Biology subjects

Martino, M. R.

Publications and source records attributed to Martino, M. R..

6 recordsLinked to original sources

bioRxiv2024

Corticostriatal ensemble dynamics across heroin self-administration to reinstatement

Corticostriatal projection neurons from prelimbic medial prefrontal cortex to the nucleus accumbens core critically regulate drug-seeking behaviors, yet the underlying encoding dynamics whereby these neurons contribute to drug seeking remain elusive. Here we use two-photon calcium imaging to visualize the activity of corticostriatal neurons in mice from the onset of heroin use to relapse. We find that the activity of these neurons is highly heterogeneous during heroin self-administration and seeking, with at least 8 distinct neuronal ensembles that display both excitatory and inhibitory encoding dynamics. These neuronal ensembles are particularly apparent during relapse, where excitatory responses are amplified compared to heroin self-administration. Moreover, we find that optogenetic inhibition of corticostriatal projection neurons attenuates heroin seeking regardless of the relapse trigger. Our results reveal the precise corticostriatal activity dynamics underlying drug-seeking behaviors and support a key role for this circuit in mediating relapse to drug seeking.

neuroscience↗

bioRxiv2024

A Model of Ethanol Self-Administration in Head-Fixed Mice

BackgroundSignificant advances in neurotechnology, such as the application of two-photon (2P) imaging of biosensors in vivo, have enabled unparalleled longitudinal and high-resolution access to neural circuits that coordinate behavior in rodents. Integration of these techniques would be groundbreaking for the study of alcohol use disorder (AUD). AUD is rooted in significant neural adaptations that could be functionally monitored and manipulated at the single-cell level across development of dependence in rodents. However, 2P imaging and related methodologies often require or are facilitated by head-fixation, and a lack of head-fixed models have hindered their integration for the study of alcohol dependence. MethodsWe developed a head-fixed model in which animals learned to self-administer ethanol across [~]14 days. Active lever responding resulted in a tone cue and ethanol reward, whereas responding on the inactive lever resulted in neither cue nor ethanol reward. Following acquisition, animals extinguished lever pressing across a minimum of 10 days. And finally, animals were tested separately for both cue- and ethanol-induced reinstatement of lever pressing. ResultsHere we show, for the first time, that in our head-fixed ethanol self-administration model male and female mice reliably pressed an active, but not inactive, lever for an oral ethanol reward. Ethanol rewards positively correlated with blood ethanol concentrations, at pharmacologically relevant levels. Furthermore, mice extinguished ethanol self-administration when the ethanol reward and cue were omitted, suggesting active lever pressing was ethanol directed. Following extinction, presentation of the ethanol-associated cue or priming with ethanol itself invigorated reinstatement of ethanol seeking, modeling relapse in a manner that replicates decades of work in freely-moving rodent studies. ConclusionsOverall, our head-fixed ethanol self-administration model will allow for incorporation of novel technologies that require or are greatly facilitated by head-fixation, improving our ability to study and understand the neural adaptations and computations that underlie alcohol dependence.

animal behavior and cognition↗

bioRxiv2023

Disruption of Hepatic Mitochondrial Pyruvate and Amino Acid Metabolism Impairs Gluconeogenesis and Endurance Exercise Capacity in Mice

Exercise robustly increases the glucose demands of skeletal muscle. This demand is met not only by muscle glycogenolysis, but also by accelerated liver glucose production from hepatic glycogenolysis and gluconeogenesis to fuel mechanical work and prevent hypoglycemia during exercise. Hepatic gluconeogenesis during exercise is dependent on highly coordinated responses within and between muscle and liver. Specifically, exercise increases the rate at which gluconeogenic precursors such as pyruvate/lactate or amino acids are delivered from muscle to the liver, extracted by the liver, and channeled into glucose. Herein, we examined the effects of interrupting gluconeogenic efficiency and capacity on exercise performance by deleting hepatic mitochondrial pyruvate carrier 2 (MPC2) and/or alanine transaminase 2 (ALT2) in mice. We found that deletion of MPC2 or ALT2 alone did not significantly affect time to exhaustion or post-exercise glucose concentrations in treadmill exercise tests, but mice lacking both MPC2 and ALT2 in liver (DKO) reached exhaustion faster and exhibited lower circulating glucose during and after exercise. Use of {superscript 2}H/{superscript 1}3C metabolic flux analyses demonstrated that DKO mice exhibited lower endogenous glucose production owing to decreased glycogenolysis and gluconeogenesis at rest and during exercise. The decreased gluconeogenesis was accompanied by lower anaplerotic, cataplerotic, and TCA cycle fluxes. Collectively, these findings demonstrate that the transition of the liver to the gluconeogenic mode is critical for preventing hypoglycemia and sustaining performance during exercise. The results also illustrate the need for interorgan crosstalk during exercise as described by the Cahill and Cori cycles.

physiology↗

bioRxiv2022

Blocking mitochondrial alanine and pyruvate metabolism in hepatocytes worsens acetaminophen-induced liver injury in mice

