Isoflurane increases norepinephrine release in the rat preoptic area and the posterior hypothalamus in vivo and in vitro: Relevance to thermoregulation during anesthesia

Commonly used anesthetics modify alcohol and (-)-trans-delta9-tetrahydrocannabinol in vivo effects on rat cerebral arterioles

BACKGROUND

Ethyl alcohol and cannabis are widely used recreational substances with distinct effects on the brain. These drugs increase accidental injuries requiring treatment under anesthesia. Moreover, alcohol and cannabis are often used in anesthetized rodents for biomedical research. Here, we compared the influence of commonly used forms of anesthesia, injectable ketamine/xylazine (KX) versus inhalant isoflurane, on alcohol- and (-)-trans-delta9-tetrahydrocannabinol (THC) effects on cerebral arteriole diameter evaluated in vivo.

METHODS

Studies were performed on male and female Sprague-Dawley rats subjected to intracarotid catheter placement for drug infusion, and cranial window surgery for monitoring pial arteriole diameter. Depth of anesthesia was monitored every 10-15 min by toe-pinch. Under KX, the number of toe-pinch responders was maximal after the first dose of anesthesia and diminished over time in both males and females. In contrast, the number of toe-pinch responders under isoflurane slowly raised over time, leading to increase in isoflurane percentage until deep anesthesia was re-established. Rectal temperature under KX remained stable in males while dropping in females. As expected for gaseous anesthesia, both males and females exhibited rectal temperature drops under isoflurane.

RESULTS

Infusion of 50 mM alcohol (ethanol, EtOH) into the cerebral circulation rendered robust constriction in males under KX anesthesia, this alcohol action being significantly smaller, but still present under isoflurane anesthesia. In females, EtOH did not cause measurable changes in pial arteriole diameter regardless of the anesthetic. These findings indicate a strong sex bias with regards to EtOH induced vasoconstriction. Infusion of 42 nM THC in males and females under isoflurane tended to constrict cerebral arterioles in both males and females when compared to isovolumic infusion of THC vehicle (dimethyl sulfoxide in saline). Moreover, THC-driven changes in arteriole diameter significantly differed in magnitude depending on the anesthetic used. Simultaneous administration of 50 mM alcohol and 42 nM THC to males constricted cerebral arterioles regardless of the anesthetic used. In females, constriction by the combined drugs was also observed, with limited influence by anesthetic presence.

CONCLUSIONS

We demonstrate that two commonly used anesthetic formulations differentially influence the level of vasoconstriction caused by alcohol and THC actions in cerebral arterioles.

Peri-anesthetic hypothermia in rodents: A factor to consider for accurate and reproducible outcomes in orthopedic device-related infection studies

Orthopedic device-related infection (ODRI) preclinical models are widely used in translational research. Most ODRI models require induction of general anesthesia, which frequently results in hypothermia in rodents. This study aimed to evaluate the impact of peri-anesthetic hypothermia in rodents on outcomes in preclinical ODRI studies. A retrospective analysis of all rodents that underwent surgery under general anesthesia to induce an ODRI model with inoculation of Staphylococcus epidermidis between 2016 and 2020 was conducted. A one-way multivariate analysis of covariance (one-way MANCOVA) was used to determine the fixed effect of peri-anesthetic hypothermia (hypothermic defined as rectal temperature <35°C) on the combined harvested tissue and implant colony-forming unit (CFU) counts, and having controlled for the study groups including treatments received, duration of surgery and anesthesia, and study period. The results showed a significant effect of peri-anesthetic hypothermia on the post-mortem combined CFU counts from the harvested tissue and implant(s) (p = 0.01) when comparing normo- versus hypothermic rodents. Using Wilks' Λ as a criterion to determine the contribution of independent variables to the model, peri-anesthetic hypothermia was the most significant, though still a weak predictor, of increased harvested CFU counts. Altogether, the data corroborate the concept that bacterial colonization is affected by abnormal body temperature during general anesthesia at the time of bacterial inoculation in rodents, which needs to be taken into consideration to decrease infection data variability and improve experimental reproducibility.

Efficacy profile of noninvasive vagus nerve stimulation on cortical spreading depression susceptibility and the tissue response in a rat model

Background

Noninvasive vagus nerve stimulation (nVNS) has recently emerged as a promising therapy for migraine. We previously demonstrated that vagus nerve stimulation inhibits cortical spreading depression (CSD), the electrophysiological event underlying migraine aura and triggering headache; however, the optimal nVNS paradigm has not been defined.

