Synaptotagmin 9 Modulates Spontaneous Neurotransmitter Release in Striatal Neurons by Regulating Substance P Secretion.

Synaptotagmin 9 (SYT9) is a tandem C2 domain Ca2+ sensor for exocytosis in neuroendocrine cells; its function in neurons remains unclear. Here, we show that, in mixed-sex cultures, SYT9 does not trigger rapid synaptic vesicle exocytosis in mouse cortical, hippocampal, or striatal neurons, unless it is massively overexpressed. In striatal neurons, loss of SYT9 reduced the frequency of spontaneous neurotransmitter release events (minis). We delved into the underlying mechanism and discovered that SYT9 was localized to dense-core vesicles that contain substance P (SP). Loss of SYT9 impaired SP release, causing the observed decrease in mini frequency. This model is further supported by loss of function mutants. Namely, Ca2+ binding to the C2A domain of SYT9 triggered membrane fusion in vitro, and mutations that disrupted this activity abolished the ability of SYT9 to regulate both SP release and mini frequency. We conclude that SYT9 indirectly regulates synaptic transmission in striatal neurons by controlling SP release.SIGNIFICANCE STATEMENT Synaptotagmin 9 (SYT9) has been described as a Ca2+ sensor for dense-core vesicle (DCV) exocytosis in neuroendocrine cells, but its role in neurons remains unclear, despite widespread expression in the brain. This article examines the role of SYT9 in synaptic transmission across cultured cortical, hippocampal, and striatal neuronal preparations. We found that SYT9 regulates spontaneous neurotransmitter release in striatal neurons by serving as a Ca2+ sensor for the release of the neuromodulator substance P from DCVs. This demonstrates a novel role for SYT9 in neurons and uncovers a new field of study into neuromodulation by SYT9, a protein that is widely expressed in the brain.

Synaptic vesicle proteins are selectively delivered to axons in mammalian neurons.

Neurotransmitter-filled synaptic vesicles (SVs) mediate synaptic transmission and are a hallmark specialization in neuronal axons. Yet, how SV proteins are sorted to presynaptic nerve terminals remains the subject of debate. The leading model posits that these proteins are randomly trafficked throughout neurons and are selectively retained in presynaptic boutons. Here, we used the RUSH (retention using selective hooks) system, in conjunction with HaloTag labeling approaches, to study the egress of two distinct transmembrane SV proteins, synaptotagmin 1 and synaptobrevin 2, from the soma of mature cultured rat and mouse neurons. For these studies, the SV reporter constructs were expressed at carefully controlled, very low levels. In sharp contrast to the selective retention model, both proteins selectively and specifically entered axons with minimal entry into dendrites. However, even moderate overexpression resulted in the spillover of SV proteins into dendrites, potentially explaining the origin of previous non-polarized transport models, revealing the limited, saturable nature of the direct axonal trafficking pathway. Moreover, we observed that SV constituents were first delivered to the presynaptic plasma membrane before incorporation into SVs. These experiments reveal a new-found membrane trafficking pathway, for SV proteins, in classically polarized mammalian neurons and provide a glimpse at the first steps of SV biogenesis.

Endoscopic endonasal transethmoidal transcribriform transfovea ethmoidalis approach to the anterior cranial fossa and skull base.

OBJECTIVE: The anterior skull base, in front of the sphenoid sinus, can be approached using a variety of techniques including extended subfrontal, transfacial, and craniofacial approaches. These methods include risks of brain retraction, contusion, cerebrospinal fluid leak, meningitis, and cosmetic deformity. An alternate and more direct approach is the endonasal, transethmoidal, transcribriform, transfovea ethmoidalis approach. METHODS: An endoscopic, endonasal approach was used to treat a variety of conditions of the anterior skull base arising in front of the sphenoid sinus and between the orbits in a series of 44 patients. A prospective database was used to detail the corridor of approach, closure technique, use of intraoperative lumbar drainage, operative time, and postoperative complications. Extent of resection was determined by a radiologist using volumetric analysis. RESULTS: Pathology included meningo/encephaloceles (19), benign tumors (14), malignant tumors (9), and infectious lesions (2). Lumbar drains were placed intraoperatively in 20 patients. The CSF leak rate was 6.8% for the whole series and 9% for intradural cases. Leaks were effectively managed with lumbar drainage. Early reoperation for cerebrospinal fluid (CSF) leak occurred in 1 patient (2.2%). There were no intracranial infections. Greater than 98% resection was achieved in 12 of 14 benign and 5 of 9 malignant tumors. CONCLUSION: The endoscopic, endonasal, transethmoidal, transcribriform, transfovea ethmoidalis approach is versatile and suitable for managing a variety of pathological entities. This minimal access surgery is a feasible alternative to transcranial, transfacial, or combined craniofacial approaches to the anterior skull base and anterior cranial fossa in front of the sphenoid sinus. The risk of CSF leak and infection are reasonably low and decrease with experience. Longer follow-up and larger series of patients will be required to validate the long-term efficacy of this minimally invasive approach.