[Effect of the Na+, K(+)-ATPase modulation in neurons of the medulla oblongata on hemodynamic effects in spontaneously hypertensive rats].

The study was conducted in normotensive and spontaneously hypertensive rats anesthetized with urethane (1600 mg/kg of animal weight, intraperitoneally). It has been shown that in normotensive rats, injections of a specific inhibitor of Na+, K(+)-ATPase ouabain (10(-8)-10(-5) mol/l) in the populations of the neurons within nucleus of the solitary tract (NTS), paramedian reticular nucleus (PMn) and lateral reticular nucleus (LRN) were accompanied by the development of the hypertensive responses in a dose-dependent fashion. These data suggest that Na+, K(+)-ATPase of the neuron somatic membranes in the medullary cardiovascular nuclei is involved in neural control of the cardiovascular function, and its inhibition by microinjections of ouabain promotes the development of hypertension. In contrast to normotensive rats, ouabain injected in the medullary nuclei of spontaneously hypertensive animals induced either enhanced hypertensive or hypotensive responses. Biochemical analysis revealed that the activity of Na+, K(+)-ATPase in the microsomal fraction of the medulla oblongata of spontaneously hypertensive rats significantly exceeded its activity in the medulla oblongata of normotensive animals. Possible mechanisms of ouabain effects in spontaneously hypertensive rats have being discussed. Activation of Na+, K(+)-ATPase activity of the cardiovascular neurons with asparkam injections in the medullary nuclei resulted in hypotensive responses in both normotensive and spontaneously hypertensive rats.

A comparison of tabun-inhibited rat brain acetylcholinesterase reactivation by three oximes (HI-6, obidoxime, and K048) in vivo detected by biochemical and histochemical techniques.

Tabun belongs to the most toxic nerve agents. Its mechanism of action is based on acetylcholinesterase (AChE) inhibition at the peripheral and central nervous systems. Therapeutic countermeasures comprise administration of atropine with cholinesterase reactivators able to reactivate the inhibited enzyme. Reactivation of AChE is determined mostly biochemically without specification of different brain structures. Histochemical determination allows a fine search for different structures but is performed mostly without quantitative evaluation. In rats intoxicated with tabun and treated with a combination of atropine and HI-6, obidoxime, or new oxime K048, AChE activities in different brain structures were determined using biochemical and quantitative histochemical methods. Inhibition of AChE following untreated tabun intoxication was different in the various brain structures, having the highest degree in the frontal cortex and reticular formation and lowest in the basal ganglia and substantia nigra. Treatment resulted in an increase of AChE activity detected by both methods. The highest increase was observed in the frontal cortex. This reactivation was increased in the order HI-6 < K048 < obidoxime; however, this order was not uniform for all brain parts studied. A correlation between AChE activity detected by histochemical and biochemical methods was demonstrated. The results suggest that for the mechanism of action of the nerve agent tabun, reactivation in various parts of the brain is not of the same physiological importance. AChE activity in the pontomedullar area and frontal cortex seems to be the most important for the therapeutic effect of the reactivators. HI-6 was not a good reactivator for the treatment of tabun intoxication.

Aromatic L-amino acid decarboxylase-immunoreactive structures in human midbrain, pons, and medulla.

The objective of the present study was to determine with precision the localization of neurons and fibers immunoreactive (ir) for aromatic L-amino acid decarboxylase (AADC), the second-step enzyme responsible for conversion of L-dihydroxyphenylalanine (L-DOPA) to dopamine (DA) and 5-hydroxytryptophan (5-HTP) to serotonin (5-hydroxytryptamine: 5-HT) in the midbrain, pons, and medulla oblongata of the adult human brain. Intense AADC immunoreactivity was observed in a large number of presumptive 5-HT neuronal cell bodies distributed in all of the raphe nuclei, as well as in regions outside the raphe nuclei such as the ventral portions of the pons and medulla. Moderate to strong immunoreaction was observable in presumptive DA cells in the mesencephalic reticular formation, substantia nigra, and ventral tegmental area of Tsai, as well as in presumptive noradrenergic (NA) cells, which were aggregated in the locus coeruleus and dispersed in the subcoeruleus nuclei. In the medulla oblongata, immunoreaction of moderate intensity was distributed in the mid and ventrolateral portions of the intermediate reticular nucleus, which constitutes the oblique plate of A1/C1 presumptive adrenergic and/or NA neurons. The dorsal vagal AADC-ir neurons were fewer in number and stained more weakly than cells immunoreactive for tyrosine hydroxylase (TH). AADC immunoreactivity was not identified in an aggregate of TH-ir neurons lying in the gelatinous subnucleus of the solitary nucleus, a restricted region just rostroventral to the area postrema. Nonaminergic AADC-positive neurons (D neurons), which are abundant in the rat and cat midbrain, pons, and medulla, were hardly detectable in homologous regions in the human brain, although they were clearly distinguishable in the forebrain.