Methods

Various intensities and doses of nVNS were tested to improve efficacy on KCl-evoked CSD frequency and electrical threshold of CSD in a validated rat model. Chronic efficacy was evaluated by daily nVNS delivery for four weeks. We also examined the effects of nVNS on neuroinflammation and trigeminovascular activation by western blot and immunohistochemistry.

Results

nVNS suppressed susceptibility to CSD in an intensity-dependent manner. Two 2-minute nVNS 5 min apart afforded the highest efficacy on electrical CSD threshold and frequency of KCl-evoked CSD. Daily nVNS for four weeks did not further enhance efficacy over a single nVNS 20 min prior to CSD. The optimal nVNS also attenuated CSD-induced upregulation of cortical cyclooxygenase-2, calcitonin gene-related peptide in trigeminal ganglia, and c-Fos expression in trigeminal nucleus caudalis.

Conclusions

Our study provides insight on optimal nVNS parameters to suppress CSD and suggests its benefit on CSD-induced neuroinflammation and trigeminovascular activation in migraine treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-022-01384-1.

Perioperative Hypothermia-A Narrative Review

Unintentional hypothermia (core temperature < 36 °C) is a common side effect in patients undergoing surgery. Several patient-centred and external factors, e.g., drugs, comorbidities, trauma, environmental temperature, type of anaesthesia, as well as extent and duration of surgery, influence core temperature. Perioperative hypothermia has negative effects on coagulation, blood loss and transfusion requirements, metabolization of drugs, surgical site infections, and discharge from the post-anaesthesia care unit. Therefore, active temperature management is required in the pre-, intra-, and postoperative period to diminish the risks of perioperative hypothermia. Temperature measurement should be done with accurate and continuous probes. Perioperative temperature management includes a bundle of warming tools adapted to individual needs and local circumstances. Warming blankets and mattresses as well as the administration of properly warmed infusions via dedicated devices are important for this purpose. Temperature management should follow checklists and be individualized to the patient's requirements and the local possibilities.

Olanzapine attenuates postoperative cognitive dysfunction in adult rats

Background

Postoperative cognitive dysfunction (POCD) is associated with poor quality of life and difficulty working. Its impact may be greater in middle-aged patients than in elderly patients. Neuroinflammation is reported to be a main cause of POCD. Olanzapine has been reported to improve learning and memory functions. We therefore investigated olanzapine's effectiveness and mechanisms in an adult rat POCD model.

Methods

Six-month-old rats underwent laparotomy and lipopolysaccharide (LPS group) or LPS + olanzapine (OLA group) intraperitoneal injection or anesthesia alone (CON group) 1 week after a Barnes maze training session. A Barnes maze test trial was then conducted the day after surgery or anesthesia. The microglial activity in the hippocampus and cytokine levels were measured by Iba1 staining and enzyme-linked immunosorbent assay, respectively.

Results

The OLA group had significantly higher success rates of Barnes maze trial than the LPS group. The success rate in time of the OLA group was inferior to that of the CON group. On the other hand, the success rate in distance of the OLA group was similar to that of the CON group. Iba1 staining areas in the LPS and OLA groups were larger than that in the CON group; however, the staining area in the OLA group was smaller than that of the LPS group. Plasma interleukin-1β concentration in the LPS and OLA groups was significantly higher than that in the CON group; however, there was no significant difference between the LPS and OLA groups.

Conclusion

Olanzapine attenuated both spatial cognitive dysfunction and microglial activity of the hippocampus, which were induced by surgery and LPS injection. These effects were unrelated to inflammatory cytokine concentrations in plasma and hippocampus.

Propofol rather than Isoflurane Accelerates the Interstitial Fluid Drainage in the Deep Rat Brain

Objective: Different anesthetics have distinct effects on the interstitial fluid (ISF) drainage in the extracellular space (ECS) of the superficial rat brain, while their effects on ISF drainage in the ECS of the deep rat brain still remain unknown. Herein, we attempt to investigate and compare the effects of propofol and isoflurane on ECS structure and ISF drainage in the caudate-putamen (CPu) and thalamus (Tha) of the deep rat brain. Methods: Adult Sprague-Dawley rats were anesthetized with propofol or isoflurane, respectively. Twenty-four anesthetized rats were randomly divided into the propofol-CPu, isoflurane-CPu, propofol-Tha, and isoflurane-Tha groups. Tracer-based magnetic resonance imaging (MRI) and fluorescent-labeled tracer assay were utilized to quantify ISF drainage in the deep brain. Results: The half-life of ISF in the propofol-CPu and propofol-Tha groups was shorter than that in the isoflurane-CPu and isoflurane-Tha groups, respectively. The ECS volume fraction in the propofol-CPu and propofol-Tha groups was much higher than that in the isoflurane-CPu and isoflurane-Tha groups, respectively. However, the ECS tortuosity in the propofol-CPu and propofol-Tha groups was much smaller than that in isoflurane-CPu and isoflurane-Tha groups, respectively. Conclusions: Our results demonstrate that propofol rather than isoflurane accelerates the ISF drainage in the deep rat brain, which provides novel insights into the selective control of ISF drainage and guides selection of anesthetic agents in different clinical settings, and unravels the mechanism of how general anesthetics function.

