µ-Opioid Receptor Activation at the Dorsal Reticular Nucleus Shifts Diffuse Noxious Inhibitory Controls to Hyperalgesia in Chronic Joint Pain in Male Rats.

BACKGROUND: The dorsal reticular nucleus is a pain facilitatory area involved in diffuse noxious inhibitory control (DNIC) through opioidergic mechanisms that are poorly understood. The hypothesis was that signaling of µ-opioid receptors is altered in this area with prolonged chronic inflammatory pain and that this accounts for the loss of DNICs occurring in this condition. METHODS: Monoarthritis was induced in male Wistar rats (n = 5 to 9/group) by tibiotarsal injection of complete Freund's adjuvant. The immunolabeling of µ-opioid receptors and the phosphorylated forms of µ-opioid receptors and cAMP response element binding protein was quantified. Pharmacologic manipulation of µ-opioid receptors at the dorsal reticular nucleus was assessed in DNIC using the Randall-Selitto test. RESULTS: At 42 days of monoarthritis, µ-opioid receptor labeling decreased at the dorsal reticular nucleus, while its phosphorylated form and the phosphorylated cAMP response element binding protein increased. [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin acetate (DAMGO) enhanced DNIC analgesia in normal animals (means ± SD: pre-DNIC: 126.9 ± 7.0 g; DNIC - DAMGO: 147.5 ± 8.0 g vs. DNIC + DAMGO: 198.1 ± 19.3 g; P < 0.001), whereas it produced hyperalgesia in monoarthritis (pre-DNIC: 67.8 ± 7.5 g; DNIC - DAMGO: 70.6 ± 7.7 g vs. DNIC + DAMGO: 32.2 ± 2.6 g; P < 0.001). An ultra-low dose of naloxone, which prevents the excitatory signaling of the µ-opioid receptor, restored DNIC analgesia in monoarthritis (DNIC - naloxone: 60.0 ± 6.1 g vs. DNIC + naloxone: 98.0 ± 13.5 g; P < 0.001), compared to saline (DNIC - saline: 62.5 ± 5.2 g vs. DNIC + saline: 64.2 ± 3.8 g). When injected before DAMGO, it restored DNIC analgesia and decreased the phosphorylated cAMP response element binding protein in monoarthritis. CONCLUSIONS: The dorsal reticular nucleus is likely involved in a facilitatory pathway responsible for DNIC hyperalgesia. The shift of µ-opioid receptor signaling to excitatory in this pathway likely accounts for the loss of DNIC analgesia in monoarthritis.

Effects of α-Synuclein Monomers Administration in the Gigantocellular Reticular Nucleus on Neurotransmission in Mouse Model.

The aim of the study was to examine the Braak's hypothesis to explain the spreading and distribution of the neuropathological changes observed in the course of Parkinson's disease among ascending neuroanatomical regions. We investigated the neurotransmitter levels (monoamines and amino acid concentration) as well as tyrosine hydroxylase (TH) and transglutaminase-2 (TG2) mRNA expression in the mouse striata (ST) after intracerebral α-synuclein (ASN) administration into gigantocellular reticular nucleus (Gi). Male C57BL/10 Tar mice were used in this study. ASN was administrated by stereotactic injection into Gi area (4 µl; 1 µg/µl) and mice were decapitated after 1, 4 or 12 weeks post injection. The neurotransmitters concentration in ST were evaluated using HPLC detection. TH and TG2 mRNA expression were examined by Real-Time PCR method. At 4 and 12 weeks after ASN administration we observed decrease of DA concentration in ST relative to control groups and we found a significantly higher concentration one of the DA metabolites-DOPAC. At these time points, we also noticed the increase in DA turnover determined as DOPAC/DA ratio. Additionally, at 4 and 12 weeks after ASN injection we noted decreasing of TH mRNA expression. Our findings corresponds with the Braak's theory about the presence of the first neuropathological changes within brainstem and then with time affecting higher neuroanatomical regions. These results obtained after administration of ASN monomers to the Gi area may be useful to explain the pathogenesis of Parkinson's disease.

[Myoclonus as a movement disorder]. / Myoklonien als Bewegungsstörung.

