Lateral Reticular Nucleus Research Articles

Distribution of novel RFamide-related peptide-like immunoreactivity in the mouse central nervous system

Recently, novel mammalian RFamide-related peptides (RFRPs) have been identified and suggested to increase prolactin release in the rodent. To assess possible functions of RFRPs, we investigated the distribution of RFRPs in the mouse central nervous system by immunochemical analyses. The quantitative analysis revealed that the concentration of RFRP-like substances was much higher in the brainstem and spinal cord than in other regions. Immunohistochemistry showed that RFRP-like immunoreactive perikarya were localized in the dorsomedial hypothalamic nucleus, the lateral superior olive, and the nucleus of the solitary tract. The dense networks of immunoreactive fibers were found in the lateral parabrachial nucleus, the lateral reticular nucleus, and the superficial layer of spinal trigeminal nucleus and dorsal horn of the spinal cord. Thus, RFRPs may participate not only in neuroendocrine functions but also in behavioral, sensory, and autonomic functions.

Nitric oxide and central antihypertensive drugs: one more difference between catecholamines and imidazolines.

NO is known to be involved in the peripheral and central regulation of the cardiovascular function. It plays a neuromodulatory role via a direct action on presynaptic nerve terminals, stimulating the release of gamma-aminobutyric acid, glutamate, and norepinephrine. Our aim was to study the possible role of NO in the cardiovascular effects of the central antihypertensive drugs clonidine, rilmenidine, and alpha-methyl-norepinephrine (alpha-MNA). Sites and mechanisms of the hypotensive action of these drugs were different; clonidine and rilmenidine acted on imidazoline receptors in the nucleus reticularis lateralis, whereas alpha-MNA acted upon alpha(2)-adrenoceptors in the nucleus tractus solitarius. The influence of N:(G)-nitro-L-arginine, an NO synthase inhibitor, on the central hypotensive effects of these drugs was investigated in pentobarbital-anesthetized rabbits. The intracisternal (IC) administration of alpha-MNA (30 microg/kg) induced hypotension (79+/-2 versus 103+/-4 mm Hg) and bradycardia (222+/-8 versus 278+/-4 bpm) (P:<0.05) (n=5). Clonidine (0.07 microg/kg IC) also induced hypotension (69+/-5 versus 99+/-4 mm Hg) and bradycardia (266+/-7 versus 306+/-10 bpm) (P:<0.05) (n=5). In addition to clonidine, rilmenidine (1 microg/kg IC) induced hypotension (64+/-4 versus 97+/-4 mm Hg) and bradycardia (264+/-11 versus 310+/-4 bpm) (P:<0.05) (n=5). Pretreatment with N:(G)-nitro-L-arginine (900 microg/kg IC) completely prevented the hypotensive effect of alpha-MNA but influenced the cardiovascular effects of neither clonidine nor rilmenidine. These results confirm that imidazoline drugs, such as clonidine, rilmenidine, and the catecholamine alpha(2)-adrenoceptor agonist alpha-MNA, have distinct mechanisms of action.

Decreased CSF pH at ventral brain stem induces widespread c-Fos immunoreactivity in rat brain neurons

Physiological evidence has indicated that central respiratory chemosensitivity may be ascribed to neurons located at the ventral medullary surface (VMS); however, in recent years, multiple sites have been proposed. Because c-Fos immunoreactivity is presumed to identify primary cells as well as second- and third-order cells that are activated by a particular stimulus, we hypothesized that activation of VMS cells using a known adequate respiratory stimulus, H(+), would induce production of c-Fos in cells that participate in the central pH-sensitive respiratory chemoreflex loop. In this study, stimulation of rostral and caudal VMS respiratory chemosensitive sites in chloralose-urethane-anesthetized rats with acidic (pH 7.2) mock cerebrospinal fluid induced c-Fos protein immunoreactivity in widespread brain sites, such as VMS, ventral pontine surface, retrotrapezoid, medial and lateral parabrachial, lateral reticular nuclei, cranial nerves VII and X nuclei, A(1) and C(1) areas, area postrema, locus coeruleus, and paragigantocellular nuclei. At the hypothalamus, the c-Fos reaction product was seen in the dorsomedial, lateral hypothalamic, supraoptic, and periventricular nuclei. These results suggest that 1) multiple c-Fos-positive brain stem and hypothalamic structures may represent part of a neuronal network responsive to cerebrospinal fluid pH changes at the VMS, and 2) VMS pH-sensitive neurons project to widespread regions in the brain stem and hypothalamus that include respiratory and cardiovascular control sites.

