Differential Anaesthetic Effects following Microinjection of Thiopentone and Propofol into the Pons of Adult Rats: A Pilot Study

Identifying the central nervous system sites of action of anaesthetics is important for understanding the link between their molecular actions and clinical effects. The aim of the present pilot study was to compare the anaesthetic effect of bilateral microinjections of propofol and thiopentone (both 200 μg/μl, in Intralipid and 0.9% saline respectively) into a recently discovered anaesthetic-sensitive region in the rat brainstem, the “mesopontine tegmental anaesthetic area” (MPTA). Microinjections (1 μl per side) were made into the MPTA of fifteen male Sprague-Dawley rats. The effect of each agent on spontaneous behaviour, postural control and nociceptive responsiveness was subjectively assessed according to established criteria. The main finding was that thiopentone induced an “anaesthesia-like” state, including complete atonia and loss of righting ability, in 20% of the subjects. Overall, thiopentone significantly reduced postural control and had a moderate antinociceptive effect compared to saline microinjections (P<0.01 and 0.05, respectively, Wilcoxon test). In contrast, propofol did not induce “anaesthesia” in any animal tested, although a similar antinociceptive effect to that of thiopentone was observed (P<0.05, Wilcoxon test). In summary, propofol and thiopentone have different effects when microinjected into the MPTA. While both agents reduced reflex withdrawal to a nociceptive stimulus, only thiopentone induced an “anaesthesia-like” state.

Inhibition of the pontine Kölliker-Fuse nucleus reduces genioglossal activity elicited by stimulation of the retrotrapezoid chemoreceptor neurons

The Kölliker-Fuse (KF) region, located in the dorsolateral pons, projects to several brainstem areas involved in respiratory regulation, including the chemoreceptor neurons within the retrotrapezoid nucleus (RTN). Several lines of evidence indicate that the pontine KF region plays an important role in the control of the upper airways for the maintenance of appropriate airflow to and from the lungs. Specifically, we hypothesized that the KF region is involved in mediating the response of the hypoglossal motor activity to central respiratory chemoreflex activation and to stimulation of the chemoreceptor neurons within the RTN region. To test this hypothesis, we combined immunohistochemistry and physiological experiments. We found that in the KF, the majority of biotinylated dextran amine (BDA)-labeled axonal varicosities contained detectable levels of vesicular glutamate transporter-2 (VGLUT2), but few contained glutamic acid decarboxylase-67 (GAD67). The majority of the RTN neurons that were FluorGold (FG)-immunoreactive (i.e., projected to the KF) contained hypercapnia-induced Fos, but did not express tyrosine hydroxylase. In urethane-anesthetized sino-aortic denervated and vagotomized male Wistar rats, hypercapnia (10% CO2) or N-methyl-d-aspartate (NMDA) injection (0.1mM) in the RTN increased diaphragm (DiaEMG) and genioglossus muscle (GGEMG) activities and elicited abdominal (AbdEMG) activity. Bilateral injection of muscimol (GABA-A agonist; 2mM) into the KF region reduced the increase in DiaEMG and GGEMG produced by hypercapnia or NMDA into the RTN. Our data suggest that activation of chemoreceptor neurons in the RTN produces a significant increase in the genioglossus muscle activity and the excitatory pathway is dependent on the neurons located in the dorsolateral pontine KF region.

Prefrontal control of cerebellum-dependent associative motor learning

Behavioral studies have demonstrated that both medial prefrontal cortex (mPFC) and cerebellum play critical roles in trace eyeblink conditioning. However, little is known regarding the mechanism by which the two brain regions interact. By use of electrical stimulation of the caudal mPFC as a conditioned stimulus, we show evidence that persistent outputs from the mPFC to cerebellum are necessary and sufficient for the acquisition and expression of a trace conditioned response (CR)-like response. Specifically, the persistent outputs of caudal mPFC are relayed to the cerebellum via the rostral part of lateral pontine nuclei. Moreover, interfering with persistent activity by blockade of the muscarinic Ach receptor in the caudal mPFC impairs the expression of learned trace CRs. These results suggest an important way for the caudal mPFC to interact with the cerebellum during associative motor learning.

Rewarding and incentive motivational effects of excitatory amino acid receptor antagonists into the median raphe and adjacent regions of the rat

RATIONALE

The motivational process that regulates approach behavior toward salient distal stimuli (i.e., incentive motivation) plays a key role in voluntary behavior and motivational disorders such as addiction. This process may be mediated by many neurotransmitter systems and a network of many brain structures, including the median and dorsal raphe regions (MR and DR, respectively).

