Pontine neurons are elements of the network responsible for the 10-Hz rhythm in sympathetic nerve discharge

The current study was designed to test the hypothesis that pontine neurons are elements of the network responsible for the 10-Hz rhythm in sympathetic nerve discharge (SND). The first series of experiments tested whether chemical inactivation of neurons in the rostral dorsolateral pons (RDLP) or caudal ventrolateral pons (CVLP) affected inferior cardiac postganglionic SND of urethan-anesthetized cats. Muscimol microinjections into either region eliminated the 10-Hz rhythm in SND, supporting the view that pontine neurons are involved in the expression of this rhythm. Additional experiments were designed to determine if pontine neurons have activity correlated to the 10-Hz rhythm in SND or whether they merely provide a tonic (nonrhythmic) driving input to the rhythm generator. Coherence analysis revealed that local field potentials recorded from the RDLP or CVLP had a 10-Hz component that was significantly correlated to SND. Also, spike-triggered averaging and coherence analysis showed that the naturally occuring discharges of individual RDLP or CVLP neurons were correlated to the 10-Hz rhythm in SND. Taken together, these data support the hypothesis that RDLP and CVLP neurons are essential for the expression of the 10-Hz rhythm in SND and that they are elements of or receive input from the rhythm generator.

Modulation of the cardiac baroreflex following reversible blockade of the parabrachial nucleus in the rat

The parabrachial nucleus (PBN) has a prominent anatomical connection with the nucleus of the solitary tract as well as other central baroreflex centres which suggests a role for the PBN in the regulation of this cardiovascular reflex. This study examined the effects of a reversible, bilateral blockade of the PBN on the cardiac baroreflex. Male Sprague-Dawley rats were anesthetized with sodium butabarbitol and instrumented to monitor blood pressure and heart rate and for the intravenous administration of drugs. The cardiac baroreflex was evoked using bolus intravenous injections of phenylephrine (PE) and sodium nitroprusside (NaNp) at various doses and a graph of baroreflex sensitivity was constructed. Bilateral microinjections of the reversible anesthetic, lidocaine (5%, 300 nl), into the PBN did not significantly change baseline blood pressure or heart rate when compared to microinjections of saline (0.9%, 300 nl) into the PBN. The pressor or depressor responses evoked by bolus injections of PE or NaNp, respectively, were not significantly affected by the bilateral pretreatment of the PBN with lidocaine when compared to saline controls. However, approximately 30 min following lidocaine injection, the amplitudes of both the evoked-reflex bradycardia and reflex tachycardia were significantly increased by approximately 98%. The cardiovascular responses to various doses of PE and NaNp were graphed and baroreflex sensitivity curves were constructed. This graph showed an increased slope of the baroreflex sensitivity curve following lesions of the PBN. Reflex changes in heart rate returned to pre-lidocaine injection levels after approximately 2 h. The results of the present investigation suggest that the PBN participates in the modulation of the cardiac baroreflex which in turn suggests a role for this nucleus in the central integration of cardiovascular reflex function.

Regional distribution of the anticonvulsant and behavioural effects of bicuculline injected into the pontine reticular formation of rats

Previous experimental work has established that activation of sites in the dorsal midbrain can suppress tonic hindlimb extension in the electroshock model of epilepsy. The most sensitive region for this effect is centred on the intercollicular area and is referred to as the dorsal midbrain anticonvulsant zone (DMAZ). Subsequent experiments have shown that the ipsilateral descending projection from this region to the ventrolateral pons is critically involved in mediating its tonic seizure-suppressing properties. The purpose of the present investigation was to test whether direct anticonvulsant effects in the electroshock model could be obtained from selective manipulation of DMAZ target regions in the ventrolateral pons. Animals were prepared with chronically implanted guide cannulae through which microinjections could be made directly into the lateral pontine reticular formation. Animals received injections of saline or bicuculline (25-100 pmol) administered either bilaterally or unilaterally. The effects of these injections on the animals' behaviour were determined in an open arena, after which maximal electroshock (1 s, 40 mA, 50 Hz AC) was administered via ear-clip electrodes and the duration of tonic hindlimb extension was recorded. Bilateral injections of bicuculline (100 pmol) suppressed tonic seizures at a significantly higher proportion of sites centred on DMAZ target regions of the ventrolateral pons than surrounding areas. For injections centred on this region the suppressive effects of bicuculline were dose-related in the range 25-100 pmol. Unilateral injections of bicuculline into the ventrolateral pons also effectively suppressed tonic seizures in the electroshock model. Within the ventral pons there was a significant association between the behavioural and anticonvulsant effects of bicuculline; injections suppressing tonic seizures were associated with the induction of fast continuous locomotor activity. These data confirm that the DMAZ recipient region of the ventrolateral pontine reticular formation is part of a circuit which can suppress the manifestation of tonic hindlimb extension in the electroshock model. Whether this property is related to the participation of this region in normal locomotion and posture remains to be determined.