Myoclonus is often a diagnostic and therapeutic challenge due to its broad phenomenological variability and limited therapeutic options. This article gives a short survey and characterizes in detail two common types of myoclonus, cortical myoclonus and reticular reflex myoclonus. Clinical testing and electrophysiological investigations provide relevant local diagnostic indications for the generating structure(s). Such indications would influence not only the strategies of neuroimaging and laboratory investigations aimed at clarifying the underlying cause but also the selection of drugs to suppress myoclonus.

Behavioral anxiolysis without reduction of hippocampal theta frequency after histamine application in the lateral septum of rats.

Hippocampal theta activity is linked to various processes, including locomotion, learning and memory, and defense and affect (i.e., fear and anxiety). Interestingly, all classes of clinically effective anxiolytics, as well as experimental compounds that decrease anxiety in pre-clinical animal models of anxiety, reduce the frequency of hippocampal theta activity elicited by stimulation of the reticular formation in freely behaving or anesthetized animals. In the present experiments, we found that bilateral histamine infusions (0.5 µg/hemisphere) into the lateral septum (LS) of rats decreased anxiety-like responses in two models of anxiety, the elevated plus maze and novelty-induced suppression of feeding test. Surprisingly, these same infusions significantly increased hippocampal theta frequency elicited by reticular stimulation in urethane-anesthetized rats. In contrast to these findings, additional experiments showed that the clinically effective anxiolytic buspirone (40 mg/kg, i.p.) reduced theta frequency, confirming previous observations. Taken together, the dissociation of behavioral anxiolysis and theta frequency reduction noted here suggest that hippocampal theta frequency is not a direct index of anxiety levels in rodents. Further, the mechanisms underlying the behavioral and physiological effects elicited by histamine in the LS require further study.

Intrinsic connections within the pedunculopontine tegmental nucleus are critical to the elaboration of post-ictal antinociception.

This study investigated the intrinsic connections of a key-structure of the endogenous pain inhibitory system, the pedunculopontine tegmental nucleus (PPTN), in post-ictal antinociceptive process through synaptic inactivation of the PPTN with cobalt chloride. Male Wistar rats (n = 6 or 7 per group), weighing 250-280 g, had the tail-flick baseline recorded and were submitted to a stereotaxic surgery for the introduction of a guide-cannula aiming at the PPTN. After 5 days of postoperative recovery, cobalt chloride (1 mM/0.2 µL) or physiological saline (0.2 µL) were microinjected into the PPTN and after 5 min, the tail-withdrawal latency was measured again at 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120 min after seizures evoked by intraperitoneal injection of pentylenetetrazole (64 mg/kg). The synaptic inactivation of PPTN decreased the post-ictal antinociceptive phenomenon, suggesting the involvement of PPTN intrinsic connections in the modulation of pain, during tonic-clonic seizures. These results showed that the PPTN may be crucially involved in the neural network that organizes the post-ictal analgesia.

Role of glutamate receptors in the dorsal reticular nucleus in formalin-induced secondary allodynia.

The role of glutamate receptors present in the medullary dorsal reticular nucleus (DRt) in the formalin test and formalin-induced secondary nociception was studied in rats. Secondary mechanical allodynia was assessed with von Frey filaments applied to the rat's hindpaw, and secondary thermal hyperalgesia was evaluated with the tail-immersion test. The selective glutamate receptor antagonists MK801 (N-methyl-D-aspartate receptor antagonist), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (AMPA/KA receptor antagonist) and A841720 (metabotropic glutamate 1 receptor antagonist) were injected into the DRt before or 6 days after formalin injection in the rat. In the formalin test, the three antagonists significantly reduced the number of flinches in both phases of the test. DRt microinjection of MK801 or A841720, but not of CNQX, reduced both secondary nociceptive behaviors. Moreover, pre-treatment with the three antagonists injected into the DRt prevented the development of secondary mechanical allodynia and secondary thermal hyperalgesia. Similarly, in these rats, the number of c-Fos-like immunoreactive neurons were markedly reduced in both the superficial and deep lamina of the dorsal horn. Our findings support the role of DRt as a pain facilitator in acute and chronic pain states, and suggest a key role of glutamate receptors during the development and maintenance of formalin-induced secondary allodynia.

