Effect of chloral hydrate on in vivo KCl-induced striatal dopamine release in the rat

The release of striatal dopamine (DA) and its metabolites in response to locally-induced K⁺ depolarization was investigated in vivo in chloral hydrate-anesthetized and freely moving rats. KCl at concentrations of 30, 50, and 100 mM induced significant dose-dependent increases in extracellular DA overflow in both chloral hydrate-anesthetized and freely moving rats (P<0.05). Extracellular levels of dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were decreased. The DA overflow in response to 30 mM KCl stimulation in anesthetized rats was significantly greater than that in freely moving rats (P<0.05). In addition, chloral hydrate anesthesia resulted in a significant decrease in extracellular levels of DOPAC and significant increases in extracellular levels of HVA and 5-HIAA in comparison with freely moving rats (P<0.05). Furthermore, the basal level of extracellular HVA in chloral hydrateanesthetized rats was significantly higher than that in freely moving rats. These results suggest that chloral hydrate anesthesia could have significant effects on the pharmacological response of the striatal dopaminergic neurons.     

Effects of electrical stimulation of the medullary raphe nuclei on respiratory movement in rats

The present study was undertaken to examine the effects of electrical stimulation of the medullary raphe nuclei on respiration in rats anesthetized with ketamine and xylazine. Train pulse stimuli (100 Hz, 10–30 μA) were applied in the regions of the caudal raphe nuclei: the raphe magnus (RM), raphe pallidus (RP) and raphe obscurus (RO). Stimulation of the RM depressed inspiratory movements measured by means of an abdominal pneumograph, whereas stimulation of the RP augmented inspiratory movements. It was revealed that stimulation of the RO induced either inhibitory or facilitatory effects on respiratory movements depending on the stimulation sites. These findings confirm and extend previous studies concerning the effects of raphe stimulation on respiratory activity in cats. The present results demonstrate that in rats the caudal raphe nuclei are involved in respiratory control.An erratum to this article can be found at     

Influence of different barbiturate anesthetics on delta-9-tetrahydrocannabinol effects on spinal monosynaptic reflexes

Two barbiturates, pentobarbital and methohexital, were used as general anesthetics to evaluate their interactions with the effects of delta-9-tetrahydrocannabinol (delta-9-THC) on spinal monosynaptic reflexes in cats with transected spinal cords and ischemically destroyed brains. In animals initially anesthetized with pentobarbital, delta-9-THC over a wide dosage range produced only an enhancement of the reflex, whereas in methohexital-treated animals only depression was elicited. Because delta-9-THC is known to produce both excitatory and depressant effects in conscious animals, the results of the present study demonstrate that the choice of anesthetic may determine which effects manifest themselves. Therefore, if anesthesia is used in the investigation of any cannabinoid, the possibility of such interactions must be considered when interpreting the results.     

Effects of sodium pentobarbital anesthesia on blood flow in skin, myocutaneous, and fasciocutaneous flaps in swine.

Drug effect on flap blood flow is most commonly determined in anesthetized animals, yet the effect of the anesthetic is often poorly understood. Halothane and nitrous oxide cause profound changes in skin blood flow and thus provide an unsuitable anesthetic technique for use in measuring drug effects on skin and myocutaneous flaps in swine. The goal of this study was to determine the effects of sodium pentobarbital anesthesia on cardiovascular parameters and blood flow in skin, myocutaneous, and fasciocutaneous flaps in pigs. In seven pigs, 7 forelimb skin flaps, 7 forelimb fasciocutaneous flaps, 14 arterial buttock flaps, and 14 latissimus dorsi flaps were created. Blood flow was measured at 2-cm intervals along each flap while the animal was awake and anesthetized. A cardiac depressant effect of pentobarbital was observed, but no change in blood flow could be demonstrated in control skin or control muscle. However, pentobarbital did significantly increase blood flow in all viable portions of arterial and random skin flaps, fasciocutaneous flaps, and the cutaneous segments of the latissimus dorsi flap. These demonstrated effects of pentobarbital should be taken into consideration in designing and analyzing studies of flap blood flow in the acute postoperative phase.     

