Urethane Anesthesia Research Articles

Cardiovascular Function and Autonomic Regulation in Urethane Anesthetized and Conscious Mice.

Urethane is widely used for its ability to induce prolonged anesthesia. Variability in previously reported cardiovascular parameters in murine models makes it challenging to definitively evaluate the cardiovascular effects of urethane anesthesia. We aimed to address these challenges, thereby advancing our understanding of urethane's effects on cardiovascular function in mice. In this study, we investigated how urethane anesthesia, with and without supplemental oxygen, impacts heart rate, arterial oxygen saturation (SpO2), blood pressure, and heart rate variability in mice. First, we conducted a literature review and found that data in mice was both limited and lacking in reproduction. Next, we conducted a series of physiological measurements to address gaps in the literature and subjected C57BL/6J mice to three conditions: 1) conscious, 2) urethane-anesthetized, and 3) urethane-anesthetized with supplemental oxygen. Blood pressure, heart rate, SpO2, and heart rate variability (via time, frequency, and M-curve analyses) were assessed. We observed an increase in heart rate with urethane anesthesia (p=0.012) compared to the conscious state. Urethane caused a decrease in heart rate variability which was independent of oxygen supplementation. Urethane anesthesia significantly reduced arterial blood pressure (p<0.001) with oxygen-supplemented mice remained hypotensive. Urethane decreased SpO2 (p=0.001), which was restored by oxygen supplementation (p<0.001). We did not observe sex effects of urethane anesthesia on blood pressure, heart rate, heart rate variability, or SpO2. Taken together, these results underscore the importance of a cautious approach when using urethane in mice, as urethane significantly impacts arterial blood pressure, heart rate, oxygen saturation, and heart rate variability.

Bladder Responses to Thoracolumbar Epidural Stimulation in Female Urethane-Anesthetized Rats with Graded Contusion Spinal Cord Injuries.

Spinal cord epidural stimulation (scES) is a therapeutic option that promotes functional improvements in sensory, motor, and autonomic functions following spinal cord injury (SCI). Previous scES mapping studies targeting the lower urinary tract (LUT) in rats demonstrated functional response variability based upon lumbosacral level, parameters used, extent of injury (spinally intact vs. chronic anatomically complete spinal transections), and sex. In the current study, female rats with clinically relevant graded incomplete T9 contusion injuries were mapped with scES at 60 days post-injury at three spinal levels (T13, L3, L6) with a novel miniature 15-electrode array designed to deliver optimal specificity. The results obtained during bladder fill and void cycles conducted under urethane anesthesia indicate frequency dependent sub-motor threshold effects on LUT function with a single row of electrodes positioned across the full medio-lateral extent of the dorsal cord. The findings of improved storage and emptying, represented by significantly longer inter-contractile intervals with T13 scES and L3 scES and by a significantly increased estimated void efficiency with L6 scES, respectively, are consistent with previous studies using intact and chronic complete transected male and female rats. The data support the efficacy of selective spinal network stimulation to drive functionally relevant networks for storage versus emptying phases of the urinary cycle. The current findings further demonstrate the translational promise of scES for SCI individuals with LUT dysfunctions, regardless of injury severity.

Serotonin (5-HT)2A/2C receptor agonist 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride improves detrusor sphincter dyssynergia by inhibiting L-type voltage-gated calcium channels in spinal cord injured rats.

To explore the role of voltage-gated calcium channels (VGCC) in 5-HT2A/2C receptor agonist 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride's improvement of spinal cord injury (SCI) induced detrusor sphincter dyssynergia and the expressions of the 5-hydroxy tryptamine (5-HT) 2A receptors and VGCCs in lumbosacral cord after SCI. Female Sprague-Dawley rats were randomized into normal control group and SCI group (N = 15 each). Cystometrogram (CMG), simultaneous CMG, and external urethral sphincter electromyography (EUS-EMG) were conducted in all groups under urethane anesthesia. Drugs were administered intrathecally during CMG and EUS-EMG. Rats were euthanized and L6-S1 spinal cord were acquired for immunofluorescence. In SCI rats, intrathecal administration of 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride or L-type VGCC blocker, nifedipine, could significantly increase voiding volume, voiding efficiency, and the number of high-frequency oscillations. They could also prolong EUS bursting activity duration on EUS-EMG. Moreover, the effect of 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride can be eliminated with the combined administration of L-type VGCC agonist, (±)-Bay K 8644. No significant differences were observed in CMG after intrathecal administration of T-type VGCC blocker TTA-P2. Additionally, immunofluorescence of the lumbosacral cord in control and SCI rats showed that the 5-HT2A receptor and Cav1.2 immunolabeling-positive neurons in the anterior horn of the lumbosacral cord were increased in SCI rats. Our study demonstrated that 5-HT2A/2C agonist 2,5-dimethoxy-4-iodophenyl-2-aminopropane hydrochloride may improve SCI-induced DSD by inhibiting the L-type voltage-gated calcium channel in lumbosacral cord motoneurons.

