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Infant rats must learn to identify their mother’s diet-dependent odor. Once learned, maternal odor controls pups’ approach to the mother, their social behavior and nipple attachment. Here we present a review of the research from four different laboratories, which suggests that neural and behavioral responses to the natural maternal odor and neonatal learned odors are similar. Together, these data indicate that pups have a unique learning circuit relying on the olfactory bulb for neural plasticity and on the hyperfunctioning noradrenergic locus coeruleus flooding the olfactory bulb with norepinephrine to support the neural changes. Another important factor making this system unique is the inability of the amygdala to become incorporated into the infant learning circuit. Thus, infant rats appear to be primed in early life to learn odors that will evoke approach responses supporting attachment to the caregiver.

Serotonin (5-HT1B) receptors play an essential role in the inhibition of aggressive behavior in rodents. CP-94,253, a 5-HT1B receptor agonist, can reduce aggression in male mice when administered directly into the ventro-orbitofrontal (VO) prefrontal cortex (PFC). The objective of the current study was to assess the effects of two selective 5-HT1B receptor agonists (CP-94,253 and CP-93,129), microinjected into the VO PFC, on maternal aggressive behavior after social instigation in rats. CP-94,253 (0.56 μg/0.2 μL, N = 8, and 1.0 μg/0.2 μL, N = 8) or CP-93,129 (1.0 μg/0.2 μL, N = 9) was microinjected into the VO PFC of Wistar rats on the 9th day postpartum and 15 min thereafter the aggressive behavior by the resident female against a male intruder was recorded for 10 min. The frequency and duration of aggressive and non-aggressive behaviors were analyzed using ANOVA and post hoc tests. CP-93,129 significantly decreased maternal aggression. The frequency of lateral attacks, bites and pinnings was reduced compared to control, while the non-aggressive behaviors and maternal care were largely unaffected by this treatment. CP-94,253 had no significant effects on aggressive or non-aggressive behaviors when microinjected into the same area of female rats. CP-93,129, a specific 5-HT1B receptor agonist, administered into the VO PFC reduced maternal aggressive behavior, while the CP-94,253 agonist did not significantly affect this behavior after social instigation in female rats. We conclude that only the 5-HT1B receptor agonist CP-93,129 administered into the VO PFC decreased aggression in female rats postpartum after social instigation.

Immunohistochemistry was used to evaluate the effects of neonatal handling and aversive stimulation during the first 10 days of life on the number of corticotrophs in the anterior lobe of the pituitary of 11-dayold male Wistar rats. Since adult rats handled during infancy respond with reduced corticosterone secretion in response to stressors and with less behavior inhibition in novel environments, we assumed that neonatal stimulation could affect pituitary morphology during this critical period of cell differentiation. Three groups of animals were studied: intact (no manipulation, N = 5), handled (N = 5) and stimulated (submitted to 3 different aversive stimuli, N = 5). The percentage of ACTH-immunoreactive cells in the anterior lobe of the pituitary (number of ACTH-stained cells divided by total number of cells) was determined by examining three slices per pituitary in which a minimum of 200 cells were counted by two independent researchers. Although animals during the neonatal period are less reactive to stresslike stimulation in terms of ACTH and corticosterone secretion, results showed that the relative number of ACTH-stained cells of neonatal handled (0.25 ± 0.01) and aversive stimulated (0.29 ± 0.03) rats was not significantly different from intact (0.30 ± 0.03) animals. Neonatal stimulation may have a differential effect on the various subpopulations of corticotroph cells in the anterior pituitary.

As experiências da criança vividas com a sua mãe ou com seu cuidador no início da vida fornecem o modelo básico para as relações sócio afetivas na vida adulta. Dentro desta perspectiva, uma série de situações ocorridas nos primeiros anos de vida podem comprometer o desenvolvimento saudável do indivíduo. As crianças institucionalizadas, apesar de receberem cuidados adequados, apresentam importantes mudanças comportamentais na vida adulta, as quais, tem sido fortemente associada à falta de um vínculo com a figura materna no início da vida. Atualmente, ainda não se sabe como os processos de adoção humana alteram a relação mãe-bebê no início da vida. Dentro desta perspectiva, a racionalidade desta tese foi representar a complexa situação da adoção humana através de um modelo animal com o propósito de explorar o seu impacto na formação do vínculo (apego) do filho com um cuidador e, assim, contribuir com o entendimento dos processos que envolvem a adoção infantil, uma situação bastante frequente, mas pouco abordada experimentalmente. Para isso foram utilizados um total de 804 ratos Wistars (88 fêmeas prenhas, 12 machos e 704 filhotes). Inicialmente, caracterizamos o perfil comportamental dos filhotes em diferentes períodos pós-natais e o padrão de comportamento materno de ratos Wistar, no mesmo ambiente em que, posteriormente estudamos os efeitos da adoção. Posteriormente, avaliamos os efeitos comportamentais da adoção cruzada repetida de fêmeas