Biology subjects

Castro, D. C.

Publications and source records attributed to Castro, D. C..

8 recordsLinked to original sources

bioRxiv2026

Pancreatic mu opioid receptors regulate metabolism and ingestive behaviors

The mu opioid receptor system has long been recognized for its role in regulating ingestive behaviors and food palatability. However, beyond their robust expression in the brain, opioid receptors are also found throughout the body, including the stomach, intestines, and pancreas. Previous studies suggest that opioids may directly regulate glycemia through actions in the endocrine pancreas, but whether these metabolic effects are linked to their influence on ingestive behavior remains unclear. Here, we used metabolic, ingestive, and genetic approaches to determine how the mu opioid receptor (MOPR) regulates in vivo phenotypes via its actions in endocrine pancreas. Glucose and insulin tolerance tests in male Oprm1 KO mice had enhanced glucose tolerance and insulin sensitivity. Conditional deletion of MOPRs in alpha cells had no effect. To test if loss of MOPRs influence overt ingestive behaviors, we measured 24-hour ad libitum food consumption using Feeding Experimental Devices (FEDs) in wild type, Oprm1 knockout (MOPR-deficient) and GCG-Cre x Oprm1fl/fl mice (10-12 weeks old). We found that Oprm1 KO male, but not female, mice exhibited increased mass and food intake, and dysregulated ingestive microstructures relative to wild type controls. Conditional deletion of MOPRs in alpha cells only recapitulated some of the phenotypes related to ingestive microstructure. These findings suggest that MOPR regulation of ingestive behaviors extends beyond typical neural circuits of reward to include peripheral metabolic organ mechanisms. Highlights- Male Oprm1 knockout mice show increased body mass and food intake - Male, but not female, Oprm1 knockout mice have enhanced glucose tolerance and insulin sensitivity - MOPR deletion in pancreatic alpha cells did not alter glucose metabolism - MOPR deletion in alpha cells increased meal frequency but reduced meal size in males - MOPR deletion in alpha cells only reduced meal size in females

animal behavior and cognition↗

bioRxiv2025

MOPRs in mouse islets of Langerhans modulate cell signaling and secretion

Article highlightsO_LIMu opioid receptors are expressed on multiple islets of Langerhans cell types C_LIO_LIMu opioid receptors on islets engage canonical Gi signaling cascades in islets C_LIO_LIMu opioid receptors on islets modulate calcium influx and oscillations C_LIO_LIMu opioid receptors on islets modulate insulin and glucagon secretion. C_LI Most clinically and recreationally used opioids drugs act on the endogenous mu opioid receptor (MOPR). While MOPR is typically studied in the context of addiction and analgesia, decades of evidence indicates that they have a strong modulatory role on metabolism and glycemia. However, whether these effects are directly driven by MOPR actions on pancreatic islets remains poorly understood. Here we sought to comprehensively profile MOPRs on islets to assess how their activity shapes cellular physiology and secretion. First, we used RNA-seq, fluorescent in situ hybridization, and immunoblotting approaches to map islet expression. We observed robust expression of MOPR across multiple cell types in islets. Next, using a FRET-based approach, we show that MOPRs recruit canonical inhibitory pathways, reducing cAMP accumulation. Correspondingly, islets from constitutive MOPR knockout mice showed increased calcium influx and oscillations. However, MOPR knockout had no effect on insulin secretion, instead increase glucagon secretion. Surprisingly, while MOPR antagonism increased overall calcium, it reduced calcium oscillations and suppressed insulin secretion. By contrast MOPR agonism suppressed calcium, increased oscillations, and had no effect on overall hormone secretion. Collectively, these results suggest that MOPR can profoundly shape islet activity, with these effects likely driven by their actions on distinct cell types.

pharmacology and toxicology↗

bioRxiv2025

Dorsal Raphe Nucleus Enkephalin Peptide Modulates Behavioral Preference

The endogenous opioid system is a powerful modulator of motivation and affect. The dorsal raphe nucleus (DRN) in the midbrain has been established as an important site of opioid action and is an integral hub in behavioral modulation. To investigate the functional significance of DRN opioid signaling in aversive and appetitive behaviors we disrupted preproenkephalin (Penk) in DRN using CRISPR-Cas9 technology in Penk-Cre mice. We found that CRISPR mediated knockdown of enkephalin peptide in the DRN (DRNPenk) enhanced inflammation-induced mechanical sensitivity and odor avoidance. Additionally, loss of DRNPenk diminished sucrose preference and engagement with a novel social stimulus. To further characterize the opioid system within the DRN, we performed Hiplex in situ hybridization of 12 genes in the same tissue. This revealed that DRNPenk is largely separate from DRN serotonin cells and is instead distributed on glutamatergic and GABAergic cells. However, subtype-specific knockdown of DRNPenk from glutamatergic and GABAergic cells did not replicate the behavioral effects of general DRNPenk knockdown. This suggests that these neurons represent a novel population that mediate motivated behaviors distinctly from canonical DRN mechanisms.