OBJECTIVE

We sought to examine whether the blockade of excitatory amino acid receptors in the MR and DR is rewarding, using intracranial self-administration, and whether the self-administration effect can be explained by drug's effectiveness to enhance incentive motivation, using a visual sensation seeking procedure.

RESULTS

Rats learned to self-administer the AMPA receptor antagonist ZK 200775 into the vicinity of the MR, DR, or medial oral pontine reticular regions, but not the ventral tegmental area. The NMDA receptor antagonist AP5 was also self-administered into the MR, while it was not readily self-administered into other regions. When ZK 200775 was noncontingently administered into the MR, rats markedly increased approach responses rewarded by brief illumination of a light stimulus. In addition, contingent administration of ZK 200775 into the MR induced a conditioning effect on approach responses.

CONCLUSIONS

Rats self-administer excitatory amino acid receptor antagonists into the MR and adjacent regions. Self-administration effect of AMPA receptor antagonists into the MR can be largely explained by the manipulation's properties to invigorate ongoing approach behavior and induces conditioned approach. Glutamatergic afferents to the median raphe and adjacent regions appear to tonically suppress incentive-motivational processes.

Role of lateral parabrachial opioid receptors in exercise-induced modulation of the hypotensive hemorrhage response in conscious male rats

Some of the benefits of exercise appear to be mediated through modulation of neuronal excitability in central autonomic control circuits. Previously, we identified that six weeks of voluntary wheel running had a protective effect during hemorrhage (HEM), limiting both the hypotensive phase of HEM and enhancing recovery. The present study was undertaken to evaluate the role of opioid release in the lateral parabrachial nucleus (LPBN) on the response to severe HEM in chronically exercised (EX, voluntary) versus sedentary (SED) controls. Male Sprague Dawley rats were allowed either free access to running wheels (EX) or normal cage conditions (SED). After 6 weeks of "training" animals were instrumented with a bilateral cannula directed toward the dorsolateral pons and arterial catheters. After a recovery period, animals underwent central microinjection of either vehicle (VEH; n=3/group) or the opioid receptor antagonist naloxone (NAL; n=6/group) followed by withdrawal of 30% of their total estimated blood volume. Following VEH injection, the drop in MAP during and following HEM was significantly attenuated in the EX vs SED animals. Alternatively, NAL microinjection in the dorsolateral pons (20 μM, 200-500 nl) reversed the beneficial effect of EX on the HEM response. NAL microinjection in SED rats did not significantly alter the response to HEM. These data suggest chronic voluntary EX has a beneficial effect on the autonomic response to severe HEM which is mediated, in part, via EX-induced plasticity of the opioid system within the dorsolateral pons.

Expression and function of serotonin 2A and 2B receptors in the mammalian respiratory network

Neurons of the respiratory network in the lower brainstem express a variety of serotonin receptors (5-HTRs) that act primarily through adenylyl cyclase. However, there is one receptor family including 5-HT_2A, 5-HT_2B, and 5-HT_2C receptors that are directed towards protein kinase C (PKC). In contrast to 5-HT_2ARs, expression and function of 5-HT_2BRs within the respiratory network are still unclear. 5-HT_2BR utilizes a Gq-mediated signaling cascade involving calcium and leading to activation of phospholipase C and IP3/DAG pathways. Based on previous studies, this signal pathway appears to mediate excitatory actions on respiration. In the present study, we analyzed receptor expression in pontine and medullary regions of the respiratory network both at the transcriptional and translational level using quantitative RT-PCR and self-made as well as commercially available antibodies, respectively. In addition we measured effects of selective agonists and antagonists for 5-HT_2ARs and 5-HT_2BRs given intra-arterially on phrenic nerve discharges in juvenile rats using the perfused brainstem preparation. The drugs caused significant changes in discharge activity. Co-administration of both agonists revealed a dominance of the 5-HT_2BR. Given the nature of the signaling pathways, we investigated whether intracellular calcium may explain effects observed in the respiratory network. Taken together, the results of this study suggest a significant role of both receptors in respiratory network modulation.

