Naive Rats Research Articles

Inbred rat heredity and sex affect oral oxycodone self-administration and augmented intake in long sessions: correlations with anxiety and novelty-seeking.

Oxycodone abuse frequently begins with prescription oral oxycodone, yet vulnerability factors (e.g. sex, genetics) determining abuse are largely undefined. We evaluated genetic vulnerability in a rat model of oral oxycodone self-administration (SA): increasing oxycodone concentration/session (0.025-0.1mg/ml; 1-, 4-, and 16-h) followed by extinction and reinstatement. Active licks and oxycodone intake were greater in females than males during 4-h and 16-h sessions (p < 0.001). Both sexes increased intake between 4-h and 16-h sessions (p < 2e-16), but a subset of strains augmented intake at 16-h (p = 0.0005). Heritability (h2) of active licks during 4-h sessions at increasing oxycodone dose ranged from 0.30 to 0.53. Under a progressive ratio (PR) schedule, breakpoints were strain-dependent (p < 2e-16). Cued reinstatement was greater in females (p < 0.001). Naive rats were assessed using elevated plus maze (EPM), open field (OF), and novel object interaction (NOI) tests. We correlated these behaviors with 28 parameters of oxycodone SA. Anxiety-defining EPM traits were most associated with SA in both sexes, whereas OF and NOI traits were more associated with SA in males. Sex and heredity are major determinants of motivation to take and seek oxycodone; intake augments dramatically during extended access in specific strains; and anxiety correlates with multiple SA parameters across strains.

Selective RNAi silencing of Schwann cell Piezo1 alleviates mechanical hypersensitization following peripheral nerve injury.

Selective RNAi silencing of Schwann cell Piezo1 alleviates mechanical hypersensitization following peripheral nerve injury.

Anwulignan Alleviates Bone Cancer Pain by Modulating the PPARα/CXCR2 Signaling Pathway in the Rat Spinal Cord.

Advanced cancer patients frequently endure severe pain from bone metastases, and few effective treatments for bone cancer pain (BCP) exist. Although Anwulignan is known for its antioxidant, anti-inflammatory, and antitumor properties, its effects on BCP remain unclear. This study aims to explore the analgesic effects and mechanisms of Anwulignan on bone cancer pain. Western blotting and immunofluorescence assessed molecular expression and localization. X-ray, micro-CT, TRAP, and ALP staining examined bone destruction in rats. MTT, colony formation assays, and invivo imaging analyzed tumor changes. RNA-Seq identified differentially expressed genes, validated by ChIP analysis. Here, we showed that Anwulignan alleviated mechanical, thermal, and cold hypersensitivity and spontaneous pain, prevented bone destruction, and suppressed local tumor growth in rats with BCP. Furthermore, Anwulignan was firmly bound to proliferator-activated receptor alpha (PPARα), increasing its thermal stability. Intrathecal (i.t.) injection of PPARα siRNA increased pain sensitivity in naive rats, and PPARα siRNA abrogated the analgesic effect of Anwulignan in BCP model rats. Moreover, the PPARα agonist pirinixic acid reduced BCP hypersensitivity and abrogated the upregulation of CXC chemokine receptor 2 (CXCR2). Importantly, PPARα bound to the CXCR2 promoter region, and Anwulignan could reverse the reduced binding of PPARα to CXCR2 caused by BCP. Taken together, these results indicate that Anwulignan is a potential antitumor and analgesic agent that exerts its effects via upregulation of PPARα expression to inhibit the expression of CXCR2 and could be used for treating BCP.

The mirror preference test: A reverse translational approach to study anomalous subjective experience in rats.

The mirror preference test: A reverse translational approach to study anomalous subjective experience in rats.

Enigmatic intractable Epilepsy patients have antibodies that bind glutamate receptor peptides, kill neurons, damage the brain, and cause Generalized Tonic Clonic Seizures.

