Phloretin as an Antagonist of Prostaglandin F2α Receptor in Cultured Rat Astrocytes

Abstract: The effect of phloretin on prostaglandin (PG) F_2α-induced phosphoinositide hydrolysis and elevation of intracellular Ca²⁺ concentration was examined in cultured rat astrocytes. Phloretin inhibited PGF_2α (1 μ M )-induced phosphoinositide hydrolysis in a concentration-dependent manner with an IC₅₀ value of 16 μ M . The inhibitory action of phloretin was specific for PGs. The addition of increasing concentrations of phloretin caused progressive shifts of the dose-response curves of PGF_2α to the right. In digitoninpermeabilized astrocytes, phloretin (100 μ M ) inhibited the stimulation induced by PGF_2α (1 μ M ) plus GTPγS (50 μ M ) without affecting that induced by GTPγS alone. PGF_2α at 1 μ M transiently increased astrocytic intracellular Ca²⁺ concentration in 39% of the cells tested. The response was completely blocked by 100 μ M phloretin and the calcium response recovered again after washing out phloretin. These results suggest that phloretin is an antagonist of PGF_2α receptor linked to phospholipase C in astrocytes.     

Behavioural and electrophysiological responses to F-prostaglandins, putative spawning pheromones, in three salmonid fishes

Behavioural and electro-olfactogram (EOG) responses to synthetic F-prostaglandins (PGFs) were recorded in the three salmonids: brown trout Salmo trutta , lake whitefish Coregonus clupeaformis and rainbow trout Oncorhynchus mykiss . Exposure to 10⁻⁸ M PGF_2α and 13, 14-dihydro-PGF_2α increased swimming activity in individually exposed brown trout in a flow-through tank. Digging and nest probing behaviours were further observed in brown trout females exposed to PGF_2α. Lake whitefish exposed to 10⁻⁸ M PGF_2α and 15-keto-PGF_2α also increased their locomotion. In rainbow trout, the absence of behavioural responses to PGFs correlates with a lack of olfactory sensitivity to these chemicals. PGFs triggered behavioural responses distinct from the feeding stimulant in brown trout. EOG measurements demonstrated that brown trout were most sensitive to PGF_2α, with a threshold concentration of 10⁻¹¹ M. Lake whitefish were most sensitive to both 15-keto-PGF_2α and 13, 14-dihydro-PGF_2α. Cross-adaptation and binary mixture experiments suggest that only one olfactory receptive mechanism is involved in PGFs detection. The behavioural and olfactory responses observed with exposure to PGF_2α and its metabolites suggest these compounds function as reproductive pheromones in brown trout and lake whitefish.     

On the Mechanism of the Involvement of Monoamine Oxidase in Catecholamine-Stimulated Prostaglandin Biosynthesis in Particulate Fraction of Rat Brain Homogenates: Role of Hydrogen Peroxide

Abstract: The mechanism of involvement of monoamine oxidase (MAO) in catecholamine-stimulated prostaglandin (PG) biosynthesis was studied in the particulate fraction of rat brain homogenates. High concentrations of either noradrenaline (NA) or dopamine (DA) stimulated effectively PGF_2α formation. The same amount of 2-phenylethylamine (PEA) acted similarly, provided that it was administered together with a catecholamine analogue or metabolite possessing the 3,4-dihydroxyphenyl nucleus–3, 4-dihydroxyphenylalanine (DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), 3,4-dihydroxyphenyl-glycol (DOPEG), 3,4-dihydroxyphenylacetaldehyde (DOPAL), or α-methylnoradrenaline (α-met-NA)–or with SnCl₂. In the absence of PEA, these compounds were ineffective with regard to stimulation of PGF_2α formation. Catalase, pargyline, or indomethacin abolished completely PGF_2α formation elicited either by catecholamines or by PEA plus a 3,4-dihydroxyphenyl compound or SnCl₂. With regard to the stimulation of PGF_2α formation in the presence of α-met-NA, PEA could be replaced by H₂O₂, generated by the glucose oxidase(GOD)-glucose system. The effect of H₂O₂ was inhibited by indomethacin or catalase, but pargyline was ineffective. It is assumed that catecholamines play a dual role in the activation of PG biosynthesis in brain tissue. During the enzymatic decomposition of catecholamines MAO produces H₂O₂, which stimulates endoperoxide synthesis. Simultaneously, catecholamines as hydrogen donors promote the nonenzymatic transformation of endoperoxides into PGF_2α. The possible physiological importance of these findings is discussed.     

