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We have shown earlier that nicotinic agonists induce the release of noradrenaline from chick sympathetic neurons in culture in two ways: (a) by activating the postsynaptic nicotinic receptors on nerve cell bodies, giving rise to spreading electrical activity and opening of voltage operated calcium channels in neuronal processes; (b) by activating the presynaptic nicotinic receptors on neuronal processes. In the present work, we investigated the contribution of various pathways to the observed Ca 2+ influx and subsequent noradrenaline release. Sympathetic neurons in culture were stimulated either by the nicotinic agonist dimethylphenylpiperazinium or electrically, in the presence or absence of tetrodotoxin and of specific blockers of calcium or nicotinic channels, and the effects on [Ca 2+ ] i in the area of neuronal processes and on noradrenaline release were measured. Under control conditions, the N-type channel blocker ω-conotoxin (0.1 μmol/1) diminished the release of noradrenaline and the increase of intraterminal Ca 2+ by 48% and 55%, respectively, whereas the L-type channel blocker (+)Bay k 8644 (1 μmol/1) diminished the release of noradrenaline by 25% and the increase of [Ca 2+ ] i by 39%. The P-type channel blocker ω-agatoxin (0.3 μmol/1) had no effect. The effects of the L-type channel ligands were complex and could only be explained on the assumption that, at high concentrations, these drugs also act as nicotinic antagonists. Tetrodotoxin blocked the Ca 2+ response evoked by electrical stimulation whereas DMPP applied in the presence of tetrodotoxin still evoked an increase of [Ca 2+ ] i and the release of noradrenaline (27% and 30% of control without tetrodotoxin, respectively). These residual responses were not blocked by any of the calcium channel blockers used or by their combination. Apparently, a substantial part of the influx of Ca 2+ induced by the activation of presynaptic nicotinic receptors is not carried by the N-, L- or P-type channels and probably occurs directly via the open channels of nicotinic receptors.

We have investigated the participation of the N-type (omega-conotoxin GVIA-sensitive) and L-type (nifedipine-sensitive) calcium channels in the alpha 2-adrenoceptor mediated autoinhibition of the release of [3H]noradrenaline from chick sympathetic neurons in culture. Blockade of 3,4-diaminopyridine-sensitive potassium channels resulted in tetrodotoxin-sensitive and calcium-dependent increase of the release of [3H]noradrenaline evoked by electrical stimulation. Nifedipine attenuated the evoked release under control conditions by 20%, but in the presence of 3,4-diaminopyridine by 51%, while omega-conotoxin decreased the release under control conditions by 87% and in the presence of 3,4-diaminopyridine by only 43%. The L-type calcium channel activator Bay k 8644 increased the evoked release of the transmitter both in the absence and in the presence of 3,4-diaminopyridine. Under control conditions, the alpha 2-adrenoceptor agonist UK 14304 decreased the evoked release by 57% and the alpha 2-adrenoceptor antagonist rauwolscine increased it by 14%. Nifedipine did not prevent this modulation. In the presence of 3,4-diaminopyridine, UK 14304 lost its effect on the release of noradrenaline, but its inhibitory action was restored when nifedipine, but not omega-conotoxin, was added. Changes in the increase of intracellular calcium concentration ([Ca2+]i) evoked by electrical stimulation, measured in the cell processes by microfluorimetry, paralleled the changes in the release of [3H]noradrenaline. Under control conditions, nifedipine attenuated the rise of intracellular calcium by only 16%, while omega-conotoxin did so by 66%. 3,4-Diaminopyridine enhanced the evoked rise of [Ca2+]i; in its presence the rise of intracellular calcium was about equally reduced by nifedipine and omega-conotoxin (by 46 and 36%, respectively). These effects were additive. UK 14304 diminished the peak concentration of [Ca2+]i elicited by the standard electrical stimulation by 31% and rauwolscine antagonised this effect. UK 14304 did not measurably inhibit the stimulation-evoked rise of intraterminal [Ca2+]i in the presence of 3,4-diaminopyridine but it produced an inhibition by 26% if nifedipine had been applied together with 3,4-diaminopyridine. Our observations show that, under control conditions, the stimulated release of [3H]noradrenaline is mainly associated with the opening of N-type channels, while in the presence of 3,4-diaminopyridine the contribution of L-type channels becomes more important. The alpha 2-adrenoceptor stimulation by UK 14304 inhibits the release of [3H]noradrenaline but, in the presence of 3,4-diaminopyridine, the inhibition of release can only be observed if the massive influx through L-type calcium channels is prevented. These data suggest that presynaptic alpha 2-adrenoceptors of chick sympathetic neurons preferentially influence the N-type calcium channels.