Epilepsy affects 1-2% of the world population, is enigmatic in 30% of cases, and is often intractable, unresponsive to antiepileptic drugs, and accompanied by cognitive, psychiatric and behavioral problems. Tests for Autoimmune Epilepsy are not performed routinely, and limited to passive diagnosis of known autoimmune antibodies, without essential functional tests to reveal active pathogenic antibodies. We investigated two young Epilepsy patients with different Epilepsy characteristics, repeated intractable seizures, and enigmatic etiology. We suspected Autoimmune Epilepsy. We found that both patients have elevated IgG antibodies, and three types of glutamate receptor antibodies, to: AMPA-GluR3B, NMDA-NR1 and NMDA-NR2 peptides. In contrast, they lack autoantibodies to: LGI1, CASPR2, GABA-RB1, Amphiphysin, CV2, PNMA1, Ri, Yo, Hu, Recoverin, Soxi and Titin. IgG antibodies of both patients bound and killed human neural cells In vitro. Moreover, In vivo video EEG studies in naive rats revealed that patient's IgG antibodies, infused continually into rat brain, bound neural cells in the hippocampus and cortex, caused neural loss in these brain regions, and induced recurrent Generalized Tonic Clonic Seizures. We assume they can do so also in the patient's brain. This is the first model of human Autoimmune Epilepsy in rats. It can serve for discovery of patient's pathogenic antibodies, and drug development. Tests for autoimmune antibodies that bind glutamate receptor peptides, and functional diagnostic tests, are obligatory in all enigmatic intractable Epilepsy patients. Current diagnosis of Autoimmune Epilepsy is insufficient! If pathogenic antibodies are found, intractable patients must receive available, suitable and potentially life-changing immunotherapies for Autoimmune Epilepsy.

On the significance of peak dose in normal tissue toxicity in spatially fractionated radiotherapy: The case of proton minibeam radiation therapy.

Spatially fractionated radiotherapy is an unconventional radiotherapy approach able to widen the therapeutic window for difficult-to-treat cases today. To unlock its full potential, accurate knowledge of the relationship between the different dosimetry and geometry parameters and the biological response is still needed. When the same beam width is used, the valley dose has been assumed to be the main parameter influencing normal tissue sparing, with peak doses having little relevance. However, a recent retrospective evaluation of preclinical data suggests peak dose plays a major role in the normal tissue sparing of minibeam radiation therapy (MBRT). The goal of this study was to experimentally validate for the first time the significance of the peak dose for normal tissue sparing in proton MBRT. We irradiated the brains of naive rats with two different configurations of pMBRT, resulting in the same valley and average doses but different peak doses. Behavioural tests and histopathological evaluations were carried out. At the same valley dose, a higher peak dose (high peak-to-valley dose ratio (PVDR), larger centre-to-centre (ctc) distance) is more detrimental than a lower peak dose (low PVDR, narrower catch). In the first case, the animals exhibited some hyperactivity in locomotor and exploration activity as well as memory alterations. In addition, the highest peak dose led to a significantly higher cumulative lesion score in the histopathology evaluations than the lowest peak dose. While our study does not exclude the relevant role of the valley dose in tissue sparing, it does highlight the importance of peak doses, contradicting previous assumptions. Our results agree with the conclusion of a recent retrospective evaluation of preclinical studies in micro and minibeam radiation therapy.

What do ultrasound vocalizations really mean in rats with different origins of pain?

This study is to assess how 22 kHz and 50 kHz spontaneous ultrasound vocalization (USV) calls would be affected by different origins of pain so as to validate the use of USV in pain studies. Five well-established rat models of pain were used to evaluate various parameters of spontaneous 22 kHz and 50 kHz calls in adult male rats in terms of both acute and chronic or inflammatory and neuropathic or somatic and visceral origins. The effects of local lidocaine blockade of the injection site and intraperitoneal administration of antidepressant (amitriptyline) and anticonvulsant (gabapentin) were examined as well in typical inflammatory and neuropathic pain models, respectively. The major new gains were as follows: (1) naive rats staying alone and engaging dyadic social interaction with a naive or a conspecific in pain emitted similar power and amounts of both 22 kHz and 50 kHz spontaneous USV calls; however, rats suffering from various origins of pain emitted significantly less USV calls of both 22 kHz and 50 kHz in terms of both number and time. (2) Local blockade of the injury sites of inflammatory pain could reverse the impaired emission of both 22 kHz and 50 kHz spontaneous calls, so did the treatment of the rats with neuropathic pain by amitriptyline and gabapentin. Emissions of both 22 kHz and 50 kHz spontaneous calls were impaired by acute and chronic pain conditions regardless of inflammatory and neuropathic or somatic and visceral origins.

