The tachykinin NK-1 receptor antagonist, RP-67580, infused into the ventral tegmental area prevents stress-induced analgesia in the formalin test

Substance P (SP) receptors in the ventral tegmental area (VTA) play a critical role in mediating the stress-induced activation of midbrain ascending dopamine (DA) neurons. Interestingly, SP acting in the VTA induces analgesia in the formalin test for tonic pain. Because exposure to stress inhibits pain in this test, we speculated that SP receptors in the VTA might mediate stress-induced analgesia. The present study explored this idea by examining the effect of blocking tachykinin NK-1 receptors in the VTA on footshock stress-induced analgesia in the formalin test. Intra-VTA infusions of the novel tachykinin NK-1 receptor antagonist, RP-67580, prevented this response. This finding suggests that exposure to stress inhibits tonic pain through the release of endogenous SP in the VTA.

Dopamine D1 receptor modulation of glutamate receptor messenger RNA levels in the neocortex and neostriatum of unilaterally 6-hydroxydopamine-lesioned rats

The effect of treatment with the D1 dopamine receptor agonist SKF 38393 on the expression of metabotropic glutamate receptor 1, 3, 4 and 5 receptor subtypes and of the glutamate N-methyl-D-aspartate ionotropic receptor subunits NRI, NR2A and NR2B was analysed using in situ hybridization. We studied the neocortex and neostriatum of normal rats and of rats unilaterally treated with 6-hydroxydopamine, a neurotoxin that, after intracerebral injection into the ventral tegmental area, causes selective degeneration of the ascending dopamine pathway. In the 6-hydroxydopamine-lesioned rats, metabotropic glutamate receptor subtype 3 messenger RNA levels were ipsilaterally increased in the neocortex and neostriatum, while the levels of metabotropic glutamate receptor subtype 4 messenger RNA were bilaterally increased in both regions. When administered to the 6-hydroxydopamine-lesioned rats, the D1 receptor agonist SKF 38393 (3 x 20 mg/kg, s.c.) produced a bilateral decrease in the expression of the metabotropic glutamate receptor subtype 1 and 5 receptor messenger RNA levels in the neocortex and neostriatum. In the neostriatum, SKF 38393 attenuated the ipsilateral increase in the expression of striatal metabotropic glutamate receptor subtype 3 messenger RNA produced by the 6-hydroxydopamine lesion. Furthermore, SKF 38393 produced a bilateral decrease in the levels of NRI receptor subunit messenger RNA and, in contrast, an increase in the striatal NR2B messenger RNA levels. All of these effects were abolished by the D1 receptor antagonist SCH 23360. These results indicate a differential D1 receptor-mediated modulation of the expression of some glutamate receptor subtypes in the neostriatum and neocortex, in agreement with the idea of a functional coupling between dopamine and excitatory amino acid systems in both regions. Thus, pharmacological targeting of excitatory amino acid systems could provide alternative or complementary treatment strategies for diseases involving dopaminergic systems in the striatum (e.g., Parkinson's disease) and cortex (e.g., schizophrenia).

Endogenous nitric oxide in the rat pons promotes sleep

Pontine cholinergic structures are known to play a key role in the regulation of vigilance states associated with desynchronised EEG, i. e., wakefulness and paradoxical sleep. As the cholinergic cells of these nuclei, the pedunculopontine tegmentum (PPT) and the laterodorsal tegmentum, are enriched with nitric oxide synthase (NOS), we tested the hypothesis that nitric oxide (NO) in the pons is implicated in wake and sleep regulation. For this reason, a NOS inhibitor, a NO precursor and a NO donor were injected in the PPT of rats. Vigilance states were recorded for 6 h following the injections. Quantification of vigilance states after drug injections were compared to those obtained in control conditions. It appeared that the NO donor had a slight effect on vigilance states, but the NOS inhibitor decreased sleep and inversely the NO precursor increased sleep. These results show for the first time in the rat that a NOS inhibitor, injected directly into the PPT, is able to reduce sleep and that a NO precursor had the opposite effect. They suggest that endogenous NO production in the PPT has a somnogenic effect. The participation of endogenous NO in vigilance regulation is discussed in light of the role attributed to pontine cholinergic system in wakefulness and sleep.