Cyclooxygenase-1 and -2 in spinally projecting neurons are involved in CRF-induced sympathetic activation.

Corticotropin-releasing factor (CRF) in the brain has been shown to stimulate sympathetic activity, leading to elevations of blood pressure, heart rate and plasma catecholamine levels and neuronal activation of the sympathetic ganglia and adrenal medulla. We previously reported that brain cyclooxygenase (COX), the rate-limiting enzyme in the synthesis of prostanoids, is involved in centrally administered CRF-induced sympathetic activation in rats. Therefore, the present study was designed to reveal the effect of centrally administered CRF (1.5 nmol/animal) on the expression of COX isozymes, COX-1 and COX-2, in spinally projecting neurons until 6h after the administration, using rats microinjected with a monosynaptic retrograde tracer into the intermediolateral cell column of the thoracic spinal cord. Retrogradely labeled neurons were detected in the paraventricular hypothalamic nucleus (PVN), locus coeruleus (LC), raphe pallidus nucleus and rostral ventrolateral medulla. Centrally administered CRF significantly increased the number of spinally projecting PVN neurons expressing COX-1 throughout the experimental period and those expressing COX-2 during only the late phase. CRF also increased the number of spinally projecting LC neurons expressing COX-2 throughout the experimental period. In other regions, the CRF administration had no effect on COXs expression in spinally projecting neurons. These results suggest that COX-1 and COX-2 in the PVN and COX-2 in the LC play roles in the CRF-induced sympathetic regulation in rats.

Organisation of the catecholaminergic system in the vagal motor nuclei of pigs: a retrograde fluorogold tract tracing study combined with immunohistochemistry of catecholaminergic synthesizing enzymes.

The vagal motor system is involved in the regulation of cardiorespiratory and gastrointestinal functions. Vagal motor neurons are localized near or adjacent to catecholaminergic neurons, but their co-localisation seems species dependent, present in the cat but absent in the rabbit. In pig, a species commonly used as an experimental model in humans brain disorders (sudden infant death syndrome, hypoxia), the relationship is poorly understood. We aimed at describing the distribution of vagal motor neurons and tyrosine hydroxylase-immunoreactive (-ir) neurons by using a double staining method in combination with retrograde tracing of vagal efferent neurons. After fluorogold impregnation of the central part of the sectioned left cervical vagal trunk, two main vagal motor neuronal populations were located in the dorsal motor nucleus of the vagus nerve (DMX) and in the area of the nucleus ambiguus (Amb). Like in the human, the DMX was composed of different subpopulations of neurons with the same morphological characteristics. Immunohistochemistry of catecholaminergic synthesizing enzymes differentiated two main sites containing vagal motor populations: the dorsomedial and the ventrolateral medulla. TH-ir was rarely seen in vagal motor neurons of the DMX, but TH-ir neurons were present around the two main vagal motor neuronal populations that contained TH-ir fibres. The anatomical organisation of the vagal motor and the catecholaminergic neuronal systems are similar to those described in humans and suggest that the involvement of the catecholamines in the control of the vagal motor system may be similar in pigs and in humans.

Hypoglossal premotor neurons of the intermediate medullary reticular region express cholinergic markers.