Single unit activity of dopaminergic neurons in freely moving cats

Single unit activity was recorded from the area of the substantia nigra in freely moving cats. A sub-population of these neurons had the following characteristics: long action potential durations (2–4 msec); relatively slow discharge rates (2–6 spikes/sec); firing as single spikes along with periods of bursting activity in which spike amplitude successively decreased; suppression of unit activity by systemic injection of apomorphine and increased activity after systemic injection of haloperidol. These characteristics are similar to those of identified dopamine neurons recorded in chloral hydrate anesthetized or peripherally paralyzed rats. Therefore, based upon these physiological and pharmacological similarities, this study represents the first systematic report providing evidence for recording the activity of dopaminergic neurons in freely moving cats. In addition, when these cells were studied across the sleep-waking cycle they displayed little variation in firing rates between waking, slow wave sleep and REM sleep.     

The use of propofol for electroejaculation in domestic cats

The objective was to evaluate the use of propofol as an anesthetic drug for electroejaculation in the domestic cat. Cortisol concentrations, heart rates and respiratory rates of 20 male domestic cats were examined. The animals were randomly allocated into three groups. Group A (n = 8), were anesthetized with propofol (10 mg/kg) and underwent electroejaculation. Group B (n = 6), were pre-medicated with buprenorphine (0.01 mg/kg), anesthetized with propofol (5 mg/kg) and underwent electroejaculation. Group C (n = 6), the cats were anesthetized with propofol (10 mg/kg) without electroejaculation (control group). Blood samples were collected at four time points (30 min before propofol administration, immediately after the surgical plane of anesthesia was induced, immediately post-electroejaculation, and at the onset of anesthetic recovery). In the control group, the sampling time coincident with the end of electroejaculation was assigned as 21 min after the induction of anesthesia. The mean (+/- S.E.M.) duration time for electroejaculation was 18 +/- 3 min. The duration of anesthesia did not differ (P > 0.05) among the three groups of cats (26 +/- 2 min). Most of the cats (17/20) recovered smoothly. Pre-anesthetic medication with buprenorphine did not reduce the requirement of propofol for anesthesia. The cortisol concentrations, heart rates and respiratory rates of the three groups of cats did not differ (P > 0.05). A marked decline in cortisol levels was observed immediately post-electroejaculation. Propofol was a useful anesthetic for electroejaculation in felids with rapid onset, optimal duration of anesthesia for performing electroejaculation, and smooth recovery.     

Response of central monoaminergic neurons to lisuride: comparison with LSD.

The response of brain serotonergic (dorsal raphe), noradrenergic (locus coeruleus) and dopaminergic (pars compacta, substantia nigra) neurons to lisuride hydrogen maleate, a non-hallucinogenic ergot, was studied in the rat using extracellular single cell recording techniques. As has been previously reported for LSD, minute intravenous infusions of lisuride (1–5 μg/kg) produced a complete but reversible suppression of raphe unit spontaneous firing. A similar depressant response was noted when lisuride was applied to raphe units by microiontophoresis. In contrast, locus coeruleus neurons were accelerated by the drug at somewhat higher doses (25–50 μg/kg). Pars compacta neurons demonstrated a predominately depressant response to lisuride but many of the cells tested were only partially suppressed and a few units were accelerated. It is suggested that the marked alterations in central monoamine turnover which have been observed with lisuride are directly paralled by changes in impulse flow in monoaminergic neurons. The fact that lisuride has powerful suppressant effects on central serotonergic neurons but no psychotomimetic actions in man challenges the “serotonin theory” of hallucinogensis; however, other pharmacological properties may account for lisuride's lack of hallucinogenic effects. Further studies with lisuride may provide insight into those drug characteristics critical to the presence or absence of hallucinogenic action.     

Antagonism of substance P induced facilitation of central neuronal activity by 2,4-dinitrophenol and depressant agents

2,4-Dinitrophenol, pentobarbital, thiopental, methoxyflurane, and halothane more often antagonized the facilitatory effects of substance P than of acetylcholine on the activity of spinal dorsal horn neurons (of unanesthetized decerebrated and spinalized cats) as well as interpeduncular and cerebral cortical cells (of either rats anesthetized with methoxyflurane, nitrous oxide, and oxygen or 'cereveau isolé' rats). The results of the studies indicate that the excitatory effects of substance P on central neurons are extremely sensitive to anesthesia.     

