for this action of apomorphine was present, indicating supersensitivity of DA receptors on cholinergic terminals; this hypersensitivity was significantly reduced in graft-bearing striata. Furthermore, because this hypersensitivity was unchanged in slices of lesioned striata under stimulation conditions (four pulses/100 Hz) avoiding inhibition by endogenously released DA, it is concluded that lesion-induced DA receptor supersensitivity is caused by an increase in receptor density or efficacy rather than by a decreased competition between endogenous and exogenous agonists. Both reuptake blockade of DA with nomifensine (10 microM) and release of endogenous DA by DL-amphetamine (3 microM) potently reduced [3H]ACh release only in control and grafted but not in lesioned tissue. In experiments using potassium-evoked [3H]ACh release, tetrodotoxin had no effect on the inhibitory activity of amphetamine and nomifensine, indicating that the DA receptors involved in their indirect inhibitory action are located directly on the cholinergic terminals.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1990

Graft-induced learning impairment despite graft-enhanced cholinergic functions in the hippocampus of rats with septohippocampal lesions.

Effects of aspirative fimbria-fornix lesions and intrahippocampal grafts of fetal septal-diagonal band or hippocampal tissue were examined, in Long Evans female rats, on spontaneous alternation, radial maze learning, hippocampal acetylcholine concentrations and [3H]choline accumulation by hippocampal slices. Septohippocampal damage decreased all of these variables. Septal-diagonal band grafts increased hippocampal acetylcholine levels as well as [3H]choline accumulation of tissue (when incubated for 45 min), but they had no effect on alternation rates and further impaired radial maze performances. No such behavioral and neurochemical effects were observed in rats with hippocampal grafts. Our data suggest that factors other than graft-induced improvement of cholinergic functions in the denervated hippocampus may be involved in the expression of behavioral effects by intrahippocampal acetylcholine-rich grafts.

Acetylcholine↗

PubMed1990

Forskolin modulates acetylcholine release in the hippocampus independently of adenylate cyclase activation.

[3H]Acetylcholine release from slices of rabbit hippocampus was elicited by electrical field stimulation (360 pulses/3 Hz). Both forskolin, commonly used as a specific activator of adenylate cyclase, as well as 1,9-dideoxy-forskolin, which fails to activate adenylate cyclase, increased the evoked transmitter release in an almost identical manner. In addition, the phosphodiesterase inhibitor, rolipram, and the membrane-permeable analogue of cAMP, 8-Br-cAMP, did not influence acetylcholine release. These data show that forskolin is not specific to adenylate cyclase and that the increase in acetylcholine release in the rabbit hippocampus occurs through a mechanism other than activation of adenylate cyclase.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1990

Differential prostaglandin formation induced by convulsions in the brain of mice susceptible (DBA/2J) and resistant (CFLP) to acoustic stimulation.

Endogenous cerebral prostanoids possess anticonvulsant properties. This study investigates possible age-dependent anomalies of prostanoid synthesis in the brain of seizure-prone DBA/2J (DBA2) mice as compared to sound stimulus-resistant CFLP mice. Irrespective of the age of the animals, a large increase of prostaglandin (PG) D2 and E2 in the brain of CFLP mice was observed in response to pentylenetetrazol (PTZ)-, or electroshock (ES)-induced seizures. Significantly less PGD2 and PGE2 was formed in the brain of DBA2 mice at day 21 after birth when subjected to PTZ or ES convulsions. At 42 days of age, however, this deficit of cerebral PGD2 synthesis in DBA2 mice disappeared concomitantly with the age-related decrease in audiogenic seizure (AS) susceptibility, whereas the deficit of PGE2 formation persisted. These results suggest that a deficiency of cerebral PGD2 synthesis may be one of the factors responsible for the AS susceptibility of the DBA2 mice. In contrast to PTZ or ES convulsions, acoustically induced seizures of the DBA2 mice were not accompanied by cerebral prostanoid synthesis. This supports the view that the pathways involved in AS are different from those involved in PTZ or ES models of epilepsy.

Acoustic Stimulation↗

PubMed1990

Regulatory proteins in presynaptic function.