Sex differences in cholinergic signaling affect functional outcomes for theta-gamma coordination in hippocampal subcircuits following experimental febrile status epilepticus.

Sex determines cognitive outcome in animal models of early life seizure, where males exhibit impaired hippocampal-dependent learning and memory compared with females. The physiological underpinnings of this sex effect are unclear. Cholinergic signaling is essential for the generation of hippocampal oscillations, and supplementation of cholinergic precursors prior to status epilepticus in immature male rats prevents subsequent memory deficits. We hypothesized that there are sex differences in acetylcholine circuits and their response to experimental febrile status epilepticus (eFSE). eFSE was induced in male and female rat pups. We transversed the hippocampus of postnatal day >60 control (CTL) and eFSE rats with a 64-channel laminar silicon probe to assay cholinergic-dependent theta oscillations under urethane anesthesia. Local field potential properties were compared during (1) baseline sensory stimulation, (2) pharmacological stimulation via acetylcholine reuptake blockade, and (3) sensory stimulation after muscarinic acetylcholine receptor block (atropine). In all groups, a baseline tail pinch could elicit theta oscillations via corticohippocampal synaptic input. Following atropine, a tail pinch response could no longer be elicited in CTL male, CTL female, or eFSE female rats. In contrast, induced slow theta power in eFSE males after atropine was not decreased to spontaneous levels. Analysis of oscillation bandwidths revealed sex differences in acetylcholine modulation of theta frequency and slow gamma frequency and power. This study also identified significant effects of both sex and eFSE on baseline theta-gamma comodulation, indicating a loss of coupling in eFSE males and a potential gain of function in eFSE females. There are differences in cholinergic modulation of theta and gamma signal coordination between male and female rats. These differences may underlie worse cognitive outcomes in males following eFSE. Promoting the efficacy of muscarinic acetylcholine signaling prior to or following early life seizures could elucidate a mechanism for the temporal discoordination of neural signals within and between hippocampus and neocortex and provide a novel therapeutic approach for improving cognitive outcomes.

Vagus nerve stimulation in bursts can efficiently modulate gastric contractions and contraction frequency at varying gastric pressures.

There has been recent clinical interest in the use of vagus nerve stimulation (VNS) for treating gastrointestinal disorders as an alternative to drugs or gastric electrical stimulation. However, effectiveness of burst stimulation has not been demonstrated. We investigated the ability of bursting and continuous VNS to influence gastric and pyloric activity under a range of stimulation parameters and gastric pressures. The goals of this study were to determine which parameters could optimally excite or inhibit gastric activity. Data were collected from 21 Sprague-Dawley rats. Under urethane anesthesia, a rubber balloon was implanted into the stomach, connected to a pressure transducer and a saline infusion pump. A pressure catheter was inserted at the pyloric sphincter and a bipolar nerve cuff was implanted onto the left cervical vagus nerve. The balloon was filled to 15 cmH2O. Stimulation trials were conducted in a consistent order; the protocol was then repeated at 25 and 35 cmH2O. The nerve was then transected and stimulation repeated to investigate directionality of effects. Bursting stimulation at the bradycardia threshold caused significant increases in gastric contraction amplitude with entrainment to the bursting frequency. Some continuous stimulation trials could also cause increased contractions but without frequency changes. Few significant changes were observed at the pylorus, except for frequency entrainment. These effects could not be uniquely attributed to afferent or efferent activity. Our findings further elucidate the effects of different VNS parameters on the stomach and pylorus and provide a basis for future studies of bursting stimulation for gastric neuromodulation.

The Effects of Volatile Anesthetics on Renal Sympathetic and Phrenic Nerve Activity during Acute Intermittent Hypoxia in Rats.