The role of 5-HT1B receptors in the regulation of serotonin cell firing and release in the rat brain

The release of 5-HT in terminal areas of the rodent brain is regulated by 5-HT1B receptors. Here we examined the role of 5-HT1B receptors in the control of 5-HT output and firing in the dorsal raphe nucleus (DR), median raphe nucleus (MnR) and forebrain of the rat in vivo. The local perfusion (30-300 microM) of the selective 5-HT1B receptor agonist CP-93,129 to freely moving rats decreased 5-HT release in the DR and more markedly in the MnR. Likewise, 300 microM CP-93,129 reduced 5-HT output in substantia nigra pars reticulata, ventral pallidum, lateral habenula and the suprachiasmatic nucleus. The effect of CP-93,129 was prevented by SB-224289, but not by WAY-100635, selective 5-HT1B and 5-HT1A receptor antagonists, respectively. SB-224289 did not alter dialysate 5-HT in any raphe nuclei. The intravenous administration of the brain-penetrant selective 5-HT1B receptor agonist CP-94,253 (0.5-2.0 mg/kg) to anesthetized rats decreased dialysate 5-HT in dorsal hippocampus and globus pallidus, increased it in MnR and left it unaltered in the DR and medial prefrontal cortex. SB-224289, at a dose known to block 5-HT1B autoreceptor-mediated effects (5 mg/kg), did not prevent the effect of CP-94,253 on MnR 5-HT. The intravenous administration of CP-94,253 (0.05-1.6 mg/kg) to anesthetized rats increased the firing rate of MnR, but not DR-5-HT neurons. The local perfusion of CP-94,253 in the MnR showed a biphasic effect, with 5-HT reductions at 0.3-3 microM and increase at 300 microM. These results suggest that 5-HT cell firing and release in midbrain raphe nuclei (particularly in the MnR) are under control of 5-HT1B receptors. The activation of 5-HT1B autoreceptors (possibly located on 5-HT nerve endings and/or varicosities within DR and MnR) reduces 5-HT release. The effects of higher concentrations of 5-HT1B receptor agonists seem more compatible with the activation of 5-HT1B heteroreceptors on inhibitory neurons.     

Real-Time Measurement of Electrically Evoked Extracellular Dopamine in the Striatum of Freely Moving Rats

Abstract: The real-time measurement of electrically evoked dopamine was established in brain extracellular fluid of freely moving rats. Dopamine was monitored by fast-scan cyclic voltammetry at carbon fiber microelectrodes lowered into the striatum by means of a detachable micromanipulator. A stimulating electrode, previously implanted in the substantia nigra, was used to evoke striatal dopamine efflux. Evoked extracellular dopamine was both current and frequency dependent. When low current intensities (±125 µA) and frequencies (10–20 Hz) were applied, detectable levels of dopamine were elicited without a perceptible behavioral response. Reproducible concentrations of extracellular dopamine could be evoked in the same rat for at least 2 months. These concentrations, moreover, were significantly higher in freely moving rats compared with rats anesthetized with Equithesin. Analysis of measured curves for dopamine uptake and release rates revealed that anesthesia inhibits release but does not affect uptake. It is concluded that (a) fast-scan cyclic voltammetry at carbon fiber microelectrodes is a viable technique for the measurement of electrically evoked dopamine in brain extracellular fluid of freely moving rats, (b) it is possible to determine in situ rate constants for dopamine release and uptake from these temporally and spatially resolved measurements of levels of dopamine, and (c) transient changes in extracellular dopamine levels elicited by electrical stimulation are affected by anesthesia.     

Influence of halothane on control of breathing in intact and decerebrated cats

The effects of halothane anesthesia have been investigated in intact and in decerebrated cats. Pulmonary ventilation and breathing pattern were studied during room-air breathing, hypercapnia, and O2 inhalation. The following results have been demonstrated. First, halothane anesthesia does not modify pulmonary ventilation, but a tachypnea much more intense in intact than in decerebrated cats is observed. This indicates that halothane-induced tachypnea originates mainly in structures rostral to the brain stem. Second, decerebrated animals exhibit a breathing pattern and a ventilatory response to CO2 similar to those of intact conscious cats, suggesting that forebrain facilitatory and inhibitory influences on brain stem are cancelled out by decerebration. However, the tidal volume vs. inspiratory duration relationship observed in decerebrated cats differs from that in conscious cats. Finally, during halothane anesthesia, ventilatory response to CO2 is markedly depressed. Third, during O2 inhalation, except in decerebrated, anesthetized animals, ventilation is only slightly depressed. This suggests that central stimulatory effect of O2 is enhanced and/or that peripheral chemoreceptor drive is reduced.     

