Biology subjects

Macpherson, T.

Publications and source records attributed to Macpherson, T..

9 recordsLinked to original sources

bioRxiv2026

Visualization of neuronal morphology of the suprachiasmatic nucleus vasopressin neurons by Cre/FLPe-based genetic two-step sparse labelling - GT-SPARCL

Resolving the morphology of individual neurons in densely packed brain regions remains challenging. Sparse labeling is essential for delineating cellular architecture, yet achieving reproducible low-density labeling e.g. < 1% has been a persistent technical hurdle/problem. We present a genetically encoded two-step strategy, GT-SPARCL (Genetic Two-Step Sparse Cre/FLPe Combination Labeling), which leverages two independent stochastic recombination events to deliver stable, tunable low-density labeling in mice. As a proof of concept, we applied this method to visualizing arginine vasopressin (AVP) neurons in the suprachiasmatic nucleus (SCN), the master circadian pacemaker composed of [~]10,000 neurons per side in mice. Using two-photon imaging of whole-mount SCN blocks, we reconstructed individual AVP neurons and uncovered previously under-resolved morphological heterogeneity. Based on axonal trajectories, we distinguished five structural types, including subclasses with commissural projections to the contralateral SCN and others extending projections beyond the nucleus. The majority ([~]70%) exhibited projections both within and outside the ipsilateral SCN, whereas the second most dominant subset ([~]20%) projected exclusively outside the SCN, representing an output-biased type. In contrast, neurons projecting exclusively within the ipsilateral SCN were exceptionally rare, suggesting that "dedicated" local-circuit AVP neurons do not form a major structural subtype. Collectively, our data indicate that AVP neurons are not structurally uniform but instead comprise diverse projection-defined subtypes, implying subtype-depen-dent contributions to intra-SCN communication, bilateral coupling, and circadian output. Beyond the SCN, our GT-SPARCL method may be applicable for achieving low-density labelling of neurons that can be defined by other specific Cre mouse lines.

neuroscience↗

bioRxiv2026

The slow-acting G-protein Gz defines the duration of circadian rest time

Duration of nightly rest is a trait that varies between individuals, influenced by a complex interplay between multiple genetic and environmental factors. The central circadian clock that orchestrates daily rhythm in behavior/sleep resides in the suprachiasmatic nucleus (SCN). Yet, how the SCN encodes the "length" of the circadian rest phase ({rho}) remains an open question. Here we demonstrate that the unique G-protein-subtype Gz contributes to this process by sculpting the waveform of the circadian cAMP-PKA activity rhythm within the SCN. Genetic deletion and subsequent rescue of Gz expression reversibly altered the {rho} duration, shifting it from [~]10 h in Gz+/+ mice to [~]7.5 h in Gz-/-; mice, accompanied by proportional changes in peak cAMP-PKA activity duration and transcriptome remodeling in the SCN. Notably, intra-SCN cAMP activation led to behavioral rest, with Gz specifically shaping this response without affecting 24-h rhythmicity. These findings suggest that the SCN is not merely a rhythm-generator, but actively allocates the {rho}-rest period via Gz signaling.

neuroscience↗

bioRxiv2026

Inside insight: decoding how insight emerges from competing world models

When and how does insight emerge? We conceptualize insight as a sudden realization arising from restructuring a world model: an internal interpretation linking actions to outcomes. Yet these latent dynamics remain difficult to access, even with behavior and verbal report. Here we developed inside insight dynamics (IID), a machine-learning framework that estimates latent world-model dynamics from behavioral data. Using IID, we analyzed mouse behavior in indirect- and direct-rule tasks, each requiring a shift from an initial world model to a rule-consistent representation. IID inferred the "when" of insight-like shifts by estimating the timing of transitions between competing world models, and examined the "how" by comparing alternative learning processes underlying them. This analysis revealed distinct mechanisms of world-model learning: the indirect- and direct-rule tasks were better explained by gated learning and parallel learning, respectively. Thus, IID opens a route to quantifying latent insight dynamics from observable behavior alone.

neuroscience↗

bioRxiv2026

NAD boosting mediated by CD38 inhibition drives reversal of a pathological vicious cycle of intracrine activity and inflammation in eyelid meibomian gland dysfunction