Adenosine A(1) receptors in mouse pontine reticular formation depress breathing, increase anesthesia recovery time, and decrease acetylcholine release.

BACKGROUND: Clinical and preclinical data demonstrate the analgesic actions of adenosine. Central administration of adenosine agonists, however, suppresses arousal and breathing by poorly understood mechanisms. This study tested the two-tailed hypothesis that adenosine A1 receptors in the pontine reticular formation (PRF) of C57BL/6J mice modulate breathing, behavioral arousal, and PRF acetylcholine release. METHODS: Three sets of experiments used 51 mice. First, breathing was measured by plethysmography after PRF microinjection of the adenosine A1 receptor agonist N-sulfophenyl adenosine (SPA) or saline. Second, mice were anesthetized with isoflurane and the time to recovery of righting response (RoRR) was quantified after a PRF microinjection of SPA or saline. Third, acetylcholine release in the PRF was measured before and during microdialysis delivery of SPA, the adenosine A1 receptor antagonist 1, 3-dipropyl-8-cyclopentylxanthine, or SPA and 1, 3-dipropyl-8-cyclopentylxanthine. RESULTS: First, SPA significantly decreased respiratory rate (-18%), tidal volume (-12%), and minute ventilation (-16%). Second, SPA concentration accounted for 76% of the variance in RoRR. Third, SPA concentration accounted for a significant amount of the variance in acetylcholine release (52%), RoRR (98%), and breathing rate (86%). 1, 3-dipropyl-8-cyclopentylxanthine alone caused a concentration-dependent increase in acetylcholine, a decrease in RoRR, and a decrease in breathing rate. Coadministration of SPA and 1, 3-dipropyl-8-cyclopentylxanthine blocked the SPA-induced decrease in acetylcholine and increase in RoRR. CONCLUSIONS: Endogenous adenosine acting at adenosine A1 receptors in the PRF modulates breathing, behavioral arousal, and acetylcholine release. The results support the interpretation that an adenosinergic-cholinergic interaction within the PRF comprises one neurochemical mechanism underlying the wakefulness stimulus for breathing.

Neural correlates of an injury-free model of central sensitization induced by opioid withdrawal in humans.

Preclinical evidence suggests that opioid withdrawal induces central sensitization (CS) that is maintained by supraspinal contributions from the descending pain modulatory system (DPMS). Here, in healthy human subjects we use functional magnetic resonance imaging to study the supraspinal activity during the withdrawal period of the opioid remifentanil. We used a crossover design and thermal stimuli on uninjured skin to demonstrate opioid withdrawal-induced hyperalgesia (OIH) without a CS-inducing peripheral stimulus. Saline was used in the control arm to account for effects of time. OIH in this injury-free model was observed in a subset of the healthy subjects (responders). Only in these subjects did opioid infusion and withdrawal induce a rise in activity in the mesencephalic-pontine reticular formation (MPRF), an area of the DPMS that has been previously shown to be involved in states of CS in humans, which became significant during the withdrawal phase compared with nonresponders. Paradoxically, this opioid withdrawal-induced rise in MPRF activity shows a significant negative correlation with the behavioral OIH score indicating a predominant inhibitory role of the MPRF in the responders. These data illustrate that in susceptible individuals central mechanisms appear to regulate the expression of OIH in humans in the absence of tissue injury, which might have relevance for functional pain syndromes where a peripheral origin for the pain is difficult to identify.

Enhanced catabolism to acetaldehyde in rostral ventrolateral medullary neurons accounts for the pressor effect of ethanol in spontaneously hypertensive rats.

