[GABA receptors in the central nervous system. Biochemical and pharmacological aspects].
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Allosteric Site↗
Biomedical subjects
M Hamon
Publications and source records attributed to M Hamon.
Suppression by perchlorate of technetium-99m and iodine-123 secretion in milk of lactating goats.
Lactating goats were infused with either technetium-99m (99mTc) or iodine-123 (123I) together with chlorine-36 (36Cl) through an indwelling catheter previously placed in an external pudic mammary artery. The radioisotope infusions were repeated together with 100 mg of sodium perchlorate. There was a rapid transfer of 99mTc and 123I into milk, reaching a peak concentration 30 min after a 15-min infusion. The fractional secretion of 99mTc and 123I in milk was reduced by 70%-80% and 60%-66%, respectively, by perchlorate. The fractional secretion of 36Cl was not affected by perchlorate, and the shape of the 36Cl secretion curve differed from those of 99mTc and 123I, which were similar. It is probable, therefore, that the latter nuclides were secreted by a transport route different from that of chloride. Available data describing the secretion of 99mTc in human milk after pertechnetate administration was reviewed, and it was concluded that perchlorate pretreatment significantly reduced the secretion of 99mTc in human breast milk.
Animals↗
[Role of halophilic and halotrophic bacteria in the chronic problems of long-term dialysis].
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Chromobacterium↗
Irreversible blockade of central 5-HT1A receptor binding sites by the photoaffinity probe 8-methoxy-3'-NAP-amino-PAT.
A new photoaffinity ligand derived from the potent 5-HT agonist, 8-OH-DPAT, has been synthesized. In the dark, this compound, 8-methoxy-2-(N-n-propyl,N-3-(2-nitro-4-azidophenyl)aminopropyl) aminotetralin or 8-methoxy-3'-NAP-amino-PAT, displaced [3H]8-OH-DPAT and [3H]5-HT bound to 5-HT1A and 5-HT1 sites in hippocampal membranes with IC50 values of 6.6 and 18.1 nM respectively. The apparent affinity of 8-methoxy-3'-NAP-amino-PAT for the 5-HT1A binding sites was at least 20 times higher than for the other 5-HT receptor sites (5-HT2 and 5-HT3) or the dopamine-related [3H]spiperone and [3H]7-OH-DPAT binding sites. Under UV irradiation (lambda = 366 nm), 8-methoxy-3'-NAP-amino-PAT produced an irreversible blockade of 5-HT1A sites which could be prevented by prior site occupancy by a saturating concentration (10 microM) of reversible 5-HT ligands such as 5-HT itself, 8-OH-DPAT or LSD. The blockade of 5-HT1A binding sites was concentration-dependent, and two successive irradiations of rat brain membranes in the presence of 30 nM 8-methoxy-3'-NAP-amino-PAT were found to be more efficient that a single exposure to 100 nM of the photosensitive ligand. Thus, a 55-60% irreversible blockade of 5-HT1A binding sites was achieved following 2 cumulative irradiations of hippocampal membranes with 30 nM 8-methoxy-3'-NAP-amino-PAT. Under such conditions, cortical 5-HT2 receptor binding sites as well as striatal 5-HT3 and dopamine-related binding sites remained unaltered.
8-Hydroxy-2-(di-n-propylamino)tetralin↗
Further evidence for a role of delta-opiate receptors in the presynaptic regulation of newly synthesized dopamine release.
The effects of the specific delta-agonist of opiate receptors, DTLET (Tyr-D-Thr-Gly-Phe-Leu-Thr), the specific mu-agonist DAGO (Tyr-D-Ala-Gly-(Me)Phe-Gly-ol) and of kelatorphan (N-((2R)-3-(hydroxyaminocarbonyl-2-benzyl-1-oxopropyl)-L-alanine), a potent inhibitor of the enkephalin-degrading enzymes, on the spontaneous release of [3H]dopamine ([3H]DA) synthesized from [3H]tyrosine were examined in rat striatal slices. DTLET (10(-7) M, 10(-6) M) and kelatorphan (5 X 10(-6) M) enhanced markedly the release of newly synthesized [3H]DA, while DAGO (10(-6) M) was inactive. The stimulatory effects of DTLET (10(-7) M) and kelatorphan (5 X 10(-6) M) were prevented in the presence of naloxone (3 X 10(-6) M; 10(-4) M respectively) or ICI 154,129 (10(-5) M), a selective antagonist of delta-opiate receptors. While DTLET (10(-7) M) stimulated the 30 mM potassium-evoked release of newly synthesized [3H]DA, it did not affect the potassium-evoked release of [3H]DA previously synthesized in tissues. A higher concentration of DTLET (10(-6) M) was required in the latter case. In contrast to the release observed with striatal slices, DTLET (10(-7) M), 10(-6) M) or DAGO (10(-6) M) did not affect the spontaneous release of newly synthesized [3H]DA from nucleus accumbens slices. In addition, DTLET (10(-6) M) was without effect on the potassium-evoked release of newly synthesized [3H]DA in this structure. The present results confirmed that delta-opiate receptors are involved in the presynaptic regulation of [3H]DA release.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Use of a new and rapid milk progesterone assay to monitor reproductive activity in the cow.
