Transneuronal transport of neurotropic viruses is widely used to define the organization of neural circuitry in the mature and developing nervous system. However, interconnectivity within complex circuits limits the ability of viral tracing to define connections specifically linked to a subpopulation of neurons within a network. Here we demonstrate a unique viral tracing technology that highlights connections to defined populations of neurons within a larger labeled network. This technology was accomplished by constructing a replication-competent strain of pseudorabies virus (PRV-263) that changes the profile of fluorescent reporter expression in the presence of Cre recombinase (Cre). The viral genome carries a Brainbow cassette that expresses a default red reporter in infected cells. However, in the presence of Cre, the red reporter gene is excised from the genome and expression of yellow or cyan reporters is enabled. We used PRV-263 in combination with a unique lentivirus vector that produces Cre expression in catecholamine neurons. Projection-specific infection of central circuits containing these Cre-expressing catecholamine neurons with PRV-263 resulted in Cre-mediated recombination of the PRV-263 genome and conditional expression of cyan/yellow reporters. Replication and transneuronal transport of recombined virus produced conditional reporter expression in neurons synaptically linked to the Cre-expressing catecholamine neurons. This unique technology highlights connections specific to phenotypically defined neurons within larger networks infected by retrograde transneuronal transport of virus from a defined projection target. The availability of other technologies that restrict Cre expression to defined populations of neurons indicates that this approach can be widely applied across functionally defined systems.

Background: Several sellar reconstruction algorithms stratify patients based on risk of postoperative cerebrospinal fluid (CSF) leak. Many proposed algorithms employ techniques that are overly complex and confer morbidity. We review our experience with sellar reconstruction following transsphenoidal pituitary surgery and propose a highly effective, yet simple and low morbidity, algorithm. Methods:A retrospective review of 582 patients who underwent transsphenoidal surgery for pituitary adenoma by a single neurosurgeon between 2005 and 2020 was performed. Patients without an intraoperative CSF leak and without a patulous diaphragm were repaired with an oxidized cellulose onlay (group 1).Patients with a low-flow intraoperative CSF leak or a patulous diaphragm were repaired with a synthetic dural substitute inlay (group 2). Patients with a persistent leak around the inlay repair or a high-flow leak were reconstructed with a synthetic dural substitute inlay and a nasoseptal flap onlay (group 3). Results: There was an overall leak rate of 1.5% (9/582) to 1.0% (2/197) in group 1, 1.7% (6/347) in group 2, and 2.6% (1/38) in group 3. Group 3 had the highest rate of postoperative morbidity, including sinusitis (23.7% vs. 8.6% and 15.0% in groups 1 and 2, p = 0.018) and crusting (42.1% vs. 4.6% and 6.3% in groups 1 and 2, p < 0.001). All techniques healed equally well radiographically. Conclusion:The proposed algorithm for sellar reconstruction is highly effective and minimizes complexity and morbidity, primarily utilizing single-layer reconstructions without the addition of packing material or lumbar drainage.

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