We have previously shown that ethanol microinjection into the rostral ventrolateral medulla (RVLM) elicits sympathoexcitation and hypertension in conscious spontaneously hypertensive rats (SHRs) but not in Wistar-Kyoto (WKY) rats. In this study, evidence was sought to implicate the oxidative breakdown of ethanol in this strain-dependent hypertensive action of ethanol. Biochemical experiments revealed significantly higher catalase activity and similar aldehyde dehydrogenase (ALDH) activity in the RVLM of SHRs compared with WKY rats. We also investigated the influence of pharmacological inhibition of catalase (3-aminotriazole) or ALDH (cyanamide) on the cardiovascular effects of intra-RVLM ethanol or its metabolic product acetaldehyde in conscious rats. Compared with vehicle, ethanol (10 µg/rat) elicited a significant increase in blood pressure in SHRs that lasted for the 60-min observation period but had no effect on blood pressure in WKY rats. The first oxidation product, acetaldehyde, played a critical role in ethanol-evoked hypertension because 1) catalase inhibition (3-aminotriazole treatment) virtually abolished the ethanol-evoked pressor response in SHRs, 2) intra-RVLM acetaldehyde (2 µg/rat) reproduced the strain-dependent hypertensive effect of intra-RVLM ethanol, and 3) ALDH inhibition (cyanamide treatment) uncovered a pressor response to intra-RVLM acetaldehyde in WKY rats similar to the response observed in SHRs. These findings support the hypothesis that local production of acetaldehyde, due to enhanced catalase activity, in the RVLM mediates the ethanol-evoked pressor response in SHRs.

Propofol and etomidate depress cortical, thalamic, and reticular formation neurons during anesthetic-induced unconsciousness.

BACKGROUND: The sites where anesthetics produce unconsciousness are not well understood. Likely sites include the cerebral cortex, thalamus, and reticular formation. We examined the effects of propofol and etomidate on neuronal function in the cortex, thalamus, and reticular formation in intact animals. METHODS: Five cats had a recording well and electroencephalogram screws placed under anesthesia. After a 5-day recovery period, the cats were repeatedly studied 3 to 4 times per week. Neuronal (single-unit) activity in the cerebral cortex (areas 7, 18 and 19), thalamus (ventral posterolateral and ventral posteromedial nuclei and medial geniculate body), and reticular formation (mesencephalic reticular nucleus and central tegmental field) was recorded before, during, and after infusion of either propofol or etomidate. Cortical neuronal action potentials were analyzed separately as either regular spiking neurons or fast spiking neurons. RESULTS: Propofol and etomidate decreased the spontaneous firing rate of cortical neurons by 37% to 41%; fast spiking neurons and regular spiking neurons were similarly affected by the anesthetics. The neuronal firing rate in the thalamus and reticular formation decreased 30% to 49% by propofol and etomidate. The electroencephalogram shifted from a low-amplitude, high-frequency pattern to a high-amplitude, low-frequency pattern during drug infusion suggesting an anesthetic effect; peak power occurred at 12 to 13 Hz during propofol infusion. There were 2 major peaks during etomidate anesthesia: one at 12 to 14 Hz and another at 7 to 8 Hz. The cats were heavily sedated, with depressed corneal and whisker reflexes; withdrawal to noxious stimulation remained intact. CONCLUSION: These data show that neurons in the cortex, thalamus, and reticular formation are similarly depressed by propofol and etomidate. Although anesthetic depression of neuronal activity likely contributes to anesthetic-induced unconsciousness, further work is needed to determine how anesthetic effects at these sites interact to produce unconsciousness.

GABA(A) receptors in the pontine reticular formation of C57BL/6J mouse modulate neurochemical, electrographic, and behavioral phenotypes of wakefulness.

Drugs that potentiate transmission at GABA(A) receptors are widely used to enhance sleep and to cause general anesthesia. The mechanisms underlying these effects are unknown. This study tested the hypothesis that GABA(A) receptors in the pontine reticular nucleus, oral part (PnO) of mouse modulate five phenotypes of arousal: sleep and wakefulness, cortical electroencephalogram (EEG) activity, acetylcholine (ACh) release in the PnO, breathing, and recovery time from general anesthesia. Microinjections into the PnO of saline (vehicle control), the GABA(A) receptor agonist muscimol, muscimol with the GABA(A) receptor antagonist bicuculline, and bicuculline alone were performed in male C57BL/6J mice (n = 33) implanted with EEG recording electrodes. Muscimol caused a significant increase in wakefulness and decrease in rapid eye movement (REM) and non-REM (NREM) sleep. These effects were reversed by coadministration of bicuculline. Bicuculline administered alone caused a significant decrease in wakefulness and increase in NREM sleep and REM sleep. Muscimol significantly increased EEG power in the delta range (0.5-4 Hz) during wakefulness and in the theta range (4-9 Hz) during REM sleep. Dialysis delivery of bicuculline to the PnO of male mice (n = 18) anesthetized with isoflurane significantly increased ACh release in the PnO, decreased breathing rate, and increased anesthesia recovery time. All drug effects were concentration dependent. The effects on phenotypes of arousal support the conclusion that GABA(A) receptors in the PnO promote wakefulness and suggest that increasing GABAergic transmission in the PnO may be one mechanism underlying the phenomenon of paradoxical behavioral activation by some benzodiazepines.