Pyruvate is a critical intermediary metabolite in gluconeogenesis, lipogenesis, as well as NADH production. As a result, there is growing interest in targeting the mitochondrial pyruvate carrier (MPC) complex in liver and metabolic diseases. However, recent in vitro data indicate that MPC inhibition diverts glutamine/glutamate away from glutathione synthesis and toward glutaminolysis to compensate for loss of pyruvate oxidation, possibly sensitizing cells to oxidative insult. Here, we explored this using the clinically relevant acetaminophen (APAP) overdose model of acute liver injury, which is driven by oxidative stress. We report that MPC inhibition does indeed sensitize the liver to APAP-induced injury in vivo, but only with concomitant loss of alanine aminotransferase 2 (ALT2). Pharmacologic and genetic manipulation of neither MPC2 nor ALT2 alone affected APAP toxicity, but liver-specific double knockout (DKO) of these proteins significantly worsened the liver damage. Further investigation confirmed that DKO impaired glutathione synthesis and increased urea cycle flux, consistent with increased glutaminolysis. Furthermore, APAP toxicity was exacerbated by inhibition of both the MPC and ALT in vitro. Thus, increased glutaminolysis and susceptibility to oxidative stress requires loss of both the MPC and ALT2 in vivo and exacerbates them in vitro. Finally, induction of ALT2 reduced APAP-induced injury.

pharmacology and toxicology↗

bioRxiv2021

Silencing alanine transaminase 2 in diabetic liver attenuates hyperglycemia by reducing gluconeogenesis from amino acids

Hepatic gluconeogenesis from amino acids contributes significantly to diabetic hyperglycemia, but the molecular mechanisms involved are incompletely understood. Alanine transaminases (ALT1 and ALT2) catalyze the interconversion of alanine and pyruvate, which is required for gluconeogenesis from alanine. We found that ALT2 was overexpressed in liver of diet-induced obese and db/db mice and that the expression of the gene encoding ALT2 (GPT2) was downregulated following bariatric surgery in people with obesity. The increased hepatic expression of Gpt2 in db/db liver was mediated by activating transcription factor 4; an endoplasmic reticulum stress-activated transcription factor. Hepatocyte-specific knockout of Gpt2 attenuated incorporation of 13C-alanine into newly synthesized glucose by hepatocytes. In vivo Gpt2 knockdown or knockout in liver had no effect on glucose concentrations in lean mice, but Gpt2 suppression alleviated hyperglycemia in db/db mice. These data suggest that ALT2 plays a significant role in hepatic gluconeogenesis from amino acids in diabetes.

physiology↗

bioRxiv2020

Antisense oligonucleotides against monoacylglycerol acyltransferase 1 (Mogat1) improve glucose metabolism independently of Mogat1

ObjectiveMonoacylglycerol acyltransferase (MGAT) enzymes catalyze the synthesis of diacylglycerol from monoacylglycerol. Previous work has suggested the importance of MGAT activity in the development of obesity-related hepatic insulin resistance. Indeed, antisense oligonucleotide (ASO)-mediated knockdown of the gene encoding MGAT1, Mogat1, reduced hepatic MGAT activity and improved glucose tolerance and insulin resistance in high fat diet (HFD) fed mice. However, recent work has suggested that some ASOs may have off-target effects on body weight and metabolic parameters via activation of the interferon alpha/beta receptor 1 (IFNAR-1) pathway. MethodsMice with whole-body Mogat1 knockout or a floxed allele for Mogat1 to allow for liver-specific Mogat1-knockout (by either a liver-specific transgenic or adeno-associated virus-driven Cre recombinase) were generated. These mice were placed on a high fat diet and glucose metabolism and insulin sensitivity was assessed after 16 weeks on diet. In some experiments, mice were treated with control or Mogat1 or control ASOs in the presence or absence of IFNAR-1 neutralizing antibody. ResultsGenetic deletion of hepatic Mogat1, either acutely or chronically, did not improve hepatic steatosis, glucose tolerance, or insulin sensitivity in HFD-fed mice. Furthermore, constitutive Mogat1 knockout in all tissues actually exacerbated HFD-induced weight gain, insulin resistance, and glucose intolerance on a HFD. Despite markedly reduced Mogat1 expression, liver MGAT activity was unaffected in all knockout mouse models. Mogat1 overexpression hepatocytes increased liver MGAT activity and TAG content in low-fat fed mice, but did not cause insulin resistance. Interestingly, Mogat1 ASO treatment improved glucose tolerance in both wild-type and Mogat1 null mice, suggesting an off target effect. Inhibition of IFNAR-1 did not block the effect of Mogat1 ASO on glucose homeostasis. ConclusionThese results indicate that genetic loss of Mogat1 does not affect hepatic MGAT activity or metabolic homeostasis on HFD and show that Mogat1 ASOs improve glucose metabolism through effects independent of targeting Mogat1 or activation of IFNAR-1 signaling. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=65 SRC="FIGDIR/small/238535v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@18d43c4org.highwire.dtl.DTLVardef@15c1974org.highwire.dtl.DTLVardef@18b396dorg.highwire.dtl.DTLVardef@16745bf_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIMogat1 liver-specific KO or KD does not improve metabolism in HFD fed mice. C_LIO_LIWhole-body Mogat1-deletion impairs insulin tolerance in HFD fed mice. C_LIO_LIMogat1 ASOs improves whole body metabolism independently of gene knockdown. C_LIO_LIBlockade of the INFR response does not prevent off-target effects of Mogat1 ASOs. C_LI

physiology↗