Muscarinic receptors mediate carbachol-induced inhibition of maximal electroshock seizures in the nucleus reticularis pontis oralis

PURPOSE

Previous reports from this laboratory indicated a role for N-methyl-D-aspartic acid (NMDA) and gamma-aminobutyric acid (GABA) receptors among the neuronal mechanisms of the nucleus reticularis pontis oralis (RPO) that regulate the tonic hindlimb extension (THE) component of maximal electroshock seizures (MESs) in rats. This study was intended to determine the role of cholinergic mechanisms in the RPO regulation of THE.

METHODS

Rats were surgically prepared with microinjection guide cannulas for the focal administration of drug solutions directly into the RPO. MES was induced with corneal electrodes.

RESULTS

RPO microinjection of carbachol significantly inhibited the incidence of THE. RPO microinjection of atropine by itself had no effect on the seizure response but significantly antagonized the anticonvulsant effect induced by RPO microinjection of carbachol. The selective nicotinic agonist dimethylpiperizinium (DMPP) by itself had no effect on THE. RPO microinjection of 10 ng pertussis toxin by itself had no effect on THE but significantly antagonized the anticonvulsant effect induced by RPO microinjection of carbachol.

CONCLUSIONS

RPO microinjection of carbachol inhibited the THE component of MESs in rats. The carbachol effect appeared to be mediated by muscarinic receptors as the anticonvulsant activity was antagonized by atropine, and the selective nicotinic agonist DMPP induced no anticonvulsant activity. Because pertussis toxin acts to inhibit muscarinic receptor-linked G proteins, the pertussis toxin antagonism of carbachol also supports a muscarinic mechanism of action.

Quantitative in situ hybridization of three gonadotropin-releasing hormone-encoding mRNAs in castrated and progesterone-treated male tilapia

We investigated the effects of castration and progesterone administration on the three gonadotropin-releasing hormone (GnRH)-encoding mRNAs in sexually mature male tilapia Oreochromis niloticus. In situ hybridization histochemistry was performed using 35S-labeled antisense oligonucleotide probes complementary to salmon-, seabream-, and chicken II-GnRH cDNAs to quantify cellular GnRH mRNA expression in the terminal nerve ganglia (nucleus olfactoretinalis), preoptic area, and midbrain tegmentum of animals castrated for 2 weeks and injected intraperitoneally with sesame oil or progesterone. Castration significantly elevated salmon-GnRH mRNA but not seabream- or chicken II-GnRH mRNA levels. Progesterone treatment had no effect on salmon-, seabream-, or chicken II-GnRH mRNA levels. Comparisons between intact, castrated, and progesterone-treated animals showed no change in the total volume of nucleus olfactoretinalis, cell sizes, and total numbers of cells expressing GnRH mRNA within the midbrain and preoptic area. These results demonstrate that salmon-GnRH but not seabream- or chicken II-GnRH-synthesizing neurons are under a gonadal steroid negative feedback control and that progesterone might not be the main hormone regulating the three GnRH-encoding mRNAs in the male tilapia.

Neurotransmitter actions on oral pontine tegmental neurons of the rat: an in vitro study

The actions of neurotransmitters involved in the sleep-wakefulness cycle on neurons located in the ventral part of the oral pontine tegmentum were studied in a rat brain-slice preparation. Results show that glutamate and histamine evoke depolarizations and spike firing while serotonin and gamma-aminobutyric acid evoke hyperpolarizations. The excitatory and inhibitory actions of these neurotransmitters increase pontine neuron activity during the conditions occurring during paradoxical sleep.