Preliminary studies on eicosanoid production by fish leucocytes, using GC-mass spectrometry

Culture supernatants from dogfish leucocytes, exposed to the Ca²⁺ ionophore A23187, were analyzed for eicosanoid production by gas chromatography-electron capture mass spectrometry. Consistently high levels of the prostaglandins (PG) D₂, F_2α and E₂ were produced, while thromboxane B₂ and leukotriene B₄ were found in smaller amounts. No 6-oxo PGF_1α, a degradation product of prostacyclin, or 13,14-dihydro-15-oxo-PGF_2α, a metabolite of PGE₂ and PGF_2α, were detected. The results are compared with similar experiments using mammalian leucocytes.     

The role of F-series prostaglandins as reproductive priming pheromones in the brown trout

Electrophysiological studies demonstrated that the olfactory epithelium of mature male brown trout Salmo trutta parr was acutely sensitive to F-series prostaglandins (PGFs) PGF_1α and PGF_2α, with detection threshold concentrations of 10⁻¹¹ M. The olfactory epithelium was also sensitive to the PGF metabolite 15-ketoPGF_2α (threshold 10⁻⁸ m), but did not detect a further metabolite, 13,14,-dihydro-15-ketoPGF_2α Immature brown trout did not detect any of the prostaglandins tested. Exposure of mature male brown trout parr to waterborne PGF_1α and PGF_2α (concentration 10⁻⁸ m), resulted in significant increases in levels of expressible milt and the plasma concentrations of 17,20β-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. The olfactory epithelium of both immature and mature male brown trout parr was sensitive to the urine and ovarian fluid from ovulated female brown trout. Exposure of mature male brown trout parr to ovarian fluid resulted in an increase in the levels of plasma 17,20β-dihydroxy-4-pregnen-3-one whilst exposure to urine increased the levels of expressible milt. In addition, PGF_2α was found to be present within both the urine and ovarian fluid of mature female brown trout. It is suggested that the F-series prostaglandins have a role as priming pheromones in male brown trout.     

Metabolism of Prostaglandin D2 by Human Cerebral Cortex into 9α, 11β-Prostaglandin F2 by an Active NADPH-Dependent 11-Ketoreductase

Abstract: In homogenates of rat cerebral neocortex prostaglandin D₂ (PGD₂) was found to be quantitatively the main PG biosynthesized by a cytosolic PGD synthetase from en-dogenously released arachidonic acid. Amounts of 628 ng/g wet weight were found after 30-min incubation periods compared with basal levels of 2.3 ng/g wet weight. In human cerebral cortex, whether obtained at biopsy or postmortem, only small amounts of PGD₂ (4.5–11.7 ng/g wet weight/30 min) were formed. Furthermore, PGD₂, added to homogenates of human biopsy temporal cortex, was converted efficiently into 9α,11β-PGF₂ by a NADPH-dependent 11-ke-toreductase as has been reported in other human tissues (liver and lung). PGF_2α was determined directly as the fl-butylbo-ronate derivative. It became clear that 9α,11β-PGF₂ was formed in considerably greater amounts than PGF_2α and that other metabolites are also formed. These results can account for the low amounts of PGD₂ found in incubations of human brain tissue. The rat brain does not contain 11-ketoreductase activity. The present results indicate that the 9α, 11β-PGF₂ must be considered along with other eicosanoids in pathophysiological situations in brain.     