Neurotransmitter networks in mouse prefrontal cortex are reconfigured by isoflurane anesthesia

This study quantified eight small-molecule neurotransmitters collected simultaneously from prefrontal cortex of C57BL/6J mice (n = 23) during wakefulness and during isoflurane anesthesia (1.3%). Using isoflurane anesthesia as an independent variable enabled evaluation of the hypothesis that isoflurane anesthesia differentially alters concentrations of multiple neurotransmitters and their interactions. Machine learning was applied to reveal higher order interactions among neurotransmitters. Using a between-subjects design, microdialysis was performed during wakefulness and during anesthesia. Concentrations (nM) of acetylcholine, adenosine, dopamine, GABA, glutamate, histamine, norepinephrine, and serotonin in the dialysis samples are reported (means ± SD). Relative to wakefulness, acetylcholine concentration was lower during isoflurane anesthesia (1.254 ± 1.118 vs. 0.401 ± 0.134, P = 0.009), and concentrations of adenosine (29.456 ± 29.756 vs. 101.321 ± 38.603, P < 0.001), dopamine (0.0578 ± 0.0384 vs. 0.113 ± 0.084, P = 0.036), and norepinephrine (0.126 ± 0.080 vs. 0.219 ± 0.066, P = 0.010) were higher during anesthesia. Isoflurane reconfigured neurotransmitter interactions in prefrontal cortex, and the state of isoflurane anesthesia was reliably predicted by prefrontal cortex concentrations of adenosine, norepinephrine, and acetylcholine. A novel finding to emerge from machine learning analyses is that neurotransmitter concentration profiles in mouse prefrontal cortex undergo functional reconfiguration during isoflurane anesthesia. Adenosine, norepinephrine, and acetylcholine showed high feature importance, supporting the interpretation that interactions among these three transmitters may play a key role in modulating levels of cortical and behavioral arousal.NEW & NOTEWORTHY This study discovered that interactions between neurotransmitters in mouse prefrontal cortex were altered during isoflurane anesthesia relative to wakefulness. Machine learning further demonstrated that, relative to wakefulness, higher order interactions among neurotransmitters were disrupted during isoflurane administration. These findings extend to the neurochemical domain the concept that anesthetic-induced loss of wakefulness results from a disruption of neural network connectivity.

Brain interstitial fluid drainage and extracellular space affected by inhalational isoflurane: in comparison with intravenous sedative dexmedetomidine and pentobarbital sodium

Brain interstitial fluid drainage and extracellular space are closely related to waste clearance from the brain. Different anesthetics may cause different changes of brain interstitial fluid drainage and extracellular space but these still remain unknown. Herein, effects of the inhalational isoflurane, intravenous sedative dexmedetomidine and pentobarbital sodium on deep brain matters' interstitial fluid drainage and extracellular space and underlying mechanisms were investigated. When compared to intravenous anesthetic dexmedetomidine or pentobarbital sodium, inhalational isoflurane induced a restricted diffusion of extracellular space, a decreased extracellular space volume fraction, and an increased norepinephrine level in the caudate nucleus or thalamus with the slowdown of brain interstitial fluid drainage. A local administration of norepinephrine receptor antagonists, propranolol, atipamezole and prazosin into extracellular space increased diffusion of extracellular space and interstitial fluid drainage whilst norepinephrine decreased diffusion of extracellular space and interstitial fluid drainage. These findings suggested that restricted diffusion in brain extracellular space can cause slowdown of interstitial fluid drainage, which may contribute to the neurotoxicity following the waste accumulation in extracellular space under inhaled anesthesia per se.

Effects of Rodent Thermoregulation on Animal Models in the Research Environment

To best promote animal wellbeing and the efficacy of biomedical models, scientific, husbandry, and veterinary professionals must consider the mechanisms, influences, and outcomes of rodent thermoregulation in contemporary research environments. Over the last 2 decades, numerous studies have shown that laboratory mice and rats prefer temperatures that are several degrees warmer than the environments in which they typically are housed within biomedical facilities. Physiologic changes to rodents that are cage-housed under standard temperatures (20 to 26 °C) are attributed to 'cold stress' and include alterations in metabolism, cardiovascular parameters, respiration, and immunologic function. This review article describes common behavioral and physiologic adaptations of laboratory mice and rats to cold stress within modern vivaria, with emphasis on environmental enrichment and effects of anesthesia and procedural support efforts. In addition, potential interventions and outcomes for rodents are presented, relative to the importance of repeating and reproducing experiments involving laboratory rodent research models of human disease.