Vicious cycles--reciprocal cause-and-effect loops that progressively intensify dysfunction--are implicated in many diseases. Here, we examined whether "intracrine" steroidogenesis, a tissue-local mode of hormone production, participates in a pathological vicious cycle in eyelid meibomian gland dysfunction (MGD), the most common cause of evaporative dry eye disease with incidence increasing with age. We show that loss of meibomian intracrine androgen production triggers inflammatory remodeling of the eyelid tarsal plate. Conversely, inflammation suppresses nicotinamide adenine dinucleotide (NAD)-dependent 3{beta}-hydroxysteroid dehydrogenase activity in the meibomian gland, thereby further weakening intracrine steroidogenesis. Mechanistically, we identified inflammation-associated accumulation of the NAD-degrading enzyme CD38 as a key down-regulator for the NAD-dependent intracrine activity. Accordingly, pharmacological inhibition of CD38 (using 78c) in aged mice, restores meibomian cellular NAD levels, rescues intracrine activity, suppresses inflammatory signatures, and promotes recovery of gland size. Thus, our data suggest that boosting NAD availability not only ameliorates meibomian gland dysfunction but also induces a reciprocal "virtuous" cycle, in which suppression of inflammation and restoration of intracrine activity mutually reinforce each other. These findings constitute a previously unknown example in which the reversal of a pathological vicious cycle into a beneficial virtuous cycle underlies the therapeutic effects of NAD boosting and may help combat age-associated meibomian gland disorder.

pathology↗

bioRxiv2026

Translational regulation of GAD1 identified by circadian and light-responsive ribosome-bound transcriptome analysis in the mouse hypothalamic suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) serves as the master circadian pacemaker, integrating regulation of clock genes in the SCN has been extensively studied, whether gene expression in the SCN is regulated at the level of mRNA translation has remained largely unexplored. Here, we report the first ribosome-profiling (Ribo-seq) dataset generated from the mouse SCN, enabling a genome-wide assessment of translational regulation in this central circadian clock. Combined time-series Ribo-seq and RNA-seq analyses identified 385 genes that exhibit rhythmic ribosome binding without corresponding oscillations in mRNA abundance, revealing widespread translational regulation in the SCN. Among these, light stimulation induced an approximately twofold increase in ribosome binding of Gad1, which encodes the major GABA-synthetic enzyme Gad67, despite only marginal changes in Gad1 mRNA levels. Importantly, immunohistochemical analyses demonstrated light-dependent accumulation of Gad67 protein selectively in light-activated SCN neurons, establishing that translational regulation of Gad1 gives rise to overt protein-level changes. In contrast, canonical clock genes were regulated predominantly at the transcriptional level and showed little evidence of translational modulation. Our data allow a systematic comparison between transcriptionally and translationally regulated genes, including their relative rhythm-amplitudes and phases, and thereby revealed translational control as a distinct modulatory layer shaping time-of-day-dependent and light-dependent gene expression in the SCN.

neuroscience↗

bioRxiv2025

Flexible value coding in the mesolimbic dopamine system depending on internal water and sodium balance

Homeostatic imbalances elicit strong cravings, such as thirst and salt appetite, to restore equilibrium. Although midbrain dopaminergic neurons are known to encode the value of foods, their nutritional state-dependency remains unknown. Here, we show that the activity of the dopaminergic mesolimbic pathway flexibly expresses the positive and negative values of water and salt depending on the internal state in mice. Mice showed behavioral preference and aversion to water and salt depending on their internal water and sodium balance. Fiber photometry recordings revealed that dopamine neurons in the ventral tegmental area and dopamine release in the nucleus accumbens flexibly showed bidirectional excitatory and inhibitory responses to water and salt intake in a state-dependent manner. Furthermore, these dopaminergic and behavioral responses could be simulated by a homeostatic reinforcement learning model. Our results demonstrate the nutritional state-dependency of value coding in mesolimbic dopamine systems, providing new insights into neural circuits underlying homeostatic regulation of appetitive and avoidance behaviors.

neuroscience↗

bioRxiv2024

Sex-dependant differences in the ability of nicotine to modulate discrimination learning and cognitive flexibility in mice.

