Hernan Navarro

Prenatal exposure to nicotine impairs nervous system development at a dose which does not affect viability or growth

Prenatal exposure to high doses of nicotine (greater than 6 mg/kg/day) via maternal infusions has been shown to impair nervous system development and to decrease viability and growth. In the current study, we have examined the effects of infusing pregnant rats with 2 mg/kg of nicotine per day from gestational days 4 through 20. At this lower dose, there was neither interference with maternal weight gain nor any increase in resorption rate. Intrauterine and postnatal growth was maintained at normal or supranormal rates in the exposed offspring. Nevertheless, sufficient nicotine penetrated the fetal brain to cause persistent alterations in [3H]nicotine binding sites, abnormalities of cellular development [assessed by measurements of ornithine decarboxylase (ODC) activity and deoxyribonucleic acid (DNA)], and impairment of development of peripheral noradrenergic projections (assessed by kidney norepinephrine levels); in each case, the neural alterations were virtually equivalent to those obtained previously at the higher, growth-suppressant dosage. These findings indicate that growth impairment alone is insufficient to predict the adverse effects of nicotine on development.

Prenatal nicotine exposure impairs β-adrenergic function: Persistent chronotropic subsensitivity despite recovery from deficits in receptor binding

Gestational exposure to nicotine has been shown to interfere with biochemical markers of development of central and peripheral noradrenergic activity. The current study examines the development and function of cardiac beta-adrenergic receptors in the offspring of pregnant rats given nicotine infusions of 6 mg/kg/day from gestational days 4 through 20, administered by subcutaneously implanted osmotic minipumps. Prenatal nicotine exposure delayed the development of beta-adrenergic receptor binding capabilities, as assessed with [125I]pindolol in membrane preparations from heart and kidney. The deficits in receptor binding were associated with marked subsensitivity of chronotropic responses to administration of a beta-adrenergic agonist, isoproterenol. Although the effects on receptor binding resolved after weaning, functional deficiencies in responsiveness to isoproterenol or to preganglionic electrical stimulation of sympathetic nerves to the heart persisted into adulthood. These results indicate that prenatal exposure to nicotine produces long-term alterations in adrenergic responsiveness of sympathetic target tissues.

Positive allosteric modulation of the human cannabinoid (CB1) receptor by RTI‐371, a selective inhibitor of the dopamine transporter

Background and purpose:  In our search for an indirect dopamine agonist as therapy for cocaine addiction, several selective inhibitors of the dopamine transporter (DAT), which are 3‐phenyltropane analogues, were assayed for their effect on locomotor activity in mice. Interestingly, several of the compounds showed a poor correlation between stimulation of locomotion and DAT inhibition. One of the compounds, 3β‐(4‐methylphenyl)‐2β‐[3‐(4‐chlorophenyl)isoxazol‐5‐yl]tropane (RTI‐371), was shown to cross the blood‐brain barrier, by binding studies in vivo, and block cocaine‐induced locomotor stimulation. As poor pharmacokinetics could not explain the behavioural effects of RTI‐371, this compound was screened through our functional assays for activity at other CNS receptors. Initial screening identified RTI‐371 as a positive allosteric modulator of the human CB1 (hCB1) receptor.

New bioactive aromatic compounds from Vismia guianensis

Five benzophenones, vismiaguianones A-E, and two benzocoumarins, vismiaguianins A and B were isolated from the CHCl3 extract of the roots of Vismia guianensis by bioassay-directed fractionation using the DNA strand-scission assay and KB cell line. Of the isolates obtained, vismiaguianone B exhibited DNA strand-scission activity, whereas vismiaguianones D and E and vismiaguianin A were found to be significantly cytotoxic.

Fetal nicotine exposure produces postnatal up-regulation of adenylate cyclase activity in peripheral tissues

Gestational exposure to nicotine has been shown to affect development of noradrenergic activity in both the central and peripheral nervous systems. In the current study, pregnant rats received nicotine infusions of 6 mg/kg/day throughout gestation, administered by osmotic minipump implants. After birth, offspring of the nicotine-infused dams exhibited marked increases in basal adenylate cyclase activity in membranes prepared from kidney and heart, as well as supersensitivity to stimulation by either a beta-adrenergic agonist, isoproterenol, or by forskolin. The altered responses were not accompanied by up-regulation of beta-adrenergic receptors: in fact, [125I]pindolol binding was significantly decreased in the nicotine group. These results indicate that fetal nicotine exposure affects enzymes involved in membrane receptor signal transduction, leading to altered responsiveness independently of changes at the receptor level.

Nutritional Influences on Adrenal Chromaffin Cell Development: Comparison with Central Neurons

ABSTRACT: Neurotransmitter systems in the developing brain are generally protected from growth retardation associated with nutritional deprivation. To investigate if such protective mechanisms extend to similar tissues in the peripheral sympathetic system, maturation of the chromaffin cells of the adrenal medulla and development of their centrally derived splanchnic innervation were evaluated in rats whose nutritional status had been altered during the neonatal period by increasing (16–17 pups/litter) or decreasing (five to six pups/litter) the litter size from the standard (11–12 pups/litter). Ontogeny of adrenal catecholamine stores and activities of catecholamine-biosynthetic enzymes tyrosine hydroxylase and phenylethanolamine N-methyltransferase were monitored, along with activity of choline acetyltransferase, a marker enzyme for the preganglionic neurons innervating the chromaffin cells. Neonatal nutritional deprivation slowed body weight gain and retarded development of the chromaffin cells, as evidenced by subnormal catecholamine stores, tyrosine hydroxylase and phenylethanolamine N-methyltransferase activities. The effects persisted despite the complete recovery of body weights postweaning. The developmental alterations were not caused by overcrowding stress, as plasma corticosterone levels were not elevated in the large litter group. Neonatal nutritional enrichment promoted body weight gain but failed to enhance development of adrenal catecholamines; tyrosine hydroxylase and phenylethanolamine N-methyltransferase activities were elevated only in the preweaning period. In contrast to effects on the chromaffin cells, altered neonatal nutritional status had only minor, transient effects on the development of the centrally derived cholinergic innervation of the adrenal and produced only small changes (<10%) in brain tyrosine hydroxylase activity. These results suggest that, unlike central transmitter systems, maturation of chromaffin cells is adversely affected by neonatal nutritional deprivation; ontogenetic gains may already be close to optimum at normal nutritional status.