Event-related potentials in an auditory oddball situation in the rat

Evoked potentials were recorded from the auditory cortex of both freely moving and anesthetized rats when deviant sounds were presented in a homogenous series of standard sounds (oddball condition). A component of the evoked response to deviant sounds, the mismatch negativity (MMN), may underlie the ability to discriminate acoustic differences, a fundamental aspect of auditory perception. Whereas most MMN studies in animals have been done using simple sounds, this study involved a more complex set of sounds (synthesized vowels). The freely moving rats had previously undergone behavioral training in which they learned to respond differentially to these sounds. Although we found little evidence in this preparation for the typical, epidurally recorded, MMN response, a significant difference between deviant and standard evoked potentials was noted for the freely moving animals in the 100-200 ms range following stimulus onset. No such difference was found in the anesthetized animals.     

Effects of almitrine on genioglossal and diaphragmatic electromyograms

We previously demonstrated dose-dependent increases in both hypoglossal and phrenic electroneurograms after almitrine in anesthetized, paralyzed, and vagotomized cats. We have now investigated the effect of this peripheral chemoreceptor stimulant on diaphragmatic and genioglossal (GG, an upper airway-maintaining muscle) electromyograms in five unanesthetized, chronically instrumented, spontaneously breathing adult cats during slow-wave sleep. In 12 studies almitrine doses of 1.0-6.0 mg/kg increased inspired minute ventilation (VI), frequency (f), and tidal volume (VT) and decreased expiratory time (TE). However, almitrine doses as high as 6.0 mg/kg failed to augment phasic inspiratory GG activity. To determine why almitrine induced phasic inspiratory upper airway activity in anesthetized, vagotomized cats but not in sleeping cats, additional studies were performed. In four dose-response studies in three pentobarbital-anesthetized cats, almitrine, 1.0-6.0 mg/kg, did not produce phasic inspiratory GG activity. Almitrine did induce phasic inspiratory GG activity in two of three studies in three vagotomized, tracheostomized, alpha-chloralose-urethan-anesthetized cats. These results suggest that almitrine would not be useful in obstructive sleep apnea, yet because almitrine markedly increased VI, f, and VT and decreased TE in unanesthetized sleeping cats the drug may be effective in patients who lack normal central neural respiratory drive, such as the preterm infant.     

The synaptic and nonsynaptic glycine transporter type-1 inhibitors Org-24461 and NFPS alter single neuron firing rate in the rat dorsal raphe nucleus. Further evidence for a glutamatergic-serotonergic interaction and its role in antipsychotic action

Single neuron firing rate was recorded from dorsal raphe nucleus of anesthetized rats. The firing rate of raphe neurons varied from 4 to 8 discharge per second before drug administration and this neuronal activity was decreased by L-701,324 (2 mg/kg i.v. injection), a competitive antagonist of glycineB binding site of N-methyl-D-aspartate (NMDA) receptors. The glycine transporter type-1 (GlyT1) antagonists Org-24461 (10 mg/kg i.v.) and NFPS (3 mg/kg i.v.) reversed the inhibitory effect of L-701,324 on single neuron activity recorded from dorsal raphe nucleus of the rat. Org-24461 and NFPS both tended to increase the raphe neuronal firing rate also when given alone but their effect was not significant. This finding serves further evidence that glutamate released from axon terminals of the cortico-striatal projection neurons stimulates serotonergic neurons in the raphe nuclei and this effect is mediated at least in part by postsynaptic NMDA receptors. Thus, GlyT1 inhibitors are able to reverse the hypofunctional state of NMDA receptors, suggesting that these drugs may have beneficial therapeutic effects in neurological and psychiatric disorders characterized with impaired NMDA receptor-mediated transmission.     

Change in Hemoglobin Levels due to Anesthesia in Mice: An Important Confounder in Studies on Hematopoietic Drugs

Analgesic and anesthetic drugs may have an impact on the results achieved from animal experiments. In the study presented here, we try to enlighten whether anesthesia with fentanyl/fluniasone and midazolam (Hypnorm and Dormicum) has an influence on measurements of hemoglobin in mice. In a cross-over study, we have compared hemoglobin levels in two groups of mice: anesthetized versus non-anesthetized and found significant decrease in hemoglobin levels in the anesthetized group (p < 0.05) unrelated to which group received the anesthesia. The mean hemoglobin levels after intraperitoneal administration of Hypnorm and Dormicum was 8.7 mmol/L compared to mean hemoglobin 9.9 mmol/L before anesthesia (p < 0.001), and the decrease lasted for more than 30 min. These results show that anesthesia can be an important confounder in studies involving measurements of hemoglobin, and this should be taken into account when planning studies and analyzing data.     