Location and quantification of muscarinic receptor subtypes in rat pons: implications for REM sleep generation

Microinjecting cholinomimetics into the pontine reticular formation produces a state that resembles natural rapid eye movement (REM) sleep. Evocation of this REM sleeplike states is anatomically site dependent within the pons and is mediated by muscarinic receptors. The cellular and molecular mechanisms underlying cholinergic REM sleep generation and muscarinic receptor subtype involvement remain to be specified. This study tested the hypothesis that muscarinic receptor subtypes are differentially distributed within the oral and caudal divisions of rat pontine reticular nucleus. In vitro receptor autoradiography was used to localize and quantify M1, M2, and M3 binding sites in the pontine reticular formation and in pontine brain stem regions known to regulate REM sleep. M1-M3 binding sites were present in some REM sleep-related nuclei, such as dorsal raphe and locus ceruleus. The pontine reticular formation was found to have a homogeneous distribution of M2 binding sites across its rostral to caudal extent, indicating that anatomic specificity of cholinergic REM sleep induction cannot be accounted for by a differential density of muscarinic receptors.

Epinephrine increases spinal cord concentrations of [3H]-clonidine hydrochloride in rabbits after epidural infusion

Epinephrine is often given with epidurally administered drugs to prolong and enhance analgesia, which is partly attributed to alpha-adrenergic processes. This investigation evaluates the effect of epinephrine on the distribution of epidurally administered [3H]-clonidine hydrochloride (clonidine HCl) in serum and in the central nervous system. After placing a lumbar epidural catheter via a laminectomy, rabbits were randomly assigned to receive 20 microCi of clonidine HCl with epinephrine (1:200,000) (n = 5) or without (control; n = 5) for 90 min. During the administration, which included bolus and slow infusion, blood samples were collected at 15-min intervals. At the end of the administration, rabbits were perfused with normal saline, leading to exsanguination. Brain and spinal cord tissues were excised for radiometric analysis. In both groups, the concentration of clonidine HCl was greatest in the lumbar cord. Epinephrine further enhanced accumulation of clonidine HCl into the lumbar cord but did not alter the concentration of clonidine HCl in serum, brain, cervical cord, and thoracic cord. We conclude that lumbar administration of epidural clonidine HCl leads to increased concentrations in the lumbar cord, which is further enhanced by epinephrine. The increased spinal cord accumulation of clonidine may be another mechanism by which epinephrine improves epidural analgesia.

Pontine microinjection of carbachol does not reliably enhance paradoxical sleep in rats

It has been repeatedly shown in cats that acute administration of carbachol into the pontine reticular formation (PRF) readily evokes a state that closely mimics natural paradoxical sleep (PS). Surprisingly, there are few corresponding studies in rats. In order to further characterize the effects of pontine carbachol in rats, 151 injections of different doses (from 3 micrograms to 0.005 microgram in 0.1 microliter saline) of carbachol were made at different sites within the PRF of 70 rats. Sleep-waking states obtained in the 4 hours following carbachol administration were compared to control values, obtained both under baseline condition (no injection) and following pontine injection of 0.1 microliter saline. On the one hand, from the whole set of carbachol injections, it appeared that: 1) most injections (112/151) did not significantly alter the sleep-wake states; 2) when carbachol was effective, it induced either increased PS (20 injections) or increased waking (19 injections); and 3) effective injection sites were intermingled with noneffective sites. Dose- or site-dependency effects can account in part, but not totally, for these discordant results. On the other hand, in accordance with previous rat studies, we found that: 1) the PRF medial and ventral to the motor trigeminal nucleus was the most effective region for carbachol to increase PS; 2) carbachol-induced PS enhancement was of moderate magnitude (+60% above control saline level over the 4-hour recording time); 3) latency to onset of the first PS episode was not shortened; and 4) only the number of PS episodes was increased, their duration was not prolonged. These characteristics of carbachol-induced PS enhancement strongly differ, both in terms of magnitude and timing, from those described in cats. We suggest that the less reliable and weaker effects of pontine carbachol injection in rats compared to cats can be due to methodological problems inherent in the intracerebral microinjection technique and also to species-related differences in the mechanisms controlling the PS state.

