Cláudio C. Filgueiras

Developmental aspects of the cholinergic system

Beyond its importance in sustaining or modulating different aspects of the activity of the central nervous system (CNS), the cholinergic system plays important roles during development. In the current review, we focus on the developmental aspects associated with major components of the cholinergic system: Acetylcholine, choline acetyltransferase, vesicular acetylcholine transporter, high-affinity choline transporter, acetylcholinesterase, nicotinic and muscarinic receptors. We describe when and where each one of these components is first identified in the CNS and the changes in their levels that occur during the course of prenatal and postnatal development. We also describe how these components are relevant to many events that occur during the development of the CNS, including progenitor cells proliferation and differentiation, neurogenesis, gliogenesis, neuronal maturation and plasticity, axonal pathfinding, regulation of gene expression and cell survival. It will be noticed that evidence regarding the developmental aspects of the cholinergic system comes mostly from studies that used agonists, such as nicotine, and antagonists, such as hemicholinium-3. Studies using immunohistochemistry and genetically altered mice also provided valuable information.

Individual differences in novelty-seeking behavior but not in anxiety response to a new environment can predict nicotine consumption in adolescent C57BL/6 mice

Considering that adolescence is associated with an increased motivation to seek out new stimuli and with low anxiety levels in exploring novel environments, and that both behavioral traits may be associated with substance abuse, we investigated whether the behavioral response to a novel environment can predict subsequent oral nicotine self-administration in adolescent C57BL/6 mice. On postnatal day 30 (PN30), the novelty-seeking behavior and anxiety levels were assessed in a hole board activity box. The total number of head-dips (DIP) was used to classify animals either into the high novelty (HN; DIP above median) or low novelty (LN; DIP below median) groups. The percentage of center squares crossed (CEN) was used to classify animals either into the high anxiety (HA; CEN below median) or low anxiety (LA; CEN above median) groups. From PN31 to PN41, all animals were given a free choice between tap water or a nicotine solution (10 microg/ml). LN mice did not change nicotine intake throughout the free choice procedure, however, HN mice presented a marked increase in consumption. There were no differences in consumption between HA and LA mice. Our results indicated that mice that presented a more intense novelty-seeking behavior increased their preference for nicotine during the free choice experiment but that anxiety levels did not predict nicotine consumption. These results suggest that higher motivation to seek out new experiences is a significant contributor to drug use in adolescents and that anxiety is probably not a major factor that determines differential nicotine consumption during adolescence.

The effects of hand preference and gender on finger tapping performance asymmetry by the use of an infra-red light measurement device.

We used an infra-red device to study the effects of gender and handwriting preference on manual asymmetry in tapping rate and intertap variability. Our sample (n=102) consisted of approximately equal number of subjects with respect to gender (52 women and 50 men) and handedness (52 right-handers and 50 left-handers). Data on overall performance indicated that men performed more quickly and regularly than women. The index used for measuring manual asymmetry was the difference between the hands as a proportion of the total. Therefore, the asymmetry index was adjusted to remove the influence of overall performance. The analyses based on asymmetry scores indicated a significant handedness effect: right-handers showed greater manual asymmetries than left-handers for both tapping rate and intertap variability. In addition, right handers exhibited a significant greater asymmetry for intertap variability than tapping rate. Taken together, these data may reflect greater hemispheric differences in right-handers, specially for intertap variability.

Rotational stress-induced increase in epinephrine levels delays cutaneous wound healing in mice

Stress impairs wound healing of cutaneous lesions; however, the mechanism is still unclear. The aim of this study was to evaluate the effects of rotational stress on cutaneous wound healing in mice and propose a mechanism. Male mice were spun at 45 rpm for 15 min every hour beginning 3 days before wounding until euthanasia. Control animals were not subjected to stress. To confirm that catecholamines participate in stress-induced delay of wound healing, mice were treated daily with propranolol. An excisional lesion was created and measured. Seven and 14 days later, animals were killed and lesions collected. Sections were stained with hematoxylin-eosin and immunostained for alpha-smooth muscle actin and proliferating cell nuclear antigen. Matrix metalloproteinase (MMP)-2 and -9 activity, nitrite levels, and tumor necrosis factor-alpha (TNF-alpha) expression were measured in the wounds. In addition, murine skin fibroblast cultures were treated with high levels of epinephrine and fibroblast activity was evaluated. Stressed mice exhibited reduced locomotor activity and increased normetanephrine plasma levels. Rotational stress was associated with decreased wound contraction, reduced re-epithelialization, reduced MMP-2 and MMP-9 activation, but with strongly increased nitrite levels. Furthermore, inflammatory cell infiltration, TNF-alpha expression, myofibroblastic differentiation, and angiogenesis were all delayed in the stress group. Propranolol administration reversed the deleterious effects of stress on wound contraction and re-epithelialization. High epinephrine concentrations increased murine skin fibroblast proliferation and nitric oxide synthesis, and strongly inhibited skin fibroblast migration and both pro- and active MMP-2. In conclusion, rotational stress impairs cutaneous wound healing due to epinephrine increased levels.