Coordinated activation of sympathetic and respiratory nervous systems is crucial in responses to noxious stimuli such as intermittent hypoxia. Acute intermittent hypoxia (AIH) is a valuable model for studying obstructive sleep apnea (OSA) pathophysiology, and stimulation of breathing during AIH is known to elicit long-term changes in respiratory and sympathetic functions. The aim of this study was to record the renal sympathetic nerve activity (RSNA) and phrenic nerve activity (PNA) during the AIH protocol in rats exposed to monoanesthesia with sevoflurane or isoflurane. Adult male Sprague-Dawley rats (n = 24; weight: 280-360 g) were selected and randomly divided into three groups: two experimental groups (sevoflurane group, n = 6; isoflurane group, n = 6) and a control group (urethane group, n = 12). The AIH protocol was identical in all studied groups and consisted in delivering five 3 min-long hypoxic episodes (fraction of inspired oxygen, FiO2 = 0.09), separated by 3 min recovery intervals at FiO2 = 0.5. Volatile anesthetics, isoflurane and sevoflurane, blunted the RSNA response to AIH in comparison to urethane anesthesia. Additionally, the PNA response to acute intermittent hypoxia was preserved, indicating that the respiratory system might be more robust than the sympathetic system response during exposure to acute intermittent hypoxia.

Developmentally Unique Cerebellar Processing Prioritizes Self- over Other-Generated Movements.

Animals must distinguish the sensory consequences of self-generated movements (reafference) from those of other-generated movements (exafference). Only self-generated movements entail the production of motor copies (i.e., corollary discharges), which are compared with reafference in the cerebellum to compute predictive or internal models of movement. Internal models emerge gradually over the first three postnatal weeks in rats through a process that is not yet fully understood. Previously, we demonstrated in postnatal day (P) 8 and P12 rats that precerebellar nuclei convey corollary discharge and reafference to the cerebellum during active (REM) sleep when pups produce limb twitches. Here, recording from a deep cerebellar nucleus (interpositus, IP) in P12 rats of both sexes, we compared reafferent and exafferent responses with twitches and limb stimulations, respectively. As expected, most IP units showed robust responses to twitches. However, in contrast with other sensory structures throughout the brain, relatively few IP units showed exafferent responses. Upon finding that exafferent responses occurred in pups under urethane anesthesia, we hypothesized that urethane inhibits cerebellar cortical cells, thereby disinhibiting exafferent responses in IP. In support of this hypothesis, ablating cortical tissue dorsal to IP mimicked the effects of urethane on exafference. Finally, the results suggest that twitch-related corollary discharge and reafference are conveyed simultaneously and in parallel to cerebellar cortex and IP. Based on these results, we propose that twitches provide opportunities for the nascent cerebellum to integrate somatotopically organized corollary discharge and reafference, thereby enabling the development of closed-loop circuits and, subsequently, internal models.

Acute ampakines increase voiding function and coordination in a rat model of SCI.

Neurogenic bladder dysfunction causes urological complications and reduces the quality of life in persons with spinal cord injury (SCI). Glutamatergic signaling via AMPA receptors is fundamentally important to the neural circuits controlling bladder voiding. Ampakines are positive allosteric modulators of AMPA receptors that can enhance the function of glutamatergic neural circuits after SCI. We hypothesized that ampakines can acutely stimulate bladder voiding that has been impaired due to thoracic contusion SCI. Adult female Sprague-Dawley rats received a unilateral contusion of the T9 spinal cord (n = 10). Bladder function (cystometry) and coordination with the external urethral sphincter (EUS) were assessed 5 d post-SCI under urethane anesthesia. Data were compared to responses in spinal-intact rats (n = 8). The 'low-impact' ampakine CX1739 (5, 10, or 15 mg/kg) or vehicle (2-hydroxypropyl-beta-cyclodextrin [HPCD]) was administered intravenously. The HPCD vehicle had no discernible impact on voiding. In contrast, following CX1739, the pressure threshold for inducing bladder contraction, voided volume, and the interval between bladder contractions were significantly reduced. These responses occurred in a dose-dependent manner. We conclude that modulating AMPA receptor function using ampakines can rapidly improve bladder-voiding capability at subacute time points following contusion SCI. These results may provide a new and translatable method for therapeutic targeting of bladder dysfunction acutely after SCI.