Anesthesia with Dexmedetomidine and Low-dose Isoflurane Increases Solute Transport via the Glymphatic Pathway in Rat Brain When Compared with High-dose Isoflurane

BACKGROUND

The glymphatic pathway transports cerebrospinal fluid through the brain, thereby facilitating waste removal. A unique aspect of this pathway is that its function depends on the state of consciousness of the brain and is associated with norepinephrine activity. A current view is that all anesthetics will increase glymphatic transport by inducing unconsciousness. This view implies that the effect of anesthetics on glymphatic transport should be independent of their mechanism of action, as long as they induce unconsciousness. We tested this hypothesis by comparing the supplementary effect of dexmedetomidine, which lowers norepinephrine, with isoflurane only, which does not.

METHODS

Female rats were anesthetized with either isoflurane (N = 8) or dexmedetomidine plus low-dose isoflurane (N = 8). Physiologic parameters were recorded continuously. Glymphatic transport was quantified by contrast-enhanced magnetic resonance imaging. Cerebrospinal fluid and gray and white matter volumes were quantified from T1 maps, and blood vessel diameters were extracted from time-of-flight magnetic resonance angiograms. Electroencephalograms were recorded in separate groups of rats.

RESULTS

Glymphatic transport was enhanced by 32% in rats anesthetized with dexmedetomidine plus low-dose isoflurane when compared with isoflurane. In the hippocampus, glymphatic clearance was sixfold more efficient during dexmedetomidine plus low-dose isoflurane anesthesia when compared with isoflurane. The respiratory and blood gas status was comparable in rats anesthetized with the two different anesthesia regimens. In the dexmedetomidine plus low-dose isoflurane rats, spindle oscillations (9 to 15 Hz) could be observed but not in isoflurane anesthetized rats.

CONCLUSIONS

We propose that anesthetics affect the glymphatic pathway transport not simply by inducing unconsciousness but also by additional mechanisms, one of which is the repression of norepinephrine release.

TRPA1 mediates the hypothermic action of acetaminophen

Acetaminophen (APAP) is an effective antipyretic and one of the most commonly used analgesic drugs. Unlike antipyretic non-steroidal anti-inflammatory drugs, APAP elicits hypothermia in addition to its antipyretic effect. Here we have examined the mechanisms responsible for the hypothermic activity of APAP. Subcutaneous, but not intrathecal, administration of APAP elicited a dose dependent decrease in body temperature in wildtype mice. Hypothermia was abolished in mice pre-treated with resiniferatoxin to destroy or defunctionalize peripheral TRPV1-expressing terminals, but resistant to inhibition of cyclo-oxygenases. The hypothermic activity was independent of TRPV1 since APAP evoked hypothermia was identical in wildtype and Trpv1^−/− mice, and not reduced by administration of a maximally effective dose of a TRPV1 antagonist. In contrast, a TRPA1 antagonist inhibited APAP induced hypothermia and APAP was without effect on body temperature in Trpa1^−/− mice. In a model of yeast induced pyrexia, administration of APAP evoked a marked hypothermia in wildtype and Trpv1^−/− mice, but only restored normal body temperature in Trpa1^−/− and Trpa1^−/−/Trpv1^−/− mice. We conclude that TRPA1 mediates APAP evoked hypothermia.

Atropine-sensitive theta rhythm in the posterior hypothalamic area: in vivo and in vitro studies

Theta rhythm is the largest, most prominent, and well-documented electroencephalography activity present in a number of mammals, including humans. Spontaneous theta activity recorded locally in the posterior hypothalamic area (PHa) has never been the subject of detailed studies. The authors have shown that local theta field potentials could be generated in urethane-anesthetized rats in the supramammillary (SuM) nuclei and posterior hypothalamic (PH) nuclei. Theta recorded in the PHa was produced independently of simultaneously occurring hippocampal theta. These data were confirmed in the PHa maintained in vitro. Local theta field activity was recorded in the SuM and PH nuclei of PHa slice preparations perfused with cholinergic agonist carbachol. Both in vivo and in vitro recorded PHa theta rhythmicity had a cholinergic-muscarinic profile, that is, it was antagonized by muscarinic antagonist atropine sulfate.

