Neuronal nicotinic acetylcholine receptors (nAChRs) are key players in both cognitive and autonomic processes. In the cognitive domains of the brain, destruction of cholinergic inputs or disruption of nAChR function result in cognitive deficits as observed in Alzheimer's disease, schizophrenia, brain trauma and aging. By contrast, moderate activation of nAChRs supports neuroprotection and improves cognitive functions. In addition, neuronal nAChRs are also expressed in important autonomic centers such as the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV) that support autonomic visceral reflexes and homeostasis. In this study, the underlying mechanisms of nAChR activation and its pharmacology were investigated in the hippocampus and the NTS, critical brain regions supporting cognitive and autonomic functions, respectively. Specific Aim 1 of this study was to determine the capacity of physiological levels of choline to activate α7 nAChRs in hippocampal CA1 pyramidal neurons and interneurons. A weak persistent activation of α7 nAChRs can be neuroprotective. These levels of activation can be achieved by selective or non-selective α7 nAChR agonists or inhibitors of ACh esterase (AChEI). However, nicotinic agonists desensitize α7 nAChRs while AChEI produces side effects limiting their overall clinical and pre-clinical effectiveness. These limitations can be avoided by using a novel class of drugs; type-II positive allosteric modulators of α7 nAChRs (α7-PAMs) such as PNU-120596 (i.e., PNU). At physiological levels, choline alone is ineffective as an α7 agonist because of its low concentration in the cerebrospinal fluid (~10 µM) and low potency for α7 activation (EC50~1.5 mM). However, the results pertaining to Specific Aim 1 demonstrate that in the presence of PNU (1-5 µM) , 10 µM choline produces persistent α7 activation expressed on CA1 pyramidal and interneurons which may be fine-tuned to achieve optimal neuroprotection and cognitive benefits. Specific Aim 2 was to test the novel concept that PNU mediated changes in α7 receptor kinetics can alter the biophysical properties of α7 channel-drug interactions and thereby increase the probability and the apparent affinity of open channel block. The results of this study suggest that the compounds (e.g., Bicuculline) that do not potently interact with α7 ion channels in the absence of PNU begin to interact potently in its presence. These emergent properties of α7 channel-drug interactions in the presence of PNU need to be recognized in drug development as they may lead to unanticipated side effects and serious misinterpretation of data. Specific Aim 3 investigated the pharmacology and mechanisms of action of pre-synaptic non-α7 and α7 nAChRs in the caudal NTS neurons. Although, activation of nAChRs is known to enhance pre-synaptic release of glutamate in subsets of caudal NTS neurons, its mechanism of action has been elusive. However, the results from this study demonstrated that nicotine-mediated enhancement of glutamate release requires Ca2+ influx via nAChRs but does not require any contribution from voltage-gated Ca2+ ion channels (VGCCs) and presynaptic Ca2+ stores. Moreover, both functional α7 and non-α7 nAChRs were found to contribute to the presynaptic effects of nicotine in subsets of NTS neurons. However, co-expression of α7 and non-α7 nAChRs on the same glutamatergic presynaptic terminals was not detected. Collectively, these studies may help in developing new therapeutic strategies to selectively target nAChR-associated pathways that support cognitive and autonomic functions in health and disease.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-02-16T14:35:21Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese Livia de Almeida Lira_ POSNEURO 2016.pdf: 2312565 bytes, checksum: 6dc0de86f266e98ad31d5c7c89d2219e (MD5) / Made available in DSpace on 2017-02-16T14:35:22Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese Livia de Almeida Lira_ POSNEURO 2016.pdf: 2312565 bytes, checksum: 6dc0de86f266e98ad31d5c7c89d2219e (MD5) Previous issue date: 2016-02-26 / FACEPE / O controle do comportamento alimentar é um fenômeno complexo dependente da interação entre os sinais originados na periferia do corpo e em várias regiões do sistema nervoso central, incluindo o núcleo do trato solitário (NTS). Esse núcleo regula muitos aspectos do comportamento alimentar e expressa receptores para vários peptídeos e hormônios indutores de saciedade, incluindo a serotonina. Prejuízos na via de sinalização e no conteúdo encefálico deste neurotransmissor estão associadas à hiperfagia e obesidade. Algumas regiões encefálicas responsáveis pela regulação do comportamento alimentar são alvos de ajustes permanentes promovidos por eventos que ocorrem durante os estágios iniciais do desenvolvimento. Nessa fase, a influência de estímulos ambientais, particularmente os nutricionais, podem modular os eventos ontogenéticos e promover sérias consequências na vida adulta. Nesse estudo, o objetivo foi investigar os efeitos da desnutrição proteica perinatal sobre aspectos morfofuncionais do NTS relacionados ao controle do comportamento alimentar. Ratos da linhagem Wistar, mantidos em