Acute ampakines increase voiding function and coordination in a rat model of SCI

Neurogenic bladder dysfunction causes urological complications and reduces the quality of life in persons with spinal cord injury (SCI). Glutamatergic signaling via AMPA receptors is fundamentally important to the neural circuits controlling bladder voiding. Ampakines are positive allosteric modulators of AMPA receptors that can enhance the function of glutamatergic neural circuits after SCI. We hypothesized that ampakines can acutely stimulate bladder voiding that has been impaired due to thoracic contusion SCI. Adult female Sprague–Dawley rats received a unilateral contusion of the T9 spinal cord (n = 10). Bladder function (cystometry) and coordination with the external urethral sphincter (EUS) were assessed 5 d post-SCI under urethane anesthesia. Data were compared to responses in spinal-intact rats (n = 8). The ‘low-impact’ ampakine CX1739 (5, 10, or 15 mg/kg) or vehicle (2-hydroxypropyl-beta-cyclodextrin [HPCD]) was administered intravenously. The HPCD vehicle had no discernible impact on voiding. In contrast, following CX1739, the pressure threshold for inducing bladder contraction, voided volume, and the interval between bladder contractions were significantly reduced. These responses occurred in a dose-dependent manner. We conclude that modulating AMPA receptor function using ampakines can rapidly improve bladder-voiding capability at subacute time points following contusion SCI. These results may provide a new and translatable method for therapeutic targeting of bladder dysfunction acutely after SCI.

Effect of hydrogen inhalation on cardiovascular and interstitial components of pulmonary hypertension in rats

Hydrogen is known to have selective antioxidant properties. It binds highly reactive hydroxyl radicals. The pathogenesis of the monocrotaline animal model of pulmonary hypertension is associated with oxidative stress and leads to all the symptoms of pulmonary hypertension (PH) and interstitial lung disease (ILD) associated with hypertension.The aim of this work was to study the effect of 4% hydrogen inhalations on the symptoms of PH and ILD in rats.Methods. To model monocrotaline-induced pulmonary hypertension (MCT-PH), two groups of animals received a single subcutaneous injection of monocrotaline (MCT) on day 1. The control group was injected subcutaneously with MCT solvent only. The animals receiving MCT were further divided into 2 subgroups. Subgroup 1 rats breathed room air and subgroup 2 rats breathed a mixture of room air and 4% hydrogen. The regular inhalations continued until day 21. On day 21, hemodynamic parameters were measured under urethane anesthesia, the heart and its components and the lungs were weighed, and lung tissue was preserved for morphological study.Results. The inhalation had no effect on the main cardiovascular symptoms of PH, but a positive effect on the state of the connective tissue of the lungs affected by PH was shown. The mast cell response was reduced both quantitatively and functionally. There was a decrease in tryptase expression by mast cells, with predominance of the forms without signs of degranulation. TGF-β secretion was also significantly reduced and visualized by immunopositive cells in alveolar cellular structures and vessel walls.Conclusion. Inhalation of 4% hydrogen reduces inflammation and fibrosis of lung tissue during the development of MCT-PH.

Cholinergic-Sensitive Theta Oscillations in Memory Encoding in Mice.

Cholinergic regulation of hippocampal theta oscillations has long been proposed to be a potential mechanism underlying hippocampus-dependent memory encoding processes. However, cholinergic transmission has been traditionally associated with type II theta under urethane anesthesia. The mechanisms and behavioral significance of cholinergic regulation of type I theta in freely exploring animals is much less clear. In this study, we examined the potential behavioral significance of cholinergic regulation of theta oscillations in the object location task in male mice that involves training and testing trials and provides an ideal behavioral task to study the underlying memory encoding and retrieval processes, respectively. Cholinergic regulation of hippocampal theta oscillations and the behavioral outcomes was examined by either intrahippocampal infusion of cholinergic receptor antagonists or knocking out cholinergic receptors in excitatory neurons or interneurons. We found that both muscarinic acetylcholine receptors (mAChRs) and α7 nicotinic AChRs (α7 nAChRs) regulated memory encoding by engaging excitatory neurons and interneurons, respectively. There is a transient upregulated theta oscillation at the beginning of individual object exploration events that only occurred in the training trials, but not in the testing trials. This transient upregulated theta is also the only theta component that significantly differed between training and testing trials and was sensitive to mAChR and α7 nAChR antagonists. Thus, our study has revealed a transient cholinergic-sensitive theta component that is specifically associated with memory encoding, but not memory retrieval, in the object location task, providing direct experimental evidence supporting a role for cholinergic-regulated theta oscillations in hippocampus-dependent memory encoding processes.

Impact of Activity-Based Training on Bowel Function in a Rat Model of Spinal Cord Injury.