Activation of alpha 2-adrenoceptors, opioid, A1-adenosine, and PGE receptors inhibited the stimulation-induced [3H]noradrenaline release in brain tissue in a concentration-dependent manner. Under experimental conditions (360 pulses/3 Hz) where the released noradrenaline activated the presynaptic alpha 2-autoreceptors, the effects of the heteroreceptor (k-opioid, A1-adenosine, PGE) agonists were decreased. By avoiding autoinhibition by either blockade of the alpha 2-autoreceptors with yohimbine or stimulating the tissue with four pulses/100 Hz, the heteroreceptor-mediated inhibition of [3H]noradrenaline release was markedly increased. The dependence of the heteroreceptor-mediated inhibition of evoked noradrenaline release on the extent of alpha 2-autoreceptor activation suggests a common postreceptor signal transduction pathway. PTX-catalyzed [32P]ADP ribosylation of synaptosomal membrane proteins revealed three bands of polypeptides with molecular weights corresponding to the alpha subunits of Go (39,000) and the Gi proteins (40,000, 41,000). Pretreatment with NEM reduced the PTX-induced 32P labeling by alkylating the alpha subunits at or near the site that is ADP ribosylated by PTX in a concentration-dependent manner. K(+)-evoked release of [3H]noradrenaline from synaptosomes indicated the presynaptic localization of the PTX-sensitive G proteins coupled to alpha 2-, k-, and A1-receptors of noradrenergic nerve terminals. Electrically evoked [3H]noradrenaline release was only increased by PTX or NEM in a time- and concentration-dependent manner when autoinhibition was present. The alpha 2-, opioid, and A1-adenosine receptor-mediated inhibition of [3H]noradrenaline release was impaired similarly by PTX or NEM treatment. In contrast, the inhibitory effect of PGE2 remained unaffected. These results indicate that presynaptic alpha 2-, opioid, and A1-receptors but not PGE receptors of noradrenergic nerve terminals are linked to PTX-sensitive G proteins. The interaction between the alpha 2-autoreceptors and the PGE receptors therefore does not occur at the level of a common pool of G proteins but at some subsequent step of the signal transduction mechanism.

Animals↗

PubMed1990

Characterization of cysteinyl-leukotriene formation in primary astroglial cell cultures.

The formation and composition of cysteinyl-leukotrienes (LT) in primary astroglial cell cultures prepared from newborn rat brain has been studied. Small amounts of cysteinyl-LT determined in terms of LTC4-like material in the supernatants of the cultures, became detectable after stimulation of the cells with 10(-5) M ionophore A23187. Cysteinyl-LT formation increased with time, reaching about 600 pg (mg protein)-1 after 60 min incubation. In contrast, considerable thromboxane (TX) B2 synthesis was found at 5 min following A23187-stimulation (about 30 ng TXB2 (mg protein)-1). The synthesis of cysteinyl-LT was abolished by 5 x 10(-5) M nordihydroguaiaretic acid (NDGA). Irrespective of the duration of incubation, blockage of prostanoid synthesis by 10(-6) M indomethacin did not result in increased cysteinyl-LT production. Reversed phase HPLC combined with radioimmunological detection showed that, after 60 min incubation in the presence of A23187, LTC4 and LTD4 accounted for practically all the LTC4-like immunoreactive material in the supernatants of cell cultures. No significant amounts of LTE4 could be detected. The results show that astrocytes may contribute to brain LTC4 and LTD4 synthesis. However, the cellular site of cerebral LTE4 formation seems to be other than the astroglia.

Animals↗

PubMed1989

3,4-Diaminopyridine-induced noradrenaline release from CNS tissue as a model for action potential-evoked transmitter release: effects of phorbol ester.

