Inositol phospholipid hydrolysis in rat cerebral cortical slices: I. Receptor characterisation

Emedastine: a potent, high affinity histamine H1-receptor-selective antagonist for ocular use: receptor binding and second messenger studies

The antihistaminic agent, emedastine, was tested for its ability to compete for [3H]pyrilamine, [3H]tiotidine and [3H]N-methyl histamine binding to rodent brain H1, H2 and H3 histamine receptors, respectively. Emedastine exhibited the highest affinity for H1-receptors (dissociation constant, Ki = 1.3 +/- 0.1 nM), and was considerably weaker at H2- (K1 = 49,067 +/- 11,113 nM) and H3-receptors (Ki = 12,430 +/- 1,282 nM). These data yielded ratios of 37744, 9562 and 4 for H2:H1, H3:H1 and H2:H3 receptor affinities, respectively, thus making emedastine a very selective H1-receptor antagonist. The H1-selectivity of emedastine was considerably superior to that of pyrilamine (H2:H1, H3:H1 and H2:H3 ratios of 11887, 12709 and 1, respectively). Similarly, the respective receptor affinity ratios for ketotifen (858, 1752, 0.5), levocabastine (420, 82, 5), pheniramine (430, 312, 1), chlorpheniramine (5700, 2216, 3) and antazoline (1163, 1110, 1) showed these antihistamines to be also markedly less H1-selective than emedastine. The potency of emedastine (IC50 = 1.44 +/- 0.3 nM) for antagonizing histamine-induced phosphoinositide turnover in human trabecular meshwork cells compared well with its binding affinity at the H1-receptor. These data indicate emedastine to be a high affinity and high potency histamine antagonist with the highest selectivity for the H1-histamine receptor.

The inositol trisphosphate receptor gene family: implications for normal and abnormal brain function

1. The phosphatidyl inositol (PI) second messenger system has been extensively investigated in the past decade. This complex pathway results in the production of two second messengers, one of which, inositol 1,4,5-trisphosphate, will be the focus of this review. 2. The intracellular receptor for this second messenger (IP3R) has been purified, reconstituted and extensively characterized in both brain and peripheral tissues. 3. Localization and functional studies show that IP3 binding causes the receptor to release portions of the intracellular calcium stores. 4. Multiple modulators of the receptor have been identified, including pH, calcium concentration, adenine nucleotide concentration and phosphorylation. 5. The cDNA for this molecule has been cloned from a number of sources. Studies of the molecular structure of the receptor have revealed additional levels of complexity including multiple alternative splicing events in the initially cloned cerebellar (Type I) receptor, as well as the existence of highly related but distinct cDNAs which likely reflect a gene family. 6. There is suggestive evidence linking the PI system, and thus the IP3R, to bipolar disorder and the actions of lithium.

Effects of chronic mianserin administration on serotonin metabolism and receptors in the 5-hydroxytryptophan depression model

1. To further investigate a previous postulate that increased serotonergic activity may cause depression, the effects of chronic mianserin administration on 5-HT, its metabolites, and the subtypes of 5-HT receptors were studied. 2. The levels of 5-HT, 5-hydroxyindoleacetic acid, 5-HTP, 5-HT turnover and their response to 5-HTP administration all exhibited no change following mianserin treatment. 3. The Bmax value of the high affinity site of the 5-HT-1A receptor increased and the Bmax value of 5-HT-2 receptor decreased with no change in the low affinity site of the 5-HT-1A receptor nor in the 5-HT-1B receptor. 4. The response to 5-HTP administration showed no change in any of these receptors. 5. These results suggest that the chronic mianserin administration might block both the 5-HT-2 and 5-HT-1A receptors in the 5-hydroxytryptophan depression model.

The neuropeptide bradykinin stimulates phosphoinositide turnover in HSDM1C1 cells: B2-antagonist-sensitive responses and receptor binding studies

Bradykinin (BK) and its analogs (1 nM-100 microM) stimulated phosphoinositide (PI) turnover in murine fibrosarcoma (HSDM1C1) cells in a concentration-dependent manner. The relative potencies (EC50) were: BK = 48 +/- 4 nM; Lys-BK = 39 +/- 3 nM; Met-Lys-BK = 158 +/- 33 nM, Des-Arg9-BK = 2617 +/- 598 nM (means +/- SEM, n = 3-14). All these analogs were full agonists and they produced up to 5.4 +/- 0.4-fold stimulation of PI turnover at the highest concentration (10-100 microM) of the peptides. In contrast, the analogs [D-Arg0-HYP3-Thienyl5,8-D-Phe7]-BK (HYP3-antagonist), [D-Arg0-HYP3-Thienyl,5,8-D-Phe7]-BK (Thienyl antagonist) and Des-Arg9-Leu8-BK were inactive, as agonists, at 0.1 nM-1 microM in this system. These data suggested that BK-induced PI turnover in these cells was mediated via B2-type of BK receptors. This was confirmed further by the fact that both the B2-selective Hyp3- and Thienyl-antagonists inhibited BK-induced PI turnover with KBS of 369 +/- 51 nM and 368 +/- 118 nM respectively while the B1-selective antagonist, Des-Arg9-Leu8-BK, was inactive at 1 microM. [3H]BK receptor binding studies revealed two binding sites, one with high affinity (Kd = 0.24 +/- 0.06 nM; Bmax = 1.4 +/- 0.4 pmol/g tissue) and the other with low affinity (Kd = 18.5 +/- 0.95 nM; Bmax = 25.1 +/- 0.52 pmol/g tissue), on HSDM1C1 cell homogenates. The rank order of affinity of BK analogs at inhibiting specific [3H]BK binding was similar to that found for PI turnover.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of postnatal or adult chronic acetylcholinesterase inhibition on muscarinic receptors, phosphoinositide turnover and m1 mRNA expression

Muscarinic receptor number, receptor-stimulated phosphoinositide hydrolysis and m1 mRNA expression were examined in the cerebral cortex and hippocampus of rats treated during postnatal development or in adult age with the organophosphate diisopropylfluorophosphate. Developing rats were treated from postnatal days 4-9 or from postnatal days 4-20 and killed on days 10 and 21, respectively, 24 h after the last administration of diisopropylfluorophosphate. Adult animals were treated for 14 days. Acetylcholinesterase activity and muscarinic receptor number were significantly reduced in all groups of treatment. Muscarinic receptor-stimulated phosphoinositide turnover, however, was significantly reduced in postnatal days 4-20 and adult treated rats but not in the postnatal days 4-9 group. No differences were observed in ED50 values. Conversely, m1 mRNA expression was significantly reduced both in the cerebral cortex and hippocampus of postnatal days 4-9 treated rats, but not of postnatal days 4-20 and adult treated rats. These results indicate that chronic inhibition of acetylcholinesterase in developing rats results in significant alterations in muscarinic neurotransmission. These alterations may delay the maturation of the cholinergic system and, therefore, may account for some of the long-lasting neurotoxic effects observed after developmental exposure to organophosphate pesticides.

Effect of lindane on phosphatidylinositol synthesis by cerebral cortex after acute and subchronic treatment

1. The incorporation of myo-[2-3H]inositol into phosphatidylinositols was unmodified in brain cortex miniprisms from convulsant rats. 2. However, the incorporation had increased by 300-400% in non convulsant rats which had received the same amount of lindane at a lower concentration. 3. This result suggests that phosphatidylinositols are implicated in the convulsion syndrome. 4. Experiments with lindane added in vitro were performed with both subchronically lindane intoxicated and untreated rats. 5. The results show an interesting lack of parallelism. 6. This might indicate the development of some resistance to the effects of lindane, possibly as the result of complex compensatory changes in inositol lipid biosynthesis.