Epoetin alfa has a potent anxiolytic effect on naive female rats

BackgroundEpoetin alfa is a derivative of the erythropoietin hormone. This study aims to investigate the epoetin alfa effect on anxiety-like behaviors.MethodsAdult female Wistar Albino rats were divided into Control (n = 8), 1000 U Epoetien alfa, and 2000 U Epoetien alpha. Epoetin alfa was administered intraperitoneally once a week for 4 weeks. The animals were then subjected to open field test, elevated plus maze, light-dark box, and the behaviors were video recorded.ResultsEpoetin alfa significantly reduced anxiety-like behaviors in both low- and high-dose groups in a dose-independent manner. This anxiolytic effect was seen in all three anxiety tests. Further, exploratory behaviors such as unsupported rearing and head-dipping behaviors increased with the application of Epoetin alfa. This protocol did not alter locomotor activity.ConclusionThe present study found beneficial effects of epoetin alfa on behaviors. Further studies on the effect of derivatives of erythropoietin hormone on anxiety-like behaviors are needed.

Inaudible airborne ultrasound affects emotional states in the olfactory bulbectomized rat depression model

Recently, exposure to sounds with ultrasound (US) components has been shown to modulate brain activity. However, the effects of US on emotional states remain poorly understood. We previously demonstrated that the olfactory bulbectomized (OBX) rat depression model is suitable for examining the effects of audible sounds on emotionality. Here, we investigated the impact of US exposure on the emotional state of OBX rats. In naive rats, exposure to 100 kHz US for 1 h did not increase the number of c-Fos-positive cells in auditory-related cortical areas, and US, as a tone cue, did not elicit a conditioned fear response in the auditory fear conditioning test. These results indicate that the frequency of 100 kHz is hard to hear for rats. However, US improved hyperemotionality (HE) scores and decreased plasma corticosterone levels in OBX rats, suggesting ameliorative effects on depression-like symptoms and stress. In contrast to HE scores, US exposure did not influence anxiety-like behaviors in the elevated plus maze. In conclusion, we demonstrated that exposure to airborne US can alleviate depressive-like symptoms in the OBX rat depression model. This is the first study to show that exposure to airborne US alone produces changes in emotional states in an animal model.

Influence of Systemic Arterial Hypertension on Memory and Motor Recovery after Permanent Focal Cerebral Ischemia in Spontaneously Hypertensive Rats

AbstractBackgroundSystemic Arterial Hypertension (SAH), distinguished by a persistent elevation of blood pressure, emerges as a risk factor for stroke and Alzheimer’s Disease (AD). Additionally, recent evidence suggests that stroke may adversely affect memory, potentially playing a role in the development of AD. This study aimed to investigate the influence of permanent focal ischemic stroke on memory, as well as on sensorimotor function (asymmetry of the front paws) and cerebral infarct size in adult male spontaneously hypertensive rats (SHR), compared to normotensive Wistar Kyoto (WKY) rats.MethodWe assessed the stroke effects on short‐ and long‐term memory through the open field task (7 and 21 days after stroke), on sensorimotor functions through the cylinder test and adhesive removal test (over 42 days after stroke), and on infarction volume through 2,3,5‐Triphenyltetrazolium chloride staining (3 and 7 days after stroke).ResultShort‐term memory was observed in both naive WKY and naive SHR rats, while SHR naive animals did not exhibit long‐term memory. Stroke disrupted short‐term memory in both WKY and SHR rats and long‐term memory in WKY rats (Fig. 01). In regards to the sensorimotor function, (cylinder test and adhesive removal) WKY rats totally recovered from the stroke‐induced asymmetry in the front paws, while SHR rats did not (Fig. 02). Concerning infarction volume, WKY rats showed decreased infarction volume from the third to the seventh day after stroke, while SHR rats did not exhibit this reduction (Fig. 03).ConclusionThese results emphasize the impact of hypertension on memory, as well as on motor outcomes and brain infarct size following stroke, potentially contributing to the risk for AD.

H3K27 Trimethylation-Mediated Downregulation of miR-216a-3p in Sensory Neurons Regulates Neuropathic Pain Behaviors via Targeting STIM1.