A neuroanatomical method to assess the integrity of fibers of passage following ibotenate-induced damage to the central nervous system

In some behavioral-lesion experiments involving animals, ibotenic acid (IBO) is used as a means of damaging brain structures. Occasionally one needs to assess the status of fibers coursing through the damaged area to determine whether the deficits observed are the result of destruction of neurons rather than fibers. In such cases, IBO, is considered to be the method of choice since it destroys cell bodies but leaves fibers of passage intact. However, if the IBO dose injected in a given area is too high, both cell bodies and fibers of passage could be damaged. The anterograde and retrograde tracer wheat germ agglutinin-horseradish peroxidase (WGA-HRP) is a useful technique to verify that fibers are intact, and is a more powerful tool in comparison with a tracer, such as HRP, which has been used in previous studies.

Discriminable excitotoxic effects of ibotenic acid, AMPA, NMDA and quinolinic acid in the rat laterodorsal tegmental nucleus

Excitotoxins are valuable tools in neuroscience research as they can help us to discover the extent to which certain neurones are necessary for different types of behaviour. They have distinctive neurotoxic effects depending on where they are infused, and this study was conducted to delineate the neurotoxic profiles of excitotoxins in the laterodorsal tegmental nucleus (LDTg). Two 0.1 microl infusions of 0.1 M ibotenate, 0.1 M quinolinate, 0.04-0.1 M NMDA, or 0.05-0.015 M AMPA, were made unilaterally into the LDTg under either pentobarbitone or Avertin anaesthesia. The injection needle was oriented at an angle of 24 degrees from vertical in the mediolateral plane. After 23-27 days, sections through the mesopontine tegmentum were processed using standard histological procedures for NADPH-diaphorase histochemistry, tyrosine hydroxylase or 5-hydroxytryptamine immunohistochemistry, and Cresyl violet. Lesions were assessed in terms of the size of the damaged area (identified by reactive gliosis), the extent of cholinergic cell loss in the mesopontine tegmentum (by counting NADPH-diaphorase-positive neurones), and neuronal loss induced in the locus coeruleus and dorsal raphe nucleus. Ibotenate induced compact lesions in the LDTg (more than 80% cholinergic loss) and did little damage to the locus coeruleus and dorsal raphe nucleus. Quinolinate and low doses of AMPA and NMDA made very small lesions with less than 35% cholinergic loss, while at higher doses, AMPA and NMDA induced large areas of reactive gliosis but killed only a proportion of the cholinergic neurones. AMPA appeared to have a particular affinity for noradrenergic neurones in the locus coeruleus, with the 0.015 M dose injected into the LDTg typically destroying the majority of these neurones. The results are discussed in the context of what is known about the mechanisms of excitotoxins and the glutamate receptor profile of mesopontine neurones.

Excitotoxic lesions of the pedunculopontine tegmental nucleus produce contralateral hemiparkinsonism in the monkey

Dopaminergic nigrostriatal neurons, degeneration of which causes Parkinson's disease, are known to receive excitatory input almost exclusively from the pedunculopontine tegmental nucleus (PPN). We report here that excitotoxic lesions of the PPN produce abnormal motor signs relevant to hemiparkinsonism in the macaque monkey. Under the guidance of extracellular unit recordings, the electrophysiologically identified PPN was injected unilaterally with kainic acid. These PPN-lesioned monkeys exhibited mild to moderate levels of flexed posture and hypokinesia in the upper and lower limbs contralateral to the lesion. In most of the monkeys, such pathophysiological events were gradually improved and became stationary in 1-2 weeks. The hemiparkinsonian symptoms observed after PPN destruction might be ascribed to a decrease in nigrostriatal neuron activity due to excitatory input ablation.