MODULATION OF CYCLIC AMP LEVELS IN THE BOVINE SUPERIOR CERVICAL GANGLION BY PROSTAGLANDIN E, AND DOPAMINE

Abstract— Dopamine, norepinephrine, carbamylcholine and PGE₁ (prostaglandin E₁). increased cyclic AMP concentrations in slices of bovine superior cervical ganglia. PGF_1α was less effective and neither PGE₂ nor PGF_2α had any effect. Dopamine and PGE, alone or in combination, did not modify low K _m cyclic AMP phosphodiesterase activity. Combinations of dopamine and PGE, showed a marked synergistic effect, increasing ganglionic cyclic AMP to a much greater extent than that observed when the two compounds were tested alone. Norepinephrine (10 μ M) , which increased cyclic AMP as much as 10 μ m -dopamine, showed no synergistic effect when tested in the presence of PGE₁ or other PGs. Phentolamine, fluphenazine and triflupromazine blocked the dopamine effect without suppressing its synergism with PGE₁ Adenylate cyclase of synaptosomes isolated from the ganglia under a variety of experimental conditions appeared to be as responsive to PGE₁ as the slices, but it was poorly stimulated by dopamine and was not synergistically modulated by dopamine in the presence of PGE₁
These and other data are interpreted as indicating the presence of both a PGE₁-sensitive and a PGE₁-modulated dopamine-sensitive adenylate cyclase in the cervical ganglion. These adenylate cyclases are tentatively assigned to pre- and post-synaptic structures respectively.     

Histidine carboxylase of Leuconostoc œnos 9204: purification, kinetic properties, cloning and nucleotide sequence of the hdc gene

Histidine decarboxylase (HDC) was purified to homogeneity from Leuconostoc ' nos 9204, a wine lactic acid bacterium. Histidine decarboxylase comprised two subunits, respectively α and β. The hdc gene was cloned and sequenced. The gene encodes a single polypeptide of 315 amino acids, demonstrating that Leuc. ' nos 9204 HDC was synthesized as a precursor proHDC π₆ (Mr 205 000). A cleavage between Ser-81 and Ser-82 generated the α (Mr 25 380) and β (Mr 8840) chains, which suggested that the holoenzyme exists as a hexameric structure (αβ)₆. At the optimal pH of 4·8, the HDC activity exhibited a simple Michaelis-Menten kinetic ( K _m = 0·33 mmol l⁻¹, V _max = 17·8 μmol CO₂ min⁻¹ mg⁻¹), while at pH 7·6 it was sigmoidal (cooperativity index of 2). Histamine acted as a competitive inhibitor ( K _i = 32 mmol l⁻¹). The similarities of these results with those described for other bacterial HDC support the assumption that the pyruvoyl enzymes evolved from a common ancestral protein and have similar catalytic mechanisms. These results also confirmed that the main lactic acid bacterial species responsible for malolactic fermentation in red wine is able to produce histamine. Bacteria carrying the HDC activity must be avoided during selection of strains for the production of malolactic starters.     

CATABOLISM OF PROSTAGLANDIN ENDOPEROXIDES INTO PROSTAGLANDIN E2 AND F2x BY THE RAT BRAIN

Abstract— Tritium labeled prostaglandin (PG) endoperoxides PGG₂ and PGH₂ were rapidly transformed (2 min, 37°C) in good yield (> 50%) by homogenates of whole rat brain into a mixture of products including prostaglandin E₂ and F_2x: under similar conditions (10min. 37°C) tritium labeled arachidonic acid remained essentially unoxidised. The ratio of PGE-like products: PGF_2x formed was approx 0.5 as determined by radio thin layer chromatography. This ratio changed to unity when homogenates of cerebral cortex or cerebral hemispheres were employed. On the other hand cerebellar homogenates formed PGF_2x in much greater amounts. The structures of the products were confirmed by mass spectrometry and were further supported by experiments using octadeuterio-endoperoxides. In the latter experiments the resulting PGE₂ and PGF_2x contained the expected seven and eight deuterium atoms respectively. Evidence for the formation of heptadeuterio PGD₂. heptadeuterio-6-keto-PGF₁, and hexadeuterio 12-hydroxyheptadecatrienoic acid was also obtained by mass spectrometry. These experiments demonstrate for the first time in brain tissue the biosynthesis of labeled prostaglandins from exogenous tritiated and deuterated precursors.     

Prostaglandin E2 Induces Interleukin-6 Synthesis in Human Astrocytoma Cells

Abstract: Prostaglandins (PGs) and cytokines, such as interleukin-1 (IL-1) and interleukin-6 (IL-6), have been implicated in the etiopathology of various inflammatory and degenerative disorders, including Alzheimer's disease (AD) and prion diseases. Nonsteroidal antiinflammatory drugs (NSAIDs), potent inhibitors of PG synthesis, appear to be beneficial in the treatment of AD. To assess whether PGs are able to induce IL-6 synthesis in cells of the CNS, IL-6 mRNA and protein syntheses were measured in a human astrocytoma cell line after stimulation with different PGs. PGE₁ and PGE₂, but not PGD₂ and PGF_2α, led to a rapid and transient induction of IL-6 mRNA, followed by IL-6 protein synthesis. Furthermore, PGE₂ potentiated IL-1β-induced IL-6 mRNA synthesis. These results are discussed with respect to the participation of PGs in neurodegenerative diseases (and its inhibition by NSAIDs) by affecting cytokine expression.     