Metabotropic and ionotropic excitatory amino acid receptor agonists induce different behavioral effects in mice

Intracerebroventricular (i.c.v.) infusion in mice of the selective metabotropic excitatory amino acid receptor agonist 1S,3R-1- aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD) (0.6-575 nmol/min) dose dependently induced face washing and scratching. In contrast, the subtype-specific ionotropic excitatory amino acid receptor agonists N-methyl-D-aspartate (NMDA), kainate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) (0.3-3.0 nmol/min) dose dependently induced clonic convulsions. I.c.v. infusion of the non-selective metabotropic receptor agonists ibotenate (6 nmol/min) or quisqualate (30 nmol/min) induced clonic convulsions. However, when ionotropic receptors were blocked with (+)-5-methyl-10,11-dihydro-5H-dibenzo-(a,d)cyclohepten-5,10-imine maleate (MK-801, dizoclipine) (3 nmol/min) or 2,3-dihydroxy-6-nitro-7- sulfamoyl-benzo(f)-quinoxaline (NBQX) (9 nmol/min), respectively, face washing and scratching behavior emerged. Neither MK-801 or NBQX (ED50 value > 100 nmol/min), nor the putative metabotropic receptor antagonist L-amino-3-phosphoro-propionic acid (L-AP3) (> 176 nmol/min); nor the dopamine receptor antagonists SCH 23390 (> 74 nmol/min), metoclopramide (> 89 nmol/min) and haloperidol (> 27 nmol/min) antagonized 1S,3R-ACPD-induced scratching (144 nmol/min). These results suggest that the behavioral consequences of i.c.v. infusion of 1S,3R-ACPD in mice reflect a selective activation of metabotropic receptors that differs from the behavioral changes observed with i.c.v. infusion of ionotropic receptor agonists.

Characterization of the effects of lithium on phosphatidylinositol (PI) cycle activity in human muscarinic m1 receptor-transfected CHO cells

1. The effects of lithium on [3H]-inositol and [3H]-cytidine incorporation into [3H]-inositol monophosphates ([3H]-InsP1) and [3H]-cytidine monophosphorylphosphatidate ([3H]-CMP-PA), respectively, and inositol 1,4,5-trisphosphate (InsP3) and inositol 1,3,4,5-tetrakisphosphate (InsP4) mass were studied in carbachol-stimulated human m1 muscarinic receptor-transfected Chinese hamster ovary cells (m1 CHO cells). 2. Lithium alone (10 mM) had no appreciable effects on any of the four parameters measured; it was only in carbachol-stimulated cells that the effects of lithium became apparent. 3. In the presence of carbachol (1 mM), lithium (10 mM) caused a relatively rapid (within 5 min) accumulation of [3H]-InsP1 and [3H]-CMP-PA which continued up to about 20-30 min, after which accumulation slowed down. On the other hand, the elevation in InsP3 and InsP4 levels produced by carbachol was not altered by lithium in the short-term and only at later times (> 20-30 min) was the response attenuated, with InsP3 and InsP4 levels approaching basal. 4. The effects of lithium on carbachol-stimulated [3H]-InsP1 and [3H]-CMP-PA accumulation and the attenuation of the carbachol-induced elevation of InsP3 and InsP4 were all dose-dependent, with EC50s in the region of 1 mM. 5. The lithium-induced effects on [3H]-CMP-PA and InsP3 and InsP4 in carbachol-stimulated cells could be reversed, in a dose-dependent manner, by preincubation with exogenous myo-inositol (EC50 = 2-3 mM) but not by the inactive analogue scyllo-inositol, indicating that these effects occur as a consequence of depletion of inositol. 6. The temporal effects of lithium are consistent with lithium inhibiting inositol monophosphatase,causing accumulation of InsP1, resulting in lower free inositol levels. This leads to accumulation of CMP-PA and reduced PI synthesis which, once agonist-linked membrane inositol phospholipids are depleted, produces attenuated InsP3 and InsP4 responses.7. These results in ml CHO cells support the hypothesis that lithium affects the PI cycle cell signalling pathway by depletion of inositol due to inhibition of inositol monophosphatase.

The cholinergic receptor-linked phosphoinositide metabolism in mouse cerebrum and cerebellum in vivo

The cholinergic receptor-linked poly-phosphoinositide hydrolysis was studied in mouse cerebrum and cerebellum after prelabeling the brain with [3H]inositol. I.p. injection of Li (8 meq/kg) to C57Bl/6J mice for 4 h resulted in 14- and five-fold increases in [3H]inositol-labeled inositol monophosphate (IP1) in cerebrum and cerebellum, respectively. The labeled inositol bisphosphate (IP2) was also increased 83 and 19% in cerebrum and cerebellum, respectively. Prior injection of atropine (100 mg/kg) resulted in inhibition of Li-induced increases in labeled IP1 by 74 and 56% in cerebrum and cerebellum, respectively. Administration of pilocarpine (20 mg/kg) to the Li-treated mice for 30 min resulted in further increases in labeled IP1 and IP2 and a concomitant decrease in labeled inositol in cerebrum but not in cerebellum. Mass measurements of IP1 and IP2 isomers by HPLC revealed that inositol 1-monophosphate (Ins(1)P), inositol 4-monophosphate (Ins(4)P) and inositol 1,4-bisphosphate (Ins(1,4)P2) were all increased by pilocarpine administration in the Li-treated mouse cerebrum. The effects of pilocarpine administration in mouse cerebrum (increases in IP1 and IP2) could be completely inhibited by preinjection of atropine. Atropine injection also decreased the levels of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. Surprisingly, a decrease in Ins(1,4,5)P3 level was also found in non-Li-treated mice after pilocarpine administration (30 mg/kg, 10-40 min). Except for the increase (20%) in [32P]-labeled PIP in the cerebrum, Li or Li together with pilocarpine administration did not alter the levels of [3H]inositol or [32P]phosphate-labeled phosphoinositides.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-mediated release of inositol phosphates in the cochlear and vestibular sensory epithelia of the rat

Various neurotransmitters, hormones and other modulators involved in intercellular communication exert their biological action at receptors coupled to phospholipase C (PLC). This enzyme catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) to inositol 1,4,5-trisphosphate (InsP3) and 1,2-diacylglycerol (DG) which act as second messengers. In the organ of Corti of the guinea pig, the InsP3 second messenger system is linked to muscarinic cholinergic and P2y purinergic receptors. However, nothing is known about the InsP3 second messenger system in the vestibule. In this study, the receptor-mediated release of inositol phosphates (InsPs) in the vestibular sensory epithelia was compared to that in the cochlear sensory epithelia of Fischer-344 rats. After preincubation of the isolated intact tissues with myo-[3H]inositol, stimulation with the cholinergic agonist carbamylcholine or the P2 purinergic agonist ATP-gamma-S resulted in a concentration-dependent increase in the formation of [3H]InsPs in both epithelia. Similarly, the muscarinic cholinergic agonist muscarine enhanced InsPs release in both organs, while the nicotinic cholinergic agonist dimethylphenylpiperadinium (DMPP) was ineffective. The muscarinic cholinergic antagonist atropine completely suppressed the InsPs release induced by carbamylcholine, while the nicotinic cholinergic antagonist mecamylamine was ineffective. Potassium depolarization did not alter unstimulated or carbamylcholine-stimulated release of InsPs in either organ. In both tissues, the P2 purinergic agonist alpha,beta-methylene ATP also increased InsPs release, but the P1 purinergic agonist adenosine did not. These results extend our previous observations in the organ of Corti of the guinea pig to the rat and suggest a similar control of the InsP3 second messenger system in the vestibular sensory epithelia.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of lithium on the phosphoinositide cycle in rat cerebral cortex, hippocampus, and striatum

The effects of lithium on muscarinic cholinoceptor-stimulated phosphoinositide turnover have been investigated in rat hippocampal, striatal, and cerebral cortical slices using [3H]inositol or [3H]cytidine prelabelling and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] mass determination methods. Carbachol addition resulted in maintained increases in Ins(1,4,5)P3 and Ins(1,3,4,5)P4 mass levels in hippocampus and cerebral cortex, whereas in striatal slices these responses declined significantly over a 30-min incubation period. Carbachol-stimulated Ins(1,4,5)P3 and Ins(1,3,4,5)P4 accumulations were inhibited by lithium in all brain regions studied in a time- and concentration-dependent manner. For example, in hippocampal slices significant inhibitory effects of LiCl were observed at times > 10 min after agonist challenge; IC50 values for inhibition of agonist-stimulated Ins(1,4,5)P3 and Ins(1,3,4,5)P4 accumulations by lithium were 0.22 +/- 0.09 and 0.33 +/- 0.13 mM, respectively. [3H]CMP-phosphatidate accumulation increased in all brain regions when slices were stimulated by agonist and lithium. The ability of myo-inositol to reverse these effects, as well as lithium-suppressed Ins(1,4,5)P3 accumulation, implicates myo-inositol depletion in the action of lithium in the hippocampus and cortex at least. The results of this study suggest that although significant differences in the magnitude and time courses of changes in inositol (poly)phosphate metabolites occur in different brain regions, lithium evokes qualitatively similar enhancements of [3H]inositol monophosphate and [3H]-CMP-phosphatidate levels and inhibitions of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 accumulations. However, the inability of striatal slices to sustain carbachol-stimulated inositol polyphosphate accumulation in the absence of lithium and the inability to reverse effects with myo-inositol may indicate differences in phosphoinositide signalling in this brain region.