The inspiratory drive to hypoglossal (XII) motoneurons originates in the caudal medullary intermediate reticular (IRt) region. This drive is mainly glutamatergic, but little is known about the neurochemical features of IRt XII premotor neurons. Prompted by the evidence that XII motoneuronal activity is controlled by both muscarinic (M) and nicotinic cholinergic inputs and that the IRt region contains cells that express choline acetyltransferase (ChAT), a marker of cholinergic neurons, we investigated whether some IRt XII premotor neurons are cholinergic. In seven rats, we applied single-cell reverse transcription-polymerase chain reaction to acutely dissociated IRt neurons retrogradely labeled from the XII nucleus. We found that over half (21/37) of such neurons expressed mRNA for ChAT and one-third (13/37) also had M2 receptor mRNA. In contrast, among the IRt neurons not retrogradely labeled, only 4 of 29 expressed ChAT mRNA (P < 0.0008) and only 3 of 29 expressed M2 receptor mRNA (P < 0.04). The distributions of other cholinergic receptor mRNAs (M1, M3, M4, M5, and nicotinic alpha4-subunit) did not differ between IRt XII premotor neurons and unlabeled IRt neurons. In an additional three rats with retrograde tracers injected into the XII nucleus and ChAT immunohistochemistry, 5-11% of IRt XII premotor neurons located at, and caudal to, the area postrema were ChAT positive, and 27-48% of ChAT-positive caudal IRt neurons were retrogradely labeled from the XII nucleus. Thus the pre- and postsynaptic cholinergic effects previously described in XII motoneurons may originate, at least in part, in medullary IRt neurons.

Characterization of GABAergic neurons in rapid-eye-movement sleep controlling regions of the brainstem reticular formation in GAD67-green fluorescent protein knock-in mice.

Recent experiments suggest that brainstem GABAergic neurons may control rapid-eye-movement (REM) sleep. However, understanding their pharmacology/physiology has been hindered by difficulty in identification. Here we report that mice expressing green fluorescent protein (GFP) under the control of the GAD67 promoter (GAD67-GFP knock-in mice) exhibit numerous GFP-positive neurons in the central gray and reticular formation, allowing on-line identification in vitro. Small (10-15 microm) or medium-sized (15-25 microm) GFP-positive perikarya surrounded larger serotonergic, noradrenergic, cholinergic and reticular neurons, and > 96% of neurons were double-labeled for GFP and GABA, confirming that GFP-positive neurons are GABAergic. Whole-cell recordings in brainstem regions important for promoting REM sleep [subcoeruleus (SubC) or pontine nucleus oralis (PnO) regions] revealed that GFP-positive neurons were spontaneously active at 3-12 Hz, fired tonically, and possessed a medium-sized depolarizing sag during hyperpolarizing steps. Many neurons also exhibited a small, low-threshold calcium spike. GFP-positive neurons were tested with pharmacological agents known to promote (carbachol) or inhibit (orexin A) REM sleep. SubC GFP-positive neurons were excited by the cholinergic agonist carbachol, whereas those in the PnO were either inhibited or excited. GFP-positive neurons in both areas were excited by orexins/hypocretins. These data are congruent with the hypothesis that carbachol-inhibited GABAergic PnO neurons project to, and inhibit, REM-on SubC reticular neurons during waking, whereas carbachol-excited SubC and PnO GABAergic neurons are involved in silencing locus coeruleus and dorsal raphe aminergic neurons during REM sleep. Orexinergic suppression of REM during waking is probably mediated in part via excitation of acetylcholine-inhibited GABAergic neurons.

Activation of ERK in the rostral ventromedial medulla is involved in hyperalgesia during peripheral inflammation.

We have previously shown that the extracellular signal-regulated kinase (ERK) is activated in the rostral ventromedial medulla (RVM) during peripheral inflammation. In the present study, the relationship between ERK signaling in the RVM and pain hypersensitivity was investigated in the rat. Microinjection of U0126, a mitogen-activated protein kinase kinase inhibitor, into the RVM decreased phosphorylated ERK at 7 h after complete Freund's adjuvant (CFA) injection into the hindpaw. The U0126 microinjection also attenuated thermal hyperalgesia in the ipsilateral hindpaw at 24 h after CFA injection. The ipsilateral paw withdrawal latency in the U0126 group (67.9%+/-5.3% vs. baseline, n=7) was significantly longer than that in the control group (52.0%+/-3.6% vs. baseline, n=8). These findings suggest that activation of ERK in the RVM contributes to thermal hyperalgesia during peripheral inflammation.

Upregulation of GAD65 mRNA in the medulla of the rat model of metabolic syndrome.