Gonadal regulation of PrRP mRNA expression in the nucleus tractus solitarius and ventral and lateral reticular nuclei of the rat

We investigated the prolactin-releasing peptide (PrRP) gene expression quantitatively in the rat brain and the involvement of estrogen and progesterone using in situ hybridization. The strongest signals were observed in the nucleus tractus solitarius (NTS), which showed approximately 70% of total PrRP mRNA in the brain. Moderate expression was observed in the ventral and lateral reticular nuclei (VLRN) of the medulla oblongata. PrRP mRNA signals in the hypothalamic ventromedial- and dorsomedial nuclei showed only 5% of total signals. The PrRP mRNA expression among female rats showing normal gonadal cycle and male rats showed that the highest levels were in female rats in proestrus. Administration of estrogen or progesterone after ovariectomy induced an increase in PrRP mRNA expression in the NTS. PrRP mRNA content in the NTS increased with the progress of the pregnancy and reached a peak on the 14th day, the mid-period of pregnancy, when plasma progesterone increases. We also observed the colocalization of PrRP and estrogen receptor alpha in the neurons distributed in the NTS by double labeling immunocytochemistry. These findings indicate that PrRP gene expression is regulated by gonadal steroid hormones in the medulla oblongata, and parts of PrRP synthesizing neurons are considered to be directly influenced by estrogen in the NTS.

Toll‐like receptor 4: the missing link of the cerebral innate immune response triggered by circulating gram‐negative bacterial cell wall components

The recent characterization of human homologues of Toll may be the missing link for the transduction events leading to NF-kappaB activity and proinflammatory gene transcription during innate immune response. Indeed, CD14 is not thought to participate directly in the cell signaling, but rather one or more of the mammalian Toll-like receptors (TLRs) acts in concert with the lipopolysaccharide (LPS) receptor to discriminate between microbial pathogens or their products and initiate transmembrane signaling. Mammalian cells may express as many as 10 distinct TLRs, although the importance of TLR4 in response to gram-negative bacteria and LPS is now supported by the fact that TLR4-mutated mice are LPS resistant. We investigated the expression of TLR4 across the rat brain under basal conditions and in response to systemic LPS and IL-1beta injection. We first cloned the rat TLR4 cDNA via RNA isolation and polymerase chain reaction (PCR) amplification with a proofreading polymerase. Total RNA was isolated from the rat liver tissue using Tri-Reagent and reverse transcribed into cDNA using Superscript II reverse transcriptase and an oligonucleotide primer with a degenerate 3' end of sequence 5'-T12(GAC)N-3'. Positive hybridization signal was found in the leptomeninges, choroid plexus (chp), subfornical organ, organum vasculosum of the lamina terminalis, median eminence, and area postrema. Scattered small cells also displayed a convincing hybridization signal within the brain parenchyma. Few well-defined nuclei exhibited positive TLR4 transcript: the supramamillary nucleus, cochlear nucleus, and the lateral reticular nucleus. The circumventricular organs, the leptomeninges, and chp also exhibited constitutive expression of the LPS receptor mCD14. In contrast to the strong up-regulation of the gene encoding mCD14 during endotoxemia, neither LPS nor IL-1beta caused a convincing increase in the TLR4 mRNA levels across the CNS. A down-regulation of the gene encoding TLR4 was found in the cerebral tissue of immune-challenged animals. The constitutive expression of both mCD14 and TLR4 may explain the innate immune response in the brain, which originates from the structures devoid of blood-brain barrier in presence of circulating LPS.

Toluene alters mu-opioid receptor expression in the rat brainstem.

Toluene is an ototoxic organic solvent widely used in industry and could be a cause of sleep apnea. Acute toluene administration in rats induces an increase in the number of neural cells immunostained for mu-opioid receptors in several brainstem nuclei, such as the inferior colliculus, dorsal and lateral periaqueductal gray and dorsal raphe, without changes in the superior colliculus and the interpeduncular and lateral reticular nuclei. These data suggest that mu-opioid receptors could be involved in toluene-induced neurotoxic effects on the physiological regulation of breathing during sleep, and auditive function.