Significant bowel-related issues after spinal cord injury (SCI) that affect morbidity and quality of life (QOL) include diminished bowel motility, loss of sphincter control, gastric ulcers, autonomic dysreflexia, pain, diarrhea, constipation, and fecal incontinence. Clinical diagnoses and research in humans have largely relied on anorectal manometry (ARM) procedures to increase understanding of the functional effects of SCI on colorectal motility and defecation physiology. Recent pre-clinical rodent studies have also used ARM to further our understanding of bowel-related dysfunctions post-SCI. In the present study, the benefits of different activity-based training (ABT) durations on bowel function were examined. Six groups of male rats including two non-training (NT; uninjured and SCI) and four ABT (quadrupedal [Quad or Q] stepping on a treadmill) groups. All ABT animals received 4 weeks of 1-h daily stepping beginning 2 weeks post-SCI followed by variable amounts for 4 additional weeks (none; daily; once a week; daily for final 4th week only). Outcome measures included fecal output (home cage; metabolic cage) throughout the study and terminal measurements (post 8-week ABT) of external anal sphincter (EAS) electromyography, resting anorectal pressure, and giant contraction (GC) activation under urethane anesthesia. The results indicate that treadmill training normalized defecation amount based on feces weight and food intake, as well as GC frequency, EAS latency and amplitude during fecal expulsion, and resting pressure in specific areas within the colorectum. The two intermittent training groups consistently showed recorded metrics comparable to the non-injured group. The results demonstrate bowel dysfunction in the rodent SCI contusion model with improvements in functional outcomes following ABT. Importantly, the benefits to bowel-related functions with versus without intermittent ABT illustrate the need for periodic therapy to maintain the functional gains of ABT.

Time-dependent progress of lower urinary tract dysfunction in streptozotocin-induced diabetic rats with or without low-dose insulin treatment.

Objectives: To examine time-dependent functional and structural changes of the lower urinary tract in streptozotocin-induced diabetic rats with or without low-dose insulin treatment and explore the pathophysiological characteristics of insulin therapy on lower urinary tract dysfunction (LUTD) caused by diabetes mellitus (DM). Methods: Female Sprague-Dawley rats were divided into five groups: normal control (NC) group, 4 weeks insulin-treated DM (4-DI) group, 4 weeks DM (4-DM) group, 8 weeks insulin-treated DM (8-DI) group and 8 weeks DM (8-DM) group. DM was initially induced by i.p. injection of streptozotocin (65 mg/kg), and then the DI groups received subcutaneous implantation of insulin pellets under the mid dorsal skin. Voiding behavior was evaluated in metabolic cages. The function of bladder and urethra in vivo were evaluated by simultaneous recordings of the cystometrogram and urethral perfusion pressure (UPP) under urethane anesthesia. The function of bladder and urethra in vitro were tested by organ bath techniques. The morphologic changes of the bladder and urethra were investigated using Hematoxylin-Eosin and Masson's staining. Results: Both 4-and 8-weeks diabetic rats have altered micturition patterns, including increased 12-h urine volume, urinary frequency/12 hours and voided volume. In-vivo urodynamics showed the EUS bursting activity duration is longer in 4-DM group and shorter in 8-DM group compared to NC group. UPP change in 8-DM were significantly lower than NC group. While none of these changes were found between DI and NC groups. Organ bath showed the response to Carbachol and EFS in bladder smooth muscle per tissue weights was decreased significantly in 4- and 8-weeks DM groups compared with insulin-treated DM or NC groups. In contrast, the contraction of urethral muscle and maximum urethral muscle contraction per gram of the tissue to EFS stimulation were significantly increased in 4- and 8-weeks DM groups. The thickness of bladder smooth muscle was time-dependently increased, but the thickness of the urethral muscle had no difference. Conclusions: DM-induced LUTD is characterized by time-dependent functional and structural remodeling in the bladder and urethra, which shows the hypertrophy of the bladder smooth muscle, reduced urethral smooth muscle relaxation and EUS dysfunction. Low-dose insulin can protect against diuresis-induced bladder over-distention, preserve urethral relaxation and protect EUS bursting activity, which would be helpful to study the slow-onset, time-dependent progress of DM-induced LUTD.