Metabolic syndrome is characterized by obesity, elevated blood pressure (BP), insulin resistance, and hypercholesterolemia. Recently an animal model of this disorder has been proposed in rats selectively bred based on their performance on a treadmill-running task. Accordingly, low capacity runner (LCR) rats exhibited all of the diagnostic criteria for metabolic syndrome, including elevated BP, as compared to their high capacity runner (HCR) counterparts [U. Wisløff, S.M. Najjar, O. Ellingsen, P.M. Haram, S. Swoap, Q. Al-Share, M. Fernstrom, K. Rezaei, S.J. Lee, L.G. Koch, S.L. Britton, Cardiovascular risk factors emerge after artificial selection for low aerobic capacity, Science 307 (2005) 418-420]. Previous studies have highlighted the importance of GABAergic neurotransmission in the medullary cardiovascular-regulatory areas in the central control of BP. Thus, we hypothesized a dysregulation in GABAergic transmission in the medullary cardiovascular-regulatory nuclei of LCR rats. To begin testing this hypothesis we carried out experiments examining expression of the GABA synthetic enzymes, GAD65 and GAD67, mRNAs in the two rat strains via radioactive in situ hybridization. Our results showed GAD65 and GAD67 mRNAs were widely expressed throughout the brainstem; quantification revealed increased GAD65 mRNA expression in LCR animals in the caudal nucleus tractus solitarius (NTS) and rostral ventrolateral medulla (VLM) as compared to HCR rats. Conversely, no differences in the expression of GAD67 were detected in these regions. These data are consistent with the notion of altered GABAergic neurotransmission in the NTS and VLM in metabolic syndrome, and point to the importance of these regions in cardiovascular regulation.

Effects of peripheral inflammation on activation of p38 mitogen-activated protein kinase in the rostral ventromedial medulla.

In the present study, the activation of p38 mitogen-activated protein kinase (p38 MAPK) in the rostral ventromedial medulla (RVM) following the injection of complete Freund's adjuvant (CFA) into the rat hindpaw was examined in order to clarify the mechanisms underlying the dynamic changes in the descending pain modulatory system after peripheral inflammation. Phospho-p38 MAPK-immunoreactive (p-p38 MAPK-IR) neurons were observed in the nucleus raphe magnus (NRM) and nucleus reticularis gigantocellularis pars alpha (GiA). Inflammation induced the activation of p38 MAPK in the RVM, with a peak at 30 min after the injection of CFA into the hindpaw, which lasted for 1 h. In the RVM, the number of p-p38 MAPK-IR neurons per section in rats killed at 30 min after CFA injection (19.4+/-2.0) was significantly higher than that in the naive group (8.4+/-2.4) [p<0.05]. At 30 min after CFA injection, about 40% of p-p38 MAPK-IR neurons in the RVM were serotonergic neurons (tryptophan hydroxylase, TPH, positive) and about 70% of TPH-IR neurons in the RVM were p-p38 MAPK positive. The number of p-p38 MAPK- and TPH-double-positive RVM neurons in the rats with inflammation was significantly higher than that in naive rats [p<0.05]. These findings suggest that inflammation-induced activation of p38 MAPK in the RVM may be involved in the plasticity in the descending pain modulatory system following inflammation.

Taste-evoked Fos expression in nitrergic neurons in the nucleus of the solitary tract and reticular formation of the rat.

The current investigation used double labeling for NADPHd and Fos-like immunoreactivity to define the relationship between nitric oxide synthase-containing neural elements and taste-activated neurons in the nucleus of the solitary tract (NST) and subjacent reticular formation (RF). Stimulation of awake rats with citric acid and quinine resulted in significant increases in the numbers of double-labeled neurons in both the NST and RF, suggesting that some medullary gustatory neurons utilize nitric oxide (NO) as a transmitter. Overall, double-labeled neurons were most numerous in the caudal reaches of the gustatory zone of the NST, where taste neurons receive inputs from the IXth nerve, suggesting a preferential role for NO neurons in processing gustatory inputs from the posterior oral cavity. However, double-labeled neurons also exhibited a preferential distribution depending on the gustatory stimulus. In the NST, double-labeled neurons were most numerous in the rostral central subnucleus after either stimulus but had a medial bias after quinine stimulation. In the RF, after citric acid stimulation, there was a cluster of double-labeled neurons with distinctive large soma in the parvicellular division of the lateral RF, subjacent to the rostral tip of NST. In contrast, in response to quinine, there was a cluster of double-labeled neurons with much smaller soma in the intermediate zone of the medial RF, a few hundred micrometers caudal to the citric acid cluster. These differential distributions of double-labeled neurons in the NST and RF suggest a role for NO in stimulus-specific gustatory autonomic and oromotor reflex circuits.