A restricted parabrachial pontine region is active during non-rapid eye movement sleep

The principal site that generates both rapid eye movement (REM) sleep and wakefulness is located in the mesopontine reticular formation, whereas non-rapid eye movement (NREM) sleep is primarily dependent upon the functioning of neurons that are located in the preoptic region of the hypothalamus. In the present study, we were interested in determining whether the occurrence of NREM might also depend on the activity of mesopontine structures, as has been shown for wakefulness and REM sleep. Adult cats were maintained in one of the following states: quiet wakefulness (QW), alert wakefulness (AW), NREM, or REM sleep induced by microinjections of carbachol into the nucleus pontis oralis (REM-carbachol). Subsequently, they were euthanized and single-labeling immunohistochemical studies were undertaken to determine state-dependent patterns of neuronal activity in the brainstem based upon the expression of the protein Fos. In addition, double-labeling immunohistochemical studies were carried out to detect neurons that expressed Fos as well as choline acetyltransferase, tyrosine hydroxylase, or GABA. During NREM, only a few Fos-immunoreactive cells were present in different regions of the brainstem; however, a discrete cluster of Fos+ neurons was observed in the caudolateral parabrachial region (CLPB). The number of Fos+ neurons in the CLPB during NREM was significantly greater (67.9±10.9, P<0.0001) compared with QW (8.0±6.7), AW (5.2±4.2), or REM-carbachol (8.0±4.7). In addition, there was a positive correlation (R=0.93) between the time the animals spent in NREM and the number of Fos+ neurons in the CLPB. Fos-immunoreactive neurons in the CLPB were neither cholinergic nor catecholaminergic; however, about 50% of these neurons were GABAergic. We conclude that a group of GABAergic and unidentified neurons in the CLPB are active during NREM and likely involved in the control of this behavioral state. These data open new avenues for the study of NREM, as well as for the explorations of interactions between these neurons that are activated during NREM and cells of the adjacent pontine tegmentum that are involved in the generation of REM sleep.

Hypofractionated radiotherapy in the treatment of diffuse intrinsic pontine glioma in children: a single institution's experience

We report herein our institutional experience in the treatment of diffuse intrinsic pontine glioma (DIPG) with a hypofractionated external-beam radiotherapy schedule. Between April 1996 and January 2004, 22 patients (age 2.9-12.5 years) with newly diagnosed DIPG were treated by hypofractionated radiation therapy delivering a total dose of 45 Gy in daily fractions of 3 Gy, given over 3 weeks. No other treatment was applied concomitantly. Fourteen of the 22 patients received the prescribed dose of 45 Gy in 15 fractions of 3 Gy, and 2 patients received a total dose of 60 and 45 Gy with a combination of two different beams (photons and neutrons). In five cases the daily fraction was modified to 2 Gy due to intolerance, and one patient died due to serious intracranial hypertension after two fractions of 3 Gy and one of 2 Gy. Among 22 children, 14 patients showed clinical improvement, usually starting in the second week of treatment. No grade 3 or 4 acute toxicity from radiotherapy was observed. No treatment interruption was needed. In six patients, steroids could be discontinued within 1 month after the end of radiotherapy. Median time to progression and median overall survival were 5.7 months and 7.6 months, respectively. External radiotherapy with a radical hypofractionated regimen is feasible and well tolerated in children with newly diagnosed DIPG. However, this regimen does not seem to change overall survival in this setting. It could represent a short-duration alternative to more protracted regimens.

Benzodiazepine receptor agonists cause drug-specific and state-specific alterations in EEG power and acetylcholine release in rat pontine reticular formation

STUDY OBJECTIVES

Benzodiazepine (BDZ) and non-benzodiazepine (NBDZ) hypnotics enhance GABAergic transmission and are widely used for the treatment of insomnia. In the pontine reticular formation (PRF), GABA inhibits rapid eye movement (REM) sleep and acetylcholine (ACh) release. No previous studies have characterized the effects of BDZ and NBDZ hypnotics on ACh release in the PRF. This study tested 2 hypotheses: (1) that microdialysis delivery of zolpidem, eszopiclone, and diazepam to rat PRF alters ACh release in PRF and electroencephalographic (EEG) delta power and (2) that intravenous (i.v.) administration of eszopiclone to non-anesthetized rat alters ACh release in the PRF, sleep, and EEG delta power.

DESIGN

A within- and between-groups experimental design.

SETTING

University of Michigan.

PATIENTS OR PARTICIPANTS

Adult male Crl:CD*(SD) (Sprague-Dawley) rats (n = 57).

INTERVENTIONS

In vivo microdialysis of the PRF in rats anesthetized with isoflurane was used to derive the concentration-response effects of zolpidem, eszopiclone, and diazepam on ACh release. Chronically instrumented rats were used to quantify the effects of eszopiclone (3 mg/kg, i.v.) on ACh release in the PRF, sleep-wake states, and cortical EEG power.

MEASUREMENTS AND RESULTS

ACh release was significantly increased by microdialysis delivery to the PRF of zolpidem and eszopiclone but not diazepam. EEG delta power was increased by zolpidem and diazepam but not by eszopiclone administered to the PRF. Eszopiclone (i.v.) decreased ACh release in the PRF of both anesthetized and non-anesthetized rats. Eszopiclone (i.v.) prevented REM sleep and increased EEG delta power.