Neuronal activity in the medulla oblongata during vocalization. A single-unit recording study in the squirrel monkey

In six squirrel monkeys ( Saimiri sciureus), the medulla oblongata was explored with microelectrodes, looking for vocalization-correlated activity. The vocalizations were elicited by microinjections of glutamate agonists into the periaqueductal grey of the midbrain. Vocalization-related cells were found in greater numbers in the nucl. ambiguus (Ab) and retroambiguus (RAb), in the parvocellular, magnocellular and central reticular formation as well as in the solitary tract nucleus and spinal trigeminal nucleus. Small numbers were also found in the vestibular complex, cuneate nuclei, inferior olive and lateral reticular nucleus. A differentiation of the neuronal responses into 12 reaction types reveals that the frequency of each reaction type varies from brain structure to brain structure, thus allowing a specification of the different vocalization-related areas. According to this specification, it is proposed that initiation of vocalization takes place via the parvocellular reticular formation; vocal pattern control is mainly brought about by the parvocellular reticular formation, Ab, solitary tract nucleus and spinal trigeminal nucleus; expiratory control and respiratory-laryngeal coordination is carried out by the RAb, Ab and central nucleus of the reticular formation; vocalization-specific postural adjustments are carried out via the vestibular and cuneate nuclei.

Origin of corticospinal neurones evoking monosynaptic excitation in C3--C4 propriospinal neurones in the cat.

Intracellular recording was made from propriospinal neurones (PNs) in the C3-C4 spinal cord segments in the cat (alpha-chloralose anaesthesia). The effect of electrical stimulation of corticospinal neurones (CSNs) in the cortex was investigated. Short C3-C4 PNs were identified by antidromic activation of their axons in the ventral horn in C6/C7 and in the lateral reticular nucleus. Long PNs were antidromically identified from Th12-13. In short PNs, monosynaptic excitory postsynoptic potentials (EPSPs) were elicited from the rostral part of the lateral sigmoid gyrus, the lateral part of the anterior sigmoid gyrus in area 4 gamma and in the adjacent area 6. Two subtypes of short PNs were identified. PNs of type I received monosynaptic EPSPs from the rostral part of the lateral sigmoid gyrus, the lateral part of the anterior sigmoid gyrus in area 4 gamma, which is from the same region as disynaptic cortical EPSPs were evoked in forelimb motoneurones. PNs of type II received monosynaptic EPSPs from regions slightly more rostrally in the anterior sigmoid gyrus in area 4 gamma and in the adjacent area 6, which is outside the region from which disynaptic EPSPs could be evoked in forelimb motoneurones. Long PNs received monosynaptic EPSPs, like the short PNs, by stimulation in the rostral part of the lateral sigmoid gyrus, the lateral part of the anterior sigmoid gyrus in area 4 gamma and in the adjacent area 6. In contrast, the long PNs also received monosynaptic EPSPs from area 3b near the border of area 1. The present results show segregation of the cortical control to functionally different premotoneuronal systems and suggest that this control could in part be separated for subtypes of short C3-C4 PNs.

Immunohistochemical localization of amylin in rat brainstem☆,☆☆

Immunohistochemical studies were conducted on rat brainstem using a specific polyclonal antiserum against the COOH-terminal (25–37) of human amylin. Amylin-immunoreactive cell bodies were observed in the vestibular, cochlear, trapezoid, and inner cerebellar nuclei and in the mesencephalic nucleus of trigeminal nerve. Positive cell bodies were also found in lateral, gigantocellular and magnocellular reticular nuclei. Numerous amylin-immunoreactive nerve fibers were shown in the trigeminal spinal tract, in the solitary area and in the area postrema. Amylin-immunoreactive cell bodies were often surrounded by a network of tyrosine hydroxylase-immunoreactive nerve fibers. These results provide morphologic evidence that amylin may play a role in some discrete sensory functions.