Activation of pedunculopontine tegmental protein kinase A: a mechanism for rapid eye movement sleep generation in the freely moving rat.

Cells in the pedunculopontine tegmentum (PPT) play a key role in the generation of rapid eye movement (REM) sleep, but its intracellular signaling mechanisms remain unknown. In the current studies, the role of PPT intracellular protein kinase A (PKA) in the regulation of REM sleep was evaluated by comparing PKA subunit [catalytic (PKA(C alpha)) and regulatory (PKA(RI), PKA(RII alpha), and PKA(RII beta)) types] expression and activity in the PPT at normal, high, and low REM sleep conditions. To compare anatomical specificity, REM sleep-dependent expressions of these PKA subunits were also measured in the medial pontine reticular formation (mPRF), medial prefrontal cortex (mPFC), and anterior hypothalamus (AHTh). The results of these PKA subunit expression and activity studies demonstrated that the expression of PKA(C alpha) and PKA activity in the PPT increased and decreased during high and low REM sleep, respectively. Conversely, PKA(C alpha) expression and PKA activity decreased with high REM sleep in the mPRF. Expression of PKA(C alpha) also decreased in the mPFC and remained unchanged in the AHTh with high REM sleep. These subunit expression and PKA activity data reveal a positive relationship between REM sleep and increased PKA activity in the PPT. To test this molecular evidence, localized activation of cAMP-dependent PKA activity was blocked using a pharmacological technique. The results of this pharmacological study demonstrated that the localized inhibition of cAMP-dependent PKA activation in the PPT dose-dependently suppressed REM sleep. Together, these results provide the first evidence that the activation of the PPT intracellular PKA system is involved in the generation of REM sleep.

Cardiovascular responses and neurotransmitter changes during static muscle contraction following blockade of inducible nitric oxide synthase (iNOS) within the ventrolateral medulla.

The enzyme nitric oxide synthase (NOS) which is necessary for the production of nitric oxide from L-arginine exists in three isoforms: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). Our previous studies have demonstrated the roles of nNOS and eNOS within the rostral (RVLM) and caudal ventrolateral medulla (CVLM) in modulating cardiovascular responses during static skeletal muscle contraction via altering localized glutamate and GABA levels (Brain Res. 977 (2003) 80-89; Neuroscience Res. 52 (2005) 21-30). In this study, we investigated the role of iNOS within the RVLM and CVLM on cardiovascular responses and glutamatergic/GABAergic neurotransmission during the exercise pressor reflex. Bilateral microdialysis of a selective iNOS antagonist, aminoguanidine (AGN; 1.0 microM), for 60 min into the RVLM attenuated increases in mean arterial pressure (MAP), heart rate (HR), and extracellular glutamate levels during a static muscle contraction. Levels of GABA within the RVLM were increased. After 120 min of discontinuation of the drug, MAP and HR responses and glutamate/GABA concentrations recovered to baseline values during a subsequent muscle contraction. In contrast, bilateral application of AGN (1.0 microM) into CVLM potentiated cardiovascular responses and glutamate concentration while attenuating levels of GABA during a static muscle contraction. All values recovered after 120 min of discontinuation of the drug. These results demonstrate that iNOS within the ventrolateral medulla plays an important role in modulating cardiovascular responses and glutamatergic/GABAergic neurotransmission that regulates the exercise pressor reflex.

Nitrergic innervation of trigeminal and hypoglossal motoneurons in the cat.