Distinct kinetic binding properties of N-[3H]-methylscopolamine afford differential labeling and localization of M1, M2, and M3 muscarinic receptor subtypes in primate brain

Three classes of muscarinic receptors in mammalian brain have been postulated on the basis of equilibrium and kinetic binding data. However, equilibrium binding assays alone have not permitted a clear demonstration of the localization of putative M1, M2, and M3 receptor subtypes in the brain because of the overlapping affinities of virtually all muscarinic antagonists. In the present study, the conditions for selective occupancy of the M1, M2, and M3 receptor subtypes in the brain of the rhesus monkey were based on the distinct kinetic and equilibrium binding properties of N-[3H]-methylscopolamine (NMS) at cloned m1-m4 muscarinic receptor subtypes expressed in A9L transfected cells. Quantitative autoradiography of the M1, M2, and M3 muscarinic receptor subtypes in the primate brain was performed according to the following strategy. The M1 (m1) receptor subtype was labeled directly with a non-saturating concentration of [3H]-pirenzepine. The M2 (m2) subtype was labeled by incubations consisting of short, two minute pulses of [3H]-NMS after a preincubation with 0.3 microM pirenzepine to occlude m1, m3, and m4 sites. Selective occupancy of the M3 (m3) receptor (subtype) was achieved by pre-incubation with 0.5 nM unlabeled NMS to partially occlude the m1, m2, and m4 sites, equilibrium with 0.5 nM [3H]-NMS, followed by a 60 minute tracer dissociation in the presence of 1 microM atropine. In vitro autoradiography demonstrated that the M1 receptor subtype was confined to forebrain structures. M1 receptors were prevalent throughout the cerebral cortical mantle, amygdala, hippocampus, and the striatum. Low to background levels of the M1 receptor subtype were measured over the thalamus, hypothalamus, and brainstem. The M2 subtype was widely distributed with elevated densities of binding sites seen over all primary sensory cortical areas, and within discrete thalamic, hypothalamic, and brainstem nuclei. The distribution of the M3 receptor subtype was largely coincident with the pattern of the M1 sites labeled by non-saturating concentrations of [3H]-pirenzepine with some notable exceptions. Within the cerebral cortical mantle, the M3 receptor exhibited an elevated gradient over the orbitofrontal gyrus and the temporal lobe. Within the striatum, the M3 subtype was elevated over the anterior and dorsal part of the caudate nucleus, while the M1 receptors were most prevalent over the ventromedial sector. Selective labeling of M3 receptors was seen over the medial division of the globus pallidus and within the substantia nigra pars reticulata. In contrast to the pattern of the M1 receptor subtype, M3 receptors were prevalent also over midline nuclei of the hypothalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of repeated organophosphate administration on carbachol-stimulated phosphoinositide hydrolysis in the rat brain

The effects of repeated exposure to two organophosphates on the turnover of phosphoinositides, the second messenger system coupled to the M1 and M3 subtypes of muscarinic receptors, were examined in the rat hippocampus. Repeated diisopropylfluorophosphate (DFP) exposure (0.2-0.8 mg/kg, SC) decreased brain acetylcholinesterase activity and muscarinic receptor density. The incorporation of [3H]myoinositol into brain slices was also decreased. Phosphoinositide turnover was measured as the accumulation of [3H]inositol phosphates (IP) in the presence of lithium. DFP did not affect basal IP accumulation, but decreased carbachol-stimulated IP accumulation in the hippocampus after 0.4 and 0.8 mg/kg. The effects of repeated disulfoton administration (2.0 mg/kg, IP) were also examined in the hippocampus. Similar to DFP, repeated disulfoton exposure decreased acetylcholinesterase activity, receptor density, and carbachol-stimulated IP accumulation. The incorporation of myoinositol, however, was increased in disulfoton-treated rats. These data indicate that repeated organophosphate exposure results in a functional decrease in muscarinic receptor activity, as well as changes in myoinositol incorporation into phospholipids.

Enhancement of the responsiveness of cortical adrenergic receptors by chronic administration of the 5-hydroxytryptamine uptake inhibitor citalopram

The aim of this study was to evaluate the effect of citalopram, a second generation antidepressant agent producing no beta-down-regulation, on the receptors and second messenger systems related to noradrenergic transmission in the cerebral cortex of the rat. We confirmed that citalopram does not bind to alpha 1-, alpha 2-, and beta 1-adrenoceptors, but we found that it attenuates the inhibitory action of the protein kinase C activator, 12-O-tetradecanoylphorbol 13-acetate, on the noradrenergic response from alpha 1-adrenoceptor. In contrast to most antidepressants, chronic treatment with citalopram does not produce beta-down-regulation, but increases the responses to noradrenaline from beta-adrenoceptors without increasing the beta 1-adrenoceptor density. Chronic treatment with citalopram also increases the maximal response from alpha 1-adrenoceptor. The results indicate that beta-down-regulation is not a necessary characteristic of an efficient antidepressant drug.

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

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

Effects of excitatory amino acids on inositol phosphate accumulation in slices of the cerebral cortex of young and aged rats

The effects of glutamate, NMDA and quisqualate on carbachol- and norepinephrine-elicited formation of inositol phosphate (IP) were evaluated in slices prepared from the cerebral cortex of 3- and 24-month Sprague-Dawley rats. Glutamate, NMDA, and quisqualate antagonized the IP response to carbachol in a concentration-dependent fashion. This antagonism was more pronounced in aged than in young rats, both for glutamate (IC5O 0.114 and 0.210 mM) and NMDA (IC5O 0.0029 and 0.127 mM), but not for quisqualate. Glutamate (but not NMDA) also antagonized in a concentration-dependent fashion the IP response to norepinephrine, IC50s were 0.061 and 0.126 mM for aged and young rats, respectively; quisqualate had an inhibitory effect only at 1 mM concentration in the two age-groups, while in aged rats some stimulatory effect was present at 0.1 mM concentration. Glutamate, NMDA and quisqualate (1 mM) did not affect basal IP accumulation in either young or aged rats; quisqualate, however, at 0.1 mM concentration had some stimulatory effect, more pronounced in aged rats. This effect was probably responsible for the biphasic effect of quisqualate in this age-group. The most important finding consists of the demonstration of an age-related increase in the inhibitory effects of NMDA on carbachol-induced IP accumulation. This implies an altered modulation of cholinergic post-receptor mechanisms by glutamatergic mechanisms.

Regulation of protein kinase C activity by sensory deprivation in the olfactory and visual systems

Environmental regulation of sensory function has provided an important model of plastic mechanisms mediating neural information processing. To define potential commonalities in information processing in different systems, we investigated molecular changes elicited by sensory deprivation in the developing rat olfactory and visual systems. Protein kinase C (PKC), an intracellular messenger implicated in synaptic plasticity and memory, was analyzed. Initial, developmental studies indicated that PKC activity in the soluble and particulate fractions of the olfactory bulb increased three- to fourfold from birth to 3 months of age. Unilateral olfactory deprivation prevented the developmental increase in both soluble and particulate PKC activities in the ipsilateral olfactory bulb and piriform cortex, the second-order relay. Phorbol ester binding localized PKC to intrinsic neuronal populations and their dendrites in the control and deprived bulbs. Moreover, PKC was similarly lower in the visual cortex of dark-reared rats than in light-reared controls. The changes in PKC were region specific, as activity was unchanged by either treatment in the parietal cortex, a control area that does not process primary olfactory or visual information. Our results suggest that the important intracellular messenger, PKC, is similarly regulated in entirely different sensory systems by different environmental stimuli. Consequently, different sensory systems may use common molecular mechanisms to process information.

Combined effects of adrenergic and intravenous anesthetic agents on inositol monophosphate levels in rat liver prisms

Combined effects of adrenergic and intravenous anesthetic agents on phosphatidylinositol (PI) turnover were studied using rat liver prisms incubated with [3H]myo-inositol. Rat liver prisms responded to epinephrine, norepinephrine and phenylephrine dose-dependently with an increase in inositol monophosphate (IP1) formation but they did not respond to ephedrine. Dopamine-induced effects were seen only at concentrations as high as 10(-4) mol.l-1. The enhancement of IP1 formation induced by epinephrine was potentiated by thiamylal at concentrations of 10(-5) mol.l-1 and 10(-4) mol.l-1, remained unaffected by ketamine, fentanyl or midazolam, but was dose-dependently inhibited by droperidol. The present results from in vitro studies of liver cell metabolism suggest that alpha-adrenergic agents in combination with barbiturates may potentiate liver cell damage by activation of PI turnover and interrelated intracellular Ca++ accumulation.