Long-term behavioral and neurochemical effects of bilateral lesions to only the infracallosal component of the "so-called" septohippocampal pathways (cingular bundle, fimbria and fornix) have not been assessed. This experiment compared the behavioral, histochemical and neurochemical effects of supracallosal (SUPRA; cingular bundle) and infracallosal (INFRA; fimbria-fornix) hippocampal denervations in Long-Evans female rats. The rats were tested, over two periods (8-52 and 92-170 days postlesion), for open field locomotion, spontaneous alternation and radial-maze performance. Subsequently, histochemical or neurochemical determinations of cholinergic, serotonergic and noradrenergic hippocampal innervations were performed using acetylcholinesterase-staining, determination of high-affinity synaptosomal uptake of choline and serotonin, and measurement of hippocampal serotonin and noradrenaline concentrations by HPLC methods. Whatever behavioral test was considered, no significant effect was found in rats with SUPRA lesions, whereas rats with INFRA lesions were permanently impaired in all tests. Histochemical and neurochemical analyses showed hippocampal cholinergic as well as serotonergic markers to be substantially decreased in INFRA rats as compared to SHAM and SUPRA rats. The SUPRA rats exhibited a weak but significant reduction of both serotonergic and noradrenergic markers compared to SHAM and INFRA rats. These results suggest that lesions limited to the infracallosal pathway induce a hippocampal denervation sufficient to account for most of the behavioral, histochemical and neurochemical deficits classically reported following extensive lesions of the anterior hippocampal connections. Since the behavioral and neurochemical deficits were found to be lasting, it is suggested that bilateral infracallosal damage to the septohippocampal pathways might constitute an interesting paradigm of partial hippocampal deafferentation to investigate the effects of neural grafts or other treatments in an animal model of Alzheimer's disease.

3t 31 days of age, Long-Evans female rats sustained aspirative lesions of the septohippocampal pathways and, 14 days later, received intrahippocampal suspension grafts prepared from the region including the medial septum and the diagonal band of Broca (Group S, n = 11), from the region including the mesencephalic raphe (Group R, n = 11) or from both regions together (Group S + R, n = 11). Sham-operated (Group Sham, n = 9) and lesion-only (Group Les, n = 11) rats served as non-grafted controls. Seven Sham, 7 Les and 8 rats from each transplant group were tested for home cage activity (6 months after grafting) and radial maze performance (between 7.5 and 8.5 months post-grafting). One month after completion of behavioral testing, the dorsal hippocampi of these rats were prepared for measuring choline acetyltransferase (ChAT) activity and high affinity synaptosomal uptake of both [ 3 H]choline and [ 3 H]serotonin. The remaining rats were used for histological verifications on brain sections stained for acetylcholinesterase (AChE). The lesions increased locomotor activitu, impaired radial maze learning and, in the dorsal hippocampus, reduced AChE positive staining, decreased ChAT activity (−73%) as well as high affinity uptake of both choline (−81%) and serotonin (−82%). Neither type of transplant produced any significant behavioral recovery. However, septal transplants increased hippocampal AChE positivity, restored ChAT activity and enhanced choline uptake to 116% and 70% of the values found in sham-operated rats, respectively; they had no significant effect on uptake of serotonin. Transplants from the raphe region had weak affects on hippocampal AChE positivity, increased both the ChAT activity and the choline uptake to 70% ad 38% of sham-operated rats, respectively, and produced an (over)compensation of the serotonin uptake which reached 324% of the values found in sham-operated rats. The co-transplantation of both regions resulted in restoration of ChAT activity (113% of sham-operated rats values), choline uptake (83% of sham-operated rats) and serotonin uptake (129% of sham-operated rats). Our neurochemical data show that after extensive denervation of the hippocampus, intrahippocampal grafts of fetal neurons may foster a neurotransmitter-specific recovery which depends upon the anatomical origin of the grafted cells; a graft rich in serotonergic neurons overcompensates the serotonergic deficit, a graft irich in cholinergic neurons attenuates the cholinergic deficit, whereas a mixture of both types of grafts produces recovery from both types of deficits. Thereby, both the feasibility and the interest of the co-grafting technique are confirmed. However, our behavioral data also suggest that separate or combined attenuation of the lesion-induced cholinergic and serotonergic deficits in the dorsal hippocampus does not seem to be a sufficient condition to induce attenuation of the lesion-induced behavioral deficits (hyperactivity, impaired memory).

