Mentoring: A three-generation perspective.

This NeuroView is intended for graduate students who are not sure how to choose or what to expect from a mentor as well as mentors who are uncertain what to give mentees. Two principal investigators and a current mentee will share their perspectives on this bidirectional relationship.

The memory orchestra: the role of astrocytes and oligodendrocytes in parallel to neurons.

For decades, the study of memory has been neuron-centric, yet neurons do not function in isolation. Today we know that neuronal activity is modulated by the environment within which it occurs, and is subject to modulation by different types of glial cells. In this review we summarize recent findings on the functional roles of astrocytes and oligodendrocytes, two major types of glia cells in the adult brain, in memory formation and its cellular underpinnings across multiple time points. We will discuss the different methods that are being used to investigate the astrocytic and oligodendroglial involvement in memory. We shall focus on chemogenetics and optogenetics, which support genetically specificity and high spatiotemporal resolution, attributes that are particularly well suited to the investigation of the contribution of unique cell types at the different stages of memory formation.

Astrocytes contribute to remote memory formation by modulating hippocampal-cortical communication during learning.

Remote memories depend on coordinated activity in the hippocampus and frontal cortices, but the timeline of these interactions is debated. Astrocytes sense and modify neuronal activity, but their role in remote memory is scarcely explored. We expressed the Gi-coupled designer receptor hM4Di in CA1 astrocytes and discovered that astrocytic manipulation during learning specifically impaired remote, but not recent, memory recall and decreased activity in the anterior cingulate cortex (ACC) during retrieval. We revealed massive recruitment of ACC-projecting CA1 neurons during memory acquisition, which was accompanied by the activation of ACC neurons. Astrocytic Gi activation disrupted CA3 to CA1 communication in vivo and reduced the downstream response in the ACC. In behaving mice, it induced a projection-specific inhibition of CA1-to-ACC neurons during learning, which consequently prevented ACC recruitment. Finally, direct inhibition of CA1-to-ACC-projecting neurons spared recent and impaired remote memory. Our findings suggest that remote memory acquisition involves projection-specific functions of astrocytes in regulating CA1-to-ACC neuronal communication.

Disentangling molecular alterations from water-content changes in the aging human brain using quantitative MRI.

It is an open question whether aging-related changes throughout the brain are driven by a common factor or result from several distinct molecular mechanisms. Quantitative magnetic resonance imaging (qMRI) provides biophysical parametric measurements allowing for non-invasive mapping of the aging human brain. However, qMRI measurements change in response to both molecular composition and water content. Here, we present a tissue relaxivity approach that disentangles these two tissue components and decodes molecular information from the MRI signal. Our approach enables us to reveal the molecular composition of lipid samples and predict lipidomics measurements of the brain. It produces unique molecular signatures across the brain, which are correlated with specific gene-expression profiles. We uncover region-specific molecular changes associated with brain aging. These changes are independent from other MRI aging markers. Our approach opens the door to a quantitative characterization of the biological sources for aging, that until now was possible only post-mortem.

Astrocytic Activation Generates De Novo Neuronal Potentiation and Memory Enhancement.

Astrocytes respond to neuronal activity and were shown to be necessary for plasticity and memory. To test whether astrocytic activity is also sufficient to generate synaptic potentiation and enhance memory, we expressed the Gq-coupled receptor hM3Dq in CA1 astrocytes, allowing their activation by a designer drug. We discovered that astrocytic activation is not only necessary for synaptic plasticity, but also sufficient to induce NMDA-dependent de novo long-term potentiation in the hippocampus that persisted after astrocytic activation ceased. In vivo, astrocytic activation enhanced memory allocation; i.e., it increased neuronal activity in a task-specific way only when coupled with learning, but not in home-caged mice. Furthermore, astrocytic activation using either a chemogenetic or an optogenetic tool during acquisition resulted in memory recall enhancement on the following day. Conversely, directly increasing neuronal activity resulted in dramatic memory impairment. Our findings that astrocytes induce plasticity and enhance memory may have important clinical implications for cognitive augmentation treatments.