Group III metabotropic glutamate receptors inhibit startle-mediating giant neurons in the caudal pontine reticular nucleus but do not mediate synaptic depression/short-term habituation of startle.

Short-term habituation is a basic form of learning that is analyzed in different species and using different behavioral models. Previous studies on mechanisms of short-term habituation yielded evidence for a potential role of group III metabotropic glutamate receptors (mGluRIIIs). Here we tested the hypothesis that mGluRIII mediate short-term habituation of startle in rats, combining electrophysiological experiments in vitro with behavioral studies in vivo. We applied different mGluRIII agonists and antagonists on rat brainstem slices while recording from startle-mediating neurons in the caudal pontine reticular nucleus (PnC) and monitoring synaptic depression presumably underlying habituation. Furthermore, we injected the mGluRIII antagonist (RS)-alpha-phosphonophenylglycine (MPPG) and the agonist L-(+)-2-amino-4-phosphonobutyric acid (L-AP4) into the PnC of rats in vivo and measured its effect on startle habituation. Our results show that activation of mGluRIIIs in the PnC strongly inhibits startle-mediating giant neurons in vitro. Accordingly, L-AP4 reduced startle responses in vivo. However, synaptic depression in the slice was not disrupted by mGluRIII antagonists or agonists. Correspondingly, the in vivo application of the mGluRIII antagonist MPPG failed to show any effect on short-term habituation of startle responses. We therefore conclude that mGluRs are expressed within the primary startle pathway and that they inhibit startle responses upon activation; however, this inhibition does not play any role in synaptic depression and short-term habituation of startle. This is in contrast to the role of mGluRIIIs in other forms of habituation and supports the notion that there are different mechanisms involved in habituation of sensory-evoked behaviors.

µ-Opioid modulation in the rostral solitary nucleus and reticular formation alters taste reactivity: evidence for a suppressive effect on consummatory behavior.

The neural control of feeding involves many neuromodulators, including the endogenous opioids that bind µ-opioid receptors (MORs). Injections of the MOR agonist, Damgo, into limbic and hypothalamic forebrain sites increase intake, particularly of palatable foods. Indeed, forebrain Damgo injections increase sucrose-elicited licking but reduce aversive responding (gaping) to quinine, suggesting that MOR activation may enhance taste palatability. A µ-opioid influence on taste reactivity has not been assessed in the brain stem. However, MORs are present in the first-order taste relay, the rostral nucleus of the solitary tract (rNST), and in the immediately subjacent reticular formation (RF), a region known to be essential for consummatory responses. Thus, to evaluate the consequences of rNST/dorsal RF Damgo in this region, we implanted rats with intraoral cannulas, electromyographic electrodes, and brain cannulas aimed at the ventral border of the rNST. Licking and gaping elicited with sucrose, water, and quinine were assessed before and after intramedullary Damgo and saline infusions. Damgo slowed the rate, increased the amplitude, and decreased the size of fluid-induced lick and gape bouts. In addition, the neutral stimulus water, which typically elicits licks, began to evoke gapes. Thus, the current results demonstrate that µ-opioid activation in the rNST/dorsal RF exerts complex effects on oromotor responding that contrast with forebrain effects and are more indicative of a suppressive, rather than a facilitatory effect on ingestion.

Buprenorphine disrupts sleep and decreases adenosine concentrations in sleep-regulating brain regions of Sprague Dawley rat.