We used rabbit hippocampus slices preincubated with [3H]noradrenaline (NA) and applied short pulses of 3,4-diaminopyridine (3,4-DAP) during superfusion to investigate the mechanism underlying the 3H overflow evoked by 3,4-DAP and the effects of the protein kinase C (PKC) activator, 4 beta-phorbol 12,13-dibutyrate (PDB), in this model. The 3H overflow evoked by 200 microM 3,4-DAP (about 4-5% of tissue-tritium) was largely Ca2+-dependent, tetrodotoxin-sensitive and markedly reduced by clonidine, but it was enhanced by yohimbine. We also demonstrated that the response could be inhibited via presynaptic adenosine (A1-) and opioid (kappa-) receptors. PDB (1 microM) markedly increased the 3,4-DAP-evoked 3H overflow, its effect being almost unchanged following activation of presynaptic alpha 2-, A1- or kappa-receptors. Inhibitors of PKC (polymyxin B, staurosporine) almost abolished the 3,4-DAP-evoked 3H overflow and antagonized the effects of PDB. It is concluded that application of 3,4-DAP (200 microM for 2 min) to brain slices leads to depolarization of the neuronal membrane, Na+ current-carried action potentials, Ca2+ influx and the exocytotic release of NA, which in many aspects resembles the release evoked by electrical field stimulation. The findings with phorbol ester further support the involvement of PKC in transmitter release. Activation of PKC apparently does not directly interfere with signal transduction mechanisms of presynaptic inhibitory receptors on noradrenergic nerve terminals.

4-Aminopyridine↗

PubMed1989

Effects of botulinum A toxin on presynaptic modulation of evoked transmitter release.

A possible influence of botulinum A toxin on the modulation of evoked neurotransmitter release was investigated in hippocampus tissue. Rabbit hippocampal slices prelabelled with [3H]noradrenaline ([3H]NA), [3H]5-hydroxytryptamine ([3H]5-HT) or [3H]choline were superfused with physiological medium and were stimulated electrically during superfusion. The evoked release of [3H]NA, [3H]5-HT and [3H]acetylcholine [( 3H]ACh) was inhibited by botulinum A toxin in a concentration- and time-dependent manner. Neither the inhibition of release of [3H]NA and [3H]5-HT by the alpha 2-adrenoceptor agonist clonidine nor facilitation of release in the presence of alpha 2-antagonists were influenced by pretreatment of the tissue with botulinum toxin. The toxin caused no [32P]ADP ribosylation of synaptosomal proteins of hippocampus. The facilitation of the stimulation-induced [3H]NA and [3H]5-HT release by the specific protein kinase C (PKC) activator 4 beta-phorbol-12,13-dibutyrate (PDB) was significantly diminished by botulinum A toxin. These results show that the evoked transmitter release is inhibited by botulinum A toxin by a mechanism which does not involve ADP ribosylation or an interaction with the alpha 2-adrenoceptor mechanism.

Acetylcholine↗

PubMed1989

Endogenous noradrenaline impairs the prostaglandin-induced inhibition of noradrenaline release.

The effects of prostaglandin E2 (PGE2) on electrically evoked noradrenaline release in rat brain cortex were studied under conditions under which autoinhibition of release was avoided. When stimulation was carried out with 36 pulses at 3 Hz, 1 mumol/l PGE2, produced about 50% inhibition of release. In the presence of the alpha 2-adrenoceptor antagonist yohimbine (1 mumol/l) the effect of PGE2 was markedly increased. When release was elicited by 3 pulses/100 Hz the period of stimulation was too short to permit development of autoinhibition by released noradrenaline. Then the concentration-response-curve for PGE2 was very similar to that obtained under the above conditions (36 pulses/3 Hz, in the presence of yohimbine). These data suggest that both the alpha 2-adrenoceptor and the PGE2-receptor are linked to a common pathway. Since indometacin (10 mumol/l) did not enhance evoked transmitter release, an influence of endogenous PG's on in vitro release of noradrenaline from rat brain cortex slices can be excluded.

Animals↗

PubMed1989

A role for protein kinase C in the electrically evoked release of [3H] gamma-aminobutyric acid in rabbit caudate nucleus.