Although the therapeutic potential of microRNA-mediated gene regulation has been investigated, its precise functional regulatory mechanism in neuropathic pain remains incompletely understood. In this study, we elucidate that miR-216a-3p serves as a critical noncoding RNA involved in the modulation of trigeminal-mediated neuropathic pain. By conducting RNA-seq and qPCR analysis, we observed a notable decrease of miR-216a-3p in the injured trigeminal ganglia (TG) of male rats. Intra-TG administration of miR-216a-3p agomir or lentiviral-mediated overexpression of miR-216a-3p specifically in sensory neurons of injured TGs alleviated established neuropathic pain behaviors, while downregulation of miR-216a-3p (pharmacologically or genetically) in naive rats induced pain behaviors. Moreover, nerve injury significantly elevated the histone H3 lysine-27 (H3K27) trimethylation (H3K27me3) levels in the ipsilateral TG, thereby suppressing the SRY-box TF 10 (SOX10) binding to the miR-216a-3p promoter and resulting in the reduction of miR-216a-3p. Inhibiting the enzymes responsible for catalyzing H3K27me3 restored the nerve injury-induced reduction in miR-216a-3p expression and markedly ameliorated neuropathic pain behaviors. Furthermore, miR-216a-3p targeted stromal interaction molecule 1 (STIM1), and the decreased miR-216a-3p associated with neuropathic pain caused a significant upregulation in the protein abundance of STIM1. Conversely, overexpression of miR-216a-3p in the injured TG suppressed the upregulation of STIM1 expression and reversed the mechanical allodynia. Together, the mechanistic understanding of H3K27me3-dependent SOX10/miR-216a-3p/STIM1 signaling axial in sensory neurons may facilitate the discovery of innovative therapeutic strategies for neuropathic pain management.

Darbepoetin alpha has an anxiolytic and anti-neuroinflammatory effect in male rats

AimsWe aimed to investigate the anxiolytic effect of darbepoetin alpha (DEPO), an erythropoietin derivative, in a neuroinflammation model regarding different behaviors and biological pathways.MethodsForty adult male Wistar albino rats were divided into four groups (control, LPS, DEPO, and DEPO + LPS). The rats were treated with 5 µg /kg DEPO once a week for four weeks, after which neuroinflammation was induced with 2 mg/kg lipopolysaccharide (LPS). The elevated plus maze, open-field, and light‒dark box tests were conducted to assess anxiety levels. Harderian gland secretions were scored via observation. Tumor necrosis factor alpha (TNF-α), Interleukin-1-beta (IL-1β), brain-derived growth factor (BDNF), serotonin, cortisol, total antioxidant/oxidant (TAS/TOS), and total/free thiol levels were measured in the prefrontal cortex, striatum, and serum.ResultsDEPO had a potent anxiolytic effect on both DEPO and DEPO + LPS groups. Compared to the control group, DEPO administration caused an increase in serotonin and BDNF levels and decreased basal cortisol and TNF-α levels in naive rats. IL-1β did not alter after DEPO administration in naive rats. Prophylactic DEPO treatment remarkably downregulated cortisol, IL-1β, and TNF-α in the DEPO + LPS group. In addition, prophylactic DEPO administration significantly attenuated the decrease in serotonin and BDNF levels in the DEPO + LPS group. Furthermore, DEPO ameliorated excessive harderian gland secretion in the DEPO + LPS group. Compared with those in the control group, the free thiol content in the serum increased after DEPO administration. No similar effect was seen in the DEPO + LPS group receiving prophylactic DEPO. TAS showed no difference among all experimental groups. DEPO administration increased TOS and OSI in the serum and prefrontal cortex but not in the striatum. This effect was not seen in the DEPO + LPS group.ConclusionDarbepoetin alpha had an anxiolytic effect on many physiological mechanisms in a neuroinflammation model and naive rats.

Neural dynamics in the orbitofrontal cortex reveal cognitive strategies.

Behavior is sloppy: a multitude of cognitive strategies can produce similar behavioral read-outs. An underutilized approach is to combine multifaceted behavioral analyses with neural recordings to resolve cognitive strategies. Here we show that rats performing a decision-making task exhibit distinct strategies over training, and these cognitive strategies are decipherable from orbitofrontal cortex (OFC) neural dynamics. We trained rats to perform a temporal wagering task with hidden reward states. While naive rats passively adapted to reward statistics, expert rats inferred reward states. Electrophysiological recordings and novel methods for characterizing population dynamics identified latent neural factors that reflected inferred states in expert but not naive rats. In experts, these factors showed abrupt changes following single trials that were informative of state transitions. These dynamics were driven by neurons whose firing rates reflected single trial inferences, and OFC inactivations showed they were causal to behavior. These results reveal the neural signatures of inference.

