Failure to confirm cyclic AMP as second messenger for norepinephrine in rat cerebellum.

Microiontophoretic applications of adenosine 3',5'-monophosphate (cyclic AMP) to spontaneously active, electrophysiologically identified Purkinje cells of the rat cerebellum failed to mimic the strong depressant action of norepinephrine on the same cells. These findings, in combination with a reevaluation of other studies, cast doubt on the hypothesis that cyclic AMP mediates the depressant actions of norepinephrine in the cerebellum.

Control of functional systems in the brainstem and spinal cord.

Progress has been made in the identification of cells, circuits, and networks involved in certain important subcortical functional systems, including swallowing, chewing, posture and locomotion, and in the shared mechanisms for selecting the network for specific motor tasks, including a role for excitatory amino acids for network activation, the shaping of the network by inhibitory control, and the selection of inputs and modulation of outputs by monoamines and other agents.

Differential projections of cat medullary raphe neurons demonstrated by retrograde labelling following spinal cord lesions.

Neurons of the medullary raphe nuclei in cats were retrogradely labelled following injection of horseradish peroxidase (HRP) into the L6 spinal cord segment. Brainstems were cut in sagittal section to facilitate examination of the rostral-caudal extent of raphe neurons projecting to the spinal cord. Large numbers of HRP-labelled neurons were found in nucleus raphe magnus, nucleus raphe pallidus, and nucleus raphe obscurus (as well as a few neurons in nucleus raphe pontis). Dorsal or ventral hemisections at the T12-L1 level restricted HRP retrograde transport to those pathways within the intact portion of spinal cord, allowing a determination of the part of the cord through which raphe neurons project to the lumbar enlargement. Neurons of nucleus raphe magnus were found to project primarily in dorsolateral fasciculus. A significant number of neurons of nucleus reticularis gigantocellularis also project in dorsolateral fasciculus. Nucleus raphe obscurus neurons were found to project primarily in ventral funiculus, while nucleus raphe pallidus neurons project in the ventrolateral fasciculi and ventral funiculus. The serotonergic (5HT) fibers described by Dahlström and Fuxe ('65) to terminate in the dorsal horn, intermediolateral cell column, and ventral horn are likely to coincide with the raphe-spinal projections documented in this work.

Depression of primate spinothalamic tract neurons by iontophoretic application of 5-hydroxytryptamine.

The effects of iontophoretic applications of 5-hydroxytryptamine (5-HT) were tested upon primate spinothalamic tract neurons recorded extracellularly in the spinal cord of anesthetized monkeys. The activity of most high threshold and wide dynamic range spinothalamic tract cells was depressed. 5-HT also reduced the responses of the cells to glutamate pulses which by themselves had a powerful excitatory action. It is concluded that 5-HT has a depressant action upon the postsynaptic membranes of spinothalamic tract cells, although the action has a slow time course. The observations are consistent with, but by no means prove, the hypothesis that serotonergic pathways descending from the brain stem produce a postsynaptic inhibiton of spinothalamic tract neurons.

C-terminals on motoneurons: electron microscope localization of cholinergic markers in adult rats and antibody-induced depletion in neonates.

C-terminals on motoneurons are defined as those accompanied by characteristic postsynaptic specializations termed subsurface cisterns. We have previously shown, by light microscope immunolabelling methods, that subsurface cisterns occur regularly beneath choline acetyltransferase- and acetylcholinesterase-containing boutons on motoneurons. In the present study, the cholinergic nature of C-terminals suggested by these results was further investigated by immunohistochemistry and electron microscopy in adult rats and in neonates treated with a murine monoclonal acetylcholinesterase antibody which was previously shown to cause immunological lesions of central cholinergic systems. In both the facial nucleus and lumbar segment of spinal cord of adult rats, C-terminals were seen intensely immunostained for the cholinergic markers choline acetyltransferase and acetylcholinesterase. Immunolabelled terminals made contact with either neuronal somata or large calibre dendrites, which were positive for the cholinergic markers, and exhibited club-shaped or thin elongated morphologies suggestive of terminal or en passant type synaptic interactions. The close relationship found between cholinergic markers and immunolabelled subsurface cisterns in adults was maintained on motoneurons of eight-day-old rats. While subcutaneous treatment of newborn rat with acetylcholinesterase antibody appeared to have no effect on the distribution of immunopositive subsurface cisterns in motoneurons when examined on postnatal day 8, the density of labelling for the two cholinergic markers around these neurons was reduced. Areas of neuropil immediately surrounding motoneurons in treated animals often showed signs of extensive swelling and deterioration indicative of a lesion event, and these motoneurons frequently displayed subsurface cisterns unapposed to C-terminals. These results support our earlier conclusion, based on light microscope investigation, that the majority if not all C-terminals are cholinergic in the areas investigated and demonstrate the potential utility of immunolesion methods in the study of C-terminal function.