A positive relationship between ambient temperature and bipolar disorder identified using a national cohort of psychiatric inpatients

OBJECTIVE

This study characterizes the positive relationship between daily temperature and bipolar disorder in a cohort of Taiwanese psychiatric inpatients.

METHODS

Meteorological data, provided by the Central Weather Bureau (CWB) of Taiwan, were interpolated to create representative estimates of mean diurnal temperatures for 352 townships. Psychiatric inpatient admissions enrolled in the national health-care insurance system were retrieved from the 1996-2007 Psychiatric Inpatient Medical Claim (PIMC) dataset. The generalized linear mixed models with Poisson distribution were used to evaluate the relative risks of mean diurnal temperature with respect to increased admissions for bipolar disorder, while adjusting for internal correlations and demographic covariates.

RESULTS

Increased relative risks of bipolar disorder admissions were associated with the increasing trends of temperature over 24.0 °C (50th ‰), especially for adults and females. The highest daily diurnal temperatures above 30.7 °C (99th ‰) had the greatest risks of bipolar hospitalizations.

CONCLUSION

Understanding the increase of bipolar disorder admissions occurring in extreme heat is important in the preparation and prevention of massive recurrences of bipolar episodes.

Electroencephalographic and convulsive effects of binge doses of (+)-methamphetamine, 5-methoxydiisopropyltryptamine, and (±)-3,4-methylenedioxymethamphetamine in rats

The abuse of drugs such as methamphetamine (MA), 3,4-methylenedioxymethamphetamine (Ecstasy, MDMA), and 5-methoxydiisopropyltryptamine (5-MeO-DIPT; Foxy) is global. Symptoms from taking these drugs include tachycardia, agitation, hyperpyrexia, and sometimes seizures. We compared the EEG effects of these drugs in male Sprague-Dawley rats (~300 g) implanted with cortical electroencephalographic (EEG) electrodes prior to testing. Animals received four subcutaneous injections of MA, MDMA, or Foxy (10 mg/kg each as freebase, administered every 2 h), or saline as these doses produce lasting effects on learning, memory, and monoamines. EEG tracings were recorded before, during, and after treatment. Animals receiving MDMA showed no significant EEG abnormalities or myoclonus. MA treatment resulted in myoclonic activity and in brief (<10 s) EEG epileptiform activity in ~50% of the rats. Longer seizure activity (10 s to 5 min) was recorded in some MA-treated rats following the third and fourth doses. The onset of myoclonic activity following Foxy treatment occurred shortly after the first dose. All rats receiving Foxy showed seizures by the second dose and this continued throughout the treatment regimen. The results show that binge doses of MA and MDMA, which mimic the neurochemical changes seen in chronic users, increase EEG abnormalities after MA but not after MDMA. While the neurochemical effects of Foxy are not known in humans, this drug causes severe EEG abnormalities and overt seizures in 100% of tested animals.

Diffusion of water in skeletal muscle tissue is not influenced by compression in a rat model of deep tissue injury

Sustained mechanical loading of skeletal muscle may result in the development of a severe type of pressure ulcer, referred to as deep tissue injury. Recently it was shown that the diffusion of large molecules (10-150kDa) is impaired during deformation of tissue-engineered skeletal muscle, suggesting a role for impaired diffusion in the aetiology of deep tissue injury. However, the influence of deformation on diffusion of smaller molecules on its aetiology is less clear. This motivated the present study designed to investigate the influence of deformation of skeletal muscle on the diffusion of water, which can be measured with diffusion tensor magnetic resonance imaging (MRI). It could be predicted that this approach will provide valuable information on the diffusion of small molecules. Additionally the relationship between muscle temperature and diffusion was investigated. During deformation of the tibialis anterior a decrease of the apparent diffusion coefficient (ADC) was observed (7.2+/-3.9%). The use of a finite element model showed that no correlation existed between the maximum shear strain and the decrease of the ADC. The ADC in the uncompressed gastrocnemius muscle decreased with 5.9+/-3.7%. In an additional experiment a clear correlation was obtained between the decrease of the ADC and the relative temperature change of skeletal muscle tissue as measured by MRI. Taken together, it was concluded that (1) the decreased diffusion of water was not a direct effect of tissue deformation and (2) that it is likely that the observed decreased ADC during deformation was a result of a decreased muscle temperature. The present study therefore provides evidence that diffusion of small molecules, particularly oxygen and carbon dioxide, is not impaired during deformation of skeletal muscle tissue.