Cholecystokinin and neurotensin inversely modulate excitatory synaptic transmission in the parabrachial nucleus in vitro

Cholecystokinin and neurotensin are present in fibres innervating the parabrachial nucleus and have previously been shown to modulate the flow of visceral afferent information through the parabrachial nucleus to the cortex in the rat. This study examined the effects of cholecystokinin and neurotensin on synaptic transmission in the parabrachial nucleus using a pontine slice preparation and the nystatin perforated-patch recording technique. Stimulation of the ventral, external lateral portion of the parabrachial nucleus elicited glutamate-mediated, excitatory postsynaptic currents in cells recorded in the parabrachial nucleus. Bath application of neurotensin dose-dependently and reversibly enhanced, while cholecystokinin attenuated, the evoked excitatory postsynaptic current. In addition, the frequency of spontaneous, miniature excitatory postsynaptic currents recorded in parabrachial nucleus cells was significantly increased by neurotensin and decreased by cholecystokinin application. Paired-pulse depression was also enhanced and decreased by neurotensin and cholecystokinin, respectively. These synaptic changes induced by neurotensin and cholecystokinin were not accompanied by changes in input resistance of parabrachial nucleus cells over a wide voltage range (although neurotensin reduced an outwardly rectifying conductance at potentials positive to -20 mV), nor did these peptides alter the inward current induced by a brief bath application of the glutamate agonist, alpha-amino-3-hydroxy-methylisoxazole-4-propionate. The neurotensin antagonist, SR48692 (100 microM), completely and reversibly blocked the neurotensin-induced enhancement of the excitatory postsynaptic current. The non-selective cholecystokinin receptor antagonist, proglumide (100 microM), completely and reversibly blocked the cholecystokinin-induced attenuation of the excitatory postsynaptic current. In addition, the selective cholecystokinin-A receptor antagonist, L-364,718 (10 microM), but not the selective cholecystokinin-B receptor antagonist, L-365,260 (100 microM), blocked the effect of cholecystokinin on synaptic transmission. These results suggest that neurotensin and cholecystokinin act at presynaptic neurotensin and cholecystokinin-A receptors, respectively, to modulate excitatory synaptic transmission in the parabrachial nucleus.

Naloxone-reversible antinociception by paracetamol in the rat

Paracetamol at the dose of 400 mg/kg i.p. displayed antinociceptive activity in the hot-plate test and the formalin test. Moreover, it induced a significant increase in brain serotonin (5-HT) concentration and a reduction in the number of 5-HT2 receptors in cortical membranes. Pretreatment with naloxone abolished this antinociceptive activity both in the hot-plate test and in the first phase of the formalin test without affecting the serum concentration of paracetamol. At the same time, naloxone prevented the increase in 5-HT concentration in the central nervous system and the reduction in 5-HT2 receptors in cortical membranes. Competition experiments demonstrated that paracetamol possesses affinity for [3H]naloxone binding sites. The action of morphine on nociception and on the serotonergic system was similar to that of paracetamol; all morphine-induced effects were blocked by naloxone. These data provide further evidence for a central antinociceptive effect of paracetamol and support the hypothesis that paracetamol exerts its antinociceptive activity through the serotonergic system. Moreover, our results point to the relationship between serotonergic and opiatergic systems in the antinociceptive activity of paracetamol.

MCI-225, a novel thienopyrimidine analog, enhances attentional eye tracking in midpontine pretrigeminal preparation