Combined Exposure to Nicotine and Ethanol in Adolescent Mice Differentially Affects Anxiety Levels during Exposure, Short-Term, and Long-Term Withdrawal

Smoking and consumption of alcoholic beverages are frequently associated during adolescence. This association could be explained by the cumulative behavioral effects of nicotine and ethanol, particularly those related to anxiety levels. However, despite epidemiological findings, there have been few animal studies of the basic neurobiology of the combined exposure in the adolescent brain. In the present work we assessed, through the use of the elevated plus maze, the short- and long-term anxiety effects of nicotine (NIC) and/or ethanol (ETOH) exposure during adolescence (from the 30th to the 45th postnatal day) in four groups of male and female C57BL/6 mice: (1) Concomitant NIC (nicotine free-base solution (50 μg/ml) in 2% saccharin to drink) and ETOH (ethanol solution (25%, 2 g/kg) i.p. injected every other day) exposure; (2) NIC exposure; (3) ETOH exposure; (4) Vehicle. C57BL/6 mice were selected, in spite of the fact that they present slower ethanol metabolism, because they readily consume nicotine in the concentration used in the present study. During exposure (45th postnatal day: PN45), our results indicated that ethanol was anxiolytic in adolescent mice and that nicotine reverted this effect. Short-term drug withdrawal (PN50) elicited sex-dependent effects: exposure to nicotine and/or ethanol was anxiogenic only for females. Although neither nicotine nor ethanol effects persisted up to 1 month postexposure (PN75), the coadministration elicited an anxiogenic response. In spite of the fact that generalizations based on the results from a single strain of mice are prone to shortcomings, our results suggest that the deficient response to the anxiolytic effects of ethanol in adolescents co-exposed to nicotine may drive higher ethanol consumption. Additionally, increased anxiety during long-term smoking and drinking withdrawal may facilitate relapse to drug use.

Increased apoptosis and reduced neuronal and glial densities in the hippocampus due to nicotine and ethanol exposure in adolescent mice.

It has been recently shown that nicotine and ethanol interact during adolescence affecting memory/learning and anxiety levels. Considering the role of the hippocampus in both anxiety and memory/learning, we investigated whether adolescent nicotine and/or ethanol administration elicit apoptotic cell death and whether this results in neuronal and/or glial density alterations in the following regions of the hippocampus: granular layer of the dentate gyrus (GrDG), molecular layer (Mol), CA1, CA2 and CA3. From the 30th to the 45th postnatal day, C57BL/6 male and female mice were exposed to nicotine free base (NIC) and/or ethanol (ETOH). Four groups were analyzed: (1) concomitant NIC (50 μg/ml in 2% saccharin to drink) and ETOH (25%, 2 g/kg i.p. injected every other day) exposure; (2) NIC exposure; (3) ETOH exposure; (4) vehicle. We evaluated cell degeneration (TUNEL assay), neuronal and glial densities (optical disector) and region thicknesses at the end of the period of exposure. Our results demonstrate that ETOH elicited an increase in TUNEL‐positive cells relative to the vehicle group in all hippocampal regions. NIC elicited less severe region‐dependent effects: the number of TUNEL‐positive cells was significantly increased in the Mol and CA1 when compared to the vehicle group. These results were paralleled by reductions in neuronal and glial cells densities, which indicate that both cell types are sensitive to the neurotoxic effects of these drugs. There were no effects on region thicknesses. On the other hand, concomitant NIC and ETOH reduced the adverse effects of the drugs when administered separately. This ability of nicotine and ethanol co‐exposure to lessen the adverse effects of nicotine and ethanol may contribute to adolescents co‐use and co‐abuse of tobacco and alcoholic beverages.

Nicotine and ethanol interact during adolescence: effects on the central cholinergic systems.

Co-occurrence of tobacco smoking and alcohol consumption during adolescence is frequent and well documented. However, little is known about the basic neurobiology of the combined exposure in the adolescent brain. Since nicotine is a cholinergic agonist and it has been shown that ethanol interferes with nicotinic acetylcholine receptors (nAChRs), the current work focused on cholinergic systems. From the 30th to the 45th postnatal day (PN), C57BL/6 male and female mice were exposed to nicotine free base (NIC) and/or ethanol (ETOH). Four groups were analyzed: 1) concomitant NIC (50 microg/ml in 2% saccharin to drink) and ETOH (25%, 2 g/kg i.p. injected every other day) exposure; 2) NIC exposure; 3) ETOH exposure; 4) vehicle. We assessed nAChR binding, choline acetyltransferase (ChAT) activity and [3H]hemicholinium-3 (HC-3) binding in the cerebral cortex and midbrain of mice on PN45. In the cortex, ETOH had no effect on nAChRs. In contrast, NIC produced nAChR upregulation while NIC+ETOH elicited a more pronounced effect. In the midbrain, neither ETOH nor NIC had effects on nAChRs. NIC+ETOH, however, elicited a robust nAChR upregulation. Regarding ChAT activity, treatment effects differed between males and females in the cortex. Male NIC mice presented an increase in ChAT. However, ETOH reversed this effect. In contrast, female NIC mice presented decreased ChAT activity. In the midbrain, ETOH increased ChAT. HC-3 binding was not affected. These results indicate that the central cholinergic system is a site at which nicotine and ethanol interact. This interaction might underlie the association between tobacco and alcohol consumption during adolescence.