Regulation of beta 1-adrenergic receptor mRNA and ligand binding by antidepressant treatments and norepinephrine depletion in rat frontal cortex

The number of beta 1-adrenergic receptor (beta 1AR) binding sites is decreased by chronic antidepressant treatments, including electroconvulsive seizure (ECS) and imipramine, whereas administration of agents that deplete norepinephrine (NE) increases the number of beta 1AR binding sites in cerebral cortex. The present study was carried out to examine the influence of these treatments on levels of beta 1AR mRNA in frontal cortex to study the molecular mechanisms that underlie the regulation of beta 1ARs in brain. Levels of beta 1AR mRNA were measured by RNase protection analysis using a riboprobe derived from rat beta 1AR cDNA, and the levels of beta AR binding were measured using the nonselective ligand [3H]CGP-12177. Studies to verify the specificity of the RNase protection assay revealed that the distribution of beta 1AR mRNA was in agreement with the reported distribution of beta 1AR ligand binding: Levels of beta 1AR mRNA were highest in cerebral cortex or frontal cortex, intermediate in neostriatum, hippocampus, lung, and heart, and lowest in cerebellum, kidney, and liver. Chronic ECS treatment (once daily for 10 days) significantly decreased levels of beta AR ligand binding and resulted in a corresponding, time-dependent down-regulation of beta 1AR mRNA levels in frontal cortex. However, imipramine administration regulated levels of beta 1AR mRNA in a biphasic manner, with treatments for 7-14 days increasing and treatments for 18-21 days decreasing levels of beta 1AR mRNA in frontal cortex. In contrast, levels of [3H]CGP-12177 ligand binding were decreased at all time points examined (3-21 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a human NK1 tachykinin receptor in the astrocytoma cell line U 373 MG

The human NK1 tachykinin receptor in the astrocytoma cell line U 373 MG was characterized using selective agonists and antagonists described for this receptor in the rat. Specific [3H]substance P binding sites were present on cell homogenates, whereas [3H]neurokinin A or [3H]-senktide binding sites were absent. The binding was saturable and reversible. The binding of [3H]substance P was inhibited by very low concentrations of [L-Pro9]substance P and [Sar9,Met(O2)11]substance P; septide was approximately 1,000-fold less potent. The most potent peptide antagonist was trans-4-hydroxy-1-(1H-indol-3-ylcarbonyl)-L-prolyl-N-methyl-N-(phe nylmethyl)-L- tyrosineamide. The rank order of potency for the nonpeptide antagonists was (S,S)-CP 96,345 > (+/-)-CP 96,345 > (+/-)-2-chlorobenzylquinuclidinone > (R,R)-CP 96,345 > RP 67580 > RP 68651. In [3H]-inositol-labeled cells, substance P stimulated phosphatidylinositol turnover. A good correlation was found when the abilities of NK1 receptor agonists for stimulating inositol phosphate production and for inhibiting [3H]substance P binding were compared. Similarly, the binding and functional assays were well correlated for the antagonists. As a result of its high sensitivity and selectivity, the U 373 MG cell line thus appears an excellent tool for investigating the pharmacology of the human NK1 receptor.

Centpropazine affinity to cortical noradrenergic receptors and effect on their responsiveness in the rat

We have studied the in-vitro effect of centpropazine on cerebral cortical noradrenergic receptors measured as the accumulation of second messengers, cyclic AMP and inositol phosphate, stimulated by noradrenaline, and the binding to alpha 1- and beta-adrenoceptors. Centpropazine inhibited inositol phosphate, but not the cyclic AMP accumulation in the cerebral cortical slices of the rat. It moderately antagonized the specific binding of [3H]prazosin, but did not affect the specific binding of the beta-adrenoceptor ligand, [3H]CGP 12177, to cerebral cortical membranes.

Studies of muscarinic receptor reserve linked to phosphoinositide hydrolysis in parotid gland and cerebral cortex

Hydrolysis of inositol phospholipids caused by muscarinic agonists was studied in the guinea-pig parotid gland (PG) and cerebral cortex (CX). The present study describes the effect of two muscarinic agonists, carbachol and oxotremorine, on stimulation of phosphoinositide hydrolysis and on binding of [3H]NMS in the presence of the irreversible muscarinic antagonist benzilyl choline mustard (BCM). Carbachol and oxotremorine stimulated the formation of inositol phosphates in PG, pD2(Carb) = 5.3 +/- 0.1, pD2(Oxo) = 5.9 +/- 0.1 and in CX, pD2(Carb) = 4.3 +/- 0.2, pD2(Oxo) = 5.8 +/- 0.2. In the present study slices from both tissues have been exposed to 0.1 microM BCM for 2, 5 and 10 min. Treatment for 10 min caused a 75-85% reduction in specific [3H]N-methyl scopolamine ([3H]NMS) binding sites in both PG and CX. Following 2 min BCM treatment of PG a marked decrease in pD2 value of the carbachol-stimulated inositol phosphate formation was found. This effect was not found in CX. The results showed that a 30-40% reduction in binding sites shifted the carbachol concentration response curve to the right by one order of magnitude and reduced the oxotremorine-induced release of inositol phosphates by approximately 20%. In PG, the BCM-induced reduction of the carbachol-stimulated inositol phosphate formation was paralleled by the reduction in receptor binding sites. Similar treatment, but in CX, showed a lower reduction of the carbachol-stimulated inositol phosphate formation as compared to the reduction in receptor-binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of 5-HT2 receptors facilitates depolarization of neocortical neurons by N-methyl-D-aspartate

The interaction between serotonin and excitatory amino acid agonists at rat neocortical neurons was investigated using the grease-gap recording method. Depolarization evoked by 50 microM N-methyl-D-aspartate was dose dependently facilitated by serotonin (5-HT) (1 to 100 microM) giving a bell-shaped dose-response curve with maximum enhancement at 30 microM. In contrast, quisqualate and kainate depolarizations were not enhanced. Subnanomolar concentrations of methysergide, ritanserin and spiperone, but not ICS 205-930, attenuated the 5-HT enhancement, compatible with 5-HT2, but not 5-HT1 or 5-HT3 receptor subtype involvement. Enhancement was observed with 5-HT2 receptor agonists, whereas 5-HT1 receptor subtype agonists had either no effect (1B and 1C) or reduced (1A) the N-methyl-D-aspartate depolarization. Scopolamine and prazosin reduced the N-methyl-D-aspartate depolarization and blocked facilitation induced by carbachol and phenylephrine, but not that due to 5-HT. Tetrodotoxin reduced the N-methyl-D-aspartate depolarization, but the facilitation by 5-HT persisted. Activators of protein kinase C (phorbol diacetate and 1-oleoyl-2-acetyl-sn-glycerol) did not mimic the serotonin facilitation. We conclude that serotonin enhances N-methyl-D-aspartate depolarization of rat cortical neurons through activation of 5-HT2 receptors, however the cellular mechanism underlying the facilitation remains to be established.

Septohippocampal cholinergic changes after destruction of the A10-septal dopaminergic pathways

Mice were injected bilaterally into the septum with 6-hydroxydopamine and 6 weeks later the hippocampi were assayed for activity of choline acetyltransferase, muscarinic receptor binding capabilities and for formation of inositol phosphate in response to direct (carbachol) or presynaptically elicited (K+) stimulation of the postsynaptic receptors. Levels of dopamine in the septum were reduced by 70% in the lesioned animals and hippocampal choline acetyltransferase was elevated by the same amount. The Bmax of muscarinic binding was significantly reduced without changes in Kd; nevertheless, carbachol-induced stimulation of formation of inositol phosphate was unaffected. The response to K+ was markedly elevated in the 6-hydroxydopamine-treated animals. Thus, the regulatory effect of A10-septal dopaminergic pathways on the septohippocampal cholinergic innervations is both on the presynaptic and postsynaptic levels.