Effect of extracellular adenosine 5'-triphosphate on principal neurons of the rat ventral tegmental area

Intracellular recordings were made in a midbrain slice preparation of the rat brain containing the ventral tegmental area (VTA). Dopaminergic principal cells were identified by their electrophysiological properties and their hyperpolarizing responses to dopamine. Superfusion with dopamine (100 microM) caused hyperpolarization and a decrease of the apparent input resistance. By contrast, two structural analogues of ATP, 2-methylthio ATP (2-MeSATP; 10 microM) and alpha,beta-methylene ATP (alpha, beta-meATP; 30 microM) had no effect, when added to the superfusion medium. Pressure applied dopamine also hyperpolarized the membrane, while both 2-MeSATP and alpha,beta-meATP were ineffective. Hence, dopaminergic principal neurons of the VTA do not possess somatic P2 purinoceptors present on peripheral and central noradrenergic neurons.

Glycine-activated chloride currents of neurons freshly isolated from the ventral tegmental area of rats

Properties of whole-cell glycine currents (IGly) of ventral tegmental area (VTA) neurons from 3- to 7-day old Sprague-Dawley rats were investigated with the patch-clamp technique. Ninety-three percent of the 126 neurons examined produced IGly in response to glycine. For 70% of these neurons, IGly did not decay in response to a threshold concentration of glycine (1-5 microM). At elevated glycine concentrations, IGly consistently decayed from a peak to a steady state (SS). IGly increased in amplitude sigmoidally as a function of the concentration of agonist with an EC50 of 32 microM. Strychnine (STR), when co-applied with glycine after a prepulse of STR, suppressed both the peak and SS IGly noncompetitively. In the absence of a prepulse, STR had a smaller effect on peak IGly while increasing its decay rate; the SS amplitude decreased. These STR effects were concentration dependent with an IC50 of 31 nM and 184 nM STR for the peak and SS IGly, with prepulse, respectively, and 732 nM and 193 nM for the peak and SS IGly, respectively, without prepulse. Picrotoxin (PTX) co-applied with glycine suppressed both the peak and the SS IGly with an IC50 of 25 microM. In contrast to STR, 1 min preincubation with PTX had no effect on IGly. Thus, PTX acts on the open channel. The inhibitory effects of both STR and PTX on IGly did not depend on the membrane potential.

Voltage-clamp analysis and computer simulation of a novel cesium-resistant A-current in guinea pig laterodorsal tegmental neurons

Increased firing of cholinergic neurons of the laterodorsal tegmental nucleus (LDT) plays a critical role in generating the behavioral states of arousal and rapid eye movement sleep. The majority of these neurons exhibit a prominent transient potassium current (IA) that shapes firing but the properties of which have not been examined in detail. Although IA has been reported to be blocked by intracellular cesium, the IA in LDT neurons appeared resistant to intracellular cesium. The present study compared the properties of this cesium-resistant current to those typically ascribed to IA. Whole cell recordings were obtained from LDT neurons (n = 67) in brain slices with potassium- or cesium-containing pipette solutions. A transient current was observed in cells dialyzed with each solution (KGluc-85%; CsGluc-79%). However, in cesium-dialyzed neurons, the transient current was inward at test potentials negative to about -35 mV. Extracellular 4-aminopyridine (4-AP; 2-5 mM) blocked both inward and outward current, suggesting the inward current was reversed IA rather than an unmasked transient calcium current as previously suggested. This conclusion was supported by increasing [K]o from 5 to 15 mM, which shifted the reversal potential positively for both inward and outward current (+17.89 +/- 0.41 mV; mean +/- SE). Moreover, recovery from inactivation was rapid (tau = 15.5 +/- 4 ms; n = 4), as reported for IA, and both inward and outward transient current persisted in calcium-free solution [0 calcium/4 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N', N'-tetraacetic acid; n = 4] and during cadmium-blockade of calcium currents (n = 3). Finally, the transient current was blocked by intracellular 4-AP indicating that adequate dialysis occurred during the recordings. Thus the Cs-resistant current is a subthreshold IA. We also estimated the voltage-dependence of activation (V1/2 = -45.8 +/- 2 mV, k = 5.21 +/- 0.62 mV, n = 6) and inactivation (V1/2 = -59. 0 +/- 2.38 mV, k = -5.4 +/- 0.49 mV, n = 3) of this current. Computer simulations using a morphologically accurate model cell indicated that except for the extreme case of only distal A-channels and a high intracellular resistivity, our parameter estimates were good approximations. In conclusion, guinea pig LDT neurons express subthreshold A-channels that are resistant to intracellular cesium ions. This suggests that these channels differ fundamentally in their ion permeation mechanism from those previously studied. It remains to be determined if Cs+ resistance is common among brain A-channels or if this property is conferred by known A-channel subunits.