The effect of the α2-adrenoceptor agonist clonidine on 3,4-diaminopyridine (3,4-DAP)-evoked [3H]noradrenaline ([3H]NA) release in rat hippocampus slices was studied in the presence or absence ( + 1 mM EGTA) of extracellular Ca2+. 3H overflow (consisting mainly of unmetabolized [3H]NA) was evoked by addition of 100 μM 3.4-DAP for 10 min to the medium, which always contained 1 μM desipramine. Ligands for L-type voltage-sensitive Ca2+ channels (VSCC) did not affect and evoked [3H]NA release, whereas the preferential N-type VSCC antagonist ω-conotoxin was inhibitory, both in the presence and even more potently in the absence of Ca2+, suggesting an involvement on N-type VSCC in the mechanism of 3,4-DAP-evoked [3H]NA release. In the absence of extracellular Ca2+ the initial influx, which has been previously proposed to liberate Ca2+ from intracellular stores for the exocytotic process, most probably occurs via N-type VSCC. Clonidine inhibited the 3,4-DAP-evoked [3H]NA release in a concentration-dependent manner, both in the presence and even more potently in the absence of Ca2+: its effects were antagonized by yohimbinc. In the presence of extracellular Ca2+ the clonidine effect was not changed by addition of ω-conotoxin. Similar effects of clonidine were found in slices from the rabbit hippocampus. Since the availability of Ca2+ from intracellular stores seems to predominate in the present model, our results lend some support to the suggestion that α2-adrenoceptor activation might affect intracellular mechanisms of Ca2+ homeostasis. On the other hand, however, the present data cannot completely exclude that α2-autoreceptor activation leads to opening of presynaptic K+ channels, or that modulation of Ca2+ influx through VSCC is involved.

Effects of aspirative fimbria-fornix lesions and intrahippocampal grafts of fetal septal-diagional 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.

The release of tritiated noradrenaline, evoked by stimulation of rat hippocampus slices with 3,4-diaminopyridine (200 microM, 2 min), was enhanced by the nitric oxide (NO) synthase substrate, L-arginine (but not by D-arginine), by NO donors (sodium nitroprusside, 3-morpholino-sydnonimine), and by 8-Br-cGMP. The effect of L-arginine was stereospecifically antagonized by NG-nitro-L-arginine, which given alone was inhibitory. From these findings we conclude that endogenously formed NO facilitates 3,4-diaminopyridine-evoked noradrenaline release in rat hippocampus.

The arachidonic acid (AA) metabolites prostaglandin D2 (PGD2), prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha) and thromboxane B2 (TXB2) were measured in the dorsal hippocampus, amygdala/pyriform cortex and parietal cortex of the rat brain following the application of kainic acid (KA, s.c. 10 mg/kg). The first significant increases in the prostanoids were seen 10 min following the KA injection, at this time the first behavioral change 'staring' was observed. In the hippocampus the highest concentrations of the PGs were reached 30 min after the injection of the neurotoxin. At this time frequent wet dog shakes (WDS) and rare focal convulsions effecting head and extremities occurred. In the amygdala/pyriform cortex and parietal cortex the maximal prostanoid formation was seen after 120 min. At this time tonic clonic seizures were registered. In contrast to other seizure models, where PGD2 was the predominant prostanoid formed, PGF2 alpha was the major AA-metabolite found in KA-treated animals. From the time-course of the seizure-related behavior and the increased prostanoid synthesis we conclude that the initiation of the prostanoid synthesis was triggered by the increased neuronal activity rather than by cell damage.

Seizures were induced in a strain of epileptic gerbils by moderate environmental stress. Concentrations of five different cyclooxygenase products (PGD2, PGF2 alpha, PGE2, 6-keto-PGF1 alpha and thromboxane B2) were measured in brain by specific radioimmunoassays before and at different time intervals after the onset of clonic-tonic convulsions. All prostanoids markedly increased subsequent to the convulsions. Maximal concentrations were reached after about 15 min. The major compound detected was PGD2, followed by PGF2 alpha and lower concentrations of the other cyclooxygenase products. Indomethacin completely prevented the convulsion-induced formation of prostanoids. Fifteen min after a first seizure almost all animals proved to be protected against a second convulsion. Indomethacin pretreatment markedly reduced the number of convulsion-resistant animals. These findings are compatible with the hypothesis that endogenous prostaglandins exert anticonvulsive effects.