condições padrões de biotério foram distribuídos aleatoriamente em dois grupos de acordo com a dieta ofertada para mães durante a gestação e lactação: grupo controle (C, caseína 17% / n = 10) ou grupo desnutrido (D, caseína 8% / n =10). Foram avaliados aos 35 e 180 dias de vida: a) peso corporal; b) ingestão alimentar; c) expressão da proteína FOS nas regiões rostral e medial do NTS em resposta ao estímulo alimentar; d) sequência comportamental de saciedade e os parâmetros microestruturais da alimentação e apenas aos 35 dias de vida: e) densidade de terminais e distribuição de receptores serotoninérgicos 5-HT1B nos subnúcleos ventrolateral, intermediário, medial e comissural do NTS. As áreas estudadas foram identificadas e quantificadas com auxílio do atlas estereotáxico de Paxinos e Watson (1998). Com base nessas avaliações, o presente trabalho demonstrou que a desnutrição perinatal promove: 1) redução do peso corporal (35 dias: C=129.06±0.20; D=68.10±0.35; 180 dias: C = 435.70±0.70; D = 370.30±0.70); (2) hiperfagia (35 dias: C = 6.8±0.6; D = 11.9±0.9; 180 dias C = 6.6±0.4; D = 10±0.8); (3) retardo na saciedade, (4) aumento no tamanho (C= 5,5 ±0,43; D= 7,8± 0,57) e duração (C=14,3± 1.8; D= 20,4±1,7) das refeições; (5) aumento na ativação neuronal nas porções rostral (35 dias: C = 134.5±22.23; D= 366.8±58.02/ 180 dias = 240.6±38.10; D = 444.2±57.05) e medial do NTS (35 dias: C = 172.8±26.28; D= 435.2±72.69/180 dias: C= 224.4±33.10; D= 434.0±45.31); (6) aumento na densidade de terminais serotoninérgicos no NTS (C= 34,4 ± 1,5 n= 5; D= 48± 3,6) e no subnúcleo intermediário (C= 28,3 ± 2; D= 43± 1,5) e (7) maior quantidade de neurônios 5-HT1B-IR no NTS (C= 159,6± 18,2;D= 317,1± 18,6) e nos subnúcleos ventrolateral (C= 20,1± 2,7/N=5D= 34,4± 3,5), intermediário (C= 20,9± 2,8/N=5; D= 49,3± 3) e medial (C= 45,6 ± 6/N=5; D= 95,4± 6). Estes resultados indicam que o NTS é uma estrutura particularmente vulnerável às influências da manipulação nutricional nos estágios iniciais do desenvolvimento e pode ser alvo de processos adaptativos do controle comportamento alimentar observados nesses animais na vida adulta. / The control of feeding behavior is dependent on the interactions among a variety of signals originated from periphery and several brain areas, such as the nucleus of the solitary tract (NTS) in the caudal brainstem. This nucleus regulates many aspects of feeding behavior and expressed receptors for several satiety inducing peptides and hormones including serotonin. Losses in the signaling pathway and the brain content of this neurotransmitter are associated with hyperphagia and obesity. Some brain regions responsible for the regulation of feeding behavior are targets of permanent adjustments promoted by events that occur during the early stages of development. At that stage, the influence of environmental stimuli, particularly the nutritional, may modulate ontogenetic events and promote serious consequences in adult life. In this study, the main aim was to investigate the effects of perinatal protein malnutrition on morphological and functional aspects of the NTS related to control of feeding behavior. Male Wistar rats were divided into two groups according to the diet offered to the dams during gestation and lactation: control group (C, diet containing 17% casein/ n=10) or isocaloric lowprotein group (LP, diet containing 8% casein/ n=10). We evaluated: a) body weight; b) food intake; c) c-Fos protein expression in the rostral and medial NTS; d) behavioural sequence satiety and micro-structural parameters of feeding and e) density of serotoninergic terminals and distribution of 5-HT1B receptor in the ventro-lateral, intermediate, medial and commissural subnucleus of NTS. The areas studied were identified and quantified with Stereotactic atlas of Paxinos and Watson (2005). Based on these evaluations, the present study showed that the malnutrition: (1) promotes perinatal) reduced body weight (35 days: C = 129.06 ± 0.20; D = 68.10 ± 0.35; 180 days: C = 435.70 ± 0.70; D = 370.30 ± 0.70); (2) hyperphagia (35 days: C = 6.8 ± 0.6; D = 11.9 ± 0.9; 180 days C = 6.6 ± 0.4; D = 10 ± 0.8); (3) delay in satiety, (4) increase in size (C = 5.5 ± 0.43; D = 7.8 ± 0.57) and duration (C = 14.3 ± 1.8; D = 20.4 ± 1.7) meals; (5) increase in neuronal activation in the rostral portions (35 days: C = ± 134.5 22.23; D = ± 366.8/58.02 180 days = 240.6 ± 38.10; D = ± 444.2 57.05) and medial NTS (35 days: C = 172.8 ± 26.28; D = ± 72.69/180 days 435.2: C = ± 224.4 33.10; D = ± 45.31 434.0); (6) increase in density of serotonergic terminals in the NTS (C = 34.4 ± 1.5 n = 5; D = 48 ± 3.6) and the intermediate subnucleus (C = 28.3 ± 2; D = 43 ± 1.5) and (7) increased amount of 5-HT1B-IR neurons in the NTS (C = 159.6 ± 18.2; D = 317.1 ± 18.6) and ventro-lateral (C = 20.1 ± 2.7/N = 5 d = 34.4 ± 3.5), intermediate (C = 20.9 ± 2.8/N = 5; D = 49.3 ± 3) and medial subnucleus (C = 45.6 ± 6/N = 5; D = 95.4 ± 6). These results indicate that the NTS is a particularly vulnerable structure to the influences of nutritional manipulation in the early stages of development and may be adaptive processes of control feeding behavior observed in these animals into adulthood.