Changes in spectral properties of ageing and senescing maize and sunflower leaves

Activity and biochemical characteristic of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase from pear ( Pyrus communis cv. Blanquilla) was determined. The enzyme showed a low K_m (57.5 μM) for ACC and was dependent on O₂ (K_m 0.44% in atmosphere). It had an absolute requirement for Fe²⁺, ascorbate and CO₂ and was inhibited by α-aminoisobutyric acid (AIB: K₁ 4.2 m M ) and cobalt. ACC oxidase has an optimum pH of 6.7 and temperature maxima at 28 and 38°C and it is concluded that the activity of ACC oxidase from pear resembles authentic in vivo activity.     

Structure and Functional Characterization of a Novel Human Low-Voltage Activated Calcium Channel

Abstract : We have isolated and characterized overlapping cDNAs encoding a novel, voltage-gated Ca²⁺ channel α₁ subunit, α_1H, from a human medullary thyroid carcinoma cell line. The α_1H subunit is structurally similar to previously described α₁ subunits. Northern blot analysis indicates that α_1H mRNA is expressed throughout the brain, primarily in the amygdala, caudate nucleus, and putamen, as well as in several nonneuronal tissues, with relatively high levels in the liver, kidney, and heart. Ba²⁺ currents recorded from human embryonic kidney 293 cells transiently expressing α_1H activated at relatively hyperpolarized potentials (-50 mV), rapidly inactivated (τ = 17 ms), and slowly deactivated. Similar results were observed in Xenopus oocytes expressing α_1H. Singlechannel measurements in human embryonic kidney 293 cells revealed a single-channel conductance of ~9 pS. These channels are blocked by Ni²⁺ (IC₅₀ = 6.6 μ M ) and the T-type channel antagonists mibefradil (~50% block at 1 μ M ) and amiloride (IC₅₀ = 167 μ M ). Thus, α_1H-containing channels exhibit biophysical and pharmacological properties characteristic of low voltage-activated, or T-type, Ca²⁺ channels.     

Interaction of α-conotoxin ImII and its analogs with nicotinic receptors and acetylcholine-binding proteins: additional binding sites on Torpedo receptor

α-Conotoxins interact with nicotinic acetylcholine receptors (nAChRs) and acetylcholine-binding proteins (AChBPs) at the sites for agonists/competitive antagonists. α-Conotoxins blocking muscle-type or α7 nAChRs compete with α-bungarotoxin. However, α-conotoxin ImII, a close homolog of the α7 nAChR-targeting α-conotoxin ImI, blocked α7 and muscle nAChRs without displacing α-bungarotoxin ( Ellison et al. 2003, 2004 ), suggesting binding at a different site. We synthesized α-conotoxin ImII, its ribbon isomer (ImII iso ), 'mutant' ImII(W10Y) and found similar potencies in blocking human α7 and muscle nAChRs in Xenopus oocytes. Both isomers displaced [¹²⁵I]-α-bungarotoxin from human α7 nAChRs in the cell line GH₄C₁ (IC₅₀ 17 and 23 μM, respectively) and from Lymnaea stagnalis and Aplysia californica AChBPs (IC₅₀ 2.0–9.0 μM). According to SPR measurements, both isomers bound to immobilized AChBPs and competed with AChBP for immobilized α-bungarotoxin ( K _d and IC₅₀ 2.5–8.2 μM). On Torpedo nAChR, α-conotoxin [¹²⁵I]-ImII(W10Y) revealed specific binding ( K _d 1.5–6.1 μM) and could be displaced by α-conotoxin ImII, ImII iso and ImII(W10Y) with IC₅₀ 2.7, 2.2 and 3.1 μM, respectively. As α-cobratoxin and α-conotoxin ImI displaced [¹²⁵I]-ImII(W10Y) only at higher concentrations (IC₅₀≥ 90 μM), our results indicate that α-conotoxin ImII and its congeners have an additional binding site on Torpedo nAChR distinct from the site for agonists/competitive antagonists.     