Kappa opioid mediation of cannabinoid effects of the potent hallucinogen, salvinorin A, in rodents.

RationaleSalvinorin A, the primary psychoactive derivative of the hallucinogenic herb Salvia divinorum, is a potent and highly selective kappa-opioid receptor (KOR) agonist. Several recent studies, however, have suggested endocannabinoid system mediation of some of its effects.ObjectivesThis study represents a systematic examination of this hypothesis.MethodsSalvinorin A was isolated from S. divinorum and was evaluated in a battery of in vitro and in vivo procedures designed to detect cannabinoid activity, including CB1 receptor radioligand and [35S]GTPγS binding, calcium flux assay, in vivo cannabinoid screening tests, and drug discrimination.ResultsSalvinorin A did not bind to nor activate CB1 receptors. In vivo salvinorin A produced pronounced hypolocomotion and antinociception (and to a lesser extent, hypothermia). These effects were blocked by the selective KOR antagonist, JDTic, but not by the CB1 receptor antagonist rimonabant. Interestingly, however, rimonabant attenuated KOR activation stimulated by U69,593 in a [35S]GTPγS assay. Salvinorin A did not substitute for Δ9-tetrahydrocannabinol (THC) in mice trained to discriminate THC.ConclusionsThese findings suggest that similarities in the pharmacological effects of salvinorin A and those of cannabinoids are mediated by its activation of KOR rather than by any direct action of salvinorin A on the endocannabinoid system. Further, the results suggest that rimonabant reversal of salvinorin A effects in previous studies may be explained in part by rimonabant attenuation of KOR activation.

Neonatal chlorpyrifos administration elicits deficits in immune function in adulthood: a neural effect?

Neural input plays a key role in the establishment of immune function, and environmental agents or drugs that interfere with the development of the nervous system elicit corresponding immunologic deficits. In the current study, we gave neonatal rats the widely used organophosphate pesticide, chlorpyrifos (CPF), and determined the immediate and long-term effects on T-lymphocyte function. Exposure of neonatal rats to 1 mg/kg of CPF daily on postnatal days (PN) 1-4 had no immediate effect (PN5) on T-cell mitogenic responses to concanavalin A challenge. However, once the animals reached adulthood, T-cell responses were significantly impaired. There were no deficits in basal T-cell replication rates, implying that the adverse effect of CPF exposure was specific to mitogenic activation. Treatment during a later neonatal period (PN11-14) elicited similar deficits in adulthood. CPF administration leads to inhibition of cholinesterase, and a cholinergic connection is supported by the fact that the results seen here correspond to those seen with a direct cholinergic stimulant (nicotine) administered during gestation or adolescence. These results indicate that exposure to CPF during a developmental period in which this organophosphate pesticide is known to produce lasting changes in neural function, elicits corresponding, long-term deficits in immune competence.

Gestational nicotine exposure alone or in combination with ethanol down-modulates offspring immune function.

Prenatal nicotine exposure has been shown to disrupt the development of a number of peripheral organs. In the current study, we examined the effects of gestational nicotine exposure, alone or in combination with ethanol exposure, on offspring immune function. Timed pregnant rats were treated with either nicotine (6 mg/kg/day) from gestation day 4-20 using subcutaneously implanted osmotic mini-pumps or ethanol administered in the drinking water (15% w/v) from gestation day 10-20. The combined exposure group received both treatments. The ability of offspring T and B cells to proliferate in response to nonspecific stimulation by Concanavalin A or lipopolysaccharide, respectively, was determined on postnatal days 9, 15, 22, 29, 64, and 86. Offspring splenocyte beta(2)-adrenoceptor binding was also measured. Nicotine or nicotine+ethanol suppressed splenocyte responsiveness to Concanavalin A or lipopolysaccharide which was similar in timing and magnitude to that seen with ethanol alone. Splenocytes from these groups remained subresponsive to stimulation well into adulthood. The combined drug treatment caused an overall reduction in spleen beta-adrenergic receptor binding whereas the individual drug treatments did not alter the development of spleen beta-adrenergic receptors.Our results indicate that prenatal nicotine exposure can cause long-term suppression of the proliferative response of offspring immune cells. Moreover, the effects of nicotine+ethanol may cause more severe deficits in adulthood.

Cytotoxic constituents from the roots of Tovomita brevistaminea.

Two known xanthones, trapezifolixanthone and manglexanthone were isolated as cytotoxic constituents from the CHCl3 extract of the roots of Tovomita brevistaminea by bioassay-guided fractionation using the KB cell line. In addition, a new compound, tovophenone C, and two known compounds, tovophenones A and B which are benzophenones, were found to be inactive constituents in this investigation. The structure of the new isolate was determined by detailed analysis of spectroscopic parameters including its 1D and 2D NMR spectroscopy data.