BACKGROUND: Buprenorphine, a partial µ-opioid receptor agonist and κ-opioid receptor antagonist, is an effective analgesic. The effects of buprenorphine on sleep have not been well characterized. This study tested the hypothesis that an antinociceptive dose of buprenorphine decreases sleep and decreases adenosine concentrations in regions of the basal forebrain and pontine brainstem that regulate sleep. METHODS: Male Sprague Dawley rats were implanted with intravenous catheters and electrodes for recording states of wakefulness and sleep. Buprenorphine (1 mg/kg) was administered systemically via an indwelling catheter and sleep-wake states were recorded for 24 h. In additional rats, buprenorphine was delivered by microdialysis to the pontine reticular formation and substantia innominata of the basal forebrain while adenosine was simultaneously measured. RESULTS: An antinociceptive dose of buprenorphine caused a significant increase in wakefulness (25.2%) and a decrease in nonrapid eye movement sleep (-22.1%) and rapid eye movement sleep (-3.1%). Buprenorphine also increased electroencephalographic delta power during nonrapid eye movement sleep. Coadministration of the sedative-hypnotic eszopiclone diminished the buprenorphine-induced decrease in sleep. Dialysis delivery of buprenorphine significantly decreased adenosine concentrations in the pontine reticular formation (-14.6%) and substantia innominata (-36.7%). Intravenous administration of buprenorphine significantly decreased (-20%) adenosine in the substantia innominata. CONCLUSIONS: Buprenorphine significantly increased time spent awake, decreased nonrapid eye movement sleep, and increased latency to sleep onset. These disruptions in sleep architecture were mitigated by coadministration of the nonbenzodiazepine sedative-hypnotic eszopiclone. The buprenorphine-induced decrease in adenosine concentrations in basal forebrain and pontine reticular formation is consistent with the interpretation that decreasing adenosine in sleep-regulating brain regions is one mechanism by which opioids disrupt sleep.

Theta synchronization between the hippocampus and the nucleus incertus in urethane-anesthetized rats.

Oscillatory coupling between distributed areas can constitute a mechanism for neuronal integration. Theta oscillations provide temporal windows for hippocampal processing and only appear during certain active states of animals. Since previous studies have demonstrated that nucleus incertus (NI) contributes to the generation of hippocampal theta activity, in this paper, we evaluated the oscillatory coupling between both structures. We compared hippocampal and NI field potentials that were simultaneously recorded in urethane-anesthetized rats. Electrical and cholinergic stimulations of the reticularis pontis oralis nucleus have been used as hippocampal theta generation models. The spectral analyses reveal that electrical stimulation induced an increase in theta oscillations in both channels, whose frequencies depended on the intensity of stimulation. The intensity range used simultaneously increased the normalized spectral energy in the fast theta band (6-12 Hz) in HPC and NI. Frequencies within the theta range were found to be very similar in both channels. In order to validate coupling, spectral coherence was inspected. The data reveal that coherence in the high theta band also increased while stimuli were applied. Cholinergic activation progressively increased the main frequency in both structures to reach an asymptotic period with stable peak frequency in the low theta range (3-6 Hz), which could be first observed in NI and lasted about 1,500 s. Coherence in this band reached values close to 1. Taken together, these results support an electrophysiological and functional coupling between the hippocampus and the reticular formation, suggesting NI to be part of a distributed network working at theta frequencies.

Cholinergic modulation differs between basal and apical dendritic excitation of hippocampal CA1 pyramidal cells.

We hypothesize that endogenous cholinergic modulation of dendritic processing of hippocampal CA1 is layer specific, and it specifically enhances spike output resulting from basal as compared with the apical dendritic excitation. Laminar profiles of evoked field potentials were recorded in the CA1 area of urethane-anesthetized rats using multichannel silicon probes and analyzed as current source density. High-frequency stimulation of the pontis oralis (PnO) attenuated the midapical more than the basal or distal apical dendritic excitatory sink. Population spike (PS) and excitatory sink-PS potentiation resulting from basal dendritic excitation were facilitated, while the PS evoked by apical dendritic stimulation was attenuated by PnO stimulation. Perfusion of cholinergic agonist carbachol onto hippocampal slices in vitro also attenuated the apical more than the basal dendritic excitatory postsynaptic potentials. Excitatory sink attenuation and PS changes after PnO stimulation were blocked by systemic or local scopolamine and by intracerebroventricular (icv) M1 receptor antagonist pirenzepine but not by icv M2 receptor antagonist AFDX-116 or nicotinic antagonists. However, a hippocampal theta rhythm activated by PnO stimulation was blocked by systemic but not by local scopolamine. We conclude that endogenous acetylcholine mediates a stronger presynaptic inhibition of the midapical than basal and distal apical excitation mainly through M1 receptors.