The presence (1) and synthesis of prostanoids under in vitro (2–10) and in vivo (11–15) conditions has been well established in the CNS of several species including man (16). These results, however, do not permit to draw conclusions on the neuronal or extraneuronal origin of prostanoids, except for prostaglandin (PG) I 2 , shown to be formed principally in blood vessels (6, 16, 17). Informations on their site of origin may be helpful to better understand the role of PGs and thromboxane (TX) in the CNS. As a model to examine the involvement of neuronal and/or glial elements in brain PG and TX biosynthesis we have chosen primary brain cultures. In this communication, we report on our first results concerning prostanoid formation in homogenates of primary neuronal and astroglial cell cultures.

The tritium overflow evoked by electrical stimulation of rabbit hippocampal slices labeled with [3H]noradrenaline was inhibited by ω-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), α 2 - adrenoceptors (idazoxan, UK-14304), protein kinase C (4β-phorbol-12,13-dibutyrate) or potassium channels (4-aminopyridine). This finding suggests that the attenuation of calcium-dependent neurotransmitter release by ω-conotoxin GVIA is relatively insensitive to alterations of such release effected by other substances.

Using newly developed radioimmunoassays for 6-keto-prostaglandin F1α and 6,15-diketo-13,14-dihydro-prostaglandin F1α, the plasma concentrations of these two prostacyclin derivatives were measured in anaesthetized cats. After the administration of angiotensin II, which releases prostacyclin into the circulation, concentrations of both derivatives rose simultaneously, the major immunoreactivity being 6,15-diketo-13,14-dihydro-prostaglandin F1α. Angiotensin II-induced prostacyclin release was not caused by vasoconstriction alone, since comparable vasopressor responses to noradrenaline and vasopressin were not accompanied by increases in prostacyclin plasma levels. Injection of exogenous prostacyclin resulted in a shortlasting peak of 6-keto-prostaglandin F1α, which rapidly declined ( t 1 2 : 1.29–1.52 min ). 6,15-diketo-13,14-dihydro-prostaglandin F1α appeared with a t 1 2 of 0.48–1.38 min and was eliminated with a t 1 2 of 8.0–9.0 min . Due to its longer half-life in the circulation 6,15-diketo-13,14-dihydro-prostaglandin F1α again was the predominant derivative after 3 min. These data suggest that in vivo prostacyclin is mainly inactivated by the 15-hydroxy-PG-dehydrogenase-, Δ13-reductase-pathway, rather than by hydrolysis. Therefore, 6,15-diketo-13,14-dihydro-prostaglandin F1α seems to be a better indicator or prostacyclin plasma levels than 6-keto-prostaglandin F1α, although under certain conditions the additional determination of this product of hydrolysis can be valuable.

Administration of prostaglandin D 2 (PGD 2 ) ) into the left lateral cerebral ventricle (i.c.v.) of urethane anaesthetized rats caused increases in blood pressure, heart rate and body temperature. Pretreatment of the animals with the α-receptor blocking drug prazosin completely prevented thePGD 2 -inducedrrise in blood pressure,but did notaffect the chronotropic and hyperpyrexic effects of PGD 2 . Pretreatment of the rats. with the β-receptor blocking drug propranoloi completely suppressed the increase in heart rate, augmented the rise in blood pressure, but reduced the temperature increase by more than 50%. These data indicate that central activation of the sympathetic nervous system mediates the cardiovascular and important parts of the temperature effects of i.c.v.-injected PGD. The peripheral vasoconstriction (due to the stimulation of sympathetic, α-receptors) causing the blood pressure increase is obviously of minor importance for the rise in body temperature. In contrast the enhanced production of heat by several organs following β-receptor activation seems to be an important factor for the temperature increase.

Slices of rabbit or rat brain cortex were preincubated with [3H]noradrenaline, and slices of rabbit caudate nucleus or rat stratum with [3H]dopamine. The slices were then superfused and stimulated electrically. In rat cortex slices, PGE2 (0.01-1 millimicronmol/l) markedly reduced the stimulation-evoked overflow of tritium. PGF2alpha (1 millimicronmol/l) caused a slight decrease only after the formation of endogenous prostaglandins had been blocked by indomethacin. PGD2 (1 millimicronmol/l) had no effect. In slices of rabbit cortex and caudate nucleus as well as in rat striatal slices, none of the prostaglandins (1 millimicronmol/l) caused any change, irrespective of whether the production of endogenous prostaglandins was intact or blocked. The results show that, of three major prostaglandins that occur in the brain, only PGE2 is a potent presynaptic inhibitor of noradrenaline release in the rat. The catecholamine neurones of rabbit brain, and the dopamine neurones of rat striatum, are resistant to these prostaglandins.