Analysis of the effects of p-methoxy-phenylethylamine on spinal cord neurones.

1 Para-methoxyphenylethylamine (PMPEA) was applied microiontophoretically onto interneurones and motoneurones in the spinal cords of acute spinal cats anaesthetized with alpha-chloralose. Its effects were compared with those of noradrenaline (NA) and 5-hydroxytryptamine (5-HT). 2 PMPEA had effects on interneurones which were similar to those of NA and/or 5-HT; its action was predominantly depressant, and it rarely affected interneurones which could not be influenced by NA or 5-HT. 3 The actions of PMPEA on interneurones excited by electrical stimulation of leg nerves showed that the population of interneurones influenced by the drug coincides with the population affected by NA and 5-HT and by intravenously administered PMPEA. 4 Renshaw cells, which are depolarized by intravenous PMPEA, were hyperpolarized by micoiontophoretically applied PMPEA. 5 Alpha motoneurones, which are depolarized by intravenous PMPEA, were hyperpolarized by micoiontophoretically applied PMPEA. Antidromic firing of the cells could be blocked by PMPEA. 6 The differences between the effects of intravenous infusion and the iontophoretic application of PMPEA upon motoneurones is most easily explained by inhibition of interneurones and a concomitant disinhibition of motoneurones. A similar mechanism may also account for the different effects seen with intravenous and iontophoretic application of PMPEA on Renshaw cells.

Acetylcholine inhibition in the intact and chronically isolated cerebral cortex.

1. Some spontaneously firing cells in the cerebral cortex of cats can be depressed by iontophoretically applied acetylcholine or acetyl-beta-methylcholine, and this depression is antagonized by atropine. Thirteen per cent of 101 spontaneously active neurones tested were depressed by cholinergic agents and 64% were excited.2. Single stimuli applied to the adjacent cortical surface excited 132 neurones orthodromically. Acetylcholine or acetyl-beta-methylcholine depressed this synaptic firing in 18% of the cells. The depression was blocked by atropine.3. The population of neurones in which cholinergic agents depressed spontaneous or synaptic firing was located within the superficial half of the cortex.4. Glutamate-induced firing was depressed by cholinergic agents in 41% of 211 cells tested; atropine and strychnine strongly antagonized this depressant action, while dihydro-beta-erythroidine was a weaker antagonist.5. Long duration inhibition of glutamate-induced firing evoked by repetitive stimulation of the cortical surface could be blocked by atropine or strychnine in both the intact and chronically isolated cortex. This provides strong evidence for a system of intracortical cholinergic neurones which make direct inhibitory contacts with neurones in the superficial layers of the cortex.

Initiation of locomotion in mammals.

Several "locomotor regions" of the mammalian brain stem can be stimulated, either electrically or chemically, to induce locomotion. Active cells labeled with c-fos within the mesencephalic locomotor region (MLR) have been found in the periaqueductal gray, the cuneiform nucleus, the pedunculopontine nucleus, and the locus coeruleus. Different subsets of these nuclei appear to be activated during locomotion produced in different behavioral contexts. The locomotor nuclei can be classified into areas associated with exploratory, appetitive, and defensive locomotion, in accordance with the proposal of Sinnamon (1993, Prog. Neurobiol. 41: 323-344). The interpretation of lesion studies designed to reveal areas of the brain essential for locomotion must be based on knowledge of the nuclei which become active in the specific locomotor task being tested. An argument is put forward in favor of the continued use of the term "mesencephalic locomotor region."