Effects of Dopaminergic Drugs on Cerebellar Prostaglandin Concentrations

Abstract: Previous data indicate that the injection of dopaminergic drugs induces changes in cerebellar 3',5'-guanosine monophosphate (cGMP) content. Accordingly, we have investigated the effects of haloperidol, sulpiride, or apomorphine on cerebellar prostaglandin (PG) concentration, a parameter related to cGMP content. Results obtained show that dopamine receptor blocking agents, such as haloperidol and sulpiride, significantly decrease cerebellar PGE₂ and PGF_2α concentrations, while opposite changes are induced by apomorphine, a dopamine receptor agonist.     

Protective mechanisms of nitrogenase against oxygen excess and partially-reduced oxygen intermediates

Diazotrophic systems have developed a number of strategies to protect nitrogenase (N₂ase; EC 1.18.6.1) from O₂ excess and active-oxygen species (AOS). Protection against O₂ excess is given by biochemical modifications of N₂ase, increased rates of low-efficiency respiration, temporal segregation of N₂ fixation and photosynthesis, physical barriers to O₂ diffusion, and hemoglobins. On the other hand, AOS may originate from oxidation of N₂ase components, ferredoxins, flavodoxins and hemoglobins; interaction among the AOS themselves, or between H₂O₂ and hemoglobins; and during reactions catalyzed by hydrogenase (EC 1.18.99.1), xanthine oxidase (EC 1.1.3.22) and uricase (EC 1.7.3.3). Active-oxygen species are scavenged enzymatically [superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6). peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11)] or through non-enzymic reaction with low-molecular-weight compounds (ascorbate, α-tocopherol, glutathione).     

Roles of Prostaglandins D2 and E2 in Interleukin-1-Induced Activation of Norepinephrine Turnover in the Brain and Peripheral Organs of Rats

Abstract: Possible roles of prostaglandins (PGs) in interleukin-1 (IL-1)-induced activation of noradrenergic neurons were examined by assessing norepinephrine (NE) turnover in the brain and peripheral organs of rats. An intraperitoneal injection of human recombinant IL-1β accelerated NE turnover in the hypothalamus, spleen, lung, diaphragm, and pancreas. A similar increase in NE turnover was also observed after intracerebroventricular injection of corticotropin-releasing hormone (CRH). Pretreatment with indomethacin (cyclooxygenase inhibitor) abolished the IL-1-induced, but not the CRH-induced, increase in hypothalamic and splenic NE turnover. To elucidate which eicosanoid-cyclooxygenase product(s) is responsible for accelerating NE turnover, PGD₂, PGE₂, PGF_2α, U-46619 (stable thromboxane A₂ analogue), or carbacyclin (stable prostacyclin analogue) was administered intracerebroventricularly. Among them, PGE₂ was the only eicosanoid effective in increasing NE turnover in spleen, whereas PGD₂ was effective in the hypothalamus. The stimulative effect of PGD₂ was abolished by pretreatment with intracerebroventricular injection of a CRH antiserum. These results suggest that the action of IL-1 is mediated through PGD₂ production to activate the noradrenergic neurons in the hypothalamus, and through PGE₂ production to increase sympathetic nerve activity in spleen.     

The role of inositol lipids in the activation of monocytes by interleukin-1 and bacterial endotoxin

Abstract The effect of interleukin-1 (IL-1) and bacterial endotoxin (lipopolysaccharide, LPS) on the activation of phosphoinositidase C (PIC) and on prostaglandin E₂ release was studied in monocytes (Mø). Both IL-1α and IL-1β increased the release of PGE₂ in a concentration-dependent manner, with EC₅₀s of 0.48 nM and 0.12 nM, respectively. Intact Mø were prelabelled with [³H]inositol and the formation of inositol phosphates (IPs) was estimated by ion exchange chromatography. PIC activity was estimated directly by measuring the conversion of [³H]phosphatidylinositol-4,5,-bisphosphate to aqueous soluble radioactivity by Mø homogenates. IL-1α (5.8 nM) increased the accumulation of IPs within 1–4 minutes and increases in IP₃ and IP₄ occured before the increase in IP₁₊₂ whereas LPS only increased the IPs level after at least 30 min. IL-1α increased PIC activity in Mø homogenates within 15 min with an EC₅₀ of 0.58 nM and IL-1β (0.1 nM) also increased activity. Neither IL-1α nor IL-1β affected the PIC activity of membrane or cytosolic fractions. LPS decreased activity in all fractions. These data indicate that IL-1, but not LPS, can directly lead to an increased activity of PIC which may be involved in eicosanoid formation in Mø.     