Dynamics of functional impairments during focal transient ischemia in three-dimensional cortical space

Ischemic injury in the cerebral cortex results in decreased electrical activity across all frequency bands and the emergence of abnormal electrophysiological patterns, including spreading depolarization (SD) and negative ultraslow potential (NUP) [1, 2]. Despite this, the specific dynamics of these changes in electrical activity within the three-dimensional cortical space during ischemia remain incompletely described and poorly understood. To simultaneously investigate changes in electrical activity across the layers of the cerebral cortex and in the horizontal cortical space, we used two linear 16-channel silicone probes (Neuronexus, USA) in combination with a flexible transparent 60-channel matrix of subdural electrodes (MIPT, Russia) and intrinsic optical signal imaging (IOS, 665 nm, transillumination mode) during focal ischemia induced by intracortical injection of the potent vasoconstrictor endothelin-1 (ET-1, 1 μL, 1 μM). These experiments were carried out in head-restrained rats under urethane anesthesia (1.5 g/kg). Formation of the ischemic lesion following ET-1 administration was correlated with clusters of SDs that demonstrated considerable variability in their propagation patterns within both vertical and horizontal planes. The initial SDs originated from the injection site of ET-1 and diffused across all cortical layers. Subsequently, the initiation point of the ensuing SDs gradually shifted towards the deeper layers while the electrical activity showed inadequate recovery between SDs within the injection site. SDs originating in the surrounding cortex did not invade the area near the injection point. Instead, they tended to spread around, often compartmentalizing in the superficial layers of the cortex. Some SDs were observed deep in the cortex, while others were detected on the surface via superficial electrodes and IOS, without leaving typical intracortical electrode traces. Electrographic activity was significantly depressed, especially in the superficial layers around the injection site, three hours after ET-1 administration. However, it returned to pre-ET-1 levels at the remote site, with a spatial gradient observed in subdural electrodes. Functional impairments corresponded to the histological lesion observed in coronal brain sections. Recently discovered NUPs were initiated by SD and were most prominent in the electrodes closest to the ET-1 injection site. These NUPs reached their maximal amplitude at one hour and subsided three hours after ET-1 injection. Our research indicates intricate dynamics in the creation of an ischemic focal point. The data gathered suggest that the emergence of cerebral harm during focal ischemia is associated with the growth of a focus extending both horizontally and vertically across cortical dimensions. This growth is fueled by the generation of SDs within the ischemic penumbra.

Prelimbic and infralimbic responsivity to amygdala input is modified by gonadal hormones in parallel to low anxiety-like behavior in ovariectomized rats

Gonadal hormones may influence sexual activity by reducing anxiety. The basolateral amygdala (BLA) and prelimbic (PL) and infralimbic (IL) cortical regions comprise a loop that is related to fear, anxiety, and social behavior. In female ovariectomized rats, actions of estradiol, progesterone, and sequential estradiol and progesterone administration were explored in the open field test (OFT) and plus maze test (PMT) to evaluate signs of anxiety-like behavior. The three hormonal treatments reduced indicators of anxiety in the PMT but did not influence behavior in the OFT. In the same behaviorally tested rats under urethane anesthesia, single-unit extracellular recordings were obtained from the PL and IL during electrical stimulation of the BLA. The analysis of 250 ms peristimulus histograms showed that BLA stimulation produced two kinds of response. A small group of neurons increased their firing rate after BLA stimulation. Most neurons exhibited a reduction of spiking. Neurons that increased their firing rate after BLA stimulation did not show any difference with the hormonal treatments. In neurons that were inhibited by BLA stimulation, estradiol reduced the neuronal firing rate in the PL and IL, and progesterone alone and the sequential administration of estradiol followed by progesterone administration 24 h later (priming) increased the firing rate during the 240 ms before BLA stimulation. Analyses of responsivity of the PL and IL during electrical stimulation of the BLA indicated that estradiol, progesterone, and estradiol followed by progesterone administration 24 h later (priming) reduced inhibitory actions of the BLA on the PL but not IL. In the BLA-IL connection, progesterone exacerbated the inhibitory response. These findings indicate that anxiolytic actions of estradiol, progesterone, and estradiol followed by progesterone administration 24 h later (priming) correspond to lower BLA-PL responsivity. Actions of progesterone on BLA-IL responsivity appear to contribute to sexual activity by interacting with other forebrain structures that are also related to sexual receptivity.