Stimulation of phosphoinositide hydrolysis by muscarinic receptor activation in the rat olfactory bulb

The effect of muscarinic receptor activation on phosphoinositide hydrolysis in the rat olfactory bulb was investigated by determining either the inositol (1,4,5) trisphosphate (Ins(1,4,5)P3) mass or the accumulation of [3H]inositol phosphates ([3H]InsPs). In miniprisms of rat olfactory bulb, carbachol produced an atropine-sensitive increase in Ins(1,4,5)P3 concentration. In a membrane preparation, the formation of Ins(1,4,5)P3 was stimulated by guanosine-5'-(3-O-thio) triphosphate (GTP gamma S), but not by carbachol. However, carbachol potentiated the GTP gamma S stimulation when the two agents were combined. In miniprisms prelabelled with [3H]myo-inositol, carbachol increased the accumulation of [3H]InsPs and this effect was significantly reduced by tissue treatment with either 1 microM phorbol 12-myristate 13-acetate or 1 mM dibutyryl cyclic AMP. Analysis of concentration-response curves indicated that carbachol (EC50 = 96 microM) and oxotremorine-M (EC50 = 8.2 microM) behaved like full agonists, whereas oxotremorine, BM5, arecoline and bethanechol were partial agonists. The carbachol stimulation of [3H]InsPs accumulation was counteracted with high affinity by the M1 antagonist pirenzepine (pA2 = 8.26), and less potently by the M3 antagonist para-fluorohexahydro-sila-difenidol (pA2 = 6.7) and the M2 antagonist AF-DX 116 (pA2 = 6.12). The biochemical and pharmacological properties of the muscarinic stimulation of phosphoinositide hydrolysis were compared with those displayed by the muscarinic stimulation of adenylate cyclase in the rat olfactory bulb.

Differences between rat dorsal and ventral hippocampus in muscarinic receptor agonist binding and interaction with phospholipase C

Carbachol, a full muscarinic receptor agonist, stimulated [3H]inositol phosphate accumulation in both the ventral and dorsal hippocampus, but its efficacy and affinity were higher in the former area. The partial agonist oxotremorine had a weak stimulatory effect in both regions. The affinity profiles of pirenzepine and AF-DX 116 in antagonizing carbachol-stimulated [3H]inositol phosphate accumulation indicated that M1 and M3 receptors contributed equally to the response in either region. On the other hand, there were no differences in the receptor density, or in the distribution of muscarinic receptor subtypes between the two regions of the hippocampus which could account for the effect as determined in binding experiments with selective antagonists. Analysis of carbachol binding curves did, instead, indicate a difference in the way the agonist interacted with the receptors within the hippocampus, i.e., carbachol recognized three agonist affinity states (superhigh, high and low) in the ventral hippocampus, and only two (high and low) in the dorsal part. The findings thus suggested that the regional diversity in the efficacy of carbachol in stimulating phosphoinositide turnover was related to the complexity with which it bound to muscarinic receptors. Transduction processes that intervene between changes in the muscarinic receptors' conformation and activation of phospholipase C might be relevant to these differences.

Histamine H1-receptor-mediated inositol phospholipid hydrolysis in DDT1MF-2 cells: agonist and antagonist properties

1. The effect of histamine H1-receptor stimulation on inositol phospholipid hydrolysis has been investigated in the hamster vas deferens smooth muscle cell line, DDT1MF-2. 2. Histamine (EC50 = 27 microM) stimulated the accumulation of [3H]-inositol phosphates in DDT1MF-2 cells prelabelled with [3H]-myo-inositol. 2-Thiazolylethylamine (EC50 42 microM) produced a maximal response of similar magnitude to histamine while the maximal response obtained with N alpha-methylhistamine (EC50 = 72 microM) and 2-pyridylethylamine (EC50 = 85 microM) were much lower (circa 65%, histamine = 100%). 3. The H1-selective agonists 2-(3-fluorophenyl)-histamine (2-FPH) and 2-(3-chlorophenyl)-histamine (2-CPH) both appeared to act as partial H1-agonists in this system. Both compounds produced maximal responses of only 30% (with respect to histamine = 100) and were able to antagonize the inositol phosphate response to histamine (estimated Kp = 10.4 and 18.9 microM for 2-FPH and 2-CPH respectively). 4. The response to histamine was antagonized by the H1-antagonists, mepyramine (KD 0.4 nM), (+)-chlorpheniramine (KD 1.2 nM) and promethazine (KD 0.3 nM). Furthermore, the (-)-isomer of chlorpheniramine was approx. three orders of magnitude less potent than the corresponding (+)-isomer. 5. The response to histamine (0.1 mM) was not altered by prior treatment of cells with pertussis toxin (100 ng ml-1; 24 h) whereas the inositol phosphate response to adenosine A1-receptor stimulation in this cell line was significantly attenuated under these conditions. 6. These data indicate that histamine-stimulated inositol phospholipid hydrolysis in DDT1MF-2 cells is mediated via a classical H1-receptor. Furthermore, the results also suggest that histamine HI- and adenosine A,-receptors activate phospholipase C in DDTMF-2 cells via two different G-protein-coupled pathways.

Training chicks on a passive avoidance task modulates glutamate-stimulated inositol phosphate accumulation

The effects of glutamate, N-methyl-D-aspartate (NMDA), (+)-5-methyl-10,11-dihydro-5H-dibenzo-(a,d)-cyclo-hepten 5,10-imine maleate (MK801), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and quisqualate on the accumulation of inositol phosphates (IP) from the breakdown of phosphoinositides in vitro have been studied in tissue prisms derived from a region of the chick forebrain, the intermediate medial hyperstriatum ventrale (IMHV). In prisms from the left IMHV, glutamate stimulated IP accumulation by 10-20%, AMPA by 55% and quisqualate by 650%. These effects were more marked in the right IMHV, where AMPA stimulated IP accumulation by 157% and quisqualate by 920%. MK801 and NMDA had no significant effect on IP accumulation in either hemisphere. The left IMHV is known to be the site of a biochemical cascade resulting in synaptic remodelling following training day-old chicks on a one-trial passive avoidance task. The effect of such training was to reduce glutamate-stimulated accumulation of IP by 27% (P < 0.05) in prisms taken 30 min after training. There was no effect on prisms taken at 5 or 180 min after training, and no effect at any time in the right IMHV. MK801, injected intraperitoneally before training at a concentration known to produce amnesia for the passive avoidance task, abolished the training-induced decrease without itself affecting IP accumulation. Taken in conjunction with pharmacological and autoradiographic evidence, these results indicate that memory formation for the passive avoidance task involves the activation of NMDA receptor channels, but not quisqualate or AMPA receptors, in the left IMHV of the chick 30 min after training.

Effect of ethanol administration and withdrawal on serotonin receptor subtypes and receptor-mediated phosphoinositide hydrolysis in rat brain

The effect of short-term (15 days) and long-term (60 days) ethanol treatment and withdrawal on agonist-stimulated phosphoinositide (Pl) hydrolysis, serotonin receptor subtypes (5HT1A and 5HT2), and alpha 1-adrenergic receptors were studied in rat cerebral cortex. Short-term ethanol treatment had no significant effect on serotonin (5HT), norepinephrine (NE), and calcium ionophore (A23187)-stimulated [3H]-inositol-1-phosphate ([3H]-IP1) formation and 5-HT2 receptors as measured by 125I-lysergic acid diethylamide (125I-LSD) binding, in rat cerebral cortex. However, 15 days of ethanol treatment, followed by 24 hr of withdrawal resulted in a decrease in Bmax of 125I-LSD binding without significant change in KD, as well as a decrease in 5HT-stimulated [3H]-IP1 formation in rat cerebral cortex. 5HT1A and alpha 1-adrenergic receptors were determined by using [3H]-8-hydroxy-2-(di-N-propylamino)tetralin and [3H]-prazosin as radioligand, respectively. We also observed that long-term ethanol treatment had no significant effect on Bmax and KD of 5HT2, 5HT1A, and alpha 1-adrenergic receptors, as well as NE and A23187-stimulated [3H]-IP1 formation, but significantly decreased the 5HT-stimulated [3H]-IP1 formation in rat cerebral cortex. It is possible that a decrease in 5HT-induced PI turnover after long-term ethanol exposure may be due to a decrease in coupling of 5HT2 receptors to G protein or PLC enzyme, whereas the decrease in 5HT-induced PI turnover after withdrawal may be due to a decrease in functional 5HT2 receptor number.