[3H]GLYCOGEN HYDROLYSIS IN BRAIN SLICES: RESPONSES TO NEUROTRANSMITTERS AND MODULATION OF NORADRENALINE RECEPTORS

Abstract— Different agents have been investigated for their effects on [C³H]glycogen synthesized in mouse cortical slices. Of these noradrenaline, serotonin and histamine induced clear concentration-dependent glycogenolysis.
[C³H]Glycogen hydrolysis induced by noradrenaline appears to be mediated by beta-adrenergic receptors because it is completely prevented by timolol, while phentolamine is ineffective. It seems to involve cyclic AMP because it is potentiated in the presence of isobutylmethylxanthine; in addition dibutyryl cyclic AMP (but not dibutyryl cyclic GMP) promotes glycogenolysis.
Lower concentrations of noradrenaline were necessary for [C³H]glycogen hydrolysis (EC₅₀= 0.5μM) than for stimulation of cyclic AMP accumulation (EC₅₀= 8μM).
After subchronic reserpine treatment the concentration-response curve to noradrenaline was significantly shifted to the left (EC₅₀= 0.09 ± 0.02 μM as compared with 0.49 ± 0.08 μM in saline-pretreated mice) without modifications of either the basal [C³H]glycogen level, maximal glycogenolytic effect, or the dibutyryl cAMP-induced glycogenolytic response.
In addition to noradrenaline, clear concentration-dependent [³H]glycogen hydrolysis was observed in the presence of histamine or serotonin. In contrast to the partial [³H]glycogen hydrolysis elicited by these biogenic amines, depolarization of the slices by 50 mM K⁺ provoked a nearly total [C³H)glycogen hydrolysis.     

A desk study of the relationship between temperature and hatching time for the eggs of five species of salmonid fishes

SUMMARY. Information on temperature (T°C) and time from fertilization to 50% hatch ( D days) for five species of salmonid fishes has been used to assess several mathematical models relating D and T . No single equation gave the best fit to all five data sets. The power law with temperature correction (α), log₁₀₁ D = log₁₀ a + b log₁₀ ( T - α) and the quadratic, log₁₀ D = log₁₀ a + bT + b ₁ T ² (where a, b, b ₁, and α are constants), each accounted for over 97 % of the variance of D and were good fits to the observed data points for all five species. There was little difference between the predictions obtained from these two equations within the range of observed temperatures. Therefore, the simpler power-law model is preferred. However, there were substantial within-species differences between values of D predicted from extrapolations of the two models from 2 or 3°C down to 0°C. When more data for low temperatures become available it will be possible to make a more objective choice of model.     

Histamine induces neural stem cell proliferation and neuronal differentiation by activation of distinct histamine receptors

Histamine has neurotransmitter/neuromodulator functions in the adult brain, but its role during CNS development has been elusive. We studied histamine effects on proliferation, cell death and differentiation of neuroepithelial stem cells from rat cerebral cortex in vitro . RT-PCR and Western blot experiments showed that proliferating and differentiated cells express histamine H₁, H₂ and H₃ receptors. Treatments with histamine concentrations (100 nM–1 mM) caused significant increases in cell numbers without affecting Nestin expression. Cell proliferation was evaluated by BrdU incorporation; histamine caused a significant increase dependent on H₂ receptor activation. Apoptotic cell death during proliferation was significantly decreased at all histamine concentrations, and cell death was promoted in a concentration-dependent manner by histamine in differentiated cells. Immunocytochemistry studies showed that histamine increased 3-fold the number of neurons after differentiation, mainly by activation of H₁ receptor, and also significantly decreased the glial (astrocytic) cell proportion, when compared to control conditions. In summary, histamine increases cell number during proliferative conditions, and has a neuronal-differentiating action on neural stem cells, suggesting that the elevated histamine concentration reported during development might play a role in cerebrocortical neurogenesis, by activation of H₂ receptors to promote proliferation of neural precursors, and favoring neuronal fate by H₁-mediated stimulation.