The effects of MCI-225, a novel psychoactive compound, and reference drugs on attention behavior were studied using visual stimulus induced vertical eye tracking movements in midpontine pretrigeminal (PTG) feline preparation. Surgery was performed under ether anesthesia and subsequently switched to nitrous oxide-fluothane which was discontinued only during experimental sessions. In addition xylocaine was locally injected. Vertical eye movements were monitored by electrooculogram (EOG) and a TV camera. To compare the effects of drugs on eye movement, numbers of spontaneous and tracking eye movements exceeding a present amplitude in EOG were counted before and during the visual stimulation, respectively. MCI-225 (1 and 3 mg/kg, i.v.) enhanced tracking movements dose-dependently without an increase in spontaneous eye movements. No or little change of the electrocorticogram (ECoG) was seen with 1 mg/kg MCI-225 and a slight increase in low voltage fast pattern was observed with 3 mg/kg, i.v.. On the other hand, tacrine (0.3 mg/kg, i.v.), physostigmine (0.03 mg/kg, i.v.) and methylphenidate (0.3 mg/kg, i.v.) enhanced both types of eye movement and induced ECoG arousal. Desipramine (3 mg/kg, i.v.) slightly increased spontaneous eye movement without affecting tracking movements. Piracetam (100 mg/kg, i.v.) decreased spontaneous eye movements only. These data clearly show that MCI-225 enhances attention to a moving object and suggest that MCI-225 could be useful in the treatment of attentional deficits and related cognitive dysfunctions in psychiatric disorders.

Alterations in brain levels of atrial and C-type natriuretic peptides after chronic moderate ethanol consumption in spontaneously hypertensive rats

Atrial (ANP) and C-type (CNP) natriuretic peptides have been found in brain regions associated with fluid homeostasis and blood pressure. Since chronic moderate ethanol consumption has been shown to prevent the age-dependent increase in blood pressure in experimental animals, the objective of the present studies was to investigate the effect of ethanol (20% (v/v) for 8 months) on the total content and concentration of ANP and CNP in the brain of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Ethanol increased the content and concentration of both ANP and CNP in the hypothalamus, pons and medulla of SHR rats. In contrast, in the WKY rats ethanol had no effect on the levels of ANP in any of the brain regions studies, but enhanced the concentration of CNP in the hypothalamus and medulla. Thus, ethanol induced changes in the content of natriuretic peptides in distinct brain regions associated with control of cardiovascular activity. Such changes may be partially responsible for the effect of chronic moderate ethanol consumption on blood pressure.

Vesicular acetylcholine transport inhibitor suppresses REM sleep

The vesamicol-like compound (+/-)-4-aminobenzovesamicol (ABV) non-competitively inhibits vesicular packaging of acetylcholine (ACh) in presynaptic terminals. This study tested the hypothesis that microinjection of ABV into the medial pontine reticular formation (mPRF) of intact, unanesthetized cats would inhibit rapid eye movement (REM) sleep. Microinjection of ABV alone or before administration of the acetylcholinesterase inhibitor neostigmine was used to evaluate the effects of ABV on natural REM sleep and on the neostigmine-induced REM sleep-like state. ABV decreased (24.8%) REM sleep and significantly reduced (33.6%) the neostigmine-induced REM sleep-like state. The results show for the first time that REM sleep generation can be disrupted by blocking a synaptic vesicle protein that modulates ACh transport in localized regions of the mPRF.

Pontine nitric oxide modulates acetylcholine release, rapid eye movement sleep generation, and respiratory rate

Pontine cholinergic neurotransmission is known to play a key role in the regulation of rapid eye movement (REM) sleep and to contribute to state-dependent respiratory depression. Nitric oxide (NO) has been shown to alter the release of acetylcholine (ACh) in a number of brain regions, and previous studies indicate that NO may participate in the modulation of sleep/wake states. The present investigation tested the hypothesis that inhibition of NO synthase (NOS) within the medial pontine reticular formation (mPRF) of the unanesthetized cat would decrease ACh release, inhibit REM sleep, and prevent cholinergically mediated respiratory depression. Local NOS inhibition by microdialysis delivery of N(G)-nitro-L-arginine (NLA) significantly reduced ACh release in the cholinergic cell body region of the pedunculopontine tegmental nucleus and in the cholinoceptive mPRF. A second series of experiments demonstrated that mPRF microinjection of NLA significantly reduced the amount of REM sleep and the REM sleep-like state caused by mPRF injection of the acetylcholinesterase inhibitor neostigmine. Duration but not frequency of REM sleep epochs was significantly decreased by mPRF NLA administration. Injection of NLA into the mPRF before neostigmine injection also blocked the ability of neostigmine to decrease respiratory rate during the REM sleep-like state. Taken together, these findings suggest that mPRF NO contributes to the modulation of ACh release, REM sleep, and breathing.