Steric and electronic requirements for muscarinic receptor-stimulated phosphoinositide turnover in the CNS in a series of arecoline bioisosteres

A series of arecoline derivatives was utilized to assess steric and electronic effects important for activating muscarinic receptors in the CNS. Arecoline derivatives in which the methyl ester moiety was replaced by hexyloxy-1,2,5-oxadiazole (2b), hexyloxythiophene (3b) or hexyloxypyrazine (4b) were compared with the hexyloxy-1,2,5-thiadiazole compound (1b) (Hexyloxy-TZTP), known from previous work to be active as an M1/M3 partial agonist. MNDO calculations showed that the N-S bonds of the alkoxythiadiazole ring were highly polarized with the ability to form H-bonds to the N's. On the other hand, the smaller oxadiazole had lower polarities in the N-O bonds and reduced ability to form H-bonds, the thiophene was of comparable size to the thiadiazole and had large C-S bond polarities without the H-bond capability and the pyrazine had limited ability to form H-bonds. The compounds were compared with respect to their abilities to stimulate phosphoinositide (Pl) turnover in the hippocampus of the rat brain. 1b was more active than 2b-4b for stimulating the Pl turnover response. The data suggest that the ability to form H-bonds is an important factor for the ability of 1 to stimulate M1 muscarinic receptors in the CNS.

Evaluation of central adrenergic receptor signal transmissions after an antidepressant administration to the rat

The effects of several antidepressants, amitriptyline, citalopram, desipramine, fluoxetine, maprotiline, mianserin, nialamide, nomifensine, tranylcypromine and viloxazine, on the accumulation of cyclic AMP and inositol monophosphates were studied in rat cerebral cortical slices. The two enzymatic systems were stimulated either by adrenergic agonists or by forskolin. Cyclic AMP and inositol monophosphates (IPs) formed were determined by a double label method. In vitro all drugs, except inhibitors of monoamine oxidase, nialamide and tranylcypromine, inhibited alpha 1-agonist-mediated production but did not modify the cyclic AMP accumulation. Otherwise, chronic desipramine but not citalopram administration decreased the accumulation of cyclic AMP (-39%) elicited by beta-adrenoceptor agonists; no change was observed in inositol phosphate metabolism after administration of these two drugs. These data support previous investigations showing a decrease in cyclic AMP production after chronic treatment with norepinephrine uptake blockers but do not confirm the hypothesis of a modification of alpha 1-adrenoceptor-stimulated inositol phosphate metabolism.

Effect of electroconvulsive shock on 5-HT2 and alpha 1-adrenoceptors and phosphoinositide signalling system in rat brain

We studied the effect of repeated administration of electroconvulsive shock (ECS) on alpha 1-adrenoceptor subtype (alpha 1A and alpha 1B) and 5-HT2 (serotonin-2) receptors and receptor-mediated phosphoinositide (PI) hydrolysis in rat cerebral cortex. We observed that repeated administration with ECS significantly increased the density of 5-HT2 receptors, as labeled by [3H]ketanserin, as well as 5-HT-stimulated [3H]inositol-1-phosphate ([3H]IP1) in rat cerebral cortex. We also observed that repeated ECS administration caused a significant increase in the number of alpha 1-adrenoceptors and the alpha 1B-adrenoceptor subtype as measured by (+/-)-beta-([125I]iodo-4-hydroxyphenyl)-ethyl-aminomethyl-tetralone binding. However, it had no significant effects on norepinephrine (NE)-stimulated [3H]IP1 formation or alpha 1A-adrenoceptor subtype. These results thus suggest that up-regulation of 5-HT2 receptors after administration with ECS is associated with increased 5-HT-stimulated [3H]IP1 formation. The lack of effects on NE-stimulated PI turnover in ECS treated rats may be due to its lack of effect on the alpha 1A-adrenoceptor subtype.

Selective dopaminergic mechanism of dopamine and SKF38393 stimulation of inositol phosphate formation in rat brain

We have previously reported that dopamine and the D1 receptor-selective agonist, SKF38393, stimulate the formation of inositol phosphates in rat brain slices (Undie and Friedman, 1990, J. Pharmacol. Exp. Ther. 253, 987). The present experiments were conducted to determine if actions at alpha-adrenoceptors or at serotonergic sites may contribute to, or interact with, the observed stimulation of phosphoinositide hydrolysis by dopamine receptor agonists. Rat striatal slices prelabeled with [3H]inositol were treated with up to 500 microM dopamine, norepinephrine, serotonin (5-HT), or the dopamine D1 receptor agonist, SKF38393, and accumulated inositol phosphates determined. The action of norepinephrine was dose-dependently blocked by the selective alpha 1-adrenoceptor antagonist, prazosin, but not by SCH23390. The actions of dopamine and SKF38393 were dose-dependently blocked by the dopamine D1 receptor antagonist, SCH23390, but not by prazosin. The effects of 5-HT were blocked by the nonselective 5-HT antagonist, methiotepin, the selective 5-HT2 antagonist, ketanserin, the mixed 5-HT2/5-HT1C antagonist, mianserin, and, with much less potency, by the selective 5-HT1C antagonist, mesulergine. On the contrary, the serotonin receptor antagonists did not block the response to SKF38393, and there was no dose-dependent blockade of the 5-HT response by SCH23390. These observations indicate that the actions of dopamine and SKF38393 in stimulating inositol phosphate formation are selectively mediated through a D1-like dopamine receptor.

α1-Adrenergic agonists act on the ventromedial hypothalamus to cause neuronal excitation and lordosis facilitation: electrophysiological and behavioral evidence

To see if activation of central alpha 1-adrenergic receptors can cause facilitation of lordosis in rats, the behavioral effects of centrally administered alpha 1-agonists, methoxamine (MA) and phenylephrine (PhE), and related agents were studied. In ovariectomized rats treated with estrogen, infusion of MA, PhE, or a beta-agonist isoproterenol, into the lateral ventricle, or bilateral infusions of MA or PhE into the ventromedial hypothalamus (VMH) facilitated lordosis. Conversely, intra-VMH infusion of the alpha 1-antagonist prazosin (PZ) inhibited lordosis. Intra-VMH infusion of isoproterenol or an alpha 2-agonist clonidine, had no effect. Neither was the intra-VMH infusion of MA effective if: (i) the rats were not primed with estrogen; (ii) the tips of the cannulae were outside the VMH; or (iii) it was preceded by an intra-VMH infusion of the alpha 1b-antagonist, chloroethylclonidine (CEC). These results not only verify implications from recent studies that alpha 1-receptors in the hypothalamus are important for lordosis facilitation, but further show that the adrenergic facilitatory effect are: (i) mediated specifically by alpha 1b-subtype of the alpha 1-receptor, (ii) estrogen-dependent, and (iii) site-specific to VMH. To investigate neural mechanisms potentially underlying the lordosis-facilitating effect of alpha 1-activation, the actions of MA and PhE on the electrical activity of single neurons of the ventromedial nucleus of the hypothalamus (VMN) in vitro were studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Influences of cholecystokinin octapeptide on phosphoinositide turnover in neonatal-rat brain cells

Cholecystokinin octapeptide (CCK-8) has been shown to be coupled to phosphoinositide turnover in pancreatic acini as well as in a kind of neuroblastoma cell and a human embryonic cell line. Little is known, however, about its link with phosphatidylinositol breakdown in the brain. The brains (minus cerebella) from 1-2-day-old neonatal rats were enzymically dissociated into single cells. The intact cells were prelabelled by incubation with myo-[3H]inositol for 3 h, and were then stimulated with agonists in the presence of 10 mM-LiCl. Carbachol at 1 mM induced an increase in InsP3 labelling in brain cells (peak at 30 min, and then a gradual decrease), and a static accumulation of InsP with time, whereas the labelling of InsP2 remained essentially unchanged. A very similar time-response curve was obtained for 10 nM-CCK-8 in stimulating phosphoinositide turnover. The dose-response curve for incubated brain cells revealed that the formation of InsP3 increased when the concentration of CCK-8 was increased from 0.1 to 10 nM. A further increase in CCK-8 concentration to 100-1000 nM resulted in a gradual decrease in InsP3 formation. InsP and InsP2 levels stayed relatively stable. The production of InsP3 stimulated by 10 nM-CCK-8 was dose-dependently suppressed by the CCK-A antagonist Devazepide in the concentration range 1-10 nM; the effect declined when the concentration was further increased to 100-1000 nM. In contrast, the CCK-B antagonist L365,260 showed a sustained suppression of InsP3 production at concentrations above 0.1 nM, i.e. in the range 1-1000 nM. The results provide evidence that CCK-8 stimulates the turnover of phosphoinositide and increases InsP3 labelling in dissociated neonatal-rat brain cells, in which both CCK-A and CCK-B receptors seem to be involved.