Evaluation of Blood–Brain Barrier Disruption Using Low- and High-Molecular-Weight Complexes in a Single Brain Sample in a Rat Traumatic Brain Injury Model: Comparison to an Established Magnetic Resonance Imaging Technique

Traumatic brain injury (TBI), a major cause of death and disability among young people, leads to significant public health and economic challenges. Despite its frequency, treatment options remain largely unsuitable. However, examination of the blood–brain barrier (BBB) can assist with understanding the mechanisms and dynamics of brain dysfunction, which affects TBI sufferers secondarily to the injury. Here, we present a rat model of TBI focused on two standard BBB assessment markers, high- and low-molecular-weight complexes, in order to understand BBB disruption. In addition, we tested a new technique to evaluate BBB disruption on a single brain set, comparing the new technique with neuroimaging. A total of 100 Sprague–Dawley rats were separated into the following five groups: naive rats (n = 20 rats), control rats with administration (n = 20 rats), and TBI rats (n = 60 rats). Rats were assessed at different time points after the injury to measure BBB disruption using low- and high-molecular-weight complexes. Neurological severity score was evaluated at baseline and at 24 h following TBI. During the neurological exam after TBI, the rats were scanned with magnetic resonance imaging and euthanized for assessment of the BBB permeability. We found that the two markers displayed different examples of BBB disruption in the same set of brain tissues over the period of a week. Our innovative protocol for assessing BBB permeability using high- and low-molecular-weight complexes markers in a single brain set showed appropriate results. Additionally, we determined the lower limit of sensitivity, therefore demonstrating the accuracy of this method.

Excessive alcohol intake produces persistent mechanical allodynia and dysregulates the endocannabinoid system in the lumbar dorsal root ganglia of genetically-selected Marchigian Sardinian alcohol-preferring rats

Excessive alcohol intake produces persistent mechanical allodynia and dysregulates the endocannabinoid system in the lumbar dorsal root ganglia of genetically-selected Marchigian Sardinian alcohol-preferring rats

Analysis of the State of Glutamate- and Gaba-Ergic Neurons in the Inferior Colliculi of Krushinsky – Molodkina Strain Rats at Early Stages of Epileptogenesis

Disturbances in the neurotransmitter systems during the development of temporal lobe epilepsy have been most detailed studied in forebrain structures – in the temporal cortex, amygdala, and hippocampus [1, 2]. It is known that during the formation of temporal lobe epilepsy in the model of audiogenic kindling there is a spread of epileptiform activity from brainstem to forebrain structures. However, the molecular mechanisms of neurotransmission dysregulation in the inferior colliculi in rodents with genetic prone to audiogenic seizures during epileptogenesis remain unknown. Changes in neurotransmitter systems of inferior colliculi may contribute significantly to the recruitment of forebrain structures during the initial stages of epileptogenesis. The current work provides a comprehensive analysis of activity markers of glutamate- and GABA-ergic neurons in inferior colliculi of Krushinsky – Molodkina (KM) rats genetically prone to audiogenic seizures. A modified audiogenic kindling protocol was used to model the early stages of temporal lobe epilepsy development. In this protocol rats were subjected to daily audiogenic seizures for seven days. Naive KM rats were used as controls. Although the rodent’s predisposition to audiogenic seizures is often associated with disruptions in GABAergic transmission, no significant changes were found in the expression of GABA synthesis enzymes or the α1 subunit of the GABAA receptor in the brains of KM rats, either 24 hours or a week after their last convulsive seizure. However, 24 hours after the last audiogenic seizure, an increase in glutamatergic transmission in the inferior colliculi was observed: the activity of ERK 1/2 kinases and the exocytosis protein synapsin 1 increased, as well as the expression of VGLUT1 and VGLUT2 and the synaptic protein SV2B. One week after the last seizure, only an increase in VGLUT1 content in the inferior colliculi was observed, suggesting that persistent changes occur in the neurons of forebrain structures, in particular, the temporal cortex.