A new and rapid enzyme-amplified immunoassay (AELIA) has been developed for the measurement of progesterone in milk. The AELIA system is a non-isotopic method that gives results within 35 minutes. Milk progesterone concentrations measured in 10 cows sampled daily at various stages of the reproductive cycle were very similar to those recorded by a validated radioimmunoassay. The results show that the speed and sensitivity of the AELIA system would make it possible to diagnose pregnancy rapidly at about 24 days after insemination, to predict the onset of behavioural oestrus from decreasing progesterone values during the third week after a preceding oestrus, and to obtain a daily record of milk progesterone levels in animals treated for infertility of ovarian origin.
Animals↗
In situ molecular sizes of the various types of 5-HT binding sites in the rat brain.
The radiation inactivation technique has been used to estimate the molecular weights of 5-HT binding sites in various regions of the rat brain. Using 3H-5-HT or 3H-8-OH-DPAT as the ligand, the same molecular weight of 55,000-60,000 daltons was calculated for the postsynaptic 5-HT1A and 5-HT1B sites in the hippocampus and cerebral cortex. Studies with 3H-ketanserin as the selective ligand indicated a molecular weight in the same range for the post-synaptic 5-HT2 binding site in the cerebral cortex. In contrast, a higher value (67,000 daltons) was found for the presynaptic 5-HT3 site selectively labelled by 3H-8-OH-DPAT in the striatum and cerebral cortex. The curvilinear pattern of the radiation-induced inactivation of 5-HT1A and 5-HT1B binding sites suggested that both sites belong to complex polymeric structures. In contrast, the 5-HT2 and 5-HT3 sites may correspond to less cooperative structures since simple monoexponential inactivation curves were observed upon irradiation.
Animals↗
Distribution of Met-enkephalin immunoreactive fibres in the thalamus of the cat.
The Met-enkephalin-like immunoreactivity was studied in the thalamus of the cat using an indirect immunoperoxidase method. The densest network of immunoreactive fibres and terminals was observed in the epithalamus and the intralaminar nuclei, particularly those located along the midline nuclei interanteromedialis, submedius, rhomboidens and reuniens. The nuclei parafascicularis and centrum medianum contained also numerous immunoreactive fibres and terminals, whereas the lamina medullaris externa had a lower density of immunoreactive terminals. Enkephalin fibres were almost totally absent in the lateral nuclei of the thalamus, and in the posterior group only the magnocellular part of the corpus geniculatum mediale contained some immunoreactive fibres.
Animals↗
Modifications in the cortical regional distribution of choline acetyltransferase, somatostatin and somatostatin binding sites in the normal rat and following lesion of the nucleus basalis.
The regional distribution of choline acetyltransferase activity, somatostatin levels and 125I-CGP 23996 (a somatostatin agonist analog) specific binding sites in 10 separate zones of the cerebral cortex was analyzed. The study was performed in normal rats as well as 15 days after unilateral excitotoxic lesion of the nucleus basalis. A significant correlation was found in the controls between the regional distribution of choline acetyltransferase activity and somatostatin concentrations, both most highly concentrated in the piriform and entorhinal cortex. In contrast, the regional density of 125I-CGP 23996 binding sites correlated neither with choline acetyltransferase activity nor with somatostatin levels. Unilateral lesions of the basal forebrain decreased choline acetyltransferase activity in the frontal and parietal cortex, while 125I-CGP 23996 binding decreased in frontal and occipital regions. No decrease in somatostatin content was observed. The results suggest that, in rats, cortical somatostatin receptors could be associated with cholinergic afferents from the nucleus basalis in the frontal cortex only.
Animals↗
Characteristics of cells derived from the girdle region of the pre-implantation blastocyst of the donkey.