CONCLUSION

The concentration-response data provide the first functional evidence that multiple GABA(A) receptor subtypes are present in rat PRF. Intravenously administered eszopiclone prevented REM sleep, decreased ACh release in the PRF, and increased EEG delta power. The effects of eszopiclone are consistent with evidence that ACh release in the PRF is lower during NREM sleep than during REM sleep, and with data showing that cholinergic stimulation of the PRF activates the cortical EEG.

The pontine respiratory group, particularly the Kölliker-Fuse nucleus, mediates phases of the hypoxic ventilatory response in unanesthetized goats

The objective of the present study was to test the hypothesis that, in the in vivo awake goat model, perturbation/lesion in the pontine respiratory group (PRG) would decrease the sensitivity to hypercapnia and hypoxia. The study reported herein was part of two larger studies in which cholinergic modulation in the PRG was attenuated by microdialysis of atropine and subsequently ibotenic acid injections neurotoxically lesioned the PRG. In 14 goats, cannula were bilaterally implanted into either the lateral (n=4) or medial (n=4) parabrachial nuclei or the Kölliker-Fuse nucleus (KFN, n=6). Before and after cannula implantation, microdialysis of atropine, and injection of ibotenic acid, hypercapnic and hypoxic ventilatory sensitivities were assessed. Hypercapnic sensitivity was assessed by three 5-min periods at 3, 5, and 7% inspired CO2. In all groups of goats, CO2 sensitivity was unaffected (P>0.05) by any PRG perturbations/lesions. Hypoxic sensitivity was assessed with a 30-min period at 10.8% inspired O2. The response to hypoxia was typically triphasic, with a phase 1 increase in pulmonary ventilation, a phase 2 roll-off, and a phase 3 prolonged increase associated with shivering and increased metabolic rate and body temperature. In all groups of goats, the phase 1 of the hypoxic ventilatory responses was unaffected by any PRG perturbations/lesions, and there were no consistent effects on the phase 2 responses. However, in the KFN group of goats, the phase 3 ventilatory, shivering, metabolic rate, and temperature responses were markedly attenuated after the atropine dialysis studies, and the attenuation persisted after the ibotenic acid studies. These findings support an integrative or modulatory role for the KFN in the phase 3 responses to hypoxia.

The effects of dexmedetomidine dosage on cerebral vasospasm in a rat subarachnoid haemorrhage model

We investigated the effect of two different doses of dexmedetomidine on vasospasm in a rat model of subarachnoid haemorrhage (SAH). SAH was induced by injecting 0.3 mL blood into the cisterna magna in all rat groups except the control (Group C). At 1 hour and 24 hours after SAH, 5 microg/kg dexmedetomidine was given to group D5, and 10 microg/kg dexmedetomidine was given to group D10. No medication was administered to the haemorrhage group (Group H). Malondialdehyde (MDA) and paraoxonase (PON) levels were measured at 48 hours after SAH. Mean wall thickness (MWT), mean luminal diameter (MLD), and proliferating cell nuclear antigen (PCNA) expression of the basilar artery were evaluated. MDA levels and MWT were lower in the dexmedetomidine groups. The lowest MDA levels and MWT were found in Group D10. The MLD was lowest in Group H. PCNA expression was observed only in Group D10. We concluded that dexmedetomidine reduces oxidative stress and vasospasm following SAH in a dose-dependent manner.

The role of the pontine respiratory complex in the response to intermittent hypoxia

These experiments were designed to determine the effects of EEG state on the response of rats to intermittent hypoxia and to test the hypotheses that short-term potentiation (STP) and ventilatory long term facilitation (vLTF) are state dependent; and that neurons with NMDA receptors in the dorso-ventral pontine respiratory group (dvPRG) modulate the development of STP and vLTF in rats. Low-doses of urethane anaesthesia (<1.3g/kg) that do not cause significant respiratory depression or reductions in sensitivity to hypoxia result in cycling between EEG states that superficially resemble wake and slow wave sleep in rats and are accompanied by changes in breathing pattern that closely resemble those seen when unanaesthetized rats cycle between wake and SWS. When changes between these states were accounted for, intermittent, poikilocapnic hypoxia did not produce a significant vLTF. However, there was a persistent STP of tidal volume and vLTF did develop after blockade of NMDAr in the region of the PBrKF complex by microinjection of MK-801. Blockade of NMDA-type glutamate receptor-mediated processes in the dorsal pons also caused animals to cycle into State III, but did not alter the response to either continuous or intermittent hypoxia indicating that the response to hypoxia was not state dependent. This shows that neurons in the region of the PRG inhibit STP and vLTF, but no longer do so if PRG NMDA receptor activation is blocked.