Regulation of α 2A-adrenoceptor expression by chronic stress in neurons of the brain stem

α 2-Adrenoceptors are supposed to be important regulatory elements in responses to stress. Previous receptor binding studies in male tree shrews have shown that chronic psychosocial stress down-regulates binding sites for α 2-adrenergic ligands in several brain stem nuclei. The aim of the present study was to quantify effects of chronic subordination stress on expression of the α 2-adrenoceptor subtype A gene in identified neurons of the brain stem. We partially cloned the α 2A-adrenoceptor cDNA of the tree shrew (1.22 kb) and localized receptor RNA expression in brain stem neurons by in situ hybridization using a 35S-labeled cRNA probe (1.06 kb). To identify neurons expressing receptor mRNA, brain sections were first immunocytochemically stained with antibodies against tyrosine hydroxylase, phenylethanolamine- N-methyltransferase, or glutamate, and then processed for in situ hybridization. Furthermore, expression of receptor-specific RNA was quantified in single neurons of animals which had been psychosocially stressed during 4 weeks and in unstressed controls. We found strong in situ hybridization in the noradrenergic neurons of the locus coeruleus, but only weak labeling of A2 neurons in the solitary tract nucleus and no labeling of A1 neurons in the caudal ventrolateral medulla. Adrenergic neurons in the solitary tract nucleus (group C2) did not express the α 2A-adrenoceptor, and C1 neurons in the rostral ventrolateral medulla showed only a minor labeling by the in situ probe. In contrast, large glutamatergic neurons in the lateral reticular nucleus were strongly labeled by the probe. Chronic psychosocial stress reduced α 2A-adrenoceptor RNA expression in locus coeruleus neurons (−24.0%), in solitary tract neurons (−31.0%), and in neurons of the lateral reticular nucleus (−18.8%). These findings show that stress not only decreases the expression of the α 2A-adrenergic autoreceptor in the locus coeruleus but also of α 2A-heteroreceptors in glutamatergic neurons.

Perinatal distribution of galanin and galanin receptor-1 mRNA in the rat hindbrain

In situ hybridisation was used to determine the distribution and levels of mRNA for galanin precursor preprogalanin (ppGAL) and galanin receptor-1 (GAL-R1) in the rat hindbrain before and after birth. Quantification of mRNA levels was performed from E21. Also, immunohistochemistry was used to study GAL-like immunoreactivity (GAL-LI) prenatally. On E16, no expression of ppGAL mRNA could be detected in any areas examined, whereas on E19 low transcript levels were observed. GAL-LI, however, was seen at relatively high levels in nerve fibres already on E16, mainly in the areas receiving primary afferents. Also, GAL-R1 mRNA was expressed at high levels in discrete areas of the hindbrain on E16. On E21 ppGAL mRNA was found in the locus coeruleus (LC), the nucleus of the solitary tract, the dorsal motor nucleus of the vagus (nX), the lateral reticular nucleus (LRn) and superficially along the ventral medullary surface. Expression increased postnatally in all these areas except in nX and LRn. GAL-R1 mRNA, on the other hand, was found to be expressed at high levels on E21 in the LC, where levels then decreased on P1. Expression of GAL-R1 mRNA was also found in other areas of the brainstem, but here no changes were detected around birth. These findings demonstrate that ppGAL and GAL-R1 mRNAs, as well as GAL-LI, are present in the brainstem in the rat fetus and that the changes in expression after birth could be of importance for the newborn in the transition from pre- to postnatal life.

Spinomedullary pathways in the pigeon (Columba livia): Differential involvement of lamina I cells

The lamina I (marginal zone) of the spinal cord dorsal horn is an important site for pain processing. In mammals, lamina I neurons have been shown to constitute a heterogeneous population made up of four morphological groups with particular neurochemical nature, supraspinal connection patterns, and nociceptive response properties. In order to obtain a comparative view of the mechanisms of nociceptive processing, the analysis of the structural morphology and supraspinal connectivity of lamina I neurons was, in this study, extended to the avian family. Cholera toxin subunit B (CTb) was injected in the nucleus tractus solitarius (NTS), nucleus centralis medullae pars dorsalis (Cnd), and the dorsolateral portion of the nucleus reticularis lateralis (RLlat) of the pigeon (Columba livia), areas equivalent to the rat caudal medulla oblongata lamina I targets, which have been shown to receive differential projections from all cell groups present in lamina I of mammals. In the pigeon, lamina I cells project to the three medullary regions and present the same morphology of spinomedullary lamina I cells of mammals: the spinal-NTS and the spinal-RLlat pathways originated from fusiform, pyramidal, and flattened neurons, and the spinal-Cnd pathway from multipolar, pyramidal, and flattened neurons. Furthermore, the relative participation of each lamina I cell type in each pathway was found to be similar to that previously observed in the rat. The observed similarities on the anatomical organization of lamina I neurons in mammalian and avian species can be taken as a phylogenetic indication of the importance of the nociceptive circuitry centered in lamina I. J. Comp. Neurol. 423:631–645, 2000. © 2000 Wiley-Liss, Inc.