Exposure to nicotine and ethanol in adolescent mice: effects on depressive-like behavior during exposure and withdrawal.

Depression and use of addictive substances are two of the most frequent public health problems of adolescents. However, little is known about the association between depression and drug use. Considering that ethanol and nicotine are the most widely used and abused drugs by adolescents, here, we evaluated the depressive-like behavior of C57BL/6 male and female mice exposed to nicotine (NIC) and/or ethanol (ETOH) from the 30th to the 45th (PN30-45) postnatal day. Four groups were analyzed: 1) concomitant NIC (50μg/ml in 2% saccharin to drink) and ETOH (25%, 2g/kg i.p. injected every other day) exposure; 2) NIC exposure; 3) ETOH exposure; 4) vehicle. Immobile behavior, an animal model of depressive behavior, was assessed in the forced swimming test (FST) while the anhedonic state was assessed in the sucrose preference test (SPT) by the end of exposure (PN45-47) as well as during short- (PN50-52) and long-term (PN75-77) withdrawal. In the FST, ETOH female mice showed a reduction in immobility time by the end of exposure while, during long-term withdrawal, immobility time was increased. Short-term withdrawal elicited an increase in immobility time only in female NIC mice. In the SPT, males from both NIC and NIC+ETOH groups showed increased sucrose consumption, suggesting a reward-craving effect during short-term withdrawal. During long-term withdrawal, NIC male mice showed an anhedonic effect. Adolescent nicotine, ethanol and nicotine+ethanol combined exposures during adolescence thus elicit gender-selective effects both during exposure and withdrawal that may contribute to the increased prevalence of depression among drug users.

Combined exposure to nicotine and ethanol in adolescent mice differentially affects memory and learning during exposure and withdrawal

Human adolescents often associate tobacco smoking and consumption of alcoholic beverages. In spite of this frequent association, little is known about the basic neurobiology of the dual exposure in the adolescent brain. In the present work, we assessed, through the use of the step-through passive avoidance box (2mA, 2s; test-retest interval of 24h), short- and long-term memory/learning effects of nicotine (NIC) and/or ethanol (ETOH) exposure during adolescence (postnatal days 30-45: PN30-45) in four groups of male and female C57BL/6 mice: (1) concomitant NIC [nicotine free base solution (50microg/ml) in 2% saccharin to drink] and ETOH [ethanol solution (25%, 2g/kg) i.p. injected every other day] exposure; (2) NIC exposure; (3) ETOH exposure; (4) vehicle. During exposure (PN44-45), deficits in memory/learning due to concomitant NIC+ETOH exposure reflected the summation of the two individual sets of effects. During a short-term drug withdrawal (PN49-50), nicotine improved memory/learning, however, ethanol blocked nicotine-induced improvements. One month post-exposure (PN74-75), a significant female-only improvement in memory/learning was observed as a result of co-administration. In conclusion, our results suggest that detrimental effects of nicotine and ethanol on memory/learning during adolescent combined exposure represent a worsened outcome from the dual exposure. However, negative effects of the combined exposure fail to persist during withdrawal. In fact, the combined exposure elicits a sex-dependent late onset beneficial effect on memory/learning during withdrawal.

Combined exposure to nicotine and ethanol in adolescent mice: effects on the central cholinergic systems during short and long term withdrawal

Relapse to drug use is a major public health problem. In this sense, understanding the biological substrates that are affected during withdrawal may provide information to prevent relapse. Both smoking and alcoholic beverage consumption usually begin during adolescence, however, little is known about the basic neurobiology of the combined adolescent exposure, particularly during withdrawal. Since nicotine is a cholinergic agonist and it has been shown that ethanol interferes with nicotinic acetylcholine receptors (nAChRs), the current study focused on the effects of drug withdrawal on the central cholinergic system. From the 30th to the 45th postnatal day (PN), C57BL/6 male and female mice were exposed to nicotine free base (NIC) and/or ethanol (ETOH). Four groups were analyzed: (1) concomitant NIC (50 microg/ml in 2% saccharin to drink) and ETOH (25%, 2 g/kg i.p. injected every other day) exposure; (2) NIC exposure; (3) ETOH exposure; (4) vehicle. We assessed nAChR binding, choline acetyltransferase (ChAT) activity and [(3)H]hemicholinium-3 (HC-3) binding in the cerebral cortex and midbrain of mice at short (PN50) and long term (PN75) withdrawal. NIC and NIC+ETOH promoted nAChR upregulation during a short-term withdrawal. NIC short-term withdrawal elicited an increase in ChAT activity that was reversed by ETOH withdrawal. In addition, NIC+ETOH elicited a decrease in ChAT activity at long term withdrawal. Regarding HC-3, ETOH and NIC+ETOH promoted a decrease that persisted at long-term withdrawal. The present study provides experimental evidence that nicotine and ethanol during adolescence interact resulting in cholinergic system alterations during withdrawal.