Biology subjects

Stackmann, M.

Publications and source records attributed to Stackmann, M..

4 recordsLinked to original sources

bioRxiv2024

A multiple Arc (mArc) tagging system to uncover the organizational principles of multiple memories

Engrams or memory traces are the neuronal ensembles that collectively store individual experiences. Genetic strategies based on immediate early genes (IEGs), such as Arc/Arg3.1, allow us to tag the ensembles active during memory encoding and compare them to those active during retrieval. However, these strategies only allow for the tagging of one neural ensemble. Here, we developed a multiple Arc (mArc) system that allows for the tagging of two Arc+ ensembles. We validated this system by investigating how context, time, and valence influence neuronal ensemble reactivation in the dentate gyrus (DG). We show that similar contextual and valenced experiences are encoded in overlapping DG ensembles. We also find that ensembles are modulated by time, where experiences closer in time are encoded in more similar ensembles. These results highlight the dynamic nature of DG ensembles and show that the mArc system provides a powerful approach for investigating multiple memories in the brain. HIGHLIGHTSO_LIThe mArc system allows for the tagging of two Arc+ ensembles in the same mouse C_LIO_LIDG ensembles labeled by the mArc system receive increased excitatory input C_LIO_LIContext, valence, and time influence DG ensemble reactivation C_LIO_LIDG neural ensembles are reactivated less with increasing time C_LI

neuroscience↗

bioRxiv2020

Recognition memory via repetition suppression in mouse hippocampal dorsal CA2 pyramidal neurons expressing the vasopressin 1b receptor

Recognition memory, often compromised in psychiatric disorders, is a major component of declarative memory, which permits the realization that an event, object or social subject has been previously encountered. The CA2 region of the dorsal hippocampus (dCA2) is involved in social memory and responds to novel objects, in time and space. However, it remains unclear how these neurons encode either social or inanimate object recognition. Here, we show that in dCA2, encoding of social recognition memory entails suppression of pyramidal neurons activity leading to a sparse representation of the familiar conspecific. We discuss the neural coding scheme by which dCA2 pyramidal neurons contribute to social memory.

neuroscience↗

bioRxiv2019

NMDA receptor in vasopressin 1b neurons is not required for short-term social memory, object memory or aggression.

The vasopressin 1b receptor (Avpr1b) plays an important role in social behaviors including aggression, social learning and memory. Genetic removal of Avpr1b from mouse models results in deficits in aggression and short-term social recognition in adults. Avpr1b gene expression is highly enriched in the pyramidal neurons of the hippocampal cornu ammonis 2 (CA2) region. Activity of the hippocampal CA2 has been shown to be required for normal short-term social recognition and aggressive behaviors. Vasopressin acts to enhance synaptic responses of CA2 neurons through a NMDA-receptor dependent mechanism. Genetic removal of the obligatory subunit of the NMDA receptor (Grin1) within distinct hippocampal regions impairs non-social learning and memory. However, the question of a direct role for NMDA receptor activity in Avpr1b neurons to modulate social behavior remains unclear. To answer this question, we first created a novel transgenic mouse line with Cre recombinase knocked into the Avpr1b coding region to genetically target Avpr1b neurons. We confirmed this line has dense Cre expression throughout the dorsal and ventral CA2 regions of the hippocampus, along with scattered expression within the caudate-putamen and olfactory bulb. Conditional removal of the NMDA receptor was achieved by crossing our line to an available floxed Grin1 line. The resulting mice were measured on a battery of social and memory behavioral tests. Surprisingly, we did not observe any differences between Avpr1b-Grin1 knockout mice and their wildtype siblings. We conclude that mice without typical NMDA receptor function in Avpr1b neurons can develop normal aggression as well as short-term social and object memory performance.\n\nSignificance StatementActivity of neurons that express vasopressin 1b receptor are essential for aggressive and social recognition behaviors. We created a novel transgenic mouse to allow selective targeting of vasopressin 1b neurons. Our studies indicate that NMDA receptor expression in vasopressin 1b neurons (including most CA2 neurons) are not required for development of the typical expression of aggression or recognition memory. Thus, CA2 neurons may have a unique way of incorporating novel stimuli into memory that deserves further investigation.

neuroscience↗

bioRxiv2019

The human-specific paralogs SRGAP2B and SRGAP2C differentially modulate SRGAP2A-dependent synaptic development

Human-specific gene duplications (HSGD) have recently emerged as key modifiers of brain development and evolution. However, the molecular mechanisms underlying the function of HSGDs remain often poorly understood. In humans, a truncated duplication of SRGAP2A led to the emergence of two human-specific paralogs: SRGAP2B and SRGAP2C. The ancestral copy SRGAP2A limits synaptic density and promotes maturation of both excitatory (E) and inhibitory (I) synapses received by cortical pyramidal neurons (PNs). SRGAP2C binds to and inhibits all known functions of SRGAP2A leading to an increase in E and I synapse density and protracted synapse maturation, traits characterizing human cortical neurons. Here, we demonstrate how the evolutionary changes that led to the emergence of SRGAP2 HSGD generated proteins that, in neurons, are intrinsically unstable and upon hetero-dimerization with SRGAP2A, reduces SRGAP2A levels in a proteasome-dependent manner. Moreover, we show that, compared to SRGAP2B, and despite only a few non-synonymous mutations specifically targeting arginine residues, SRGAP2C is unique, compared to SRGAP2B, in its ability to induce long-lasting changes in synaptic density throughout adulthood. The non-synonymous mutations specifically targeting arginine residues led to the unique ability of SRGAP2C to inhibit SRGAP2A function and thereby contribute to the emergence of human-specific features of synaptic development during evolution.

neuroscience↗