Autoradiographic demonstration of the projections from the mesencephalic locomotor region.

An autoradiographic tracing technique was used to examine the projections of the classically defined mesencephalic locomotor region (MRL). Injections of [3H]proline and [3H]leucine were made into sites in the caudal mesencephalon which can be stimulated to produce locomotion. The injection sites were confined to the cuneiform nucleus (stereotaxic coordinates P2.0, L4.0, H-1.0). Descending projections were primarily ipsilateral to the gigantocellular and magnocellular reticular formation of the pons and medulla, the dorsal tegmental reticular nucleus, and the nucleus raphe magnus. Some sparse contralateral projections were also observed within the magnocellular and gigantocellular reticular formation. Direct axonal connections with the spinal cord were not consistently observed. Ascending projections were observed to the subthalamic nucleus, caudal hypothalamic nuclei, the centrum medianum nucleus of the thalamus, the ventral tegmental area of Tsai, the superior colliculus, and the periaqueductal gray region. The ascending projections were also ipsilateral, with sparse contralateral labeling confined to areas which received ipsilateral projections. Projections to the contralateral cuneiform nucleus were also consistently observed. The results, when compared to those of another study, suggest that the classical MLR is anatomically distinct from the more medial sites in the mesencephalon which can also induce locomotion.

Initiation of locomotion from the mesencephalic locomotor region: effects of selective brainstem lesions.

The effects of selected brainstem lesions on controlled treadmill locomotion produced by stimulation of the mesencephalic locomotor region (MLR) in postmamillary cats were determined in these experiments. The importance for the initiation of locomotion of projections from the MLR to rostral brainstem structures, described in a preceding paper, were examined by selective lesioning or by adjusting the level of the decerebration. The role played by the lateral vestibulospinal tract (LVST) in the initiation of locomotion was examined by lesioning Deiters' nucleus bilaterally. Contrary to previous claims, the results of the present experiments show that areas of the brainstem rostral to the MLR are not required for the initiation of locomotion by MLR stimulation. This finding eliminates the ventral tegmental area of Tsai and the substantia nigra, both implicated in the initiation of locomotion, as required participants in MLR stimulated locomotion. Bilateral Deiters' nucleus (DN) lesions did not significantly affect the initiation of locomotion from the MLR, nor did such lesions alter in a systematic fashion the amplitude or timing of EMG activity in flexor or extensor muscles of the hindlimb during MLR evoked walking. Joint angle changes during the locomotor cycle were also essentially unaltered by DN lesions. The significance of these findings regarding the brainstem structures which must be involved in the initiation of locomotion are discussed.

Effect of noradrenaline and 5-hydroxytryptamine depletion on locomotion in the cat.

It has recently been hypothesized that stimulation of the mesencephalic locomotor region (MLR) can give rise to locomotion in mesencephalic cats due to activation of descending monoaminergic pathways to the spinal cord. This notion is based on the findings that monoamine agonists and precursors can induce hindlimb stepping in acute low spinal animals, and on the similarities between the effects of the noradrenaline (NA) precursor, L-DOPA, and stimulation of the MLR. The hypothesis that the descending monoamine systems comprise the only pathways which control the initiation of locomotion has been tested in the present study. NA was depleted from the CNS using intraspinal and intraventricular injections of 6-hydroxydopamine and i.v. injections of the NA synthesis inhibitor, alpha-methyltyrosine. Depletion of 5-hydroxytryptamine (5-HT) was achieved using intraventricular injections of 5,6-dihydroxytryptamine and i.p. p-chlorophenylalanine. These treatments did not abolish evoked locomotion in spite of substantial depletion of NA and 5-HT in the spinal cord and brain stem (maximal depletions of NA up to 14% of control in lumbar cord and 16% of control in pons; maximal depletions of 5-HT up to 19% of control in sacral cord and 25% of control in medulla). Combined depletion of NA and 5-HT did not abolish evoked locomotion in mesencephalic cats, although the treated animals displayed pronounced ataxia prior to decerebration. Depletion of NA or 5-HT alone did not alter locomotion in otherwise intact animals. A previous report that phenoxybenzamine antagonizes the effects of MLR stimulation was not confirmed. The results therefore do not support the hypothesis that descending pathways containing monoamines are essential for locomotion evoked by brain stem stimulation.

