VEGF-D Downregulation in CA1 Pyramidal Neurons Exerts Asymmetric Changes of Dendritic Morphology without Correlated Electrophysiological Alterations

Dendritic axon origin enables information gating by perisomatic inhibition in pyramidal neurons

Information processing in neuronal networks involves the recruitment of selected neurons into coordinated spatiotemporal activity patterns. This sparse activation results from widespread synaptic inhibition in conjunction with neuron-specific synaptic excitation. We report the selective recruitment of hippocampal pyramidal cells into patterned network activity. During ripple oscillations in awake mice, spiking is much more likely in cells in which the axon originates from a basal dendrite rather than from the soma. High-resolution recordings in vitro and computer modeling indicate that these spikes are elicited by synaptic input to the axon-carrying dendrite and thus escape perisomatic inhibition. Pyramidal cells with somatic axon origin can be activated during ripple oscillations by blocking their somatic inhibition. The recruitment of neurons into active ensembles is thus determined by axonal morphological features.

Chronic VEGFR-3 signaling preserves dendritic arborization and sensitization under stress

Dendritic arborization is critical for the establishment and maintenance of precise neural circuits. Vascular endothelial growth factor D (VEGF-D), well-characterized as a "lymphangiogenic" growth factor, reportedly maintains dendritic arborization and synaptic strength in the hippocampus of adult mice through VEGF receptor (VEGFR-3) signaling. Here, we investigated the effect of chronic VEGFR-3-specific activation on adipose arbor morphometry using the Adipo-VD mouse, a model of inducible, adipose-specific VEGF-D overexpression. We examined whether adipose tissue innervation was preserved or functionally different in Adipo-VD mice during stress in vivo and if VEGFR-3 signaling afforded neuroprotection to challenged neurons in vitro. Chronic VEGFR-3 signaling in Adipo-VD subcutaneous adipose tissue resulted in a reduction in the dendrite length, dendritic terminal branches (filament length), and dendritic terminal branch volume (filament volume), but increased dendrite branching. We also identified reduced stimulus-evoked excitatory sympathetic nerve activity in Adipo-VD mice. Following 6-hydroxydopamine (6-OHDA) denervation, Adipo-VD dendritic arbors were preserved, including improved dendritic branch volume, length, and dendritic branches than in wildtype tissues. In vitro, we found that chronic elevation of VEGFR-3 signaling in developing mVC neurons changes the dendritic arbor complexity and improves stress-induced structure remodeling. Developing neurons are conferred neuroprotection against stress, potentially by upregulation of proteolytic conversion of pro-BDNF to mature BDNF. Mature neurons, however, display improved dendritic arbor complexity, and unaltered dendritic structural remodeling and improved resistance to stress with VEGFR-3 signaling. Overall, chronically increasing VEGFR-3 signaling in neurons has a synergistic impact on neurosensitization and neuroprotection during stress.

Chronic Stress Alters Astrocyte Morphology in Mouse Prefrontal Cortex

BACKGROUND

Neuromorphological changes are consistently reported in the prefrontal cortex of patients with stress-related disorders and in rodent stress models, but the effects of stress on astrocyte morphology and the potential link to behavioral deficits are relatively unknown.

METHODS

To answer these questions, transgenic mice expressing green fluorescent protein (GFP) under the glial fibrillary acid protein (GFAP) promotor were subjected to 7, 21, or 35 days of chronic restraint stress (CRS). CRS-induced behavioral effects on anhedonia- and anxiety-like behaviors were measured using the sucrose intake and the PhenoTyper tests, respectively. Prefrontal cortex GFP+ or GFAP+ cell morphology was assessed using Sholl analysis, and associations with behavior were determined using correlation analysis.

RESULTS

CRS-exposed male and female mice displayed anxiety-like behavior at 7, 21, and 35 days and anhedonia-like behavior at 35 days. Analysis of GFAP+ cell morphology revealed significant atrophy of distal processes following 21 and 35 days of CRS. CRS induced similar decreases in intersections at distal radii for GFP+ cells accompanied by increased proximal processes. In males, the number of intersections at the most distal radius step significantly correlated with anhedonia-like behavior (r = 0.622, P < .05) for GFP+ cells and with behavioral emotionality calculated by z-scoring all behavioral measured deficits (r = -0.667, P < .05). Similar but not significant correlations were observed in females. No correlation between GFP+ cell atrophy with anxiety-like behavior was found.

CONCLUSION

Chronic stress exposure induces a progressive atrophy of cortical astroglial cells, potentially contributing to maladaptive neuroplastic and behavioral changes associated with stress-related disorders.