The present study was undertaken to determine the location of trigeminal and hypoglossal premotor neurons that express neuronal nitric oxide synthase (nNOS) in the cat. Cholera toxin subunit b (CTb) was injected into the trigeminal (mV) or the hypoglossal (mXII) motor nuclei in order to label the corresponding premotor neurons. CTb immunocytochemistry was combined with NADPH-d histochemistry or nNOS immunocytochemistry to identify premotor nitrergic (NADPH-d(+)/CTb(+) or nNOS(+)/ CTb(+) double-labeled) neurons. Premotor trigeminal as well as premotor hypoglossal neurons were located in the ventro-medial medullary reticular formation in a region corresponding to the nucleus magnocellularis (Mc) and the ventral aspect of the nucleus reticularis gigantocellularis (NRGc). Following the injection of CTb into the mV, this region was found to contain a total of 60 +/- 15 double-labeled neurons on the ipsilateral side and 33 +/- 14 on the contralateral side. CTb injections into the mXII resulted in 40 +/- 17 double-labeled neurons in this region on the ipsilateral side and 16 +/- 5 on the contralateral side. Thus, we conclude that premotor trigeminal and premotor hypoglossal nitrergic cells coexist in the same medullary region. They are colocalized with a larger population of nitrergic cells (7200 +/- 23). Premotor neurons in other locations did not express nNOS. The present data demonstrate that a population of neurons within the Mc and the NRGc are the source of the nitrergic innervation of trigeminal and hypoglossal motoneurons. Based on the characteristics of nitric oxide actions and its diffusibility, we postulate that these neurons may serve to synchronize the activity of mV and mXII motoneurons.

Response of NADPH-diaphorase-exhibiting neurons in the medullar reticular formation to high spinal cord injury.

1. The effect of hemisection of the cervical spinal cord on NADPH-diaphorase staining in the reticular nuclei of the rabbit medulla was investigated using histochemical technique. 2. A quantitative assessment of somal and neuropil NADPH-diaphorase staining was made by an image analyzer in a selected area of each reticular nucleus of the rabbit medulla. 3. On the 7th postsurgery day, the highest up-regulation of somatic NADPH-diaphorase staining was observed in regions regulating cardiorespiratory processes; however, the highest increase of neuropil NADPH-diaphorase staining was found in the reticular nuclei modulating the tonus of postural muscles. 4. The degeneration of non-NADPH-diaphorase-stained neurons was detected throughout the reticular formation of the medulla, but the extent of neuronal death did not correlate with the up-regulation of the NADPH-diaphorase staining in the reticular nuclei of the medulla. 5. The findings provide evidence that NADPH-diaphorase-exhibiting neurons are refractory to the hemisection of the cervical spinal cord and that the neuronal up-regulation of NADPH-diaphorase at the medullar level is probably not a causative factor leading to the death of the reticulospinal neurons.

[Nitric oxide and reflectory regulation of blood circulation in rats]. / Oksyd azotu i reflektorna rehuliatsiia krovoobihu u shchuriv.

In acute experiments on anaesthetized with urethane normotensive rats we studied the ways of participation of nitric oxide (NO) in reflector control of the cardiovascular system by the medullary neurons within n.tractus solitarii (NTS), dorsal nucleus of the vagus nerve (DNV), n. ambiguus (AMB), and the lateral reticular nucleus (LRN). Modulations of the activities of neuronal NO-synthase (nNOS) in the populations of the cardiovascular neurons within the medullary nuclei which are involved in the reflector cardiovascular control were induced by intramedullary injections of sodium nitroprusside as NO donor, L-arginine as NO precursor, L-NNA as an inhibitor of NOS, as well as by intraperetoneal injections of 7-nitroindazol (nNOS inhibitor). We have determined that stimulation of nNOS activity in the populations of the medullary neurons resulted in both remarkable shifts in the SAP level and in inhibiting the chemoreceptor reflector responses. After preliminary inhibiting nNOS chemoreceptor reflexes induced by epinephrine were found to be enhanced in most experiments.

Evidence that dopamine-beta-hydroxylase immunoreactive neurons in the lateral reticular nucleus project to the spinal cord in the rat.

The existence of noradrenergic projections from the lateral reticular nucleus (LRt) to the dorsal quadrant of cervical, thoracic, or lumbar spinal cord was investigated using a combined method of WGA-apo-HRP-gold retrograde tracing and dopamine-beta-hydroxylase (DBH) immunocytochemistry. Preliminary retrograde tracing studies indicated that LRt neurons projecting to cervical, thoracic, or lumbar spinal cord were characteristically located near the perimeter of the LRt. Double-labeling experiments demonstrated that a portion of these peripherally-located, spinal-projecting neurons were DBH-immunoreactive. Double-labeled neurons were also located at the parvocellular division of the contralateral LRt in the thoracic injection cases. Double-labeled neurons were not observed at the subtrigeminal division in cervical, thoracic, or lumbar injection case. The results suggest the possibility that the noradrenergic LRt-spinal pathway might be involved in a variety of pain processing and cardiovascular regulatory functions in the rat.