Nitrous oxide and xenon increase noradrenaline release in the cerebral cortex in vivo and in vitro

Noradrenaline in the central nervous system plays an important role in regulating physiological functions, and is a key mechanistic component of general anesthesia. The purpose of this present study was to determine if nitrous oxide and xenon modulate noradrenaline release in the cerebral cortex. We performed a series of in vivo and in vitro experiments in rats. For the in vivo experiments, noradrenaline release was measured by microdialysis in the prefrontal cortex with exposure to 0, 30 or 60% nitrous oxide. For the in vitro experiments, noradrenaline release was measured from cerebrocortical slices before and after incubation with 0, 15, 30, or 60% nitrous oxide in Ca(2+)-containing buffer, Ca(2+)-free buffer, or in Ca(2+)-containing buffer with 10(-6)M tetrodotoxin (TTX). For the in vivo and in vitro experiments 60% xenon was also used. In the in vivo experiment, following exposure to nitrous oxide, noradrenaline release concentration-dependently increased. In the in vitro experiment, under Ca(2+)-containing conditions, noradrenaline release from cerebrocortical slices increased significantly during exposure to nitrous oxide in a concentration-dependent manner. Under Ca(2+)-free conditions, 60% nitrous oxide produced a significant release of noradrenaline. There were no significant differences in nitrous oxide-increased noradrenaline release between with and without TTX. Xenon also significantly increased noradrenaline release in the prefrontal cortex and from the cerebrocortical slices. The nitrous oxide-induced increase in noradrenaline release may be due to both excitation of the locus coeruleus-noradrenergic neuron and direct stimulation of its axon terminals.

Saturated norepinephrine transporter occupancy by atomoxetine relevant to clinical doses: a rhesus monkey study with (S,S)-[(18)F]FMeNER-D (2)

PURPOSE

In a previous PET study on norepinephrine transporter (NET) occupancy in the nonhuman primate brain, the relationship between NET occupancy and atomoxetine plasma concentration, and occupancies among different brain regions, were not demonstrated adequately. It may therefore be difficult to translate the results to the clinical situations. In the present study, the detailed change of NET occupancy was investigated among a wider range of doses in a more advanced manner.

METHODS

Two rhesus monkeys were examined using a high-resolution PET system with (S,S)-[(18)F]FMeNER-D(2) under baseline conditions and after steady-state infusion of different doses of atomoxetine (0.003 to 0.12 mg/kg per hour). NET occupancy of the thalamus, brainstem and anterior cingulate cortex was calculated using BP(ND) obtained with the simplified reference tissue model.

RESULTS

NET occupancy increased regionally and uniformly as the plasma concentration of atomoxetine increased. The estimated Kd value (the amount to occupy 50% of NET) in the thalamus was 16 ng/ml.

CONCLUSION

The results indicate that clinical doses of atomoxetine would occupy NET almost completely.

Long-term assessment of motor and cognitive behaviours in the intraluminal perforation model of subarachnoid hemorrhage in rats

The endovascular perforation model of subarachnoid hemorrhage (SAH) is a commonly used model in rats as it is performed without a craniotomy and accurately mimics the physiological effects of SAH in humans. The long-term behavioural profile of the model, however, has not been characterized. Given that humans often have cognitive deficits following SAH, we set out to characterize the behavioural profile as well as the spontaneous temperature changes of rats following intraluminal perforation. Rats were pre-trained on three motor tasks (tapered beam, limb-use asymmetry and the horizontal ladder tasks) prior to receiving a SAH. The animals were then assessed on post-surgical days 3, 7, 14 and 21 on these tasks. At the completion of motor testing, the rats were assessed on a moving platform version of the Morris water task. Despite significant mortality (33%), SAH did not result in lasting motor deficits on any of the tasks examined. However, the SAH group did show a minor cognitive impairment in the Morris water task. In addition, SAH produced a slight, but significant elevation in body temperature (vs. sham operated rats) despite an acute decrease in general home cage activity. The majority of the animals did not have any observable infarcts and the SAH did not significantly affect cortical thickness. In summary, the endovascular perforation model of SAH results in no lasting motor deficits and only minor cognitive impairment in survivors, which alone would be difficult to evaluate in neuroprotection or rehabilitation studies.