Cholinergic hyperinnervation in the cerebral cortex of microencephalic rats does not result in muscarinic receptor down-regulation or in alteration of receptor-stimulated phosphoinositide metabolism

Administration of methylazoxymethanol (MAM; 25 mg/kg) to pregnant rats at gestational day 15 (GD 15) induces a marked reduction of telencephalic areas of the offspring brain. Previous neurochemical studies demonstrated a marked cholinergic hyperinnervation in the cerebral cortex of microencephalic rats. In this study we have evaluated whether this cholinergic hyperinnervation could result in altered functionality of muscarinic receptors. Acetylcholinesterase activity (AChE) was increased by 69% in the cerebral cortex of MAM treated rats, confirming a relative hyperinnervation, whereas in the hippocampus and striatum no significant changes were observed. Despite the marked hyperinnervation, in the cerebral cortex of microencephalic rats neither muscarinic receptor-stimulated phosphoinositide metabolism nor muscarinic receptor density were altered. No differences in receptor density were also observed in the hippocampus and striatum. Chronic diisopropylfluorophosphate (DFP) administration induced a marked decrease of AChE activity and down-regulation of muscarinic receptors whereas atropine administration resulted in receptor up-regulation in cerebral cortex, striatum and hippocampus of both control and MAM rats. The results confirm a relative cholinergic hyperinnervation in the cerebral cortex of microencephalic rats and demonstrate that the regulation of muscarinic receptor-stimulated phosphoinositide metabolism and muscarinic receptor plasticity is not modified in a condition of increased cholinergic presynaptic terminals.

Influence of the acute stress on agonist-stimulated phosphoinositide hydrolysis in the rat cerebral cortex

1. The present study was carried out in order to elucidate the influence of the acute stress on alpha 1-adrenergic, serotonin-2 (5-HT2) and muscarinic cholinergic (M-Ach) receptors-mediated phosphoinositide (PI) hydrolysis in rat cerebral cortex slices. 2. In rat cerebral cortex slices, noradrenaline (NA), serotonin (5-HT) and carbachol stimulated [3H]inositol-monophosphate (IP1) accumulation in a concentration-dependent manner. 3. The forced swimming test (FST) for 15 min induced a significant reduction of 5-HT-stimulated [3H]IP1 accumulation, but this stress situation did not produce a significant alteration of NA- and carbachol-stimulated [3H]IP1 accumulation. 4. The FST for 15 min did not affect the density and affinity of alpha 1-adrenergic, 5-HT2 and M-Ach receptors. 5. In a mild acute stress situation, the intracellular signal transduction mediated by 5-HT was promptly inhibited as compared to the signal transduction mediated by NA or carbachol. This inhibition may be induced by an acute uncoupling of 5-HT2 receptor-mediated intracellular signal transduction.

Increase in cytoplasmic free Ca2+ elicited by noradrenalin and serotonin in cultured local interneurons of mouse olfactory bulb

Effects of noradrenalin and serotonin on cytoplasmic free Ca2+ concentrations ([Ca2+]i) were studied by using the fluorescent indicator fura-2 in cultured local interneurons of mouse olfactory bulb. Application of noradrenalin (0.1-100 microM) caused a rapid and concentration-dependent rise in [Ca2+]i, while isoproterenol was ineffective at concentrations up to 100 microM. The noradrenalin (1 microM)-induced increase in [Ca2+]i was completely inhibited by pretreatment with alpha 1-antagonist, prazosin (100 nM), whereas the inhibitory effect of alpha 2-antagonist, yohimbine, was about 100-times less potent. Serotonin (0.1-100 microM) also caused the dose-dependent rise in [Ca2+]i, which was inhibited by serotonin2 antagonist, ketanserin. Even in the absence of the extracellular calcium, the noradrenalin- or serotonin-induced increase in [Ca2+]i was observed. These results indicate that both noradrenalin and serotonin elicit the rise in [Ca2+]i in local interneurons of the olfactory bulb. They also suggest that the rise in [Ca2+]i is mediated by alpha 1-adrenergic and serotonin2 receptors, and that the increased calcium is mainly derived from intracellular calcium storage sites. The above results provide evidence to suggest that in the olfactory bulb, noradrenergic and serotonergic centrifugal fibers exert modulatory influences on synaptic interactions between mitral/tufted cells and local interneurons by increasing cytoplasmic Ca2+ in local interneurons.

Influence of stress and antidepressant treatment on 5-HT-stimulated phosphoinositide hydrolysis in rat brain

The aim was to elucidate the role of 5-hydroxytryptamine (5-HT)-stimulated phosphoinositide (PI) metabolism in stress situations and in the behavioral improvement produced by chronic antidepressant treatment. Rat cerebral cortex slices were used for the purpose. Forced swimming for 15 min and longer induced changes in behavioral activities of rats associated with a significant reduction of 5-HT-stimulated PI metabolism, without any changes in density and affinity of 5-HT2 receptors. This suggests that modulation of the receptor coupling process but not of the 5-HT2 receptor binding characteristics may be responsible for the significant reduction of 5-HT-stimulated PI metabolism in stress situations. Chronic antidepressant treatment tended to reduce 5-HT-stimulated PI metabolism. This treatment improved significantly the behavioural activities during forces swimming, and prevented the forced swimming-induced reduction of 5-HT-stimulated PI metabolism. It is postulated that chronic antidepressant treatment may improve behavioral activities in relation to PI metabolism in stress situations.

Inhibitory effects of okadaic acid on thyrotropin and prolactin secretion from rat anterior pituitaries

The present study was undertaken to elucidate the effects of okadaic acid, a potent inhibitor of protein phosphatases, on thyrotropin (TSH) and prolactin (PRL) secretion, and on the hydrolysis of inositol phospholipids in rat anterior pituitaries. Preincubation of anterior pituitaries with okadaic acid caused a dose dependent decrease in TRH- and K(+)-induced TSH secretion, whereas basal secretion of TSH was not affected by pretreatment with okadaic acid. In contrast, okadaic acid resulted in a marked inhibition in both basal, and TRH- and K(+)-stimulated PRL release from anterior pituitaries. In addition, pretreatment with okadaic acid caused a slight, but significant decrease in the formation of [3H]inositol phosphate ([3H]IP) in rat anterior pituitaries. The present study suggests that okadaic acid blocks the release of TSH and PRL by inhibiting Ca2+ influx and that inhibitory effects of okadaic acid on PRL release are, at least in part, due to the inhibition of inositol phospholipid hydrolysis.

Agonist-Stimulated Inositol Polyphosphate Formation in Cerebellum

The accumulation of inositol polyphosphates in the cerebellum in response to agonists has not been demonstrated. Guinea pig cerebellar slices prelabeled with [3H]inositol showed the following increases in response to 1 mM serotonin: At 15 s, there was a peak in 3H label in the second messenger inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], decreasing to a lower level in about 1 min. The level of 3H label in the putative second-messenger inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] increased rapidly up to 60 s and increased slowly thereafter. The accumulation of 3H label in various inositol phosphate isomers at 10 min, when steady state was obtained, showed the following increases due to serotonin: inositol 1,3,4-trisphosphate [Ins(1,3,4)P3], eight-fold; Ins(1,3,4,5)P4, 6.4-fold; Ins(1,4,5)P3, 75%; inositol 1,4-bisphosphate [Ins(1,4)P2], 0%; inositol 3,4-bisphosphate, 100%; inositol 1-phosphate/inositol 3-phosphate, 30%; and inositol 4-phosphate, 40%. [3H]Inositol 1,3-bisphosphate was not detected in controls, but it accounted for 7.2% of the total inositol bisphosphates formed in the serotonin-stimulated samples. The fact that serotonin did not increase the formation of Ins(1,4)P2 could be due to the fact that Ins(1,4)P2 is rapidly degraded or that Ins(1,4,5)P3 is metabolized primarily by Ins(1,4,5)P3-3'kinase to form Ins(1,3,4,5)P4. In the presence of pargyline (10 microM), [3H]Ins(1,3,4,5)P4 and [3H]Ins(1,3,4)P3 levels were increased, even at 1 microM serotonin. Ketanserin (7 microM) completely inhibited the serotonin effect, indicating stimulation of serotonin2 receptors. Quisqualic acid (100 microM) also increased the levels of [3H]Ins(1,4,5)P3, [3H]Ins(1,3,4,5)P4, and [3H]Ins(1,3,4)P3, but the profile of these increases was different.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscarinic binding sites in a catecholaminergic human neuroblastoma cell line