Striking Differences in Transmission of Corticospinal Excitation to Upper Limb Motoneurons in Two Primate Species

There is considerable debate as to the relative importance, for cortical control of upper limb movements, of direct cortico-motoneuronal (CM) versus indirect, propriospinal transmission of corticospinal excitation to cervical motoneurons. In the cat, which has no CM connections, a significant proportion of corticospinal excitation reaches forelimb motoneurons via a system of C(3)-C(4) propriospinal neurons (PN). In contrast, in the macaque monkey most motoneurons receive direct CM connections, and, under the same experimental conditions as in the cat, there is little evidence for PN transmission. We have investigated corticospinal transmission in the New World squirrel monkey (Saimiri sciureus) because its CM projections are weaker than in the macaque. Intracellular recordings were made from motoneurons identified from the ulnar, median, and deep radial (DR) nerves in four adult squirrel monkeys under chloralose anesthesia and neuromuscular paralysis. Responses to stimulation of the contralateral medullary pyramid were recorded before and after a lesion to the dorsolateral funiculus (DLF) at C(5), designed to interrupt direct corticospinal inputs to the lower cervical segments and unmask PN-mediated effects. This lesion greatly reduced the proportion of motoneurons showing either CM EPSPs or disynaptic IPSPs, but the proportion showing late EPSPs with segmental latencies beyond the monosynaptic range, evoked by repetitive but not single PT stimuli, was unaffected: 23 of 29 motoneurons (79%) before and 32 of 37 (86%) after the lesion; 41% of these late EPSPs had strictly disynaptic latencies after the lesion, only 14% before. These results are in striking contrast to the macaque (late EPSPs in only 18% of motoneurons before a C(5) lesion, 19% after it). Transmission of the late EPSPs via C(3)-C(4) PNs in the squirrel monkey was indicated by their absence after an additional C(2) DLF lesion. Nearly all tested motoneurons also responded with short latency EPSPs to stimulation in the ipsilateral lateral reticular nucleus. By analogy with the cat, these EPSPs probably reflect antidromic activation of ascending collaterals of C(3)-C(4) PNs with monosynaptic connections to motoneurons; the EPSPs were significantly smaller than in the cat but larger than in the macaque. These results suggest that the positive correlation across species between more advanced hand function and the strength of the CM system is accompanied by a negative correlation between hand function and the strength of the PN system. We hypothesize that in primates with more advanced hand function, the CM system effectively replaces PN-mediated control. This would include a contribution to the control of reaching movements, which are said to be specifically under the control of the PN system in the cat, and we speculate that these differences may be related to the degree of dexterity exhibited by the different species. This interpretation of the results predicts that in man, where the CM system is highly developed, the PN system is unlikely to be responsible for significant transmission of cortical commands to upper limb motoneurons.

Involvement of nitric oxide in regulation of the medullary respiratory rhythm in neonatal rats

The NADPH-diaphorase (as a neuronal NO-synthase) reactivity in the medullary structures of the respiratory rhythm (RR) generator and the role of NO in the regulation of respiratory activity in the phrenic nerve of artificially superfused semi-isolated medulla-spinal cord preparations were investigated in newborn rats. NADPH-diaphorase positive neurons were found in all nuclei of both dorsal and ventral respiratory groups of neurons. The maximal density of stained cells was present within the rostral part of the ventrolateral medulla (VLM), in the region of the lateral paragigantocellular reticular nucleus. It was found that endogenous NO mediates the mechanism of tonic inhibitory control of the RR frequency located in the rostral VLM under normal and hypoxic conditions, and appears to be involved in generation of the basic RR by the more caudal structures of VLM. It was shown that NO biosynthesis mediates the effect of NMDA receptors activation on the RR.