Encoding of corneal input in two distinct regions of the spinal trigeminal nucleus in the rat: cutaneous receptive field properties, responses to thermal and chemical stimulation, modulation by diffuse noxious inhibitory controls, and projections to the parabrachial area

To determine whether corneal input is processed similarly at rostral and caudal levels of the spinal trigeminal nucleus, the response properties of second-order neurons at the transition between trigeminal subnucleus interpolaris and subnucleus caudalis (Vi/Vc) and at the transition between subnucleus caudalis and the cervical spinal cord (Vc/C1) were compared. Extracellular single units were recorded in 68 Sprague-Dawley rats under chloralose or urethan/chloralose anesthesia. Neurons that responded to electrical stimulation of the cornea at the Vi/Vc transition region (n = 61) and at laminae I/II of the Vc/C1 transition region (n = 33) were classified regarding 1) corneal mechanical threshold; 2) cutaneous mechanoreceptive field, if present; 3) electrical input characteristics (A and/or C fiber); 4) response to thermal stimulation; 5) response to the small-fiber excitant, mustard oil (MO), applied to the cornea; 6) diffuse noxious inhibitory controls (DNIC); and 7) projection status to the contralateral parabrachial area (PBA). On the basis of cutaneous receptive field properties, neurons were classified as low-threshold mechanoreceptive (LTM), wide dynamic range (WDR), nociceptive specific (NS), or deep nociceptive (D). All neurons recorded at the Vc/C1 transition region were either WDR (n = 19) or NS (n = 14). In contrast, 54% of the Vi/Vc neurons had no cutaneous receptive field. Of those Vi/Vc neurons that had a cutaneous receptive field, 57% were LTM, 25% were WDR, and 18% were D. All Vc/ C1 neurons responded to noxious thermal and MO stimulation. Only 22 of 47 and 13 of 19 Vi/Vc corneal units responded to thermal or MO stimulation, respectively. At the Vc/C1 transition region, 12 of 17 neurons demonstrated DNIC, whereas at the Vi/Vc transition region, DNIC was present in only 4 of 26 neurons. Of 15 Vc/C1 corneal units, 12 could be antidromically activated from the contralateral PBA (average latency 6.29 ms, range 1.8-26 ms). None of 22 Vi/Vc corneal units tested could be antidromically activated from the PBA. These findings suggest that neurons in laminae I/II at the Vc/C1 transition and at the Vi/Vc transition process corneal input differently. Neurons in laminae I/II at the Vc/C1 transition process corneal afferent input consistent with that from other orofacial regions. Corneal-responsive neurons at the Vi/Vc transition region may be important in motor reflexes or in recruitment of descending antinociceptive controls.

Involvement of non-NMDA and NMDA receptors in glutamate-induced pressor or depressor responses of the pons and medulla

1. Fifty-five intact and six baroreceptor denervated and vagotomized cats of either sex were anaesthetized intraperitoneally with urethane (400 mg/kg) and alpha-chloralose (40 mg/kg). Responses of the systemic arterial pressure (SAP), mean SAP (MSAP) and sympathetic vertebral nerve (VNA) and renal nerve activities (RNA) were recorded. 2. In intact animals, monosodium L-glutamate (Glu, 0.1 mol/L, 50 nL) was microinjected into pressor areas of the locus coeruleus (LC), gigantocellular tegmental field (GTF), rostral ventrolateral medulla (RVLM) and dorsomedial medulla (DM), and the depressor areas of caudal ventrolateral medulla (CVLM). The induced actions were compared before and after microinjection of either glutamate antagonists, glutamate diethylester (GDEE, 0.5 mol/L, 50-100 nL), a competitive AMPA receptor blocker, or 2-amino-5-phosphonovaleric acid (D-AP5, 0.025 mol/L, 50-100 nL), a competitive N-methyl-D-aspartate (NMDA) receptor blocker. GDEE completely blocked the increases of SAP and VNA elicited from all pressor areas. D-AP5 only partially blocked the pressor but slightly blocked VNA and RNA responses from LC, GTF and DM, particularly those from RVLM. Neither GDEE nor D-AP5 blocked the depressor responses of SAP and two nerve activities elicited from CVLM. 3. In baroreceptor denervated animals, NMDA (2 mmol/L, 50-100 nL) and AMPA (0.2 mmol/L, 50-100 nL) were micro-injected into the same pressor areas of GTF, RVLM and DM and the depressor area of CVLM responsive to Glu activation (0.1 mol/L, 30 nL). In RVLM, DM and CVLM, the results of either NMDA or AMPA were similar to those induced by Glu. However, in GTF, microinjection of either NMDA or AMPA did not induce similar responses to Glu. This suggests that the nature of GTF may differ from RVLM and DM. 4. The above results suggest that the Glu-induced pressor responses from LC, GTF, DM and especially RVLM, are primarily mediated through AMPA receptors. The Glu-induced depressor responses from CVLM may not be predominantly mediated by either AMPA or NMDA receptors. 5. In both baroreceptor-intact and -denervated cats stimulation of the pressor areas often produced an increase of VNA and a decrease of RNA, while in the depressor CVLM decreased both VNA and RNA. The VNA, but not RNA were positively correlated with the pressor responses, while both VNA and RNA were positively correlated with the depressor responses. This may suggest that neurons of the sympathetic vertebral and renal nerves are topographically organized in the brain.