Coupling changes in cortical and pontine sigma and theta frequency oscillations following monoaminergic lesions in rat

PURPOSE

Sigma and theta frequency electroencephalogram (EEG) oscillations exhibit substantial and well-recognized shifts with transitions across sleep and wake states. We aimed in this study to test the changes in coupling between these characteristic oscillations of non-rapid-eye-movement (NREM)/rapid-eye-movement (REM) sleep within and between cortical and pontine EEGs following monoaminergic lesion, by using the Pearson's product-moment correlation coefficients.

METHODS

Experiments were performed in 14 adult, male Sprague Dawley rats chronically instrumented for sleep recording. We lesioned the dorsal raphe nucleus axon terminals in four rats using PCA neurotoxin (p-chloroamphetamine; Sigma-Aldrich, MO) administered as two intraperitoneal (IP) injections (6 mg/kg) 24 h apart. Lesioning of locus coeruleus axon terminals was performed in five rats using DSP-4 neurotoxin (N-2-chloroethyl-N-ethyl-2-bromobenzilamine; Sigma-Aldrich, MO) in a single IP dose of 50 mg/kg.

RESULTS & CONCLUSIONS

Our previous study [Saponjic et al., Physiol Behav 90:1-10, 2007] demonstrated that these systemically induced monoaminergic lesions failed to produce significant changes in sleep/wake distribution from control conditions. The present study, by using spectral analysis and by examining the Pearson's correlation coefficients and their approximate probability density (APD) distribution profiles in control and lesion condition, demonstrates significant augmentation of the sigma/theta coupling strength, an inversion of cortical sigma/theta coupling direction and emergence of an additional sigma/theta coupling "mode" specific to the post-lesion state only within the cortex. By using the Pearson's correlation coefficients and their APD profiles, instead of classical sleep/wake distribution analysis, as a measure of direction and strength of sigma/theta coupling within and between cortex and pons, we were able to uncover the impact of a tonically decreased level of brain monoamines as altered strength and mode of coupling between sigma and theta oscillations. Specifically, a new mode of sigma/theta coupling emerged following lesion, which was specific to NREM sleep, suggests that loss of monoaminergic signaling interferes with NREM sleep consolidation. Our results also indicate an importance of monoamines in control of the sleep spindle and theta rhythm generators.

Stress sensitive female macaques have decreased fifth Ewing variant (Fev) and serotonin-related gene expression that is not reversed by citalopram

Female cynomolgus monkeys exhibit different degrees of reproductive dysfunction with moderate metabolic and psychosocial stress. When stressed with a paradigm of relocation and diet for 60 days or two menstrual cycles, highly stress resilient monkeys (HSR) continued to ovulate during the stress cycles whereas stress sensitive monkeys (SS) did not. After cessation of stress, monkeys characterized as HSR or SS were administered placebo (PL) or S-citalopram (CIT) for 15 weeks at doses that normalized ovarian steroid secretion in the SS animals and that maintained blood CIT levels in a therapeutic range. After euthanasia, the brain was perfused with 4% paraformaldehyde. The pontine midbrain was blocked and sectioned at 25 microm. The expression of four genes pivotal to serotonin neural function was assessed in the four groups of monkeys (n=4/group). Fev (fifth Ewing variant) ETS transcription factor, tryptophan hydroxylase 2 (TPH2), the serotonin reuptake transporter (SERT), and the 5HT1A autoreceptor were determined at 7-8 levels of the dorsal raphe nucleus with in situ hybridization (ISH) using radiolabeled- and digoxygenin-incorporated riboprobes. Positive pixel area and cell number were measured with Slidebook 4.2 in the digoxigenin assay for Fev. Optical density (OD) and positive pixel area were measured with NIH Image software in the radiolabeled assays for TPH2, SERT and 5HT1A. All data were analyzed with two-way ANOVA. SS monkeys had significantly fewer Fev-positive cells and lower Fev-positive pixel area in the dorsal raphe than HSR monkeys. SS monkeys also had significantly lower levels of TPH2, SERT and 5HT1A mRNAs in the dorsal raphe nucleus than HSR monkeys. However, CIT did not alter the expression of either Fev, TPH2, SERT or 5HT1A mRNAs. These data suggest that SS monkeys have fewer serotonin (5-HT) neurons than HSR monkeys, and that they have deficient Fev expression, which in turn, leads to deficient TPH2, SERT and 5HT1A expression. In addition, the therapeutic effect of CIT is probably achieved through mechanisms other than alteration of 5-HT-related gene expression.

