Horizontal Hippocampal Slices of the Mouse Brain

Maternal immune activation-induced proBDNF-mediated neural information processing dysfunction at hippocampal CA3-CA1 synapses associated with memory deficits in offspring

Prenatal exposure to maternal infection increases the risk of offspring developing schizophrenia in adulthood. Current theories suggest that the consequences of MIA on mBDNF secretion may underlie the increased risk of cognitive disorder. There is little evidence for whether the expression of its precursor, proBDNF, is changed and how proBDNF-mediated signaling may involve in learning and memory. In this study, proBDNF levels were detected in the hippocampal CA1 and CA3 regions of male adult rats following MIA by prenatal polyI:C exposure. Behaviorally, learning and memory were assessed in contextual fear conditioning tasks. Local field potentials were recorded in the hippocampal CA3-CA1 pathway. The General Partial Directed Coherence approach was utilized to identify the directional alternation of neural information flow between CA3 and CA1 regions. EPSCs were recorded in CA1 pyramidal neurons to explore a possible mechanism involving the proBDNF-p75NTR signaling pathway. Results showed that the expression of proBDNF in the polyI:C-treated offspring was abnormally enhanced in both CA3 and CA1 regions. Meanwhile, the mBDNF expression was reduced in both hippocampal regions. Intra-hippocampal CA1 but not CA3 injection with anti-proBDNF antibody and p75NTR inhibitor TAT-Pep5 effectively mitigated the contextual memory deficits. Meanwhile, reductions in the phase synchronization between CA3 and CA1 and the coupling directional indexes from CA3 to CA1 were enhanced by the intra-CA1 infusions. Moreover, blocking proBDNF/p75NTR signaling could reverse the declined amplitude of EPSCs in CA1 pyramidal neurons, indicating the changes in postsynaptic information processing in the polyI:C-treated offspring. Therefore, the changes in hippocampal proBDNF activity in prenatal polyI:C exposure represent a potential mechanism involved in NIF disruption leading to contextual memory impairments.

Dissection of Mouse Hippocampus with Its Dorsal, Intermediate and Ventral Subdivisions Combined with Molecular Validation

Many research methods applied in molecular neuroscience require the collection of hippocampal samples, but a still poorly recognized problem is contamination with the choroid plexus during brain dissection. Because of a distinct pattern of gene expression, its inclusion in brain samples can obscure or even confound conclusions drawn from molecular studies. Therefore, we tested our dissection method designed for removal of tissue contamination using expression of the transthyretin gene (Ttr) as a marker of the choroid plexus. Additionally, we also validated dissection of the entire hippocampus into its dorsal, intermediate and ventral subdivisions using the expression of Trhr and Lct genes as molecular markers of anatomical subdivisions. The PCR analysis showed that Ttr is expressed at a residual level in hippocampal samples that display an mRNA level several hundred lower than the adjacent control tissue colocalized with the choroid plexus. This indicates that the applied method for dissecting the hippocampus from a fresh brain allows for replicable removal of the majority of choroid plexus from hippocampal samples. In turn, differences in expression of Lct and Trhr confirmed the proper dissection of dorsal, intermediate and ventral subdivisions from fresh brain tissue. Therefore, a special emphasis on the removal of tissue contamination and avoidance of tissue distortions makes our protocol especially suitable for molecular experiments performed either on the entire hippocampus or its subdivisions.