Tyrosine hydroxylase (TH) a characteristic enzyme activity for the catecholaminergic clonal cell line LA-N-1 and choline acetyltransferase (ChAT) a characteristic enzyme activity for the cholinergic clonal cell line LA-N-2 were previously shown to be increased in these cells exposed to 10(-5) M retinoic acid (RA) as differentiating agent. An investigation of the receptor characteristics suggests a complementarity between the two cell lines. The binding of QNB, a muscarinic ligand, was undetectable with the LA-N-2 cells but was present in the LA-N-1 cells and possessed a kD of 1.8 nM and 2.2 nM and a Bmax of 0.56 and 0.68 for control and RA grown cells respectively. There was a gradual increase in QNB binding to LA-N-1 cells from 2 days in vitro (DIV) until 6 DIV in both control and RA grown cells. An IC50 of 2.5 x 10(-8) M and 0.9 x 10(-8) M for atropine inhibition was obtained for the control and RA grown cells respectively. The corresponding values for carbachol inhibition were 7 x 10(-2) M and 3 x 10(-2) M respectively. The inhibition by the agonist oxotremorine is comparable to that of carbachol and 1 mM pilocarpine inhibited the binding by 21%. QNB binding showed a low affinity for pirenzepine and for AF-DX-116 but was inhibited with a rather high affinity by 4-DAMP (IC50:110 microM) thus suggesting the presence of an M3 receptor. Acetylcholine (100 microM) plus eserine (50 microM) and BW284c55 (1 microM), an acetylcholinesterase inhibitor, reduced the binding of QNB by approximately 25%.(ABSTRACT TRUNCATED AT 250 WORDS)

Li+ increases accumulation of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in cholinergically stimulated brain cortex slices in guinea pig, mouse and rat. The increases require inositol supplementation in mouse and rat but not in guinea pig

Li+, beginning at a concentration as low as 1 mM, produced a time- and dose-dependent increase in accumulation of [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4,5)P4 in acetylcholine (ACh)-stimulated guinea-pig brain cortex slices prelabelled with [3H]inositol and containing 1 mM-inositol in the final incubation period. Similar results were obtained by mass measurement of samples incubated with 10 mM-Li+ by using a receptor-binding assay, although the percentage stimulation of Ins(1,4,5)P3 accumulation by Li+ was somewhat less by this assay. The increase in accumulation of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 by Li+ was absolutely dependent on the presence of ACh. In the absence of added inositol, 1-5 mM-Li+ produced smaller increases in Ins(1,4,5)P3, but the Li(+)-dependent increase in Ins(1,3,4,5)P4 was not as affected by inositol omission. In previous studies with cholinergically stimulated rat and mouse brain cortex slices, Li+ inhibited accumulation of Ins(1,4,5)P3 in rat and inhibited Ins(1,3,4,5)P4 accumulation in rat and mouse [Batty & Nahorski (1987) Biochem. J. 247, 797-800; Whitworth & Kendall (1988) J. Neurochem. 51, 258-265]. We found that Li+ inhibited both Ins(1,4,5)P3 and Ins(1,3,4,5)P4 accumulation in these species, but we could reverse this inhibition by adding 10-30 mM-inositol; we then observed a Li(+)-induced increase in Ins(1,4,5)P3 and Ins(1,3,4,5)P4. The species differences observed in the absence of supplemented inositol were explained by the fact that a much higher concentration of inositol was required to bring the Li(+)-elevated levels of CDP-diacylglycerol (CDPDG) down to baseline in the rat and mouse. These data suggest that inositol is more rate-limiting for phosphatidylinositol synthesis in the presence of Li+ in rat and mouse, which can account for the previous reports of inhibition of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 accumulation by this ion in these species. Thus, in all species examined. Li+ could be shown to increase accumulation of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 in cholinergically stimulated brain cortex slices if the slices were supplemented with sufficient inositol to bring the Li(+)-elevated level of CDPDG down to near baseline, as seen in the absence of Li+. In guinea-pig brain cortex slices, increases in Ins(1,4,5)P3 and Ins(1,3,4,5)P4 accumulation could then be seen at Li+ concentrations as low as 1 mM, which falls within the therapeutic range of plasma concentrations in the treatment of manic-depressive disorders. These observations may have therapeutic implications.

Galanin receptors and their second messengers in the lumbar dorsal spinal cord

The ligand binding properties of galanin receptors were examined in crude synaptosomal fraction preparations of lumbar dorsal spinal cord, using chloramin-T mono-iodinated porcine Tyr26 galanin as ligand. The equilibrium binding of [125I]galanin showed the presence of a single population of high-affinity binding sites with KD = 0.6 +/- 0.2 nM in a concentration of 55 +/- 15 fmol mg-1 protein (Bmax). The N-terminal fragments galanin (1-16) and galanin (1-12) fully displaced specific [125I]galanin binding from membranes with IC50 values 6 nM and 4 microM, respectively. The C-terminal fragment galanin (17-29) did not displace [125I]galanin when applied in the concentration range 10(-11)-10(-4) M. GTP inhibited the specific binding of [125I] galanin in a concentration dependent manner, with 54% inhibition at 1 mM, suggesting that the galanin receptor found in lumbar dorsal spinal cord is G-protein coupled. Second messenger systems, through which the galanin receptor in lumbar dorsal spinal cord may exert its effect, were also studied. A galanin (10 microM) produced inhibition (58%) of the depolarization induced cGMP increase was found, whereas galanin (10 microM) did not inhibit the noradrenalin (100 microM) activated cAMP synthesis or phosphoinositide turnover in tissue slices of the spinal cord. Bilateral transection of the sciatic nerve at midthigh level 14 days prior to the binding experiment was performed, a treatment which is known to cause a dramatic increase of galanin-like immunoreactivity in the superficial layers of the dorsal spinal cord, dorsal root ganglion and in galanin mRNA levels, but no significant effect on Bmax or KD of the galanin receptor was found.

Analysis of muscarinic cholinoceptors mediating phosphoinositide hydrolysis in guinea pig cardiac muscle

The muscarinic receptor mediating stimulation of PI hydrolysis in guinea pig atria and ventricles has been studied. The non-selective muscarinic agonist (+)-cis-dioxolane elicited this response, concentration-dependently, with a potency indicative of a low receptor reserve. The potency of a novel, M2-selective agonist, L-660,863 (-log EC50 = 6.3, atria; 6.0, ventricles) was observed to be lower than its apparent affinity (-log KA = 7.6) for M2 receptors, indicating an action probably mediated by a population distinct from that producing negative inotropy in the same tissue. The inhibition of the response to (+)-cis-dioxolane by several muscarinic antagonists (atropine, pirenzepine, AF-DX 116, methoctramine, HHSiD and pFHHSiD) generated an affinity profile for this receptor also dissimilar to that described for the receptor mediating the classical cardiac 'M2' response. Although no other muscarinic receptor mRNA has been detected in this tissue, these data suggest the presence of a second population of muscarinic sites, which may signify an M2 receptor diversity.

5-HT1C receptors mediate phosphoinositide turnover activation in the immature rat hippocampus

The activation of phosphoinositide turnover in rat cerebral cortex and choroid plexus is triggered by the stimulation of 5-HT2 and 5-HT1C receptors, respectively. To characterize the 5-HT receptor subtype mediating the activation of phosphoinositide turnover in the hippocampus, the potency of several 5-HT agonists and antagonists on total [3H]inositol phosphate formation has been compared in the hippocampus, cerebral cortex and choroid plexus of immature rats. 5-HT, alpha-methyl-5-HT, quipazine, MK-212, mCPP (m-chlorophenylpiperazine) and TFMPP (m-trifluoromethylphenylpiperazine) are less potent and efficient in stimulating phosphoinositide turnover in the hippocampus and cerebral cortex than in the choroid plexus. However, for a number of 5-HT receptor antagonists (ketanserin, spiperone, ritanserin, pizotifen, cyproheptadine, mesulergine, mianserin, methiothepin, methysergide) there is a good correlation (r = 0.82) between their antagonistic potency in the hippocampus and choroid plexus while such correlation is not observed for the hippocampus and cerebral cortex. The specific 5-HT2 receptor antagonist spiperone only partially antagonizes (37% inhibition at 1 microM) the stimulation by 5-HT of phosphoinositide turnover in the hippocampus. These results suggest that in the immature rat hippocampus the activation of phosphoinositide turnover by 5-HT is mainly mediated by the 5-HT1C receptor subtype.