NMDA receptors in the pontine brainstem are necessary for fear potentiation of the startle response

The fear-potentiated startle model in rats is a valuable animal test for the investigation of the neural and neurochemical basis of fear. In this model, rats are trained to associate a neutral stimulus with an aversive stimulus, so that after conditioning the conditioned stimulus alone elicits a state of fear leading to an exaggerated acoustic startle response. The fear-potentiated startle model does not require instrumental responding for the indication of states of fear. The acoustic startle response is mediated by a simple brainstem circuit, with the caudal pontine reticular nucleus as an interface that receives input from startle-enhancing circuits. In the present study, we tested the hypothesis that N-methyl-D-aspartate (NMDA) receptors on neurones of the caudal pontine reticular nucleus are involved in the mediation of fear-potentiated startle. After fear-conditioning, we injected the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (AP-5), into the caudal pontine reticular nucleus of awake rats and tested the effect on the expression of fear-potentiated startle. Injections of AP-5 (0.125-0.5 nmol) into the caudal pontine reticular nucleus dose dependently attenuated fear-potentiated startle without affecting the baseline amplitude of the acoustic startle response. The results suggests that, in the caudal pontine reticular nucleus, glutamate may mediate fear-potentiated startle via NMDA receptors.

The one-and-a-half syndrome in systemic lupus erythematosus

We report a case of one-and-a-half syndrome occurring as the first manifestation of central nervous system (CNS) involvement in systemic lupus erythematosus (SLE). The lesion in the pons was documented with magnetic resonance imaging (MRI). The patient responded quite satisfactorily to high-dose i.v. methyl-prednisolone therapy.

Lesions of the lateral parabrachial nucleus block the aversive motivational effects of both morphine and morphine withdrawal but spare morphine's discriminative properties

This study examined if the aversive properties of morphine, the aversive properties of morphine withdrawal, and the discriminative properties of morphine are mediated by common neurobiological substrates. Lesions of the lateral parabrachial nucleus, which blocked the aversive properties of morphine in the conditioned taste aversion paradigm, also blocked the acquisition of conditioned place aversions to environments paired with the aversive properties of morphine withdrawal in morphine-dependent rats. When morphine and saline were used as cues in a discrimination task, however, both sham-operated and lesioned rats were able to solve the task.

Hyperphagia induced by direct administration of midazolam into the parabrachial nucleus of the rat

Benzodiazepine receptor agonists increase food intake in many different species, yet there has been little investigation of the central site of actions of these drugs on ingestive behaviour. In the present experiments, direct administration of the benzodiazepine receptor agonist midazolam (3-30 micrograms/microliter) into the parabrachial nucleus of the pons significantly increased the consumption of a wet mash diet and a 3% sucrose solution in adult non-deprived rats. The hyperphagic response was blocked by pre-treatment with the selective benzodiazepine receptor antagonist flumazenil. Injection of midazolam into the parabrachial nucleus had no effect on locomotor activity, despite the fact that in the same animals an increase in mash intake was observed following intra-parabrachial midazolam. These data suggest that benzodiazepine receptors located in the parabrachial nucleus may be an important site of action for the effects of benzodiazepines specifically on ingestive behaviour.

