NMDA receptors potentiate activity‐dependent dendritic release of neuropeptides from hypothalamic neurons

Abstract

Key points Using ‘sniffer’ cell biosensors, we evaluated the effects of specific firing patterns and frequencies on activity‐dependent somatodendritic release of vasopressin from paraventricular nucleus neurones. Somatodendritic release of vasopressin was rarely observed during continuous firing but was strengthened by clustered activity. Moreover, release evoked at any given frequency was robustly potentiated by NMDA receptor (NMDAR)‐mediated firing. Differently from axonal release, NMDAR activation was necessary for somatodendritic release to occur at physiological firing frequencies, acting thus as a gating mechanism by which activity‐dependent release from these two neuronal compartments could be independently regulated. The NMDAR‐mediated potentiation was independent of a specific firing pattern and was not accompanied by increased spike broadening, but correlated with higher dendritic Ca2+ levels. Our studies provide fundamental novel information regarding stimulus–secretion coupling at somatodendritic compartments, and shed light into mechanisms by which activity‐dependent release of neuronal signals from axonal terminals and dendrites could be regulated in a spatially compartmentalized manner. Abstract Dendrites are now recognized to be active transmitting neuronal compartments subserving complex brain functions, including motor behaviours and homeostatic neurohumoral responses. Still, the precise mechanisms underlying activity‐dependent release of dendritic signals, and how dendritic release is regulated independently from axonal release, remains largely unknown. We used ‘sniffer’ biosensor cells to enable the measurement and study of activity‐dependent dendritic release of vasopressin (VP) from hypothalamic neurones in brain slices. SnifferVP responses were dose‐dependent, with a threshold detection level of 0.5 nM for VP, being thus a highly sensitive tool to detect endogenous physiological levels of the neuropeptide. Somatodendritic release of VP was rarely observed in response to a burst of action potentials fired in continuous mode, but was strengthened by clustered firing activity. Moreover, release evoked at any given frequency was robustly potentiated when firing was triggered by NMDA receptor (NMDAR) activation. Differently from axonal release, NMDAR activation was necessary for dendritic release to occur at physiological firing frequencies. Thus, we propose that NMDARs may act as a gating mechanism by which activity‐dependent release from these two neuronal compartments can be independently regulated. The NMDAR‐mediated potentiation of dendritic release was independent of a particular action potential waveform, firing pattern evoked, or a more pronounced spiked broadening, but correlated with higher dendritic Ca2+ levels. Overall, our studies provide fundamental novel information regarding stimulus–secretion coupling at neuronal dendrites, and shed light into mechanisms by which activity‐dependent release of neuronal signals from axonal terminals and dendrites can be regulated in a spatially ...

Sniffer cells for the detection of neural Angiotensin II in vitro

“…The results indicate that sniffer cells specific for ANG II and ANG III can be used to detect release of these peptides in vitro consistent with earlier studies focusing on vasopressin 23,24 and oxytocin 25,26 . While these previous studies have typically used transient transfections, our studies have extended this approach to the creation of stable cell lines that might limit some of the variability of the expression of the receptor of interest and the calcium indicator.…”

“…High-pressure liquid chromatography is a more sensitive method for the detection of neuropeptides but is expensive and still subject to the same impairments in temporal and spatial resolution as microdialysis. Genetically modified HEK or CHO cells have recently been used to measure vasopressin 23,24 or oxytocin 25,26 release in brain slices. This approach has also been combined with patch-clamping to study GABA and glutamate release 27,28 and optogenetics to study peptide release from axons transfected with channel rhodopsin 25,26 .…”

Brain-Derived Neurotrophic Factor and Supraoptic Vasopressin Neurons in Hyponatremia

“…The changes in the activity of AVP neurons caused by BDNF may represent an adaptation to excess activity that contributes to inappropriate AVP release in a variety of experimental models. While the KCC2 data suggest that this mechanism is related to changes in GABA, several recent experiments suggest that excitatory mechanisms are also important [57,58]. In addition, the knockdown of BDNF in the SON reduced the thirst and urine excretion associated with liver failure.…”

α‐Melanocyte‐stimulating hormone inhibition of oxytocin neurons switches to excitation in late pregnancy and lactation

“…While both depend on intracellular calcium, axon terminal secretion and somato-dendritic secretion can occur independently from oxytocin neurons, suggesting that different mechanisms control secretion from different compartments of the neurons (Pitra et al, 2019), which would allow for differential modulation of the two modes of secretion by afferent inputs (Ludwig & Leng, 2006). Alpha-melanocyte-stimulating hormone (α-MSH) is synthesized by proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus and has been shown to differentially modulate axon terminal secretion and somatodendritic secretion of oxytocin.…”