Mitragynine inhibits hippocampus neuroplasticity and its molecular mechanism

BackgroundMitragynine (MIT), the primary indole alkaloid of kratom (Mitragyna speciosa), has been associated with addictive and cognitive decline potentials. In acute studies, MIT decreases spatial memory and inhibits hippocampal synaptic transmission in long-term potentiation (LTP). This study investigated the impacts of 14-day MIT treatment on hippocampus synaptic transmission and its possible underlying mechanisms.MethodsUnder urethane anesthesia, field excitatory post-synaptic potentials (fEPSP) of the hippocampal CA1 region were recorded in the Sprague Dawley (SD) rats that received MIT (1, 5, and 10 mg/kg), morphine (MOR) 5 mg/kg, or vehicle (ip). The effects of the treatments on basal synaptic transmission, paired-pulse facilitation (PPF), and LTP were assessed in the CA1 region. Analysis of the brain's protein expression linked to neuroplasticity was then performed using a western blot.ResultsThe baseline synaptic transmission's amplitude was drastically decreased by MIT at 5 and 10 mg/kg doses, although the PPF ratio before TBS remained unchanged, the PPF ratio after TBS was significantly reduced by MIT (10 mg/kg). Strong and persistent inhibition of LTP was generated in the CA1 region by MIT (5 and 10 mg/kg) doses; this effect was not seen in MIT (1 mg/kg) treated rats. In contrast to MIT (1 mg/kg), MIT (5 and 10 mg/kg) significantly raised the extracellular glutamate levels. After exposure to MIT, GluR-1 receptor expression remained unaltered. However, NMDAε2 receptor expression was markedly downregulated. The expression of pCaMKII, pERK, pCREB, BDNF, synaptophysin, PSD-95, Delta fosB, and CDK-5 was significantly downregulated in response to MIT (5 and 10 mg/kg) exposure, while MOR (5 mg/kg) significantly raised synaptophysin and Delta fosB expression.ConclusionFindings from this work reveal that a smaller dose of MIT (1 mg/kg) poses no risk to hippocampal synaptic transmission. Alteration in neuroplasticity-associated proteins may be a molecular mechanism for MIT (5 and 10 mg/kg)-induced LTP disruption and cognitive impairments. Data from this work posit that MIT acted differently from MOR on neuroplasticity and its underlying mechanisms.Graphical abstract

Decreased bladder contraction interval induced by periaqueductal grey stimulation is reversed by subthalamic stimulation in a Parkinson’s disease model rat

The medial prefrontal cortex (mPFC) regulates bladder contractions via the periaqueductal grey (PAG). Subthalamic nucleus deep brain stimulation (STN-DBS) modulates urinary afferent information from PAG in Parkinson’s disease (PD). We do not know how STN-DBS modulates the activities of mPFC induced by PAG stimulation. We aim to clarify how STN-DBS modulates the neuronal activity of mPFC induced by PAG stimulation and its effects on bladder contraction Experiments were conducted under urethane anesthesia in normal (n = 9) and 6-hydroxydopamine hemi-lesioned PD rats (n = 7). Left-sided PAG stimulation and STN-DBS were applied with simultaneous bladder contraction monitoring. Local field potential (LFP) recording and collection of extracellular fluid in the mPFC were performed before stimulation, during PAG stimulation, during PAG+STN stimulation, and after stimulation. The bladder inter-contraction intervals significantly decreased with PAG stimulation with a concomitant decrease in mPFC LFP power in PD rats. Adding STN stimulation to PAG stimulation significantly increased the bladder inter-contraction intervals with a concomitant increase in mPFC LFP power in PD rats. Several mPFC catecholamine levels were modulated by PAG or PAG+STN stimulation in PD rats. The present study revealed that STN-DBS modulate the activities of mPFC induced by PAG, thereby leading to normalization of bladder contraction.

Effects of isoflurane and urethane anesthetics on glutamate neurotransmission in rat brain using in vivo amperometry