A possible participation of protein kinase C (PKC) in depolarization-induced release of gamma-aminobutyric acid (GABA) in rabbit caudate nucleus was examined by means of phorbol esters and staurosporine. Slices of caudate nucleus were loaded with [3H]GABA, then superfused and stimulated electrically (3 ms, 5 Hz, 24 mA, 5 V/cm) for 2 min. Aminooxyacetic acid and the uptake inhibitor nipecotic acid were present throughout. The PKC activator 4 beta-phorbol 12,13-dibutyrate (4 beta-PDB) markedly enhanced the evoked [3H]GABA release. In contrast, its biologically inactive isomer, 4 alpha-PDB, did not facilitate transmitter release. Staurosporine, an inhibitor of PKC, diminished [3H]GABA release and counteracted the effects caused by 4 beta-PDB. The above results suggest a participation of PKC in depolarization-induced GABA release in rabbit caudate nucleus. The mechanism underlying the modulation of GABA release by PKC seems to be independent of presynaptic GABA, dopamine and 5-hydroxytryptamine receptors.

Alkaloids↗

PubMed1989

Presynaptic kappa-opioid receptors on noradrenergic nerve terminals couple to G proteins and interact with the alpha 2-adrenoceptors.

Stimulation-induced noradrenaline (NA) release in rabbit hippocampus is inhibited by activation of presynaptic alpha 2-adrenoceptors and kappa-opioid receptors. The purpose of the present study was to investigate (a) an interference between the alpha 2- and kappa-mechanisms, and (b) a coupling of the opioid receptors to pertussis toxin (PT)-sensitive guanine nucleotide-binding proteins (G proteins), as has been previously shown for the alpha 2-receptors. [3H]NA release from hippocampal slices was evoked by electrical field stimulation (360 pulses/3 Hz). Inhibition of stimulation-evoked NA release by the preferential kappa-receptor agonist ethylketocyclazocine (EKC) was increased in the presence of the alpha 2-adrenoceptor antagonist yohimbine (0.1 or 1.0 microM). When autoinhibition was completely removed, EKC (1 microM) almost abolished transmitter release. Pretreatment of hippocampal tissue with either PT (8 micrograms/ml; 18 h) or N-ethylmaleimide (NEM) (30 microM; 30 min), which has been shown to alkylate PT substrates, diminished the EKC-produced inhibition of NA release. The kappa-mechanism was still impaired by these compounds when the alpha 2-receptors were blocked with yohimbine. An effect of NEM on the active site of the kappa-receptor seems to be unlikely, because NEM diminished the EKC-induced inhibition of release irrespective of whether or not the opioid receptor was occupied by EKC during exposure to NEM. The present results suggest an interference of both alpha 2- and kappa-opioid receptor-coupled signal transduction possibly through competition for a common pool of G proteins.

Animals↗

PubMed1989

Formation and function of eicosanoids in the central nervous system.

Neuronal firing during experimental convulsions triggered a large increase in brain eicosanoid synthesis. Mature astrocytes are an important source of cerebral prostanoids. Endogenously formed prostaglandins possess anticonvulsive properties of biological relevance. These conclusions suggest new ideas that might explain the formation and functions of prostanoids in the brain. First, as augmented neuronal discharge is a prerequisite for enhanced prostanoid synthesis during seizures, a functional coupling between firing neurons and prostanoid-forming astrocytes may be expected. Second, the anticonvulsive effects of endogenous prostanoids suggest that astroglia-derived substances might regulate neuronal activity. The phenomenon of convulsion-induced prostanoid synthesis may, therefore, represent a new example of neuron-glia interaction. Neither K+-induced membrane depolarization nor receptor activation by drugs with affinity to alpha or beta adrenoceptors, dopamine, serotonin, muscarine, histamine, GABA, glutamate, aspartate, adenosine, and opioid receptors evoked eicosanoid synthesis in astrocytes. The only physiologically relevant ligand that induced prostanoid synthesis concentration dependently in astrocytes was ATP and related nucleotide triphosphates, as well as nucleotide disphosphates. In peripheral nerves ATP serves as a cotransmitter. The effect of the P2 agonists was reduced by pertussis toxin. The mechanism by which eicosanoids regulate neuronal activity remains to be elucidated.

Animals↗

PubMed1988

Phorbol ester-mediated enhancement of hippocampal noradrenaline release: which ion channels are involved?