The establishment of a monolayer culture of cells derived from the girdle region of a 34-day-old donkey conceptus is described. These cells have had over 100 repeated passages in culture. Low levels of pregnant mares' serum gonadotrophin (PMSG, eCG) could be detected in the cells by indirect immunofluorescence using some monoclonal anti-eCG antibodies, but the cells did not secrete eCG as measured by radioimmunoassay or inhibition of haemagglutination. There was marked nuclear polymorphism with binucleate and occasional multinucleate cells. The cells were strongly reactive with wheatgerm agglutinin and concanavalin A suggesting the synthesis of many glycosylated products. Some cells were reactive with antisera to prekeratin, others with antisera to vimentin. The cells also contained actin (showing peculiar intercellular communications), alpha-actinin and tubulin. They were able to metabolize certain steroid precursors, but there was no definitive evidence for the presence of aromatase or delta 5-3 beta-hydroxysteroid dehydrogenase in these cells. This cell line appears to resemble trophectodermal girdle epithelium at a stage of development prior to the onset of eCG production, and may be useful in studies on the control of expression of this substance.
Animals↗
Differentiation of pre- and post-synaptic high affinity serotonin receptor binding sites using physico-chemical parameters and modifying agents.
The two 3H-labeled agonists [3H]8-hydroxy-2-(di-n-propylamino) tetralin ([3H]8-OH-DPAT) and [3H]serotonin ([3H]5-HT) have been used to examine the effects of physico-chemical parameters and modulatory agents on the high affinity 5-HT receptor binding sites in various regions of the rat central nervous system. Sites labeled by [3H]8-OH-DPAT and [3H]5-HT were differentially sensitive to changes in incubation temperature and pH, such that the optimal interaction of [3H]8-OH-DPAT with specific sites in the striatum was at 30 degrees C and pH 7.4, whereas [3H]5-HT sites in the same region were most easily labeled at 2-23 degrees C and pH 8.2. Micromolar concentrations of Mn2+ enhanced [3H]5-HT binding but inhibited markedly [3H]8-OH-DPAT binding to striatal membranes. In contrast, both [3H]5-HT and [3H]8-OH-DPAT binding were increased by the cation in hippocampal membranes. Conversely, GTP reduced the binding of either ligand in the hippocampus but affected only [3H]5-HT binding in the striatum. Furthermore, N-ethylmaleimide inhibited equally [3H]5-HT and [3H]8-OH-DPAT binding to hippocampal membranes, but was markedly less potent against [3H]8-OH-DPAT binding to striatal membranes. These results led to the definition of assay conditions for studying separately [3H]8-OH-DPAT binding to "hippocampal-like" (HL) and "striatal-like" (SL) sites. [3H]8-OH-DPAT HL binding sites were particularly abundant in the hippocampus, septum and cerebral cortex, and exhibited pharmacological properties typical of the postsynaptic 5-HT1A subsites previously characterized with [3H]5-HT as the ligand. The regional distribution of [3H]8-OH-DPAT SL binding sites was strikingly different from that of HL sites, but similar to that of serotoninergic terminals identified by their capacity to take up [3H]5-HT. The selective lesion by 5,7-dihydroxytryptamine of serotoninergic projections induced a marked loss of [3H]8-OH-DPAT SL binding sites in the striatum and the cerebral cortex, indicating that these sites were located presynaptically. In contrast, [3H]5-HT binding sites remained unchanged in lesioned rats, which confirmed further their exclusive postsynaptic location in brain.
5,7-Dihydroxytryptamine↗
The lesion of serotonergic neurons does not prevent antidepressant-induced reversal of escape failures produced by inescapable shocks in rats.
The present study was aimed at testing the hypothesis (based mainly on biochemical evidence) of the implication of brain serotonergic neurons in the induction of learned helplessness (escape deficit) and its reversal by antidepressants in rats. After desipramine (25 mg/kg IP)-pretreatment rats were either sham-operated or infused with 5,7-dihydroxytryptamine (5,7-DHT, 3 micrograms of free base in 0.4 microliter saline containing 0.02% ascorbic acid) into the midbrain raphe area. Three weeks later, experimental animals were exposed to 60 randomized inescapable shocks (0.8 mA; 15 sec duration), control rats being not shocked, and 48 hr later, they were subjected to daily shuttle-box sessions (30 trials/day; ITI = 30 sec) on 3 consecutive days in order to assess escape deficits. After inescapable shock pretreatment separate groups of rats were given twice daily injections of clomipramine (total daily dose: 32 mg/kg), desipramine (24 mg/kg), imipramine (32 mg/kg), nialamide (32 mg/kg) or saline. After behavioral testing, animals were sacrificed, and tryptophan hydroxylase activity was assayed in the cerebral cortex, the hippocampus and the striatum. We found that damage to serotonergic neurons associated with a 70% loss of tryptophan hydroxylase activity altered neither escape deficits produced by prior exposure to inescapable shock, nor the ability of either antidepressant studied to reverse escape failures in the shuttle-box paradigm. These findings cast some doubts on the hypothesized crucial role of serotonergic neurons in helpless behavior and its reversal by antidepressants.