1Nicotine, an addictive compound found in tobacco, functions as an agonist of nicotinic acetylcholine receptors (nAChRs) in the brain. Interestingly, nicotine has been reported to act as a cognitive enhancer in both human subjects and experimental animals. However, its effects in animal studies have not always been consistent, and sex differences have been identified in the effects of nicotine on several behaviors. Specifically, the role that sex plays in modulating the effects of nicotine on discrimination learning and cognitive flexibility in rodents is still unclear. Here, we evaluated sex-dependent differences in the effect of daily nicotine administration at various doses (0.125, 0.25, and 0.5 mg/kg) on visual discrimination (VD) learning and reversal (VDR) learning in mice. In male mice, nicotine significantly improved performance in VDR, but not VD, task, while, in female mice, nicotine significantly worsened performance in the VD, but not VDR, task. Next, to investigate the cellular mechanisms that underlie the sex differences in the effects of nicotine on cognition, transcriptomic analyses were performed on prefrontal cortex tissue samples from male and female mice that had undergone VD and VDR tasks. Pathway enrichment analysis and Protein-protein interaction (P-PI) analysis using gene sets with altered gene expression found three types of effects of nicotine: those common to both sexes, those in males only, and those in females only. Decreased expression of postsynaptic-related genes in males and increased expression of innate immunity-related genes in females were identified as possible molecular mechanisms related to sex differences in the effects of nicotine on cognition in discrimination learning and cognitive flexibility.

animal behavior and cognition↗

bioRxiv2023

Dual roles for nucleus accumbens core dopamine D1-expressing neurons projecting to the substantia nigra pars reticulata in limbic and motor control

The nucleus accumbens (NAc) is a critical component of a limbic basal ganglia circuit that is thought to play an important role in decision-making and the processing of rewarding stimuli. As part of this circuit, dopamine D1 receptor-expressing medium spiny neurons (D1-MSNs) of the NAc core are known to send a major projection to the substantia nigra pars reticulata (SNr). However, the functional role of this SNr-projecting NAc D1-MSNs (NAcD1-MSN-SNr) pathway is still largely uncharacterized. Moreover, as the SNr is thought to belong to both limbic and motor information processing basal ganglia loops, it is possible that the NAcD1-MSN-SNr pathway may be able to influence both limbic and motor functions. In this study we investigated the effect of optogenetic activation of the NAcD1-MSN-SNr pathway on reward-learning and locomotor behavior. Stimulation of the axon terminals of NAc core D1-MSNs in the SNr induced a preference for a laser-paired location, self-stimulation via a laser-paired lever, and augmented instrumental responding for a liquid reward-paired lever. Additionally, stimulation was observed to increase locomotor behavior when delivered bilaterally and induced contralateral turning behavior when delivered unilaterally. These findings indicate that the NAcD1-MSN-SNr pathway is able to control both reward learning and motor behaviors.

neuroscience↗

bioRxiv2021

Distinct Roles of Dopamine D1 and D2 Receptor-expressing Neurons in the Nucleus Accumbens for a Strategy Dependent Decision Making

To optimize decision making, animals need to execute not only a strategy to choose a good option but sometimes also one to avoid a bad option. A psychological study indicates that positive and negative information is processed in a different manner in the brain. The nucleus accumbens (NAc) contains two different types of neurons, dopamine D1 and D2 receptor-expressing neurons which are implicated in reward-based decision making and aversive learning. However, little is known about the neural mechanisms by which D1 or D2 receptor-expressing neurons in the NAc contribute to the execution of the strategy to choose a good option or one to avoid a bad option under decision making. Here, we have developed two novel visual discrimination tasks for mice to assess the strategy to choose a good option and one to avoid a bad option. By chemogenetically suppressing the subpopulation of the NAc neurons, we have shown that dopamine D2 receptor-expressing neurons in the NAc selectively contribute to the strategy to avoid a bad option under reward-based decision making. Furthermore, our optogenetic and calcium imaging experiments indicate that dopamine D2 receptor-expressing neurons are activated by error choices and the activation following an error plays an important role in optimizing the strategy in the next trial. Our findings suggest that the activation of D2 receptor-expressing neurons by error choices through learning enables animals to execute the appropriate strategy.

neuroscience↗