Developmental transition by spinal cord plasma membranes of embryonic chick from permissive to restrictive substrates for the morphological differentiation of neuroblastoma x glioma hybrid NG108-15 cell.

Recent studies of spinal cord development and plasticity, in chick, have demonstrated a loss of regenerative ability correlating to embryonic day (E) 13 of the 21-day developmental period. Here we describe membrane fractions from embryonic chick spinal cords as permissive or restrictive substrates for the neuron-like differentiation of neuroblastoma x glioma hybrid NG108-15 cells, in vitro. Plasma membranes were purified from the thoracic spinal cord of embryos at a series of developmental stages (E10-E18). Micro-well plates were coated with the fractions and NG108-15 cells cultured thereon. Cells adhered to the E10-coated wells and began to differentiate after 2 h, becoming highly differentiated, with neurites 2-3 times longer than the diameter of the cell body after 24 h in in culture. In contrast, cells cultured in E18-coated wells remained as clusters of undifferentiated cells of rounded morphology, even after 48 h in culture. As well, the permissive and restrictive plasma membranes were assessed semiquantitatively as the number of adhering cells after 20 h of culture. Adhesion of cells to the substrate decreased as the embryonic age of the plasma membrane substrate increased. Examination of the plasma membrane fractions, using SDS-PAGE, revealed several proteins in the 40-60 kDa range that varied substantially between E12, E14 and E18. Results of this study provide in vitro confirmation of previous in vivo findings; namely, that early embryonic spinal cord is initially permissive for neuritic outgrowth becoming restrictive around E13.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of a descending pathway in the spinal cord which is necessary for controlled treadmill locomotion.

The spinal cord pathways which are important for controlled treadmill locomotion evoked by stimulation of the mesencephalic locomotor region (MLR) were investigated in cats subjected to subtotal spinal cord lesions at the C1-C2 level. Locomotion could be evoked following bilateral lesions of the dorsal columns, the dorsolateral funiculi, and the ventromedial funiculi, and after combined lesions of the dorsolateral and ventromedial funiculi, but not after bilateral lesions of the ventrolateral quadrant. Unilateral lesions of the ventrolateral quadrant abolished locomotion in the limbs is ipsilateral to the lesion. It is suggested that MLR stimulation may give rise to locomotion by activation of pontine and medullary reticulospinal pathways projecting through the ventrolateral quadrant.

A variable resolution x-ray detector for computed tomography: II. Imaging theory and performance.

A computed tomography (CT) imaging technique called variable resolution x-ray (VRX) detection provides variable image resolution ranging from that of clinical body scanning (1 cy/mm) to that of microscopy (100 cy/mm). In this paper, an experimental VRX CT scanner based on a rotating subject table and an angulated storage phosphor screen detector is described and tested. The measured projection resolution of the scanner is > or = 20 lp/mm. Using this scanner, 4.8-s CT scans are made of specimens of human extremities and of in vivo hamsters. In addition, the system's projected spatial resolution is calculated to exceed 100 cy/mm for a future on-line CT scanner incorporating smaller focal spots (0.1 mm) than those currently used and a 1008-channel VRX detector with 0.6-mm cell spacing.

The role of serotonin in reflex modulation and locomotor rhythm production in the mammalian spinal cord.