Hypocretin mechanisms in nicotine addiction: evidence and speculation

BACKGROUND

The hypocretin/orexin system has been implicated in arousal mechanisms, sleep, and sleep disorders, including narcolepsy, and more recently in drug addiction. Theoretically, hypocretin (hcrt) mechanisms appear to be potential substrates for nicotine addiction: arousal and attentional mechanisms influence use and withdrawal symptoms, and hcrt systems overlap anatomically with a number of brain regions associated with nicotine addiction.

OBJECTIVE

This review summarizes the studies that have examined hcrt mechanisms in the effects of nicotine and describes hcrt innervation of, and effects in, several brain regions implicated in nicotine addiction. The review speculates on the possible mechanisms by which hcrt may contribute to nicotine addiction in these regions, with the objective of encouraging research in this area.

RESULTS

In a small literature, both experimenter-administered and self-administered nicotine have been shown to elicit or depend on hcrt signaling. However, although untested in experimental designs, there is compelling evidence that hcrt mechanisms in the ventral tegmental area, the pontine region, thalamocortical circuits, the prefrontal cortex, and the amygdala could have a broad influence on nicotine addiction.

CONCLUSIONS

Evidence reviewed leads to the conclusion that hcrt mechanisms could mediate several dimensions of nicotine addiction, including a multi-faceted regulation of mesocorticolimbic dopaminergic function, but beyond dopaminergic mechanisms, hcrt could influence nicotine use and relapse during abstinence through broadly based arousal/attentional effects. These speculative ideas need to be examined experimentally; the potential gains are a more thorough understanding of the pathophysiology of nicotine addiction, and the discovery of novel targets for the development of pharmacotherapeutics.

Activating mu-opioid receptors in the lateral parabrachial nucleus increases c-Fos expression in forebrain areas associated with caloric regulation, reward and cognition

The pontine parabrachial nucleus (PBN) has been implicated in the modulation of ingestion and contains high levels of mu-opioid receptors (MOPRs). In previous work, stimulating MOPRs by infusing the highly selective MOPR agonist [d-Ala2, N-Me-Phe4, Gly5-ol]enkephalin (DAMGO) into the lateral parabrachial region (LPBN) increased food intake. The highly selective MOPR antagonist d-Phe-Cys-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) prevented the hyperphagic action of DAMGO. The present experiments aimed to analyze both the pattern of neural activation and the underlying cellular processes associated with MOPR activation in the LPBN. Male Sprague-Dawley rats received a unilateral microinfusion of a nearly maximal hyperphagic dose of DAMGO into the LPBN. We then determined the level of c-Fos immunoreactivity in regions throughout the brain. MOPR activation in the LPBN increased c-Fos in the LPBN and in the nucleus accumbens, hypothalamic arcuate nucleus, paraventricular nucleus of the thalamus and hippocampus. Pretreatment with CTAP prevented the increase in c-Fos translation in each of these areas. CTAP also prevented the coupling of MOPRs to their G-proteins which was measured by [(35)S] guanosine 5'-O-[gamma-thio]triphosphate ([(35)S]GTPgammaS) autoradiography. Together, these data strongly suggest that increasing the coupling of MOPRs to their G-proteins in the LPBN disinhibits parabrachial neurons which subsequently leads to excitation of neurons in regions associated with caloric regulation, ingestive reward and cognitive processes in feeding.

Local antagonism of intertrigeminal region metabotropic glutamate receptors exacerbates apneic responses to intravenous serotonin