Evidence for ascending visceral nociceptive information in the dorsal midline and lateral spinal cord

The effect of acute, mid-cervical spinal cord lesions on neuronal and reflex activity evoked by the noxious visceral stimulus, colorectal distension (CRD; 80 mmHg, 20 s), was determined in halothane-anesthetized rats. Extracellular recordings were performed of neurons stereotaxically located within the ventrobasal group of the thalamus and in the region of the medullary lateral reticular nucleus. CRD-evoked activity of thalamic neurons was attenuated by lesions of the dorsal midline, but minimally affected by lateral lesions of the spinal cord. In contrast, CRD-evoked activity of medullary neurons was attenuated by lateral lesions ipsilateral to the recording site, but minimally affected by contralateral lateral lesions or dorsal midline lesions. Pseudaffective visceromotor/cardiovascular responses were vigorous in rats with dorsal midline lesions and absent/attenuated in rats with bilateral lateral spinal lesions. This study presents evidence that visceral nociceptive information ascends in the spinal cord by both dorsal midline and lateral spinal pathways.

Effect of stress exposure on the activation pattern of enkephalin-containing perikarya in the rat ventral medulla.

We examined the effects of acute and chronic psychogenic stress on the activation pattern of enkephalin-containing perikarya in the rat ventrolateral medulla. Rats allocated to the chronic stress groups were subjected to 90 min of immobilization for 10 days. On the 11th day, the chronically stressed rats were exposed to homotypic (90-min immobilization) or to heterotypic but still psychogenic (90-min immobilization coupled to air jet stress) stress. The acute stress group was subjected once to an acute 90-min immobilization. For each group, the rats were anesthetized either before stress (time 0) or 90, 180, and 270 min after the onset of stress. Brain sections were then processed using immunocytochemistry (Fos protein) followed by radioactive in situ hybridization histochemistry (enkephalin mRNA). Following immobilization, the acute group displayed a marked increase in the number of activated enkephalin-containing perikarya within the paragigantocellularis and lateral reticular nuclei. This level of activation was sustained up to 180 min following the onset of the immobilization stress and had returned to baseline levels by 270 min from the initiation of the stress. However, this stress-induced activation of enkephalin-containing perikarya of the ventrolateral medulla was not seen following either homotypic or heterotypic stress in the chronically stressed group. These results provide evidence that enkephalin-containing perikarya of the ventrolateral medulla may constitute a potential circuit through which they regulate some aspect of the stress responses. Conversely, this enkephalinergic influence from the ventrolateral medulla was shown to be absent following chronic stress exposure. This would suggest a decrease in enkephalin inhibitory input originating from the ventrolateral medulla, thereby allowing a neuroendocrine and/or autonomic response to chronic stress.

Distribution of the neurotensin receptor NTS1 in the rat CNS studied using an amino-terminal directed antibody

The distribution of neurotensin receptor 1 immunoreactivity in the rat brain was studied using an antibody against the amino-terminal of the receptor expressed as a fusion protein with glutathione-S transferase. Affinity purified antibodies detected the fusion protein and the complete neurotensin receptor sequence expressed in Escherichia coli. The immunostaining was abolished by preabsorption with the amino-terminal fusion protein. Immunoreactive neurotensin receptor 1 immunoreactivity was detected on cell bodies and their processes in a number of CNS regions. In agreement with previous binding studies neurotensin receptor 1 immunoreactivity was particularly localised in cell bodies in the basal forebrain, nucleus basalis and substantia nigra. At the electron microscope level immunoreactivity was found both in axonal bouton and dendrites and spines in the basal forebrain indicating that neurotensin may act both pre- and post-synaptically. There were several regions such as the substantia gelatinosa, ventral caudate-putamen and the lateral reticular nucleus where the neurotensin receptor 1 positive cells had not previously been reported, indicating that distribution of this receptor is widespread.

Arteether-induced brain injury in Macaca mulatta. I. The precerebellar nuclei: the lateral reticular nuclei, paramedian reticular nuclei, and perihypoglossal nuclei.