Periaqueductal gray activates antipredatory neural responses in the amygdala of foraging rats.

Pavlovian fear conditioning research suggests that the interaction between the dorsal periaqueductal gray (dPAG) and basolateral amygdala (BLA) acts as a prediction error mechanism in the formation of associative fear memories. However, their roles in responding to naturalistic predatory threats, characterized by less explicit cues and the absence of reiterative trial-and-error learning events, remain unexplored. In this study, we conducted single-unit recordings in rats during an 'approach food-avoid predator' task, focusing on the responsiveness of dPAG and BLA neurons to a rapidly approaching robot predator. Optogenetic stimulation of the dPAG triggered fleeing behaviors and increased BLA activity in naive rats. Notably, BLA neurons activated by dPAG stimulation displayed immediate responses to the robot, demonstrating heightened synchronous activity compared to BLA neurons that did not respond to dPAG stimulation. Additionally, the use of anterograde and retrograde tracer injections into the dPAG and BLA, respectively, coupled with c-Fos activation in response to predatory threats, indicates that the midline thalamus may play an intermediary role in innate antipredatory-defensive functioning.

Periaqueductal gray activates antipredatory neural responses in the amygdala of foraging rats

Pavlovian fear conditioning research suggests that the interaction between the dorsal periaqueductal gray (dPAG) and basolateral amygdala (BLA) acts as a prediction error mechanism in the formation of associative fear memories. However, their roles in responding to naturalistic predatory threats, characterized by less explicit cues and the absence of reiterative trial-and-error learning events, remain unexplored. In this study, we conducted single-unit recordings in rats during an ‘approach food-avoid predator’ task, focusing on the responsiveness of dPAG and BLA neurons to a rapidly approaching robot predator. Optogenetic stimulation of the dPAG triggered fleeing behaviors and increased BLA activity in naive rats. Notably, BLA neurons activated by dPAG stimulation displayed immediate responses to the robot, demonstrating heightened synchronous activity compared to BLA neurons that did not respond to dPAG stimulation. Additionally, the use of anterograde and retrograde tracer injections into the dPAG and BLA, respectively, coupled with c-Fos activation in response to predatory threats, indicates that the midline thalamus may play an intermediary role in innate antipredatory-defensive functioning.

Perineuronal Nets in the Rat Medial Prefrontal Cortex Alter Hippocampal-Prefrontal Oscillations and Reshape Cocaine Self-Administration Memories.

The medial prefrontal cortex (mPFC) is a major contributor to relapse to cocaine in humans and to reinstatement in rodent models of cocaine use disorder. The output from the mPFC is potently modulated by parvalbumin (PV)-containing fast-spiking interneurons, the majority of which are surrounded by perineuronal nets. We previously showed that treatment with chondroitinase ABC (ABC) reduced the consolidation and reconsolidation of a cocaine conditioned place preference memory. However, self-administration memories are more difficult to disrupt. Here we report in male rats that ABC treatment in the mPFC attenuated the consolidation and blocked the reconsolidation of a cocaine self-administration memory. However, reconsolidation was blocked when rats were given a novel, but not familiar, type of retrieval session. Furthermore, ABC treatment prior to, but not after, memory retrieval blocked reconsolidation. This same treatment did not alter a sucrose memory, indicating specificity for cocaine-induced memory. In naive rats, ABC treatment in the mPFC altered levels of PV intensity and cell firing properties. In vivo recordings from the mPFC and dorsal hippocampus (dHIP) during the novel retrieval session revealed that ABC prevented reward-associated increases in high-frequency oscillations and synchrony of these oscillations between the dHIP and mPFC. Together, this is the first study to show that ABC treatment disrupts reconsolidation of the original memory when combined with a novel retrieval session that elicits coupling between the dHIP and mPFC. This coupling after ABC treatment may serve as a fundamental signature for how to disrupt reconsolidation of cocaine memories and reduce relapse.

Withdrawal from chronic alcohol impairs the serotonin-mediated modulation of GABAergic transmission in the infralimbic cortex in male rats

Withdrawal from chronic alcohol impairs the serotonin-mediated modulation of GABAergic transmission in the infralimbic cortex in male rats