Enhancement of neurotransmitter release following phorbol ester-induced activation of protein kinase C (PKC) may be mediated by changes in ion conductance through the presynaptic membrane. This question was studied with rabbit hippocampal slices preincubated with [3H]noradrenaline ([3H]NA). NA release was evoked by pulses of either high K+ or Ca2+ (in the presence of high K+), or by electrical field stimulation. 4 beta-Phorbol 12,13-dibutyrate (PDB) increased and polymyxin B (PMB) reduced the K+-evoked NA release independent of the K+ concentration used for depolarization. The effects of PDB and PMB were not reduced by tetrodotoxin. PDB still enhanced the NA release triggered by short Ca2+ pulses in depolarized, axon terminal membranes (30 mM K+ and no Ca2+). The electrically evoked NA release was markedly enhanced by PDB even in the absence of Cl- in the medium or in the presence of the K+ channel blockers, tetraethylammonium, 4-amino- and 3,4-diaminopyridine. The inhibitory effect of the Ca2+ channel blocker, Cd2+, remained almost unchanged in the presence of PDB. It is concluded that PKC activation facilitates NA release in the hippocampus but not via presynaptic changes in Na+, K+ or Cl- currents. Whether phorbol ester mediates an increased intracellular Ca2+ availability, or whether a triggering 'normal' Ca2+ influx simply initiates, and synergistically supports, the PKC-mediated reactions leading to enhanced exocytosis, cannot be decided from the results of the present experiments.

Animals↗

PubMed1988

Omega-conotoxin GVIA and pharmacological modulation of hippocampal noradrenaline release.

The tritium overflow evoked by electrical stimulation of rabbit hippocampal slices labeled with [3H]noradrenaline was inhibited by omega-conotoxin GVIA, a peptide modulator of the N-type voltage-sensitive calcium channel (N-VSCC). The magnitude of this inhibition was unchanged in the presence of substances which interact with N- and/or L-VSCCs (cadmium, neomycin, (-)- and (+)-202-791), alpha 2-adrenoceptors (idazoxan, UK-14304), protein kinase C (4 beta-phorbol-12,13-dibutyrate) or potassium channels (4-aminopyridine). This finding suggests that the attenuation of calcium-dependent neurotransmitter release by omega-conotoxin GVIA is relatively insensitive to alterations of such release effected by other substances.

Aminopyridines↗

PubMed1988

P2-purinoceptor induced prostaglandin synthesis in primary rat astrocyte cultures.

Adenosine triphosphate (ATP) is one of the cotransmitters that are commonly released at catecholaminergic and cholinergic nerve terminals. The glial cell type most closely associated with the synapse is the astrocyte and, thus, is the next cellular element beside the postsynaptic neuron to face the transmitters released. This report gives evidence of P2-purinoceptors on cultured astroglial cells. Upon stimulation with nucleoside triphosphates and nucleoside diphosphates, the cells respond with synthesis of prostaglandins of the D2 type, which is the predominant prostaglandin made in rat brain. Nucleoside triphosphate analogues, such as 5'-adenyl-imido diphosphate, beta,gamma-methylene, or alpha,beta-methylene ATP were less effective than ATP or its non-hydrolysable analogue ATP [gamma S]. The receptor was desensitized by ATP [gamma S] within 15 min, whereas desensitization by alpha,beta-methylene ATP was significantly delayed. 8-phenyl-theophylline (10(-4) M) had no influence on ATP-stimulated prostaglandin synthesis. Adenosine 5'-monophosphate (AMP) and adenosine were unable to stimulate prostaglandin D2 formation. According to the common nomenclature for purinoceptors, the described astroglial receptor would fulfill the characteristics of a P2-purinoceptor. Furthermore, it is shown that pertussis toxin sensitive G-proteins influence some early step in prostaglandin synthesis. The inactivation of these proteins results in reduced prostaglandin formation. It is assumed that ATP serves as an important mediator in the cross-talk between neurons and astroglial cells at the synaptic cleft.

Adenosine Triphosphate↗

PubMed1988

Intrastriatal dopaminergic grafts restore inhibitory control over striatal cholinergic neurons.