The metabolism of endogenous PGI 2 (released by angiotensin II or bradykinin) and exogenous PGI 2 by 15-hydroxy-PG-dehydrogenase and Δ 13 -reductase was studied in five different vascular beds of the anaesthetized cat. Plasma concentrations of 6-keto-PGF 1α (the product of spontaneous hydrolysis of PGI 2 ) and 6,15-diketo-13,14-dihydro-PGF 1α (the metabolite formed from PGI 2 by 15-hydroxy-PG-dehydrogenase and Δ 13 -reductase) were determined in the efferent vessels of the respective vascular beds by specific radioimmunoassays. No major metabolism of PGI 2 by 15-hydroxy-PG-dehydrogenase and Δ 13 -reductase was detected in the head and the hindlimbs of the cat. In the lung exogenous (circulating) PGI 2 was not metabolized, whereas PGI 2 synthetized in the lung itself was converted to 6,15-diketo-13,14-dihydor-PGF 1α . No significant amounts of 6,15-diketo-13,14-dihydro-PGF 1α -immunoreactivity were detected in hepatic venous blood after infusion of PGI 2 into the portal vein. However as also no 6-keto-PGF 1α was found, the liver seems to efficiently extract PGI 2 from the circulation. The cat kidney had the highest capacity of all vascular beds investigated to release endogenous and exogenous PGI 2 as 6-15-diketo-13,14-dihydro-PGF 1α . In other organs (vascular beds) investigated PGI 2 is either metabolized less efficiently by the 15-hydroxy-PG-dehydrogenase or further transformed to other metabolites.

The effect of β-endorphin on isoprenaline-induced vasopressin release was investigated in rats. β-Endorphin (0.29 nmol i.c.v. or 2.9 nmol i.v.) suppressed markedly the increase in plasma vasopressin concentrations in response to isoprenaline without altering the concomitant increase in plasma renin concentration or fall in mean arterial blood pressure. Naloxone (1 mg/kg) prevented this inhibition as did chronic morphine pretreatment. These results show that β-endorphin can inhibit isoprenaline-induced vasopressin release by acting on opiate receptors.

Slices of hippocampus from the rabbit were preincubated with [3H]5-HT), then superfused continuously and twice stimulated electrically. The stimulation-evoked overflow of tritium was inhibited by the 5-HT autoreceptor ligands 5-carboxamido-tryptamine (5-COHT), 5-HT, 5-methoxy-N,N-dimethyl-tryptamine (5-MeOMT), (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), methysergide and (+/-)-cyanopindolol in a concentration-dependent manner. These effects were competitively inhibited by the 5-HT autoreceptor antagonists, metitepin and metergoline. (+/-)-Cyanopindolol also reduced the evoked release of 5-HT from slices of cortex from the rat. The inhibitor of the uptake of 5-HT, 6-nitroquipazine diminished the autoreceptor-mediated depression of release of 5-HT. In cortex tissue from the rat, 6-nitroquipazine reversed the decreased release of 5-HT, due to (+/-)-cyanopindolol, to a facilitation. The disinhibition of the release of 5-HT by autoreceptor antagonists was further enhanced by 6-nitroquipazine. Non-linear regression analysis of concentration-response curves for 5-COHT yielded the following pKd of endogenous 5-HT at the autoreceptor: 7.753 +/- 0.116. This value corresponds to the pKd of 5-HT at the 5-HT1B binding site. The 5-HT biophase concentration at the autoreceptor of 10(-8.220 +/- 0.132)M was markedly enhanced by 6-nitroquipazine (10(-6)M) to 10(-7.476 +/- 0.132)M. It is concluded that the 5-HT autoreceptor belongs to the 5-HT1B subtype of receptor; the corresponding 5-HT biophase concentration can be estimated quantitatively; 8-OH-DPAT decreased the evoked release of 5-HT through both 5-HT autoreceptors and alpha 2-heteroreceptors and (+/-)-cyanopindolol acts as partial agonist at the 5-HT autoreceptor.

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.