Mesencephalic THmRNA-reduced expression by blocking axonal transport with colchicine

Colchicine, an axonal transport blocking agent, was unilaterally injected in the medial forebrain bundle of rats. As early as 18 h after the injection a rapid decrease in TH-mRNA level was observed in the substantia nigra and the ventral tegmental area (SN/VTA) on the injected side. In contrast, TH protein levels remained stable for 48 h, and decreased later in both cells bodies and terminals (caudate/putamen). The number of TH-immunopositive cells in SN/VTA increased after colchicine equally in both sides, excluding a neurotoxic effect. These results suggest that TH gene expression is controlled by a retrogradely transported activating factor rather than by feedback inhibition by the end product, i.e. TH protein.

Haloperidol induces persistent down-regulation of tyrosine hydroxylase immunoreactivity in substantia nigra but not ventral tegmental area in the rat

The dopamine antagonist haloperidol can cause tardive side-effects that may persist after the drug is withdrawn. We studied the time course of changes in dopaminergic neurons of the substantia nigra and ventral tegmental area following withdrawal of haloperidol. Rats received daily intraperitoneal injections of saline or haloperidol for eight weeks and were killed at two, four or 12 weeks after the final injection. Sections of substantia nigra and ventral tegmental area were processed for tyrosine hydroxylase immunohistochemistry. Quantitative morphometric analysis was carried out blinded in order to determine the number, cell body size and topography of tyrosine hydroxylase-positive cells, and the immunoreactive area of the substantia nigra and ventral tegmental area. In haloperidol-treated rats, tyrosine hydroxylase-positive cell counts were normal in ventral tegmental area but were decreased in substantia nigra by 34% at two weeks withdrawal and by 52% at four weeks withdrawal; cell counts were almost fully recovered by 12 weeks withdrawal. Cross-sectional area of tyrosine hydroxylase immunoreactivity within the substantia nigra demonstrated a similar pattern of reduction, with full recovery by 12 weeks withdrawal. Mean cell size, by contrast, was essentially unchanged at two and four weeks withdrawal, but was significantly decreased in sub-regions of substantia nigra at 12 weeks withdrawal. These results indicate that haloperidol can produce selective changes in midbrain dopamine neurons that persist long after discontinuation of the drug. This decrease in tyrosine hydroxylase-immunoreactive cell counts may play a role in the neurobiology of the persistent tardive syndromes associated with the use of neuroleptics.

Increase of extracellular glutamate and expression of Fos-like immunoreactivity in the ventral tegmental area in response to electrical stimulation of the prefrontal cortex

Electrical stimulation of the medial prefrontal cortex caused glutamate release in the ventral tegmental area (VTA) of freely moving animals. Cathodal stimulation was given through monopolar electrodes in 0.1-ms pulses at an intensity of 300 microA and frequencies of 4-120 Hz. Glutamate was measured in 10-min perfusate samples by HPLC coupled with fluorescence detection following precolumn derivatization with o-phthaldialdehyde/beta-mercaptoethanol. The stimulation-induced glutamate release was frequency dependent and was blocked by the infusion of the sodium channel blocker tetrodotoxin (10 microM) through the dialysis probe. The stimulation also induced bilateral Fos-like immunoreactivity in ventral tegmental neurons, with a significantly greater number of Fos-positive cells on the stimulated side. These findings add to a growing body of evidence suggesting that the medial prefrontal cortex regulates dopamine release in the nucleus accumbens via its projection to dopamine cell bodies in the VTA.