neuroscience↗

bioRxiv2024

The role of mu-opioid receptors in pancreatic islet alpha cells

30% of people in the United States have diabetes or pre-diabetes. Many of these individuals will develop diabetic neuropathy as a comorbidity, which is often treated with exogenous opioids like morphine, oxycodone, or tramadol. Although these opioids are effective analgesics, growing evidence indicates that they may directly impact the endocrine pancreas function in human and preclinical models. One common feature of these exogenous opioid ligands is their preference for the mu opioid receptor (MOPR), so we aimed to determine if endogenous MOPRs directly regulate pancreatic islet metabolism and hormone secretion. We show that pharmacological antagonism of MOPRs enhances glucagon secretion, but not insulin secretion, from human islets under high glucose conditions. This increased secretion is accompanied by increased cAMP signaling. mRNA expression of MOPRs is enriched in human islet -cells, but downregulated in T2D islet donors, suggesting a link between metabolism and MOPR expression. Conditional genetic knockout of MOPRs in murine -cells increases glucagon secretion in high glucose conditions without increasing glucagon content. Consistent with downregulation of MOPRs during metabolic disease, conditional MOPR knockout mice treated with a high fat diet show impaired glucose tolerance, increased glucagon secretion, increased insulin content, and increased islet size. Finally, we show that MOPR-mediated changes in glucagon secretion are driven, in part, by KATP channel activity. Together, these results demonstrate a direct mechanism of action for endogenous opioid regulation of endocrine pancreas.

physiology↗

bioRxiv2023

Integrative Multiscale Biochemical Mapping of the Brain via Deep-Learning-Enhanced High-Throughput Mass Spectrometry

Elucidating the spatial-biochemical organization of the brain across different scales produces invaluable insight into the molecular intricacy of the brain. While mass spectrometry imaging (MSI) provides spatial localization of compounds, comprehensive chemical profiling at a brain-wide scale in three dimensions by MSI with single-cell resolution has not been achieved. We demonstrate complementary brain-wide and single-cell biochemical mapping via MEISTER, an integrative experimental and computational mass spectrometry framework. MEISTER integrates a deep-learning-based reconstruction that accelerates high-mass-resolving MS by 15-fold, multimodal registration creating 3D molecular distributions, and a data integration method fitting cell-specific mass spectra to 3D data sets. We imaged detailed lipid profiles in tissues with data sets containing millions of pixels, and in large single-cell populations acquired from the rat brain. We identified region-specific lipid contents, and cell-specific localizations of lipids depending on both cell subpopulations and anatomical origins of the cells. Our workflow establishes a blueprint for future developments of multiscale technologies for biochemical characterization of the brain.

biochemistry↗

bioRxiv2022

Medial accumbens shell spiny projection neurons encode relative reward preference

Medial nucleus accumbens shell (mNAcSh) is a critical brain region for driving motivated behaviors. Despite this well-established role, the underlying reward processing of individual neurons, circuits and cell-types within mNAcSh remains largely unknown. Here, we leverage deep brain 2-photon calcium imaging through endoscopic lenses to record mNAcSh spiny projection neuron (SPN) ensemble responses to rewards of different concentrations and to reward-predictive cues across cue-reward learning. Reward responses were found to be heterogeneous and particularly differentiated based on reward concentration and cell type. A large subpopulation of reward-excited enkephalinergic SPNs were found to be specifically recruited during consumption of high concentration, unpreferred reward. A major enkephalinergic efferent projection from mNAcSh to ventral pallidum (VP) was also found to be recruited to high concentration but unpreferred reward and to causally drive low positive reward preference. Enkephalin and dynorphinergic SPNs in mNAcSh distinctly represent rewards of different preference and propagate distinct signals through efferent projections to drive consummatory behavior.

neuroscience↗

bioRxiv2022

Opto-MASS: a high-throughput engineering platform for genetically encoded fluorescentsensors enabling all optical in vivo detection of monoamines and neuropeptides

Fluorescent sensor proteins are instrumental for detecting biological signals in vivo with high temporal accuracy and cell-type specificity. However, engineering sensors with physiological ligand sensitivity and selectivity is difficult because they need to be optimized through individual mutagenesis in vitro to assess their performance. The vast mutational landscape proteins constitute an obstacle that slows down sensor development. This is particularly true for sensors that require mammalian host systems to be screened. Here, we developed a novel high-throughput engineering platform that functionally tests thousands of variants simultaneously in mammalian cells and thus allows the screening of large variant numbers. We showcase the capabilities of our platform, called Optogenetic Microwell Array Screening System (Opto-MASS), by engineering novel monoamine and neuropeptide in vivo capable sensors with distinct physiological roles at high-throughput.

bioengineering↗

bioRxiv2021

An endogenous opioid circuit determines state-dependent appetitive behavior

Mu-opioid peptide receptor (MOPR) stimulation alters respiration, analgesia, and reward behavior, and can induce addiction and drug overdose. Despite its evident importance, the endogenous mechanisms for MOPR regulation of appetitive behavior have remained unknown. Here we report that endogenous MOPR regulation of appetitive behavior in mice acts through a specific dorsal raphe to nucleus accumbens projection. MOPR-mediated inhibition of raphe terminals is necessary and sufficient to determine appetitive behavioral state while select enkephalin-containing NAc ensembles are engaged prior to reward consumption, suggesting that local enkephalin release is the source of endogenous MOPR ligand. Selective modulation of NAc enkephalin neurons and CRISPR-Cas9-mediated disruption of enkephalin substantiate this finding. These results isolate a fundamental endogenous opioid circuit for state-dependent appetitive behavior and suggest alternative mechanisms for opiate modulation of reward.

neuroscience↗