Determinants of frequency long-term facilitation following acute intermittent hypoxia in vagotomized rats

Acute intermittent (AIH), but not acute sustained hypoxia (ASH) elicits a form of respiratory plasticity known as long-term facilitation (LTF). In anesthetized rats, LTF is expressed as increased respiratory-related nerve burst amplitude, with variable effects on burst frequency. We analyzed a large data set from multiple investigators using the same experimental protocol to determine factors influencing frequency LTF. Our meta-analysis revealed that AIH elicits both phrenic amplitude and frequency LTF in anesthetized and vagotomized rats, but frequency LTF is small in comparison with amplitude LTF (12% versus 60%, respectively). ASH elicits a small, but significant frequency and amplitude LTF (8% and 10%, respectively) that is not significantly different than controls. Similar to all published reports, analysis of this large data set confirms that phrenic amplitude LTF following AIH is significantly greater than ASH. Multiple regression analysis revealed a strong correlation between baseline burst frequency and frequency LTF. Variations in baseline burst frequency may contribute to variation in frequency LTF and may underlie the apparent effects of some drug treatments.

In vivo PET imaging of cardiac presynaptic sympathoneuronal mechanisms in the rat

The sympathetic nervous system of the heart plays a key role in the pathophysiology of various cardiac diseases. Small-animal models are valuable for obtaining further insight into mechanisms of cardiac disease and therapy. To determine the translational potential of cardiac neuronal imaging from rodents to humans, we characterized the rat sympathetic nervous system using 3 radiotracers that reflect different subcellular mechanisms: (11)C-meta-hydroxyephedrine (HED), a tracer of neuronal transport showing stable uptake and no washout in healthy humans; (11)C-phenylephrine (PHEN), a tracer of vesicular leakage and intraneuronal metabolic degradation with initial uptake and subsequent washout in humans; and (11)C-epinephrine (EPI), a tracer of vesicular storage with stable uptake and no washout in humans.

METHODS

We used a small-animal PET system to study healthy male Wistar rats at baseline, after desipramine (DMI) pretreatment (DMI block), and with DMI injection 15 min after tracer delivery (DMI chase). The rats were kept under general isoflurane anesthesia while dynamic emission scans of the heart were recorded for 60 min after radiotracer injection. A myocardial retention index was determined by normalizing uptake at 40 min to the integral under the arterial input curve. Washout rates were determined by monoexponential fitting of myocardial time-activity curves.

RESULTS

At baseline, HED showed high myocardial uptake and sustained retention, EPI showed moderate uptake and significant biphasic washout, and PHEN showed moderate uptake and monoexponential washout. The average (+/- SD) left ventricular retention index for HED, PHEN, and EPI was 7.38% +/- 0.82%/min, 3.43% +/- 0.45%/min, and 4.24% +/- 0.59%/min, respectively; the washout rate for HED, PHEN, and EPI was 0.13% +/- 0.23%/min, 1.13% +/- 0.35%/min, and 0.50% +/- 0.24%/min, respectively. The DMI chase resulted in increased washout only for HED. DMI block decreased myocardial uptake of all tracers by less than 90%.

CONCLUSION

Kinetic profiles of HED in the rat myocardium were similar to those of HED in humans, suggesting comparable neuronal transport density. Unlike in humans, however, significant washout of EPI and faster washout of PHEN were encountered, consistent with high intraneuronal metabolic activity, high catecholamine turnover, and reduced vesicular storage. This evidence of increased neuronal activity in rodents has implications for translational studies of cardiac neuronal biology in humans.

Modulation of neuronal activity in CNS pain pathways following propofol administration in rats: Fos and EEG analysis

We studied Fos expression in the central nociceptive pathways at different sedative levels in order to clarify the central mechanism of propofol's nociceptive action. Sprague-Dawley rats received propofol (PRO) or pentobarbital (PEN) and were divided into two groups with different doses of drug administration (light and deep sedative levels) based on the electroencephalogram analysis. Rats at each sedative level received heat stimulation to their face and Fos immunohistochemistry was performed at various brain sites. We also infused lidocaine into the jugular vein to test whether PRO directly activated nociceptors distributed in the vein. Fos expression in two major ascending pain pathways (lateral and medial systems) and descending modulatory system were precisely analyzed following intravenous (i.v.) administration of PRO or PEN. Many Fos protein-like immunoreactive (Fos protein-LI) cells were expressed in the trigeminal spinal nucleus caudalis (Vc), parabrachial nucleus, parafascicular nucleus, a wide area of the primary somatosensory cortex, anterior cingulate cortex, amygdala, periaqueductal gray, solitary tract nucleus, and lateral hypothalamus following heating of the face during PRO or PEN infusion. The number of Fos protein-LI cells was significantly greater in many Central nervous system regions during PRO infusion compared with PEN. Fos expression was significantly greater in the Vc and Periaqueductal gray following greater amount of PRO infusions compared, whereas they were significantly smaller in the Vc in the rats with PEN infusion. The Fos expression was significantly depressed following i.v. infusion of lidocaine before PRO administration. The present findings suggest that PRO is involved in the enhancement of Vc activity through direct activation of the primary afferent fibers innervating veins, resulting in pain induction during infusion.