Injections of a broad spectrum glutamate receptor antagonist into the pontine intertrigeminal region (ITR) exacerbate vagal reflex apnea produced by intravenous serotonin infusion. This effect is not reproduced by ITR injections with either NMDA or AMPA receptor antagonists. Here, we tested the hypothesis that ITR injection with a metabotropic glutamate antagonist would alter respiratory responses to serotonin (5-HT) intravenous infusions. In anesthetized adult male rats (N=20; Sprague-Dawley) AIDA (1-aminoindan-1,5-dicarboxylic acid), a specific antagonist of the type 1 metabotropic glutamate receptor (mGlu1R), was microinjected unilaterally into the ITR to block 5-HT evoked apnea. Respiratory pattern changes evoked by ITR-glutamate injection and by intravenous serotonin (5-HT) infusion (0.5 microl, 0.05 M; or 2.5x10(-8) mol) were characterized according to apnea expression and duration, as well as coefficients of variation for breath duration (CVTT) and amplitude (CVVT) before and after ITR AIDA injection. Unilateral AIDA blockade of the ITR significantly increased the duration of apnea evoked by 5-HT infusion (p<0.03 for each dose tested) during the 30s following infusion in a dose-dependent fashion, with the two highest doses resulting in intermittent apneas for at least 10 min following a bolus 5-HT infusion. Similar prolonged increases in CVTT and CVVT with respect to control were associated with ITR AIDA injections. These findings suggest that brief perturbations of vagal afferent pathways can produce ongoing respiratory dysrhythmia, including spontaneous apnea, and that glutamatergic neurotransmission within ITR may be important for damping such disturbances. The present observations also suggest that such respiratory damping may be mediated by mGlu1 receptors. These findings extend our understanding of the role of the intertrigeminal region in modulating respiratory reflexes.

Lateral parabrachial nucleus mediates shortening of expiration during hypoxia

Acute hypoxia elicits complex time-dependent responses including rapid augmentation of inspiratory drive, shortening of inspiratory and expiratory durations (T(I), T(E)), and short-term potentiation and depression. The central pathways mediating these varied effects are largely unknown. Here, we show that the lateral parabrachial nucleus (LPBN) of the dorsolateral pons specifically mediates T(E)-shortening during hypoxia and not other hypoxic response components. Twelve urethane-anesthetized and vagotomized adult Sprague-Dawley rats were exposed to 1-min poikilocapnic hypoxia before and after unilateral kainic acid or bilateral electrolytic lesioning of the LPBN. Bilateral lesions resulted in a significant increase in baseline T(E) under hyperoxia. After unilateral or bilateral lesions, the decrease in T(E) during hypoxia was markedly attenuated without appreciable changes in all other hypoxic response components. These findings add to the mounting evidence that the central processing of peripheral chemoafferent inputs is segregated into parallel integrator and differentiator (low-pass and high-pass filter) pathways that separately modulate inspiratory drive, T(I), T(E) and resultant short-term potentiation and depression.

Respiratory response to systemic inhibition of the Na+/H+ exchanger type 3 in intact rats

The Na+/H+ exchangers (NHEs) are a family of antiporters involved in the maintenance of neural steady-state intracellular pH. The NHE3 seems to be the predominant subtype in central chemosensitive cells. We aimed to analyze the effect of a selective NHE3 inhibition on the respiratory pattern in spontaneously breathing rats with intact vagi. Rats were intravenously infused for 10 min with the selective NHE3 inhibitor AVE1599 (Aventis Pharma Deustchland, 0.5 and 2 mg/kg) or with phosphate buffer. Whole-body plethysmography was used to monitor breathing pattern before, during, and up to 30 min after the drug infusion. Immunohistochemistry for the c-Fos protein was performed in the animal brains and c-Fos-positive cells were counted along the brainstem. Selective NHE3 inhibition induced a significant increase in the respiratory frequency and in the number of c-Fos immunopositive cells in the lateral parabrachial nucleus, the pre-Bötzinger complex and a rostral extension of the retrotrapezoid nucleus/parapyramidal region (p<0.05, ANOVA). We conclude that systemic administration of AVE1599 increases respiratory frequency and activates ponto-medullary areas implicated in the central control of breathing and chemoreception.

Blockade of GABA, type A, receptors in the rat pontine reticular formation induces rapid eye movement sleep that is dependent upon the cholinergic system

The brainstem reticular formation is an area important to the control of rapid eye movement (REM) sleep. The antagonist of GABA-type A (GABA(A)) receptors, bicuculline methiodide (BMI), injected into the rat nucleus pontis oralis (PnO) of the reticular formation resulted in a long-lasting increase in REM sleep. Thus, one factor controlling REM sleep appears to be the number of functional GABA(A) receptors in the PnO. The long-lasting effect produced by BMI may result from secondary influences on other neurotransmitter systems known to have long-lasting effects. To study this question, rats were surgically prepared for chronic sleep recording and additionally implanted with guide cannulas aimed at sites in the PnO. Multiple, 60 nl, unilateral injections were made either singly or in combination. GABA(A) receptor antagonists, BMI and gabazine (GBZ), produced dose-dependent increases in REM sleep with GBZ being approximately 35 times more potent than BMI. GBZ and the cholinergic agonist, carbachol, produced very similar results, both increasing REM sleep for about 8 h, mainly through increased period frequency, with little reduction in REM latency. Pre-injection of the muscarinic antagonist, atropine, completely blocked the REM sleep-increase by GBZ. GABAergic control of REM sleep in the PnO requires the cholinergic system and may be acting through presynaptic modulation of acetylcholine release.

