Cutaneomuscular reflexes (CMRs) can be recorded in the hand muscle of human subjects after stimulation of a digital nerve. We hypothesized that repeated synchronous stimulation of nerves from two digits may lead to long-term plastic changes in CMR, by the mechanisms of spike-timing–dependent plasticity (STDP). To test this idea, we conducted experiments in 27 healthy human volunteers. After baseline measurement of CMR, one of four 30-min-long stimulation conditions were tested; the CMR was then remeasured. The four conditions were simultaneous index finger and thumb stimulation; asynchronous index finger and thumb stimulation; thumb 5 ms before index finger stimulation; and thumb-only stimulation. Neither the early (E1) nor late excitatory (E2) components of the CMR showed consistent changes after any stimulation condition. The inhibitory (I1) component was slightly reduced in all cases. To understand why paired stimulation did not produce long-term changes, we conducted a further experiment. In this, we m...

Maintenance of normal structure of the enteric nervous system (ENS), which regulates key gastrointestinal functions, requires robust homeostatic mechanisms, since by virtue of its location within the gut wall, the ENS is subject to constant mechanical, chemical, and biological stressors. Using transgenic and thymidine analog-based experiments, we previously discovered that neuronal turnover—where continual neurogenesis offsets ongoing neuronal loss at steady state—represents one such mechanism. Although other studies confirmed that neuronal death continues into adulthood in the myenteric plexus of the ENS, the complicated nature of thymidine analog presents challenges in substantiating the occurrence of adult neurogenesis. Therefore, it is vital to employ alternative, well-recognized techniques to substantiate the existence of adult enteric neurogenesis in the healthy gut. Here, by using established methods of assessing nuclear DNA content and detecting known mitotic marker phosphor-histone H3 (pH3) in Hu+...

In models of visual spatial attention control, it is commonly held that top–down control signals originate in the dorsal attention network, propagating to the visual cortex to modulate baseline neural activity and bias sensory processing. However, the precise distribution of these top–down influences across different levels of the visual hierarchy is debated. In addition, it is unclear whether these baseline neural activity changes translate into improved performance. We analyzed attention-related baseline activity during the anticipatory period of a voluntary spatial attention task, using two independent functional magnetic resonance imaging datasets and two analytic approaches. First, as in prior studies, univariate analysis showed that covert attention significantly enhanced baseline neural activity in higher-order visual areas contralateral to the attended visual hemifield, while effects in lower-order visual areas (e.g., V1) were weaker and more variable. Second, in contrast, multivariate pattern anal...

Singular strategies for promoting axon regeneration and motor recovery after spinal cord injury (SCI) have been attempted with limited success. For instance, the deletion of RhoA and phosphatase and tensin homolog ( Pten ) (an extrinsic and intrinsic modulating factor, respectively) in corticospinal neurons (CSNs) promotes axon sprouting after thoracic SCI; however, it is unable to restore motor function. Here, we examine the effects of combining RhoA/Pten deletion in CSNs with chemogenetic neuronal stimulation on axonal growth and motor recovery after SCI in mice. We find that this combinatorial approach promotes greater axonal growth and presynaptic bouton formation in CSNs within the spinal cord compared with RhoA ; Pten deletion alone. Furthermore, chemogenetic neuronal stimulation of RhoA ; Pten -deleted CSNs improves forelimb performance in behavioral tasks after SCI compared with RhoA ; Pten deletion alone. These results demonstrate that combination therapies pairing genetic modifications with neuro...

Recent findings have shifted the view of cholecystokinin (CCK) from being a cellular neuronal marker to being recognized as a crucial neuropeptide pivotal in synaptic plasticity and memory processes. Despite its now appreciated importance in various brain regions and abundance in the basal ganglia, its role in the striatum, which is vital for motor control, remains unclear. This study sought to fill this gap by performing a comprehensive investigation of the role of CCK in modulating striatal medium spiny neuron (MSN) membrane properties, as well as the secondary somatosensory cortex S2 to MSN synaptic transmission and plasticity in rodents. Using in vivo optopatch-clamp recording in mice on identified MSNs, we showed that the application of CCK receptor Type 2 (CCK2R) antagonists decreases corticostriatal transmission in both direct and indirect pathway MSNs. Moving to an ex vivo rat preparation to maximize experimental access, we showed that CCK2R inhibition impacts MSN membrane properties by reducing sp...