lactantes (RCF) sobre a formação do vínculo mãe-filhote em dois períodos importantes do desenvolvimento pósnatal: no período sensível a aprendizagem do apego (dias pós-natal 1 a 3) e no período pós-sensível a aprendizagem de apego (dias pós-natal 9 a 11), tanto na perspectiva da mãe adotiva quanto na perspectiva dos filhotes adotivos. O protocolo de RCF realizado precocemente (dias pós-natal 1 a 3) reduziu a capacidade dos filhotes de preferir o odor da figura materna – filhotes machos RCF [Mdn: 0 (0-0)] vs. filhotes machos controles [Mdn: 25,67 (3,33-33,58)] e filhotes fêmeas RCF [Mdn: 0 (0-2,75)] vs. filhotes fêmeas controles [Mdn 14,17 (9,5-26,58)]. Entretanto, a adoção realizada tardiamente (dias pósnatal 9 a 11) não alterou significativamente a capacidade dos filhotes de preferirem o odor materno – filhotes machos RCF (32,53 ± 4,14) vs. filhotes controles (36,12 ± 3,84); e filhotes fêmeas RCF (37,11 ± 5,28) vs. filhotes controle (31,03 ± 5,72). Além disso, a adoção precoce reduziu o cuidado materno no dia DPN 2 – mães RCF (25,67 ± 3,50) vs. mães controles (53,75 ± 2,34); e no dia DPN 3 mães RCF (21,83 ± 2,91) vs. mães controles (37,17 ± 2,10). A adoção precoce também reduziu a motivação materna para recolher os filhotes e levá-los para o ninho – tempo para recolhimento do primeiro filhote: mães RCF [Mdn 39 (18-89,75)] vs. mães controles [Mdn 16 (8,25-28,50)]; e quinto filhote: mães RCF [Mdn 167 (79-410,5)] vs. mães controles [Mdn. 86,5 (61,75-160,3). A adoção tardia reduziu o cuidado materno no dia DPN 9 em relação as mães do grupo controle - mães RCF (23,33 ± 2,49) vs mães controle (37,17 ± 5,21). Esse estudo forneceu evidências de que o RCF, realizado durante o período sensível a aprendizagem do apego infantil (adoção precoce), criou um ambiente instável para o estabelecimento da interação mãe-filhote e, como resultado, reduziu significativamente o comportamento materno e diminuiu as respostas dos filhotes ao odor materno. Por outro lado, o procedimento de RCF realizado durante o período pós- sensível a aprendizagem do apego (adoção tardia) reduziu ligeiramente o cuidado materno, porém não alterou as respostas comportamentais dos filhotes ao odor materno. Child experiences with their mother or caregiver early in life provide the basic model for socio-affective relationships in adult life. Within this perspective, a series of situations which have happened in the first years of life can compromise a healthy development of the individual. Institutionalized children, despite receiving adequate care, exhibit important behavioral changes in adult life, which have been strongly associated with lack of attachment to the maternal figure in early life. It is not yet known how the processes of human adoption change the mother-infant relationship early in life. In this perspective, the rationale of this thesis was to represent the complex situation of human adoption through an animal model in order to explore its impact in the formation of the offspring's attachment to a caregiver and, thus, contribute to the understanding of the processes that involve child adoption, a situation that is quite frequent but little discussed experimentally. A total of 804 Wistars rats (88 pregnant females, 12 males and 704 pups) were used. Initially, we characterized the behavioral profile of postnatal pups and the pattern of maternal behavior of Wistar rats, in the same environment where the effects of adoption were later studied. We evaluated the behavioral effects of repeated cross-fostering of lactating females (RCF) on the formation of the mother-infant bond in two important periods of postnatal development: in the sensitive period of attachment learning (postnatal days (PND) 1 to 3) and in the post-sensitive period of attachment learning (postnatal days 9 to 11), both from the perspective of the adoptive mother and from the perspective of the adopted pups. The RCF protocol performed early (PND 1 to 3) reduced the pups' ability to prefer the maternal odor – RCF male pups RCF [Mdn: 0 (0-0)] vs. control male pups [Mdn: 25,67 (3,33-33,58)]; and RCF female pups [Mdn: 0 (0-2,75)] vs. control female pups [Mdn 14,17 (9,5-26,58)]. However, late adoption (PND 9 to 11) did not affect the pups’ ability to prefer maternal odor – RCF male pups (32,53 ± 4,14) vs. control male pups (36,12 ± 3,84) and RCF female pups (37,11 ± 5,28) vs. control female pups (31,03 ± 5,72). Moreover, early adoption reduced maternal care on PND 2 – RCF mothers (25,67 ± 3,50) vs. control mothers (53,75 ± 2,34); and on PND 3 – RCF mothers (21,83 ± 2,91) vs. control mothers (37,17 ± 2,10). Early adoption reduced motivation in pups retrieval test – time for first pup: RCF mothers [Mdn 39 (18-89,75)] vs. control mothers [Mdn 16 (8,25-28,50)]; and fifth pup: RCF mothers [Mdn 167 (79-410,5)] vs. control mothers [Mdn. 86,5 (61,75-160,3)]. On the other hand, late adoption reduced maternal care on PND 9 – RCF mothers (23,33 ± 2,49) vs. control mothers (37,17 ± 5,21). This study provided evidence that RCF performed during the sensitive period of infant attachment learning (early adoption) developed an unstable environment for mother-infant interaction to occur in a healthy and adequate way and, as a result, significantly reduced maternal behavior and pups' response to maternal odor. On the other hand, the RCF procedure performed after the attachment learning period (late adoption) slightly reduced maternal care and it did not alter the behavioral responses of the pups to the maternal odor.