Differential involvement of opioidergic and serotonergic systems in the antinociceptive activity of N-arachidonoyl-phenolamine (AM404) in the rat: comparison with paracetamol

It is recognized that paracetamol undergoes a metabolic transformation to N-arachydonylphenolamine (AM404), a CB(1) receptor ligand and anandamide uptake inhibitor. Using hot-plate and paw pressure tests, we decided to establish whether AM404 may act through opioidergic and serotonergic mechanisms. Thus, we pretreated rats with opioid mu(1) (naloxonazine) and kappa (MR2266) or 5-HT(1A) (NAN-190), 5-HT(2) (ketanserin), and 5-HT(3) (ondansetron) receptor antagonists. We investigated the possible changes in 5-hydroxyindoleacetic acid/serotonin ratio in the frontal cortex and pons. The antinociceptive effect of AM404 (10 mg/kg, intraperitoneally) or paracetamol (400 mg/kg, intraperitoneally) in either test was abolished by naloxonazine or MR2266. Ondansetron prevented AM404 activity; NAN-190 and ketanserin were ineffective. Ketanserin antagonized paracetamol activity; NAN-190 and ondansetron were inactive. AM404 did not change serotonergic activity, while paracetamol decreased serotonin turnover. The diverse antinociceptive potency of the compounds might be explained by the different influence on the serotonergic system, despite a similar involvement of opioidergic one.

Role of the serotoninergic system in the sodium appetite control

The present article reviews the role of the serotoninergic system in the regulation of the sodium appetite. Data from the peripheral and icv administration of serotoninergic (5-HTergic) agents showed the participation of 5-HT2/3 receptors in the modulation of sodium appetite. These observations were extended with the studies carried out after brain serotonin depletion, lesions of DRN and during blockade of 5-HT2A/2C receptors in lateral parabrachial nucleus (LPBN). Brain serotonin depletion and lesions of DRN increased the sodium appetite response, in basal conditions, after sodium depletion and hypovolemia or after beta-adrenergic stimulation as well. These observations raised the hypothesis that the suppression of ascending pathways from the DRN, possibly, 5-HTergic fibers, modifies the angiotensinergic or sodium sensing mechanisms of the subfornical organ involved in the control of the sodium appetite. 5-HTergic blockade in LPBN induced to similar results, particularly those regarded to the natriorexigenic response evoked by volume depletion or increase of the hypertonic saline ingestion induced by brain angiotensinergic stimulation. In conclusion, many evidences lead to acceptation of an integrated participation resulting of an interaction, between DRN and LPBN, for the sodium appetite control.

Enhancement of meal-associated hypertonic NaCl intake by moxonidine into the lateral parabrachial nucleus

alpha2-Adrenoceptor activation with moxonidine (alpha2-adrenergic/imidazoline receptor agonist) into the lateral parabrachial nucleus (LPBN) enhances angiotensin II/hypovolaemia-induced sodium intake and drives cell dehydrated rats to ingest hypertonic sodium solution besides water. Angiotensin II and osmotic signals are suggested to stimulate meal-induced water intake. Therefore, in the present study we investigated the effects of bilateral injections of moxonidine into the LPBN on food deprivation-induced food intake and on meal-associated water and 0.3M NaCl intake. Male Holtzman rats with cannulas implanted bilaterally into the LPBN were submitted to 14 or 24h of food deprivation with water and 0.3M NaCl available (n=6-14). Bilateral injections of moxonidine (0.5nmol/0.2microl) into the LPBN increased meal-associated 0.3M NaCl intake (11.4+/-3.0ml/120min versus vehicle: 2.2+/-0.9ml/120min), without changing food intake (11.1+/-1.2g/120min versus vehicle: 11.2+/-0.9g/120min) or water intake (10.2+/-1.5ml/120min versus vehicle: 10.4+/-1.2ml/120min) by 24h food deprived rats. When no food was available during the test, moxonidine (0.5nmol) into the LPBN of 24h food-deprived rats produced no change in 0.3M NaCl intake (1.0+/-0.6ml/120min versus vehicle: 1.8+/-1.1ml/120min), nor in water intake (0.2+/-0.1ml/120min versus vehicle: 0.6+/-0.3ml/120min). The results suggest that signals generated during a meal, like dehydration, for example, not hunger, induce hypertonic NaCl intake when moxonidine is acting in the LPBN. Thus, activation of LPBN inhibitory mechanisms seems necessary to restrain sodium intake during a meal.