COMPARISON OF BLOOD PRESSURE AND THERMAL RESPONSES IN RATS EXPOSED TO MILLIMETER WAVE ENERGY OR ENVIRONMENTAL HEAT

Electromagnetic fields at millimeter wave lengths are being developed for commercial and military use at power levels that can cause temperature increases in the skin. Previous work suggests that sustained exposure to millimeter waves causes greater heating of skin, leading to faster induction of circulatory failure than exposure to environmental heat (EH). We tested this hypothesis in three separate experiments by comparing temperature changes in skin, subcutis, and colon, and the time to reach circulatory collapse (mean arterial blood pressure, 20 mmHg) in male Sprague-Dawley rats exposed to the following conditions that produced similar rates of body core heating within each experiment: (1) EH at 42 degrees C, 35 GHz at 75 mW/cm, or 94 GHz at 75 mW/cm under ketamine and xylazine anesthesia; (2) EH at 43 degrees C, 35 GHz at 90 mW/cm, or 94 GHz at 90 mW/cm under ketamine and xylazine anesthesia; and (3) EH at 42 degrees C, 35 GHz at 90 mW/cm, or 94 GHz at 75 mW/cm under isoflurane anesthesia. In all three experiments, the rate and amount of temperature increase at the subcutis and skin surface differed significantly in the rank order of 94 GHz more than 35 GHz more than EH. The time to reach circulatory collapse was significantly less only for rats exposed to 94 GHz at 90 mW/cm, the group with the greatest rate of skin and subcutis heating of all groups in this study, compared with both the 35 GHz at 90 mW/cm and the EH at 43 degrees C groups. These data indicate that body core heating is the major determinant of induction of hemodynamic collapse, and the influence of heating of the skin and subcutis becomes significant only when a certain threshold rate of heating of these tissues is exceeded.

Antinociceptive and hypothermic effects of Salvinorin A are abolished in a novel strain of kappa-opioid receptor-1 knockout mice

Salvia divinorum is a natural occurring hallucinogen that is traditionally used by the Mazatec Indians of central Mexico. The diterpene salvinorin A was identified as an active component of S. divinorum over 20 years ago, but only recently has biochemical screening indicated that a molecular target of salvinorin A in vitro is the kappa-opioid receptor. We have examined whether salvinorin A, the C2-substituted derivative salvinorinyl-2-propionate, and salvinorin B can act as kappa-opioid receptor agonists in vivo. We found that following intracerebroventricular injection over a dose range of 1 to 30 microg of both salvinorin A and salvinorinyl-2-propionate produces antinociception in wild-type mice but not in a novel strain of kappa-opioid receptor knockout mice. Moreover, both salvinorin A and salvinorinyl-2-propionate reduce rectal body temperature, similar to conventional kappa-opioid receptor agonists, in a genotype-dependent manner. In addition, we determined that salvinorin A has high affinity for kappa 1- but not kappa 2-opioid receptors, demonstrating selectivity for this receptor subclass. Finally, treatment over the same dose range with salvinorin B, which is inactive in vitro, produced neither antinociceptive nor hypothermic effects in wild-type mice. These data demonstrate that salvinorin A is the active component of S. divinorum, selective for kappa(1)-opioid receptors, and that salvinorin A and specific structurally related analogs produce behavioral effects that require the kappa-opioid receptor.

Microdialysis as a tool in local pharmacodynamics

In many cases the clinical outcome of therapy needs to be determined by the drug concentration in the tissue compartment in which the pharmacological effect occurs rather than in the plasma. Microdialysis is an in vivo technique that allows direct measurement of unbound tissue concentrations and permits monitoring of the biochemical and physiological effects of drugs throughout the body. Microdialysis was first used in pharmacodynamic research to study neurotransmission, and this remains its most common application in the field. In this review, we give an overview of the principles, techniques, and applications of microdialysis in pharmacodynamic studies of local physiological events, including measurement of endogenous substances such as acetylcholine, catecholamines, serotonin, amino acids, peptides, glucose, lactate, glycerol, and hormones. Microdialysis coupled with systemic drug administration also permits the more intensive examination of the pharmacotherapeutic effect of drugs on extracellular levels of endogenous substances in peripheral compartments and blood. Selected examples of the physiological effects and mechanisms of action of drugs are also discussed, as are the advantages and limitations of this method. It is concluded that microdialysis is a reliable technique for the measurement of local events, which makes it an attractive tool for local pharmacodynamic research.