脑桥呼吸调整中枢向中缝大核下行投射的研究

实验在23只苯巴比妥钠麻醉(i.p.30mg/kg)的成年猫上进行。在脑桥呼吸调整中枢(NPBM-KF)共记录到67个单位放电可被电刺激中缝大核(NRM)所逆行兴奋。其中有7个单位为呼吸相关性单位(吸气性6、呼气性1),占脑桥87个呼吸相关性单位总数的8％。逆行兴奋潜伏期在0.4—2.5ms之间,平均1.2ms。中缝大核内微量注入麦角辣根过氧化酶(WGA-HRP)后在NPBM-KF区观察到大量HRP标记神经元。本实验结果表明,发自脑桥呼吸调整中枢神经元的轴突可投射到中缝大核。这一投射通路可能与呼吸及痛觉调节有关。     

Electrically elicited cardiovascular and respiratory responses from the nucleus tractus solitarii in unrestrained cats

Heart rate, arterial blood pressure and respiratory rate responses to electrical stimulation of the nucleus tractus solitarii (NTS) were studied in unanaesthetized freely moving cats. Complex cardiovascular response patterns, mainly pressor responses, were obtained from stimulation of the portion of the NTS rostral to the obex. No significant difference was observed between the effects produced by stimulation of the NTS on the right and on the left side. These results indicate that the rostral portion of the NTS also plays a role in the cardiovascular control, and a functional asymmetry between the two sides does not exist at the level of the NTS.     

Inhibition of stress- or anxiogenic-drug-induced increases in dopamine release in the rat prefrontal cortex by long-term treatment with antidepressant drugs

The effects of long-term treatment with imipramine or mirtazapine, two antidepressant drugs with different mechanisms of action, on the response of cortical dopaminergic neurons to foot-shock stress or to the anxiogenic drug FG7142 were evaluated in freely moving rats. As expected, foot shock induced a marked increase (+ 90%) in the extracellular concentration of dopamine in the prefrontal cortex of control rats. Chronic treatment with imipramine or mirtazapine inhibited or prevented, respectively, the effect of foot-shock stress on cortical dopamine output. Whereas acute administration of the anxiogenic drug FG7142 induced a significant increase (+ 60%) in cortical dopamine output in control rats, chronic treatment with imipramine or mirtazapine completely inhibited this effect. In contrast, the administration of a single dose of either antidepressant 40 min before foot shock, had no effect on the response of the cortical dopaminergic innervation to stress. These results show that long-term treatment with imipramine or mirtazapine inhibits the neurochemical changes elicited by stress or an anxiogenic drug with an efficacy similar to that of acute treatment with benzodiazepines. Given that episodes of anxiety or depression are often preceded by stressful events, modulation by antidepressants of the dopaminergic response to stress might be related to the anxiolytic and antidepressant effects of these drugs.     

Inhibition of serotonergic medullary raphe obscurus neurons suppresses genioglossus and diaphragm activities in anesthetized but not conscious rats.

Although exogenous serotonin at the hypoglossal motor nucleus (HMN) activates the genioglossus muscle, endogenous serotonin plays a minimal role in modulating genioglossus activity in awake and sleeping rats (Sood S, Morrison JL, Liu H, and Horner RL. Am J Respir Crit Care Med 172: 1338-1347, 2005). This result therefore implies that medullary raphe neurons also play a minimal role in the normal physiological control of the HMN, but this has not yet been established because raphe neurons release other excitatory neurotransmitters onto respiratory motoneurons in addition to serotonin. This study tests the hypothesis that inhibition of medullary raphe serotonergic neurons with 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) suppresses genioglossus and diaphragm activities in awake and sleeping rats. Ten rats were implanted with electrodes to record sleep-wake states and genioglossus and diaphragm activities. Microdialysis probes were also implanted into the nucleus raphe obscurus (NRO). Experiments in 10 anesthetized and vagotomized rats were also performed using the same methodology. In anesthetized rats, microdialysis perfusion of 0.1 mM 8-OH-DPAT into the NRO decreased genioglossus activity by 60.7+/-9.0% and diaphragm activity by 13.3+/-3.4%. Diaphragm responses to 7.5% CO2 were also significantly reduced by 8-OH-DPAT. However, despite the robust effects observed in anesthetized and vagotomized rats, there was no effect of 0.1 mM 8-OH-DPAT on genioglossus or diaphragm activities in conscious rats awake or asleep. The results support the concept that endogenously active serotonergic medullary raphe neurons play a minimal role in modulating respiratory motor activity across natural sleep-wake states in freely behaving rodents. This result has implications for pharmacological strategies aiming to manipulate raphe neurons and endogenous serotonin in obstructive sleep apnea.