RESUMO

Most mammals have sensory tactile hairs, also known as whiskers or vibrissae. Traditionally, whiskers are associated with diverse survival skills, including tactile discrimination, distance assessment, food acquisition, gap crossing, and social interaction. Vibrissae functions are processed in the somatosensorial cortex, commonly referred to as the barrel cortex. Hence, most of the whisker-related research has been focused on this cortical region. However, increasing evidence indicates that the vibrissal system modulates several aspects of hippocampal physiology. This graphical review aims to summarize cumulative evidence indicating that whiskers regulate the neural function and cellularity in several hippocampal subfields. Interestingly, lack of whiskers notably affects neuronal firing in CA1 and CA3 hippocampal subfields, alters spatial mapping, impairs navigational skills, modifies cytoarchitecture, and reduces the adult neurogenesis in the dentate gyrus. This evidence extends our understanding of how whiskers are related to hippocampal function and offers insights to explore novel associations between whisker functions and neural plasticity in the hippocampus.

RESUMO

Cyclohexane (CHX) is an organic solvent commonly used as a drug-of-abuse. This drug increases the oxidative stress and glial reactivity in the hippocampus, which suggests that this brain region is vulnerable to CHX effects. This study aimed to establish the behavioral changes and the pathological alterations that occur in the Cornu Ammonis 3 (CA3) and Dentate Gyrus (DG) after a long-lasting exposure to CHX. We exposed CD1 mice to a recreational-like dose of CHX (~ 30,000 ppm) for 30 days and explored its consequences in motor skills, reward-seeking behavior, and the CA3 and DG hippocampal subfields. Twenty-four hours after the last administration of CHX, we found a significant decrease in the number of c-Fos+ cells in the hippocampal CA3 and DG regions. This event coincided with an increased in NMDAR1 expression and apoptotic cells in the CA3 region. At day 13th without CHX, we found a persistent reduction in the number of c-Fos+ and TUNEL+ cells in DG. At both time points, the CHX-exposed mice showed a strong overexpression of neuropeptide Y (NPY) in the CA3 stratum lucidum and the hippocampal hilus. In parallel, we used an operant-based task to assess motor performance and operant conditioning learning. The behavioral analysis indicated that CHX did not modify the acquisition of operant conditioning tasks, but affected some motor skills and increased the reward-seeking behavior. Altogether, this evidence reveals that CHX exposure provokes long-lasting changes in the hippocampal subfields, induces motor impairments and increases the motivation-guided behavior. These findings can help understand the deleterious effect of CHX into the adult hippocampus and unveil its potential to trigger addiction-like behaviors.

Assuntos

Envelhecimento/patologia , Comportamento Animal , Cicloexanos/administração & dosagem , Hipocampo/patologia , Recompensa , Administração por Inalação , Animais , Região CA3 Hipocampal/metabolismo , Região CA3 Hipocampal/patologia , Contagem de Células , Giro Denteado/metabolismo , Giro Denteado/patologia , Hipocampo/metabolismo , Masculino , Camundongos , Motivação , Atividade Motora , Neuropeptídeo Y/metabolismo , Postura , Proteínas Proto-Oncogênicas c-fos/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Reforço Psicológico , Análise e Desempenho de Tarefas

RESUMO

Facial vibrissae, commonly known as whiskers, are the main sensitive tactile system in rodents. Whisker stimulation triggers neuronal activity that promotes neural plasticity in the barrel cortex (BC) and helps create spatial maps in the adult hippocampus. Moreover, activity-dependent inputs and calcium homeostasis modulate adult neurogenesis. Therefore, the neuronal activity of the BC possibly regulates hippocampal functions and neurogenesis. To assess whether tactile information from facial whiskers may modulate hippocampal functions and neurogenesis, we permanently eliminated whiskers in CD1 male mice and analyzed the effects in cellular composition, molecular expression and memory processing in the adult hippocampus. Our data indicated that the permanent deprivation of whiskers reduced in 4-fold the density of c-Fos+ cells (a calcium-dependent immediate early gene) in cornu ammonis subfields (CA1, CA2 and CA3) and 4.5-fold the dentate gyrus (DG). A significant reduction in the expression of calcium-binding proteincalbindin-D28k was also observed in granule cells of the DG. Notably, these changes coincided with an increase in apoptosis and a decrease in the proliferation of neural precursor cells in the DG, which ultimately reduced the number of Bromodeoxyuridine (BrdU)+NeuN+ mature neurons generated after whisker elimination. These abnormalities in the hippocampus were associated with a significant impairment of spatial memory and navigation skills. This is the first evidence indicating that tactile inputs from vibrissal follicles strongly modify the expression of c-Fos and calbindin in the DG, disrupt different aspects of hippocampal neurogenesis, and support the notion that spatial memory and navigation skills strongly require tactile information in the hippocampus.