Deficits in vertical and torsional eye movements after uni- and bilateral muscimol inactivation of the interstitial nucleus of Cajal of the alert monkey

The mesencephalic interstitial nucleus of Cajal (iC) is considered the neural integrator for vertical and torsional eye movements and has also been proposed to be involved in saccade generation. The aim of this study was to elucidate the function of iC in neural integration of different types of eye movements and to distinguish eye movement deficits due to iC impairment from that of the immediately adjacent rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). We addressed the following questions: (1) According to the neural integrator hypothesis, all eye movements including the saccadic system and the vestibulo-ocular reflex (VOR) share a common neural integrator. Do iC lesions impair gaze-holding function for vertical and torsional eye positions and the torsional and vertical VOR gain to a similar degree? (2) What are the dynamic properties of vertical and torsional eye movements deficits after iC lesions, e.g., the specificity of torsional and vertical nystagmus? (3) Is iC involved in saccade generation? We performed 13 uni- and three bilateral iC inactivations by muscimol microinjections in four alert monkeys. Three-dimensional eye movements were studied under head-stationary conditions during vertical and torsional VOR. Under static conditions, unilateral iC injections evoked a shift of Listing's plane to the contralesional side (up to 20 degrees), which increased (ipsilesional ear down) or decreased (ipsilesional ear up) by additional static vestibular stimulation in the roll plane, i.e., ocular counterroll was preserved. The monkeys showed a spontaneous torsional nystagmus with a profound downbeat component. The fast phases of torsional nystagmus always beat toward the lesion side (ipsilesional). Pronounced gaze-holding deficit for torsional and vertical eye positions (neural integrator failure) was reflected by the reduction of time constants of the exponential decay of the slow phase to 330-370 ms. Whereas the vertical oculomotor range was profoundly decreased (up to 50%) and vertical saccades were reduced in amplitude, saccade velocity remained normal and horizontal eye movements were not affected. Bilateral iC injections reduced the shift of Listing's plane caused by unilateral injections, i.e., back toward the plane of zero torsion. Torsional nystagmus reversed its direction and ceased, whereas vertical nystagmus persisted. In contrast to unilateral injection, there was additional upbeating nystagmus. Time constants of the position integrator of the gaze-holding system did not differ between unilateral and bilateral injections. The range of stable vertical eye positions and saccade amplitude was smaller when compared with unilateral injections, but the main sequence remained normal. Dynamic vestibular stimulation after unilateral iC injections had virtually no effect on torsional and vertical VOR gain and phase at the same time when time constants already indicated severe integrator failure. Torsional VOR elicited a constant slow-phase velocity offset up to 30 degrees toward the contralesional side, i.e., in the opposite direction to spontaneous torsional nystagmus. Likewise, vertical VOR showed a velocity offset in an upward direction, i.e., opposite to the spontaneous downbeat nystagmus. Contralesional torsional and upward vertical quick phases were missing or severely reduced in amplitude but showed normal velocity. In contrast, bilateral iC injections reduced the gain of the torsional and vertical VOR by 50% and caused a phase lead of 10-20 degrees (eye compared with head velocity). We propose that the slow-phase velocity offset during torsional and vertical VOR reflects a vestibular imbalance. It therefore appears likely that the vertical and torsional nystagmus after iC lesions is not only caused by a neural integrator failure but also by a vestibular imbalance. Unilateral iC injections have clearly differential effects on the VOR and the gaze-holding function. (ABSTRACT TRUNCATED)

Repeated cocaine administration alters extracellular glutamate in the ventral tegmental area

