Individual arcuate nucleus proopiomelanocortin neurons project to select target sites

Proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARH) are a diverse group of neurons that project widely to different brain regions. It is unknown how this small population of neurons organizes its afferent projections. In this study, we hypothesized that individual ARH POMC neurons exclusively innervate select target regions. To investigate this hypothesis, we first verified that only a fraction of ARH POMC neurons innervate the lateral hypothalamus (LH), the paraventricular nucleus of the hypothalamus (PVN), the periaqueductal gray (PAG), or the ventral tegmental area (VTA) using the retrograde tracer cholera toxin B (CTB). Next, two versions of CTB conjugated to distinct fluorophores were injected bilaterally into two of the regions such that PVN and VTA, PAG and VTA, or LH and PVN received tracers simultaneously. These pairs of target sites were chosen based on function and location. Few individual ARH POMC neurons projected to two brain regions at once, suggesting that there are ARH POMC neuron subpopulations organized by their afferent projections. We also investigated whether increasing the activity of POMC neurons could increase the number of ARH POMC neurons labeled with CTB, implying an increase in new synaptic connections to downstream regions. However, chemogenetic enhancement of POMC neuron activity did not increase retrograde tracing of CTB back to ARH POMC neurons from either the LH, PVN, or VTA. Overall, subpopulations of ARH POMC neurons with distinct afferent projections may serve as a way for the POMC population to organize its many functions.

Quantitation of lower urinary tract afferents in 3D reconstruction of lumbosacral spinal cord sections v1

This protocol details the 3D reconstruction of the lumbosacral spinal cord using alternating cryosections, and then goes through the steps required to quantify lower urinary tract afferents. Using TissueMaker (MBF Bioscience), images of alternating sections can be ordered and aligned prior to the production of a single image stack. In Neurolucida 360 (MBF Bioscience), regions of interest can be defined within the image stack, and the bouton-like immunolabelling of cholera toxin B can be segmented. Once saved, this data can then be extracted using Neurolucida Explorer (MBF Bioscience).

Prefrontal cortex neural compensation during an operant devaluation task

Deficits in goal-directed action are reported in multiple neuropsychiatric conditions, including schizophrenia. However, dysfunction is not always apparent in early stages of schizophrenia, possibly due to neural compensation. We designed a novel devaluation task in which goal-directed action could be guided by stimulus-outcome (S-O) [presumably orbitofrontal cortex (OFC)-mediated] or response-outcome (R-O) associations [presumably prelimbic cortex (PL)-mediated]. We previously found suggestive evidence that OFC and PL could compensate for each other in this task, and we more directly assessed this potential compensation here. In Experiment 1, rats received OFC, PL, combined OFC+PL, or sham lesions and then completed our devaluation task. The OFC+PL lesion group exhibited impaired devaluation. In Experiment 2, rats received cholera-toxin-b (CTb) into OFC and either neurotoxic or sham PL lesions. Rats were then sacrificed on the last training day to double-label for Arc and CTb. We found increased Arc+CTb in mediodorsal thalamus (MD) and increased Arc+ neurons in OFC when PL was lesioned, suggesting that PL lesions lead to a compensatory increased activation of the MD->OFC circuit. Our results suggest that our devaluation task can model neural compensation between OFC and PL and this compensation may be regulated by MD.

Cholera Toxin as a Probe for Membrane Biology

Cholera toxin B-subunit (CTxB) has emerged as one of the most widely utilized tools in membrane biology and biophysics. CTxB is a homopentameric stable protein that binds tightly to up to five GM1 glycosphingolipids. This provides a robust and tractable model for exploring membrane structure and its dynamics including vesicular trafficking and nanodomain assembly. Here, we review important advances in these fields enabled by use of CTxB and its lipid receptor GM1.

Spray-Dried Formulation of Epicertin, a Recombinant Cholera Toxin B Subunit Variant That Induces Mucosal Healing

Epicertin (EPT) is a recombinant variant of the cholera toxin B subunit, modified with a C-terminal KDEL endoplasmic reticulum retention motif. EPT has therapeutic potential for ulcerative colitis treatment. Previously, orally administered EPT demonstrated colon epithelial repair activity in dextran sodium sulfate (DSS)-induced acute and chronic colitis in mice. However, the oral dosing requires cumbersome pretreatment with sodium bicarbonate to conserve the acid-labile drug substance while transit through the stomach, hampering its facile application in chronic disease treatment. Here, we developed a solid oral formulation of EPT that circumvents degradation in gastric acid. EPT was spray-dried and packed into enteric-coated capsules to allow for pH-dependent release in the colon. A GM1-capture KDEL-detection ELISA and size-exclusion HPLC indicated that EPT powder maintains activity and structural stability for up to 9 months. Capsule disintegration tests showed that EPT remained encapsulated at pH 1 but was released over 180 min at pH 6.8, the approximate pH of the proximal colon. An acute DSS colitis study confirmed the therapeutic efficacy of encapsulated EPT in C57BL/6 mice upon oral administration without gastric acid neutralization pretreatment compared to vehicle-treated mice (p < 0.05). These results provide a foundation for an enteric-coated oral formulation of spray-dried EPT.

TOXICOLOGICAL FINDINGS OF A RECOMBINANT CHOLERA TOXIN B SUBUNIT VARIANT WITH THERAPEUTIC POTENTIAL IN ULCERATIVE COLITIS

Background The cholera toxin B subunit (CTB) is the nontoxic and homopentameric component of the holotoxin. Upon binding to GM1 ganglioside on the surface of epithelial cells, CTB mediates entry and retrograde transport through the endomembrane system and disengages the catalytic A subunit in the endoplasmic reticulum (ER). EPICERTIN (EPT) is a recombinant variant of CTB with a non-native C-terminal extension harboring an ER-retention motif, KDEL. We have found that increased ER-retention time resulting from this modification allowed EPT to induce an unfolded protein response and TGF-β signaling in colon epithelial cells, triggering wound healing activity in preclinical colitis models. The unique epithelial repair activity of EPT hints at its therapeutic potential in ulcerative colitis. Objective We aim to develop data supporting a first-in-human clinical trial with an EPT enema indicated for ulcerative colitis. Here, we evaluated the efficacy and toxicity of intrarectal (IR) administration of EPT in preclinical rodent models. Results IR administration of EPT at 0.1 and 1 µM to female C57/BL6 mice (0.6 and 6.1 μg/animal) with acute dextran sodium sulfate (DSS)-induced colitis resulted in decreased disease activity index scores and increased body weight recovery, supporting a target therapeutic dose of ≤1 µM for clinical administration. A dose-escalation study was performed following a single IR exposure at 1, 2 and 5 µM (61.4, 122.8 and 307 μg/animal) in male and female Sprague Dawley rats. No drug-related adverse effects were evident in clinical observations, including clinical pathology and gross necropsy, even at the highest dose tested. A pharmacokinetics study was performed in male and female mice dosed with a 1 or 10 µM (6.1 and 61.4 μg/animal) IV bolus of EPT. Plasma samples were collected periodically for up to 24 h postdose. EPT concentrations were highest at first collection and decreased steadily until unquantifiable by 4 h. The elimination phase half-life was 0.26 to 0.3 h. When healthy and DSS-induced colitic mice (n = 72) were dosed with 1 or 10 µM EPT IR, marginal amounts of EPT were found in only 4 plasma samples scattered across groups and time points, suggesting that systemic exposure after IR administration is negligible. Conclusion These data support further development of EPT as a potential therapeutic for ulcerative colitis.