Changes in neurons of medulla oblongata nuclei under conditions of chronic NO-synthase inhibition.

Nucleus tractus solitarius and giant-cell and lateral reticular nuclei were studied using the reaction to NADPH-diaphorase in 7-, 10-, 14-, 30-, 45-, 60-day-and 3- and 6-month-old rats receiving L-NAME (50 µg/kg, 2 times a day) on days 1-6 of life. In 7-14-day-old rats, the compound reduced NO-synthase activity in the majority of NO-neurons and the total number and to a lesser degree the relative number of these neurons, while cell cross-section areas remained practically unchanged. The differences in the corresponding quantitative parameters between the control (D-NAME administration) and experimental groups decreased with time after the last L-NAME injection and became undetectable starting from the age of 30-45 days. In the nucleus tractus solitarius, the changes in metric parameters after exposure to NO-synthase inhibitor were more pronounced than in the reticular formation nuclei.

Cerebellar Golgi cells in the rat receive convergent peripheral inputs via a lateral reticular nucleus relay.

Golgi cells are important players in the function of the cerebellar cortex, controlling the flow of incoming information from mossy fibres to the granule cells, which excite other cortical neurons. We recently showed that in anaesthetized rats most Golgi cells respond to stimulation of afferents from a very wide peripheral receptive field with a long-lasting depression of firing. These responses are mediated via a crossed ascending afferent pathway but the supraspinal part of this pathway is unknown. Here we have examined the hypothesis that the lateral reticular nucleus, a brainstem nucleus with known broad afferent convergence that projects mossy fibres to much of the cerebellum, is involved. First, we showed that single-pulse electrical microstimulation within the lateral reticular nucleus can elicit long-lasting depressions in Golgi cells, which are qualitatively similar to those evoked by peripheral afferent stimulation. Second, we showed that the amplitude of the depressions of Golgi cell firing evoked by peripheral stimulation can be reduced by pharmacological manipulation of the lateral reticular nucleus, either ipsilateral or contralateral to the stimulus site, with local injections of either the GABA(A) receptor agonist muscimol or the AMPA receptor blocker 6-cyano-7-nitroquinoxaline-2,3-dione. This evidence suggests that the lateral reticular nucleus is a relay nucleus in the brainstem for peripheral afferent information in a pathway that generates Golgi cell long-lasting depression responses.

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.

Hypocretin and GABA interact in the pontine reticular formation to increase wakefulness.

STUDY OBJECTIVES: Hypocretin-1/orexin A administered directly into the oral part of rat pontine reticular formation (PnO) causes an increase in wakefulness and extracellular gamma-aminobutyric acid (GABA) levels. The receptors in the PnO that mediate these effects have not been identified. Therefore, this study tested the hypothesis that the increase in wakefulness caused by administration of hypocretin-1 into the PnO occurs via activation of GABAA receptors and hypocretin receptors. DESIGN: Within/between subjects. SETTING: University of Michigan. PATIENTS OR PARTICIPANTS: Twenty-three adult male Crl:CD*(SD) (Sprague Dawley) rats. INTERVENTIONS: Microinjection of hypocretin-1, bicuculline (GABAA receptor antagonist), SB-334867 (hypocretin receptor-1 antagonist), and Ringer solution (vehicle control) into the PnO. MEASUREMENTS AND RESULTS: Hypocretin-1 caused a significant concentration-dependent increase in wakefulness and decrease in rapid eye movement (REM) sleep and non-REM (NREM) sleep. Coadministration of SB-334867 and hypocretin-1 blocked the hypocretin-1-induced increase in wakefulness and decrease in both the NREM and REM phases of sleep. Coadministration of bicuculline and hypocretin-1 blocked the hypocretin-1-induced increase in wakefulness and decrease in NREM sleep caused by hypocretin-1. CONCLUSION: The increase in wakefulness caused by administering hypocretin-1 to the PnO is mediated by hypocretin receptors and GABAA receptors in the PnO. These results show for the first time that hypocretinergic and GABAergic transmission in the PnO can interact to promote wakefulness.