The aim of the study was to examine the influence of intrastriatal dopaminergic grafts on the functioning of striatal cholinergic neurons using an in vitro superfusion method. Rats bearing unilateral 6-hydroxydopamine lesion of the nigrostriatal dopaminergic system received a cell suspension obtained from ED 14 rat embryonic mesencephali which was injected into the denervated striatum. Lesioned animals displayed an ipsilateral rotation in response to amphetamine (5 mg/kg i.p.). This rotational response disappeared following grafting and there was even a significant contralateral rotation in response to the drug. Apomorphine (0.1 mg/kg s.c.) induced a contralateral rotation following the lesion. This latter response was attenuated in the grafted group. Three months after grafting 350 microns thick slices were prepared from striata from the control and experimental sides of lesioned and graft-bearing animals. The slices were preincubated either with 3H-dopamine (10(-7) M) or 3H-choline (10(-7) M) and then superfused with an oxygenated Krebs-Ringer solution. Stimulation with electrical pulses following preincubation with 3H-dopamine elicited a marked increase of tritium outflow from control slices. Stimulation-evoked overflow was of similar magnitude from slices from striata containing the graft, while it was much reduced in slices from lesioned striata. Amphetamine markedly potentiated the effect of electrical stimulation in slices obtained from control and graft-containing striata. Nomifensine (a dopamine uptake blocker) led to a significant decrease of the overflow of 3H-acetylcholine evoked by electrical stimulation from control striatal slices. This inhibition was antagonized by domperidone, a D2 dopamine receptor blocker, a finding which indicates that the action of nomifensine was indeed due to a potentiation of the action of endogenous dopamine released by the electrical stimulation. A similar, although somewhat attenuated, action of nomifensine and domperidone was observed for striatal slices containing the graft. Amphetamine inhibited the stimulation evoked overflow of 3H-acetylcholine in a dose-dependent manner from striatal slices obtained both from the intact and experimental sides of graft-bearing animals, while it had no action on slices from denervated striata. Finally, the dose-response curve for the inhibition of 3H-acetylcholine release by apomorphine was significantly shifted to the left for slices from the lesioned striata as compared with control slices. This leftward shift was totally abolished in the slices from the graft-containing striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗

PubMed1988

Participation of protein kinase C and regulatory G proteins in modulation of the evoked noradrenaline release in brain.

1. In the present paper two questions are discussed: (A) Does protein kinase C (PKC) participate in the modulation of evoked noradrenaline release in brain tissue? and (B) Is there any link between presynaptic alpha 2-adrenoceptors and regulatory G proteins? 2. Slices of the middle part of the rabbit hippocampus, labeled with 3H-noradrenaline, were superfused with medium containing the reuptake inhibitor cocaine. During superfusion the tissue was stimulated twice electrically for 2 min each. 3. The PKC activators 4 beta-phorbol 12,13-dibutyrate (4 beta-PDB) and 12-O-tetradecanoyl phorbol 13-acetate (TPA) increased the stimulation-evoked transmitter release in a concentration-dependent manner. 4 alpha-PDB and 4-O-methyl-TPA, which do not activate PKC, were without effect on transmitter release. Polymyxin B, an inhibitor of PKC, diminished the stimulus-evoked overflow and counteracted the effects of the phorbol esters. The increases in release caused by phorbol esters and the alpha 2-adrenoceptor antagonist yohimbine were additive. 4. Treatment of hippocampal tissue with islet-activating protein (IAP) or N-ethylmaleimide (NEM), both known to inactivate the regulatory G proteins Gi and Go by chemical modification, led to a marked increase in evoked noradrenaline release. In addition, the effects of both the alpha 2-adrenoceptor agonist clonidine and the alpha 2-adrenoceptor antagonist yohimbine were inhibited. 5. The facilitatory effects of IAP and NEM on transmitter release were not additive. In synaptosomes prepared from rabbit hippocampus two polypeptides with molecular weights corresponding to those of alpha i and alpha o were 32P-ADP-ribosylated with IAP. Pretreatment of synaptosomes with NEM reduced the subsequent ADP ribosylation by IAP concentration dependently. 6. The above results suggest that PKC is involved in the modulation of noradrenaline release in the rabbit hippocampus. The presynaptic alpha 2-autoreceptors modulate transmitter release by a mechanism which is not directly affected by PKC. The alpha 2-autoreceptor-mediated signals seem to be transduced across the plasma membrane via regulatory G proteins.

Adenylyl Cyclases↗