The present study determined if repeated cocaine injections alter the effect of cocaine on extracellular glutamate in the ventral tegmental area (VTA). All rats were treated with daily cocaine (15 mg/kg i.p. x 2 days, 30 mg/kg i.p. x 5 days) or saline for 7 days. At 21 days after discontinuing the daily injections, a dialysis probe was placed into the VTA and the extracellular levels of glutamate were estimated. A systemic injection of cocaine (15 mg/kg i.p.) elevated extracellular glutamate in the VTA of rats pretreated with daily cocaine but not in the daily saline-pretreated subjects. No significant change in glutamate was produced by a saline injection in either pretreatment group. In a group of rats pretreated with daily cocaine, the D1 antagonist SCH-23390 (30 microM) was infused through the dialysis probe prior to the acute injections of saline and cocaine. SCH-23390 prevented the increase in extracellular glutamate associated with the acute administration of cocaine. Behavioral data were collected simultaneously with the measures of extracellular glutamate. The behavioral stimulant effect of cocaine was greater in cocaine-pretreated than saline-pretreated subjects, and the behavioral augmentation in cocaine-pretreated rats was partly blocked by SCH-23390. These data support the hypotheses that repeated cocaine administration produces an increase in the capacity of D1 receptor stimulation to release glutamate in the VTA and that this mechanism partly mediates behavioral sensitization produced in rats treated with daily cocaine injections.

Opioid receptor modulation of feeding-evoked dopamine release in the rat nucleus accumbens

Feeding is associated with increases in the activity of the mesolimbic dopamine (DA) system which originates in the ventral tegmental area (VTA) and projects heavily to the nucleus accumbens. The present study used in vivo brain microdialysis to assess the contribution of opioid receptors in feeding-evoked DA release in the nucleus accumbens. Feeding in 18 h food-deprived rats increased DA release by about 50% above baseline. Systemic injection of the opioid receptor antagonist naltrexone (1 mg/kg, s.c.) blocked the effect of feeding on DA release and reduced the amount of food consumed. Unilateral application of naltrexone (100 microM) in the VTA via a microdialysis probe failed to affect the DA response to feeding, the amount of food consumed, or the latency to eat. In contrast, intra-VTA naltrexone significantly reduced the effect of systemic heroin (0.5 mg/kg, s.c.) on accumbal DA release. These results indicate that: (1) opioid receptor activation is a component of the neural substrates of deprivation-induced feeding: (2) opioid receptors in the VTA do not contribute significantly to feeding-associated increases in DA release in the nucleus accumbens; and (3) heroin-induced increases in accumbal DA release are mediated, at least in part, by opioid receptors in the VTA.

Cardiovascular depressor responses to stimulation of substantia nigra and ventral tegmental area

Experiments were done in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of L-glutamate (Glu) stimulation of the substantia nigra (SN) and ventral tegmental area (VTA) on arterial pressure (AP) and heart rate (HR). Glu stimulation of the SN pars compacta (SNC) elicited decreases in both mean AP (MAP; -18.9 +/- 1.3 mmHg; n = 52) and HR (-26.1 +/- 1.6 beats/min; n = 46) at 81% of the sites stimulated. On the other hand, stimulation of the SN pars lateralis or pars reticulata did not elicit cardiovascular responses. Stimulation of the adjacent VTA region elicited similar decreases in MAP (-18.0 +/- 2.6 mmHg; n = 20) and HR (-25.4 +/- 3.8 beats/min; n = 17) at approximately 74% of the sites stimulated. Intravenous administration of the dopamine D2-receptor antagonist raclopride significantly attenuated both the MAP (70%) and the HR (54%) responses elicited by stimulation of the transitional region where the SNC merges with the lateral VTA (SNC-VTA region). Intravenous administration of the muscarinic receptor blocker atropine methyl bromide had no effect on the magnitude of the MAP and HR responses to stimulation of the SNC-VTA region, whereas administration of the nicotinic receptor blocker hexamethonium bromide significantly attenuated both the depressor and the bradycardic responses. These data suggest that dopaminergic neurons in the SNC-VTA region activate a central pathway that exerts cardiovascular depressor effects that are mediated by the inhibition of sympathetic vasoconstrictor fibers to the vasculature and cardioacceleratory fibers to the heart.