Animals↗
Serotonin initiates and autoamplifies its own synthesis during mouse central nervous system development.
Some cells from cultured embryonic mouse hypothalamus were found to express aromatic-L-amino acid decarboxylase (EC 4.1.1.28) activity and serotonin uptake and storage. These neuron-like cells differed from serotoninergic neurons in cultured embryonic mouse brain stem since they did not contain tryptophan hydroxylase. We studied the effect of the serotonin agonist 8-hydroxy-2-[di-(n-propyl)amino]tetralin on neuronal differentiation of hypothalamic cells from 12- to 15-day embryos. Repeated treatment of cultures with the serotonin agonist for 10 days resulted in an increased number of serotonin cells containing high levels of decarboxylase activity. Both the increase in cell numbers and the elevated decarboxylase activity could be suppressed by the addition of the serotonin antagonist metergoline to the culture medium. These data show that serotonin (or an agonist), acting on specific receptors, can initiate and amplify its own synthesis in embryonic hypothalamic neurons, as observed in the primitive hypothalamic nerve cell line F7 [De Vitry, F., Catelon, J., Dubois, M., Thibault, J., Barritault, D., Courty, J., Bourgoin, S. & Hamon, M. (1986) Neurochem. Int. 9, 43-53]. Such an autocrine-like mechanism may be active during nervous system development and may represent an example of learning at the cellular level.
8-Hydroxy-2-(di-n-propylamino)tetralin↗
Is dopamine-induced inhibition of adenylate cyclase involved in the autoreceptor-mediated negative control of tyrosine hydroxylase in striatal dopaminergic terminals?
The mechanism of the negative control of tyrosine hydroxylase (TH) activity induced by the stimulation of presynaptic 3,4-dihydroxyphenylethylamine (dopamine, DA) autoreceptors was investigated using rat striatal slices and synaptosomes incubated under control ([ K+] = 4.8 mM) or depolarizing ([ K+] = 60 mM) conditions. The stimulation of DA autoreceptors by 7-hydroxy-2-(di-n-propylamino)tetralin (1 microM 7-OH-DPAT) produced a significant decrease in TH activity extracted from striatal slices maintained under control conditions. This effect was associated with the complete conversion of TH into an enzyme form with a low affinity for its pterin cofactor (Km approximately 0.80 mM). Furthermore, compared to TH extracted from control tissues, that from 7-OH-DPAT-exposed striatal slices was more sensitive to the stimulatory effects of exogenous heparin and cyclic AMP-dependent phosphorylation. Such changes were opposite to those induced by incubating striatal slices with the adenylate cyclase activator forskolin. Indeed, forskolin treatment completely converted TH into an enzyme form with a high affinity for its pterin cofactor (Km approximately 0.16 mM). Such conversion was associated with a shift in the optimal pH for TH activity from 5.8 (control) to 7.2 (forskolin). Under depolarizing conditions, the blockade by (-)-sulpiride of the stimulation of DA autoreceptors by endogenous DA was associated with a marked activation of TH. Modifications of enzymatic characteristics triggered by (-)-sulpiride were then similar to those induced by forskolin treatment. These data suggest that presynaptic DA autoreceptors modulate the activity of TH by controlling the degree of cyclic AMP-dependent phosphorylation of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
8-Hydroxy-2-(di-n-propylamino)tetralin↗
Presynaptic dopamine autoreceptors control tyrosine hydroxylase activation in depolarized striatal dopaminergic terminals.