Catecholamine monoamine oxidase a metabolite in adrenergic neurons is cytotoxic in vivo.

3,4-Dihydroxyphenylglycolaldehyde is the monoamine oxidase-A metabolite of two catecholamine neurotransmitters, epinephrine and norepinephrine. This aldehyde metabolite and its synthesizing enzymes increase in cell bodies of catecholamine neurons in Alzheimer's disease. To test the hypothesis that 3,4-dihydroxyphenylglycolaldehyde, but not epinephrine or its major metabolite 4-hydroxy-3-methoxyphenylglycol, is a neurotoxin, we injected 3,4-dihydroxyphenylglycolaldehyde onto adrenergic neurons in the rostral ventrolateral medulla. Injections of epinephrine or 4-hydroxy-3-methoxyphenylglycol were made into the same area of controls. A dose response and time study were performed. Adrenergic neurons were identified by their content of the epinephrine synthesizing enzyme, phenylethanolamine N-methyltransferase, immunohistochemically. Apoptosis was evaluated by in situ terminal deoxynucleotidyl-transferase mediated dUTP nick end label staining. Injection of 3,4-dihydroxyphenylglycolaldehyde in amounts as low as 50 ng results in loss of adrenergic neurons and apoptosis after 18 h. The degree of neurotoxicity is dose and time dependent. Doses of 3,4-dihydroxyphenylglycolaldehyde 10-fold higher produce necrosis. Neither epinephrine nor 4-hydroxy-3-methoxyphenylglycol are toxic. A 2.5 microg injection of 3,4-dihydroxyphenylglycolaldehyde is toxic to cortical neurons but not glia. Active uptake of the catecholamine-derived aldehyde into differentiated PC-12 cells is demonstrated. Implications of these findings for catecholamine neuron death in neurodegenerative diseases are discussed.

Aggregates of cAMP-dependent kinase RIalpha characterize a type of cholinergic neurons in the rat brain.

Acetylcholine is synthesized by different types of neurons, showing a distinct biochemical phenotype. Aggregates of RIalpha regulatory subunit of cAMP-dependent protein kinases are visualized by immunohistochemistry only in some cholinergic neurons, since they tightly colocalize with two different markers, choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT). These neurons are present mainly in brain areas related to the limbic system. None of the other regulatory subunits of cAMP dependent kinases colocalize with cholinergic markers.

GABA in the deep layers of the superior Colliculus/Mesencephalic reticular formation mediates the enhancement of startle by the dopamine D1 receptor agonist SKF 82958 in rats.

GABA transmission in the deep layers of the superior colliculus/deep mesencephalic reticular formation (deep SC/Me) mediates several motor responses, including those expressed after systemic administration of dopamine agonists. In the present study we examined the role of the deep SC/Me in the modulation of the acoustic startle reflex and its enhancement by the dopamine D(1) agonist SKF 82958. Rats were implanted with bilateral cannulas into the deep SC/Me or superficial layers of the SC (super SC) and 1 week later were infused with various compounds. The GABA(A) antagonist bicuculline (0, 5, and 10 ng) produced a dose- and time-dependent enhancement of startle after infusion into the deep SC/Me, but not the super SC. Infusion of the GABA(A) agonist muscimol (0.1 microg) into the deep SC/Me, but not the super SC, blocked the enhancement of startle by systemic SKF 82958 (1 mg/kg) but had no effect on baseline startle by itself. This effect was not produced by infusion of the D(1) antagonist SCH 23390(1 microg) or the glutamate antagonist NBQX (0.1 microg). Deposits of FluoroGold into the deep SC/Me, combined with immunohistochemistry for glutamic acid decarboxylase (GAD), confirmed a direct GABAergic input from the substantia nigra pars reticulata (SNr) to the deep SC/Me. These results suggest that GABA tone in the deep SC/Me modulates the expression of startle as well as the enhancement of startle by dopamine D(1) agonists. On the basis of these data and previous work, we have proposed a striatonigral-tectal-reticular neural pathway mediating the effects of dopamine D(1) agonists on startle.