Systemic morphine-induced Fos protein in the rat striatum and nucleus accumbens is regulated by mu opioid receptors in the substantia nigra and ventral tegmental area

To characterize how systemic morphine induces Fos protein in dorsomedial striatum and nucleus accumbens (NAc), we examined the role of receptors in striatum, substantia nigra (SN), and ventral tegmental area (VTA). Morphine injected into medial SN or into VTA of awake rats induced Fos in neurons in ipsilateral dorsomedial striatum and NAc. Morphine injected into lateral SN induced Fos in dorsolateral striatum and globus pallidus. The morphine infusions produced contralateral turning that was most prominent after lateral SN injections. Intranigral injections of [D-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO), a mu opioid receptor agonist, and of bicuculline, a GABAA receptor antagonist, induced Fos in ipsilateral striatum. Fos induction in dorsomedial striatum produced by systemic administration of morphine was blocked by (1) SN and VTA injections of the mu1 opioid antagonist naloxonazine and (2) striatal injections of either MK 801, an NMDA glutamate receptor antagonist, or SCH 23390, a D1 dopamine receptor antagonist. Fos induction in dorsomedial striatum and NAc after systemic administration of morphine seems to be mediated by dopamine neurons in medial SN and VTA that project to medial striatum and NAc, respectively. Systemic morphine is proposed to act on mu opioid receptors located on GABAergic interneurons in medial SN and VTA. Inhibition of these GABA interneurons disinhibits medial SN and VTA dopamine neurons, producing dopamine release in medial striatum and NAc. This activates D1 dopamine receptors and coupled with the coactivation of NMDA receptors possibly from cortical glutamate input induces Fos in striatal and NAc neurons. The modulation of target gene expression by Fos could influence addictive behavioral responses to opiates.

Identification of the midbrain locomotor nuclei and their descending pathways in the teleost carp, Cyprinus carpio

In order to identify the mesencephalic spinal pathways for initiation of swimming in the carp, we employed electrical and chemical microstimulation of the mesencephalic tegmentum. Electrical stimulation of the midbrain in decerebrate carp produced bilateral or unilateral rhythmic movements of the tail. Bilateral alternating movements were induced by stimulation with the lowest threshold currents to the brain region just beneath the third ventricle at the level of the mid mesencephalon. The region included the nucleus of medial longitudinal fasciculus (Nflm), the medial longitudinal fasciculus (flm), the red nucleus (Nrb). To specify the nuclei of the origin of the descending pathway, we microinjected 0.1 M L-glutamic acid to the region. Both bilateral and unilateral tail movements were induced, the majority being the latter. The unilateral movements were accompanied with tail flips toward the ipsilateral side of stimulation sites. The smallest injection volume required for initiation of the movement was recorded at the Nflm. Bilateral tail movements were produced only by injections into the medial region between the nucleus of the both sides. The present results imply a crucial role of Nflm neurons in the initiation of swimming Nflm neurons on one side project through flm to the ipsilateral spinal cord along its entire length and regulate activities of the individual central pattern generators.

Alcohol intake of P rats is regulated by muscarinic receptors in the pedunculopontine nucleus and VTA