Pentobarbitone-anaesthetized cats were injected i.v. with equal doses of prostacyclin and 6-keto-PGF1 alpha. Subsequently the time course of plasma levels of 6-keto-PGF1 alpha-immunoreactivity (i.r.) and 6,15-diketo-13, 14-dihydro-PGFi alpha-i.r. was determined in arterial blood by specific radioimmunoassays. Injection of both prostacyclin and 6-keto-PGF1 alpha resulted in short lasting peaks of 6-keto-PGF1 alpha-i.r. with maxima after 1 min, which rapidly declined. After injection of prostacyclin plasma 6,15-diketo-13, 14-dihydro-PGF1 alpha-i.r. increased to about one third of the height of the 6-keto-PGF1 alpha-peak and the maximum was reached after 6 min. On the other hand after administration of the same dose of 6-keto-PGFi alpha 6,15-diketo-13, 14-dihydro-PGF1 alpha-i.r. rose to about the same level as the 6-keto-PGF1 alpha-immunoreactive peak and the maximum was already attained after 2 min. When 6,15-diketo-13, 14-dihydro-PGF1 alpha itself was injected no increase in 6-keto-PGF1 alpha-i.r. was seen, whereas the 6,15-diketo-13, 14-dihydro-PGFi alpha-i.r. markedly increased, reaching its maximum after 1 min. These data indicate that in the cat in vivo 6-keto-PGF1 alpha can be rapidly metabolized to a 6,15-diketo-13, 14-dihydro-PGF1 alpha-like compound. The smaller conversion of prostacyclin as compared to 6-keto-PGF1 alpha could be explained by differences in compartmentalization of the two prostaglandins.

12-O-Tetradecanoyl phorbol-13-acetate (TPA), an activator of protein kinase C (PKC), enhanced the electrically evoked overflow of [ 3 H]noradrenaline in a concentration-dependent manner in rabbit hippocampal slices. 4-O-Methyl-TPA, which lacks the ability to activate PKC had no effect on the evoked tritium overflow. The enhancement of noradrenaline release by TPA was affected by neither the α 2 -adrenoceptor antagonist yohimbine nor the α 2 -adrenoceptor agonist clonidine. It is concluded from these results that PKC in involved in the mechanism of stimulus-secretion coupling in noradrenergic nerve terminals of the rabbit hippocampus.

Prostaglandin (PG) and thromboxane (TX) biosynthesis in primary neuronal and astroglial cell cultures was studied. Cultures obtained from fetal (15-16 days old) and neonatal rat brain hemispheres were characterized by chemical and immunocytochemical staining techniques as predominantly neurons or mature and immature astrocytes, respectively. Six-day old neuronal cell cultures grown in the presence of cytosine arabinoside (2 ?M) from the day 3 onwards were contaminated up to 10% with glioblasts. In astroglial cultures up to 3% of the cells were postively stained with a marker for oligodendroglial cells. Fibroblast contamination was below 1% in both cultures. Prostanoid formation (measured by specific radioimmunoassays) in 6-day old neuronal cell cultures was low (sum of the amount of PGs and TX formed: 1.16 +/- 0.17 (ng/mg protein/15 min) as compared to 14-day old cultured astroglial cells: 21.27 +/- 2.53 (ng/mg protein/15 min). Also the pattern of prostanoids formed was different in neuronal (PGD(2) ? PGF(2?)TXB(2) ? PGE(2)) and astroglial cells (PGD(2)TXB(2) ? PGF(2?) ? PGE(2) ? 6-ketoPGF(1?)). Preincubation with arachidonic acid (1 ?g/ml) did not affect prostanoid formation in both cultures, whereas it was stimulated 4-6-fold by addition of the calcium ionophore A23187 (1 ?M). These results, although found on cultured neuronal and glial cells of different stages of development, support the view that astroglial cells might play a crucial role in brain prostanoid synthesis.

Basal levels of 5 cerebral prostanoids (PGD 2 , PGF 2α , PGE 2 , 6-keto-PGF 1α and throm☐ane/TX/B 2 ) were measured radioimmunologically in normal and convulsion-prone gerbils. Significantly less PGD 2 , PGE 2 and 6-keto-PGF 1α was found in the brain of seizure-sensitive animals. After treatment with indomethacin, which reduced the amount of brain cyclo-oxygenase products, also normal gerbils exhibited convulsions following environmental stress. The results are in accordance with the hypothesis that endogenous prostanoids play a role in the regulation of seizure susceptibility.