Self-administration of addictive substances like heroin can couple the rewarding/euphoric effects of the drug with drug-associated cues, and opioid cue reactivity contributes to relapse vulnerability in abstinent individuals recovering from an opioid use disorder (OUD). Opioids are reported to alter the intrinsic excitability of medium spiny neurons (MSNs) in the nucleus accumbens (NAc), a key brain reward region linked to drug seeking, but how opioids alter NAc MSN neuronal excitability and the impact of altered MSN excitability on relapse-like opioid seeking remain unclear. Here, we discovered that self-administered, but not experimenter-administered, heroin reduced NAc protein levels of the voltage-gated sodium channel auxiliary subunit, SCN1b, in male and female rats. Viral-mediated reduction of NAc SCN1b increased the intrinsic excitability of MSNs, but without altering glutamatergic and GABAergic synaptic transmission. While reducing NAc SCN1b levels had no effect on acquisition of heroin self-admini...

While ketamine, an NMDA receptor antagonist, is effective in treating major depression, studies have not addressed the safety of repeated ketamine infusions in depressed patients with comorbid alcohol use disorder (AUD). In this study, we aimed to determine whether a history of chronic social isolation and alcohol exposure alter the reinforcing properties of ketamine in male and female rats. Rats were pair-housed or socially isolated for 12 weeks and underwent intermittent access to 20% alcohol. Subsequently, rats underwent intravenous ketamine self-administration under a fixed ratio 1 schedule, followed by extinction training and one session of cue-induced reinstatement. Dendritic spine morphology was examined in the nucleus accumbens, an important area implicated in reward and motivation. Our results show that females self-administered more ketamine than males, a history of alcohol increased ketamine intake in females, and a history of isolation or alcohol independently increased ketamine intake in males...

Alexander disease (AxD) is a rare neurological disorder caused by dominant gain-of-function mutations in the gene for glial fibrillary acidic protein. Expression of mutant protein results in astrocyte dysfunction that ultimately leads to developmental delay, failure to thrive, and intellectual and motor impairment. The disease is typically fatal, and at present there are no preventative or effective treatments. To gain a better understanding of the link between astrocyte dysfunction and behavioral deficits in AxD, we have recently developed a rat model that recapitulates many of the clinical features of the disease, including failure to thrive, motor impairment, and white matter deficits. In the present study, we show that both male and female AxD model rats exhibit a neurodegenerative profile with a progressive neuroinflammatory response combined with reduced expression of synaptic and mitochondrial proteins. Consistent with these results, AxD rats show reduced hippocampal long-term potentiation and are c...

Binocular disparity is used for perception and action in three dimensions. Neurons in the primary visual cortex respond to binocular disparity in random dot patterns, even when the contrast is inverted between eyes (false depth cue). In contrast, neurons in the ventral stream largely cease to respond to false depth cues. This study evaluated whether GABAergic inhibition is involved in suppressing false depth cues in the human ventral visual cortex. We compared GABAergic inhibition (GABA+) and glutamatergic excitation (Glx) during the viewing of correlated and anticorrelated binocular disparity in 18 participants using single-voxel proton magnetic resonance spectroscopy. Measurements were taken from the early visual cortex (EVC) and the lateral occipital cortex (LO). Three visual conditions were presented per voxel location: correlated binocular disparity, anticorrelated binocular disparity, or a blank gray screen with a fixation cross. To identify differences in neurochemistry, GABA+ or Glx levels were com...

The external globus pallidus (GPe) is a central part of the basal ganglia indirect pathway implicated in movement and decision-making. As a hub connecting the dorsal striatum and subthalamic nucleus (STN), the GPe guides repetitive and routine behaviors. However, it remains unknown how diverse GPe cells engage in routine formation while learning action sequences in repetitive reward-seeking conditioning. Here, in male mice, we investigated the Ca2+ dynamics of two GPe cell types, astrocytes and parvalbumin-expressing neurons, during routine formation. Our findings show that the dynamics of GPe astrocytes may be involved in action sequence refinement, a characteristic potentially contributing to more efficient reward-seeking behavior.