Experiments were conducted to determine whether muscarinic receptors within the pedunculopontine nucleus (PPN) and ventral tegmental area (VTA) are involved in regulating ethanol drinking behavior in the alcohol-preferring P line of rats. Female P rats were given limited access (2 h/day) to 10% (v/v) ethanol and 0.0125% (g/100 ml) saccharin solutions. Food was available ad libitum. Cholinergic agents were microinjected unilaterally into the PPN or VTA immediately prior to ethanol access. Intra-PPN carbachol (1-4 microg/0.5 microl), which can inhibit cholinergic neuronal activity within the PPN, decreased ethanol (70% decrease at the highest dose; p < 0.05) and saccharin (90% decrease at the highest dose; p < 0.05) intake in a dose-dependent manner within the first 30 min. Intra-PPN scopolamine (5-15 microg/0.5 microl), which can stimulate cholinergic neuronal activity within the PPN, decreased ethanol intake in a dose-dependent manner within the first 30 min (65% decrease at the highest dose; p < 0.05) without reducing saccharin intake. Intra-VTA methylscopolamine (1-10 microg/0.5 microl), a muscarinic antagonist, significantly (p < 0.05) reduced ethanol (60% decrease at the highest dose) and saccharin (50% decrease at the highest dose) intakes during the 2-h access period. Intra-VTA carbachol, a cholinergic agonist (1 and 2 microg/0.5 microl) decreased ethanol consumption in a dose-dependent manner within the first 60 min (50% decrease at the highest dose) without reducing saccharin intake. Overall, these results support an involvement of the cholinergic PPN-VTA system in regulating alcohol drinking and general consummatory behaviors of the P line of rats.

Serotonin at the laterodorsal tegmental nucleus suppresses rapid-eye-movement sleep in freely behaving rats

Serotonin [5-hydroxytryptamine (5-HT)] is believed to play an important inhibitory role in the regulation of rapid-eye-movement (REM) sleep. 5-HT may exert this effect on neurons of the laterodorsal tegmental (LDT) nuclei that are implicated as important in the generation of REM sleep and phasic REM events such as ponto-geniculo-occipital (PGO) waves and respiratory variability. In rat brainstem in vitro, 5-HT hyperpolarizes and inhibits the bursting properties of LDT neurons assumed to be involved in generating REM sleep and PGO waves. This study tests the hypothesis that in vivo 5-HT at the LDT nuclei suppresses REM sleep and phasic REM events. Ten rats were implanted with bilateral cannulae aimed at the LDT and with electrodes for recording the electroencephalogram, neck electromyogram, PGO waves, and diaphragm electromyogram. During REM sleep, 5-HT (100 nl; 1-1.5 mM), saline, or sham microinjections were performed; repeated microinjections were separated by approximately 1 hr. After the first microinjection, REM sleep as a percent of the total sleep time was reduced with 5-HT (mean percent REM, 19.9 +/- 2.5% for 5-HT vs 26.8 +/- 2.4% for saline; p = 0.02). REM duration was reduced by 37% with 5-HT (p = 0.01), but REM episode frequency was changed less consistently (p = 0.21), suggesting that 5-HT mainly disrupted REM sleep maintenance. Per unit time of REM sleep, 5-HT had no effect on the amount or variability of REM PGO activity (p > 0.740) or on the mean or coefficient of variation of REM respiratory rate (p > 0.11). With subsequent microinjections, the effects of 5-HT on REM sleep were similar. A dose-dependent REM sleep suppression with 5-HT was observed in five rats tested. These data suggest that in vivo 5-HT at the LDT nuclei suppresses REM sleep expression. Although 5-HT did not disproportionately reduce the occurrence of phasic events within REM, total REM phasic activity was reduced because of less REM sleep after 5-HT.

Cerebellar ataxia and peripheral neuropathy due to chronic bromvalerylurea poisoning

A patient with chronic bromvalerylurea poisoning showed cerebellar ataxia and peripheral neuropathy. The patient was a 42-year-old Japanese man who developed consciousness disturbance, diplopia, slurred speech, ataxia and gait disturbance after having taken bromvalerylurea for ten years. Magnetic resonance imaging revealed atrophy of the cerebellum and pontine tegmentum. An electrophysiological study revealed decreased motor nerve conduction velocity and amplitude of compound muscle action potentials of the right tibial nerve. Histological findings of the left sural nerve indicated a slightly decreased large myelinated fiber diameter, which suggested chronic axonal damage.