The possible control of tyrosine hydroxylase (TH) activity by dopaminergic receptor-dependent mechanisms was investigated using rat striatal slices or synaptosomes incubated in the presence of various 3,4-dihydroxyphenylethylamine (dopamine or DA) agonists and antagonists. Under "normal" conditions (4.8 mM K+ in the incubating medium), the DA agonists apomorphine, 6,7-dihydroxy-N,N-dimethyl-2-aminotetralin (TL-99), 7-hydroxy-N,N-dipropyl-2-aminotetralin (7-OH-DPAT), Trans-(-)-4,4a,5,6,7,8,8a,9-octahydro-5-propyl-2H-pyrazolo-3,4- quinoline, and 3-(3-hydroxyphenyl)-N-n-propylpiperidine decreased TH activity in soluble extracts of incubated tissues. In the case of the catechol-containing drugs apomorphine and TL-99, this effect was partly due to a direct inhibition of the enzyme, but in all other cases it appeared to depend on the stimulation of presynaptic DA autoreceptors. No effect of DA antagonists was detected on TH activity under "normal" conditions. In contrast, when tissues were incubated in a K+ -enriched (60 mM) medium, (-)-sulpiride and other DA antagonists enhanced TH activation due to depolarization whereas DA agonists were ineffective. Because (-)-sulpiride also increased the enzyme activity in striatal slices exposed to drugs inducing release of DA, such as veratridine and d-amphetamine, it is concluded that the stimulating effect of the DA antagonist resulted in fact from the blockade of the negative control of TH normally triggered by endogenous DA acting on presynaptic autoreceptors. In contrast to TH activation due to K+ -induced depolarization, the activation evoked by tissue incubation with dibutyryl cyclic AMP was unaffected by the typical agonist 7-OH-DPAT or the antagonist (-)-sulpiride. This would suggest that TH control via presynaptic DA autoreceptors normally concerns possible modulations of the cyclic AMP-dependent phosphorylation of the enzyme.
Amphetamine↗
Kinetics of transfer of 125I-labelled epidermal growth factor from blood into mammary secretions of goats.
125I-Labelled mouse epidermal growth factor (125I-EGF) was transferred intact and undegraded from circulating blood into milk in conscious lactating goats. Greater than 90% of the total radioactivity present in milk from the infused gland was in the aqueous phase and more than 72% was acid-precipitable. This radiolabelled material co-eluted with authentic EGF through gel filtration and was immunoprecipitable by a specific rabbit anti-mouse EGF immunoglobulin. Mammary uptake of 125I-EGF infused into mammary arterial blood (close-arterial infusion) for 1 h varied from 20 to 83% at different stages of the reproductive cycle. Only 0.5-2.9% of the infused 125I-EGF was transferred into milk during the first 3 h after the start of the infusion, which represents 0.7-6.3% of mammary uptake of EGF. The kinetics of transfer of 125I-EGF were followed in two lactating goats. Radioactivity reached peak levels in milk about 120 min after the start of a 1 h close-arterial infusion into the mammary gland, with an initial lag of about 30 min when little transfer occurred. Transfer was slower in two non-lactating goats with maximal levels of activity in milk being reached after about 180 min. The results are consistent with a transcellular transfer, whereby the factor is bound to receptors on the baso-lateral membrane, internalized by epithelial cells and subsequently secreted across the apical membrane into the alveolar lumen. The low level of degraded labelled EGF in milk (and mammary vein blood) suggests a modification of the normal pathway of EGF degradation such that the delivery of internalized factor to lysosomes is avoided.
Animals↗
Quantitative autoradiography of multiple 5-HT1 receptor subtypes in the brain of control or 5,7-dihydroxytryptamine-treated rats.
The distribution of the 2 main types (A and B) of 5-HT1 binding sites in the rat brain was studied by light-microscopic quantitative autoradiography. The 5-HT1A sites were identified using 3H-8-hydroxy-2-(N-dipropylamino)tetralin (3H-8-OH-DPAT) or 3H-5-HT as the ligand. In the latter case, it was shown that 3H-5-HT binding to 5-HT1A sites corresponded to that displaceable by 0.1 microM 8-OH-DPAT or 1 microM spiperone. The "non-5-HT1A" sites labeled by 3H-5-HT in the presence of 0.1 microM 8-OH-DPAT corresponded mainly to 5-HT1B sites. 5-HT1A binding was notably high in limbic regions (dentate gyrus, CA1 and CA3 hippocampal regions, lateral septum, frontal cortex), whereas 5-HT1B binding was particularly concentrated in extrapyramidal areas (caudate nucleus, globus pallidus, substantia nigra). Except in the latter regions, where only one class of 5-HT1 sites was found, both 5-HT1A and 5-HT1B sites existed in all areas examined. The selective degeneration of serotoninergic neurons produced by an intracerebral injection of 5,7-dihydroxytryptamine was associated only with a significant loss of 5-HT1A binding to the dorsal raphe nucleus (-60%) and of 5-HT1B binding to the substantia nigra (-37%). These results are discussed in relation to the possible identity of 5-HT1A and/or 5-HT1B sites with the presynaptic 5-HT autoreceptors controlling nerve impulse flow and neurotransmitter release in serotoninergic neurons.
5,7-Dihydroxytryptamine↗
Increase in met-enkephalin level and antinociceptive effects induced by kelatorphan in the rat spinal cord.
Kelatorphan, a mixed inhibitor of "enkephalinases" is used for demonstrating the implication of endogenous enkephalins in nociceptive transmission at the spinal level.
Analgesics↗