O córtex piriforme anterior (aPC) modulado pela ação da noradrenalina (NA) está envolvido no circuito neural que suporta o aprendizado do apego do roedor infante com sua mãe em um período específico do desenvolvimento anterior ao dia pós-natal (P) 10. O aPC está envolvido no processamento e discriminação de odores e durante o primeiro mês de vida pós-natal sofre mudanças morfológicas e funcionais. Estudos de imunohistoquímica e registros de potencial de campo sugerem uma progressiva maturação na inibição cortical no aPC, a qual está envolvida na integração e afinamento da atividade cortical para o input olfatório entrante e representação do odor. O propósito da presente tese foi contribuir para o entendimento dos mecanismos neurobiológicos envolvidos no apego do rato infante para sua mãe mediado por odor, por meio da análise do papel da transmissão sináptica GABAérgica no aPC. Assim, o estudo da tese foi realizado para: 1) descrever as características da transmissão sináptica GABAérgica no aPC durante o período sensível (P5-P8) e pós-sensível (P14-P17) para o aprendizado do apego e para, 2) explorar a contribuição das características da transmissão sináptica GABAérgica no aPC em um circuito neural artificial integrado para o processamento do odor nesses períodos. O desenho experimental incluiu estudos combinados de eletrofisiologia celular in vitro e de modelagem computacional. Os resultados eletrofisiológicos demonstraram que a transmissão sináptica GABAérgica e as propriedades intrínsecas passivas e ativas das células piramidais da camada 2/3 do aPC são substancialmente diferentes em P5-P8 e P14-P17. Esses dados experimentais foram integrados em um circuito neural artificial onde foi simulado o processamento de odor em condições etológicas (odor de baixa intensidade e odor de alta intensidade com ação da NA). A análise das simulações sugere que o input GABAérgico nas células piramidais parece contribuir com um efeito despolarizante nos dois períodos de idade. Além disso, o perfil de rápida adaptação na frequência de disparo de potenciais de ação para o input despolarizante é maior nas células piramidais em P5-P8 que em P14-P17. Assim, o nosso estudo sugere que essas duas condições maduracionais no aPC garantem em P5-P8 um perfil de processamento de odor, que quando reforçado pela ação da NA, leva a um rápido melhoramento na eficácia sináptica, contribuindo assim para uma rápido aprendizado do apego que caracteriza o período sensível; enquanto esse mecanismo parece ocorrer em menor grau para aPC no período P14-P17. The anterior pyriform cortex (aPC) modulated by the action of noradrenaline (NA) is involved in the neural circuitry that supports the early attachment learning in infant rodents within a specific period of development before the postnatal day (P) 10. The aPC is involved in the processing and discrimination of odors and during the first month of postnatal life goes through morphological and functional changes. Field potential recording and immunohistochemical studies suggest a progressive maturation of cortical inhibition in aPC, which is involved in the integration and tuning of cortical activity for the incoming olfactory input and odor representation. The purpose of this thesis was to contribute to the understanding of the neurobiological mechanisms involved in the rodent infant attachment by analyzing the role of GABAergic synaptic transmission in aPC. Thus, the study of the thesis was performed 1) to describe the characteristics of GABAergic synaptic transmission in the aPC during the sensitive (P5-P8) and post-sensitive (P14-P17) periods for infant attachment learning, and 2) to explore the contribution of the characteristics of GABAergic synaptic transmission in aPC in an integrated artificial neural circuit for odor processing. The experimental design included combined studies of in vitro cellular electrophysiology and computational modeling. Electrophysiological results demonstrate that GABAergic synaptic transmission and the passive and active intrinsic properties of 2/3 layer aPC pyramidal cells are substantially different in P5-P8 and P14-P17. These experimental data were integrated into an artificial neural circuit where the odor processing was simulated under ethological conditions (low-intensity odor and high-intensity odor with NA action). The analysis of the output of the simulations suggests that the GABAergic input in the pyramidal cells appears to contribute with a depolarizing effect on pyramidal cells in both periods. Moreover, the profile of rapid spike frequency adaptation is greater in P5-P8 pyramidal cells than in P14-P17 pyramidal cells. Thus, our study suggests that these two maturational conditions in aPC guarantee in P5-P8 an odor processing profile, which when reinforced by the action of NA leads to a rapid improvement in synaptic efficacy, contributing to a rapid attachment learning that characterizes the sensitive period. This mechanism seems to occur in lesser extent manner for aPC in the post-sensitive period.