BackgroundAspects of glutamate neurotransmission implicated in normal and pathological conditions are predominantly evaluated using in vivo recording paradigms in rats anesthetized with isoflurane or urethane. Urethane and isoflurane anesthesia influence glutamate neurotransmission through different mechanisms; however, real-time outcome measures of potassium chloride (KCl)-evoked glutamate overflow and glutamate clearance kinetics have not been compared within and between regions of the brain. In order to maintain rigor and reproducibility within the literature between the two most common methods of anesthetized in vivo recording of glutamate, we compared glutamate signaling as a function of anesthesia and brain region in the rat strain most used in neuroscience.MethodsIn the following experiments, in vivo amperometric recordings of KCl-evoked glutamate overflow and glutamate clearance kinetics (uptake rate and T80) in the cortex, hippocampus, and thalamus were performed using glutamate-selective microelectrode arrays (MEAs) in young adult male, Sprague-Dawley rats anesthetized with either isoflurane or urethane.ResultsPotassium chloride (KCl)-evoked glutamate overflow was similar under urethane and isoflurane anesthesia in all brain regions studied. Analysis of glutamate clearance determined that the uptake rate was significantly faster (53.2%, p < 0.05) within the thalamus under urethane compared to isoflurane, but no differences were measured in the cortex or hippocampus. Under urethane, glutamate clearance parameters were region-dependent, with significantly faster glutamate clearance in the thalamus compared to the cortex but not the hippocampus (p < 0.05). No region-dependent differences were measured for glutamate overflow using isoflurane.ConclusionsThese data support that amperometric recordings of KCl-evoked glutamate under isoflurane and urethane anesthesia result in similar and comparable data. However, certain parameters of glutamate clearance can vary based on choice of anesthesia and brain region. In these circumstances, special considerations are needed when comparing previous literature and planning future experiments.

Impaired nitric oxide mechanisms underlying lower urinary tract dysfunction in aging rats.

The study aimed to investigate the bladder and urethral activity and nitric oxide (NO)-related molecular changes in aging rats. Rats were divided into two groups: Group Y (young rats; 12 wk) and Group A (aging rats; 15 mo). A 24-h voiding assay was performed, and the urodynamic parameters were evaluated using awake cystometry (CMG) and urethral perfusion pressure (UPP) recordings under urethane anesthesia. The mRNA expression levels of NO-, ischemia-, and inflammation-related markers in urethra and bladder tissues and cGMP levels in the urethra were assessed. Body weight was significantly higher in Group A than in Group Y. Voiding assay results (24 h) were insignificant. In the CMG, the number of non-voiding contractions per voiding cycle and post-void residual volume were significantly higher in Group A than in Group Y; voiding efficiency was significantly lower in Group A than in Group Y. In the UPP recordings, the urethral pressure reduction and high-frequency oscillation (HFO) amplitude were significantly lower in Group A than in Group Y. The mRNA expression levels of Hif-1α, Vegf-a, and Tgf-β1 in the bladder were significantly higher in Group A than in Group Y. The mRNA expression levels of Nos1 and Prkg1 and the cGMP concentrations in the urethra were significantly lower in Group A than in Group Y. Aging rats can be useful models for studying the natural progression of age-related lower urinary tract dysfunctions, for which impaired NO-mediated transmitter function is likely to be an important mechanism.NEW & NOTEWORTHY Aging rats can be useful models for studying the natural progression of age-related lower urinary tract dysfunctions, for which impaired nitric oxide-mediated transmitter function is likely to be an important mechanism.

Effects of low-intensity extracorporeal shock wave therapy on lipopolysaccharide cystitis in a rat model of interstitial cystitis/bladder pain syndrome.

To investigate the effect of low-intensity extracorporeal shock wave therapy (LiESWT) on lipopolysaccharide (LPS)-induced cystitis in an animal model of interstitial cystitis/bladder pain syndrome (IC/BPS). Sprague-Dawley rats were divided into three groups: control, cystitis (LPS group, intravesical injection of LPS (1mg) twice), and cystitis with LiESWT (LiESWT group). On the third and fourth days, LiESWT was administered (0.12mJ/mm2, 300 shots each time) on the lower abdomen toward the bladder. On the seventh day, the rats underwent pain assessment and a metabolic cage study. Subsequently, a continuous cystometrogram (CMG) was performed under urethane anaesthesia. Immunohistochemical studies were also performed, including S-100 staining, an immunohistochemical marker of Schwann cells in the bladder. In the LPS group, the pain threshold in the lower abdomen was significantly lower than that in the control group. In the metabolic cage study, the mean voided volume in the LPS group significantly increased. The CMG also revealed a significant decrease in bladder contraction amplitude, compatible with detrusor underactivity in the LPS group. Immunohistochemical studies showed inflammatory changes in the submucosa, increased fibrosis, and decreased S-100 stain-positive areas in the muscle layer of the LPS group. In the LiESWT group, tactile allodynia and bladder function were ameliorated, and S-100 stain-positive areas were increased. By restoring nerve damage, LiESWT improved lower abdominal pain sensitivity and bladder function in an LPS-induced cystitis rat model. This study suggests that LiESWT may be a new therapeutic modality for IC/BPS.