Local administration of dopaminergic drugs into the ventral tegmental area modulates cataplexy in the narcoleptic canine

Cataplexy in the narcoleptic canine may be modulated by systemic administration of monoaminergic compounds. In the present study, we have investigated the effects of monoaminergic drugs on cataplexy in narcoleptic canines when perfused locally via microdialysis probes in the amygdala, globus pallidus/putamen, basal forebrain, pontine reticular formation and ventral tegmental area of narcoleptic and control Doberman pinchers. Cataplexy was quantified using the Food-Elicited Cataplexy Test and analyzed by electroencephalogram, electroculogram and electromyogram. Local perfusion with the monoaminergic agonist quinpirole, 7-OH-DPAT and BHT-920, into the ventral tegmental area produced a dose-dependent increase in cataplexy without significantly reducing basal muscle tone. Perfusion with the antagonist raclopride in the same structure produced a moderate reduction in cataplexy. Local perfusion with quinpirole, 7-OH-DPAT and BHT-920 into the globus pallidus/putamen also produced an increase, while raclopride produced a decrease, in cataplexy in narcoleptic canines. In control animals, none of the above drugs produced cataplexy or muscle atonia when perfused into either the ventral tegmental area or the globus pallidus/putamen. Other monoaminergic drugs tested in these two brain areas; prazosin, yohimbine, amphetamine, SKF 38393 and SCH 23390 had no effects on cataplexy. Local perfusion with each of the above listed drugs had no effect on cataplexy in any of the other brain regions examined. These findings show that cataplexy may be regulated by D2/D3 dopaminergic receptors in the ventral tegmental area and perhaps the globus pallidus/ putamen. It is suggested that neurons in the mesolimbic dopamine system of narcoleptics are hypersensitive to dopaminergic autoreceptor agonists.

The alpha 2 adrenoreceptor agonist clonidine suppresses seizures, whereas the alpha 2 adrenoreceptor antagonist idazoxan promotes seizures: pontine microinfusion studies of amygdala-kindled kittens

This is the first report showing that microinfusion of alpha 2 adrenoreceptor agonists and antagonists into the vicinity of the locus ceruleus (LC) have contrasting effects on evoked amygdala-kindled seizure susceptibility. Microinfusion (1 microliter) of the alpha 2 agonist clonidine (CLON) and of the alpha 2 antagonist idazoxan (IDA) were made over 1 min through cannulae in the LC ipsilateral to the kindled amygdala in 6 kittens. Order of administered drugs (CLON vs. IDA) and dosages (n = 3 each) were partly counterbalanced. Focal and convulsive seizure thresholds were evaluated 10-12 min post-infusion and compared to thresholds obtained during two, interspersed control conditions (vehicle control = 1 microliter microinfusion of sterile saline; sham control = needle insertion only). CLON significantly elevated focal and generalized seizure thresholds, whereas IDA significantly reduced seizure thresholds when compared to controls. Magnitude of effects was dose-dependent. These findings confirm that norepinephrine (NE) is a potent antiepileptic agent. Results also suggest that pontine microinfusions could eventually provide an alternative treatment option for medically refractory limbic epilepsy.

Glycine-mediated inhibitory postsynaptic potentials in the medial pontine reticular formation of the rat in vitro

Glycinergic neurotransmission was examined in rat medial pontine reticular formation neurons in vitro. Intracellular recordings using glass microelectrodes were made in acutely prepared brainstem slices 400 microns thick. Spontaneous and electrically evoked synaptic activity was blocked by the glycine antagonist strychnine (1-5 microM) but not by the GABA antagonists bicuculline methiodide (40 microM) or picrotoxin (40 microM). Strychnine-sensitive spontaneous and evoked postsynaptic potentials persisted in the presence of the glutamate antagonist (kynurenate, 1 mM). Whole-cell voltage-clamp recordings were carried out in organotypic cultures of rat brainstem. The reversal potential of synaptic currents and responses to exogenously applied glycine were similar and were sensitive to manipulations of the chloride equilibrium potential. Synaptic activity but not responses to exogenous glycine were blocked by tetrodotoxin (0.3 microM). These results indicate the presence of robust, chloride ion-mediated glycinergic inhibition of medial pontine reticular formation neurons, and suggest that glycinergic neurons play an important role in controlling pontine premotor circuitry.