Malaria poses a threat across several continents: Eurasia (Asia and parts of Eastern Europe), Africa, Central and South America. Bradley (1991) estimates human exposure at 2,073,000,000 with infection rates at 270,000,000, illnesses at 110,000,000, and deaths at 1,000,000. Significant mortality rates are attributed to infection by the parasite Plasmodium falciparum, with an estimated 90% among African children. A worldwide effort is ongoing to chemically and pharmacologically characterize a class of artemisinin compounds that might be promising antimalarial drugs. The U.S. Army is studying the efficacy and toxicity of several artemisinin semi-synthetic compounds: arteether, artemether, artelinic acid, and artesunate. The World Health Organization and the U.S. Army selected arteether for drug development and possible use in the emergency therapy of acute, severe malaria. Male Rhesus monkeys (Macaca mulatta) were administered different daily doses of arteether, or the vehicle alone (sesame oil), for a period of either 14 days, or 7 days. Neuropathological lesions were found in 14-day arteether treated monkeys in the precerebellar nuclei of the medulla oblongata, namely: (1) the lateral reticular nuclei (subnuclei magnocellularis, parvicellularis, and subtrigeminalis), (2) the paramedian reticular nuclei (subnuclei accessorius, dorsalis, and ventralis), and the perihypoglossal nuclei (n. intercalatus of Staderini, n. of Roller, n. prepositus hypoglossi). The data demonstrate that the simina meduallry precerebellar nuclei have a high degree of vulnerability when arteether is given for 14 days at dose levels between 8mg/kg per day and 24 mg/kg per day. The neurological consequences of this treatment regimen could profoundly impair posture, gait, and autonomic regulation, while eye movement disorders might also be anticipated.

Pontomedullary distribution of 5-HT2A receptor-like protein in the rat

Serotonin (5-HT) exerts excitatory effects in many brainstem regions involved in autonomic, somatic, motor, and sensory functions, and in control of vigilance. To determine the potential role of 5-HT2A receptors in these effects, we immunohistochemically mapped the distribution of 5-HT2A receptor-like protein in the rat pontomedullary brainstem. Areas containing the densest labeling included the trigeminal, facial, hypoglossal, dorsal vagal motor nuclei, medullary linear nucleus, and the inferior olive. In the nucleus ambiguus, labeled cells were located in the areas containing pharyngeal and laryngeal motoneurons. Intensely labeled cells were loosely scattered in the reticular formation adjacent to the raphe magnus and obscurus nuclei, in the gigantocellular region, in the caudal pedunculopontine and laterodorsal tegmental nuclei, dorsomedial pontine reticular formation, and nucleus subcoeruleus. In the nucleus prepositus hypoglossi, all vestibular, abducens, cuneate, and lateral reticular nuclei, labeled neurons commingled with unlabeled ones. Few labeled neurons were located in the rostral and caudal ventrolateral medulla and parvicellular reticular formation. In the nucleus of the solitary tract, two patches of diffuse labeling not associated with cellular profiles were present: one in the medial, and the other in the interstitial subnucleus. Similar diffuse labeling was present in the lateral parabrachial region and the lateral rim of the caudal spinal trigeminal sensory nucleus. No labeled cells were found in the locus coeruleus, dorsal raphe, superior olive, or area postrema. The distinct pontomedullary distribution of 5-HT2A receptors, combined with the known arousal-dependent activity of serotonergic neurons, show that these receptors may mediate post- and presynaptic effects in the motor, selected somatic and visceral sensory, oculo-vestibulo-precerebellar, and sleep-related regions.

NADPH-Diaphorase-containing neurons in the medullary structures involved in generation of the respiratory activity in neonatal rats

Using a histochemical technique, we examined distribution of the neurons containing a marker of nitric oxide synthase (NOS), NADPH-diaphorase (NADPH-d), on frontal slices of the medulla and upper cervical spinal segments of 4-day-old rats. It was demonstrated that NADPH-d-positive cells are present within the dorsal and ventral medullary respiratory groups. The highest density of the labeled middle-size multipolar neurons (27.9±2.6 cells per 0.1 mm2 of the slice) was observed in the rostral part of the ventral respiratory group, within the reticular lateral paragigantocellular nucleus. Similar NADPH-d-positive neurons were also observed in other reticular formation structures: rostroventrolateral reticular, gigantocellular, and ventral medullary nuclei, and in the ventral part of the paramedial nucleus. There were no labeled neurons in the lateral reticular nucleus. Single small and medium-size labeled neurons were found at all rostro-caudal levels of thenucl. ambiguous (nuclei retrofacialis, ambiguous, andretroam-biguous). Groups of NADPH-d-positive neurons were also revealed within the dorsal respiratory group, along the whole length of thenucl. tractus solitarii (mostly in its ventrolateral parts). Single labeled neurons were also observed in thenucl. n. hypoglossi, and their groups were observed in the dorsal motor part of thenucl. n. vagus. Involvement of the structures containing NADPH-d-positive neurons in the processes related to generation of the respiratory activity is discussed. Our neuroanatomical experiments prove that in early postnatal mammals NO is actively involved in generation and regulation of the medullary respiratory rhythm.