Over the past 40 years, much has been learned about the role of serotonin in spinal cord reflex modulation and locomotor pattern generation. This review presents an historical overview and current perspective of this literature. The primary focus is on the mammalian nervous system. However, where relevant, major insights provided by lower vertebrate models are presented. Recent studies suggest that serotonin-sensitive locomotor network components are distributed throughout the spinal cord and the supralumbar regions are of particular importance. In addition, different serotonin receptor subtypes appear to have different rostrocaudal distributions within the locomotor network. It is speculated that serotonin may influence pattern generation at the cellular level through modulation of plateau properties, an interplay with N-methyl-D-aspartate receptor actions, and afterhyperpolarization regulation. This review also summarizes the origin and maturation of bulbospinal serotonergic projections, serotonin receptor distribution in the spinal cord, the complex actions of serotonin on segmental neurons and reflex pathways, the potential role of serotonergic systems in promoting spinal cord maturation, and evidence suggesting serotonin may influence functional recovery after spinal cord injury.

Cytochemical characteristics of cat spinal neurons activated during fictive locomotion.

Using standard immunohistochemical and histochemical techniques, we have examined the neurochemical characteristics of a subpopulation of locomotor-related neurons as labeled by the activity-dependent marker c-fos. Results were compared to those obtained from a small sample of intracellularly labeled locomotor-related neurons. In the paralyzed, decerebrate cat, fictive locomotion was evoked by electrical stimulation of the mesencephalic locomotor region. Most c-fos-immunoreactive neurons were distributed in medial lamina VI and VII and in lamina VIII and X. Double labeling of c-fos with various cytochemical markers revealed that about one-third of the c-fos-immunoreactive neurons were choline acetyltransferase immunoreactive, about one-third were glutamate immunoreactive, and about one-third were aspartate immunoreactive. In addition, approximately 15% of the c-fos-labeled neurons contained NADPH-diaphrorase reaction product, while almost 40% appeared to receive close contacts from calcitonin gene-related peptide-immunoreactive fibers and boutons. Choline acetyltransferase- or aspartate immunoreactivity was observed in some intracellularly labeled neurons. These findings have implications regarding the putative neurotransmitters utilized by subpopulations of locomotor-related neurons in the cat spinal cord.

Intracellular labeling of cat spinal neurons using a tetramethylrhodamine-dextran amine conjugate.

Tetramethylrhodamine-dextran is a highly fluorescent neuroanatomical tracer that, in its 10,000 MW form, has seen widespread use as a sensitive anterograde tract-tracing label. We report here the use of a lower molecular weight tetramethylrhodamine-dextran (3000 MW; Molecular Probes, OR) as an in vivo intracellular marker of locomotor-related spinal neurons. In the paralyzed, decerebrate cat preparation, fictive locomotion was evoked by electrical stimulation of the mesencephalic locomotor region. Extracellular and intracellular potentials of rhythmically active spinal neurons were recorded using microelectrodes filled with 2% tetramethylrhodamine-dextran (3000 MW) in 0.9% saline (impedance 5-20 Mohm). Following impalement and electrophysiological characterization, neurons were iontophoretically injected for 2-30 min with 3-10 nA of pulsed positive current. Animals were then perfused 30 min to 7 h postinjection with a variety of paraformaldehyde- and glutaraldehyde-containing fixatives. After tissue sectioning, more than 90% of the injected neurons were recovered. Choline acetyltransferase-immunoreactivity could be demonstrated in a subpopulation of tetramethylrhodamine-dextran-labeled neurons. This technique, in addition to producing high-quality electrodes, has the advantages of rapid yet extensive filling of neuronal processes, no tissue processing prior to visualization, and compatibility with immunohistochemistry.

Critical decisions in the management of endoscopic perforations of the colon.

The ideal management of suspected colon perforation following colonoscopy remains elusive because the incidence is only 0.1 to 2.0 per cent. The patient with obvious perforation deserves immediate exploration, but the patient with equivocal findings poses a diagnostic dilemma. We propose an algorithm based on the results of water-soluble contrast enema that allows for rapid, definitive surgical decision-making. If perforation is confirmed, early operation allows for primary repair without resection or colostomy, or if no perforation is identified, medical management can be undertaken with confidence. This algorithm should ensure that the surgical management of this potentially lethal complication is not unnecessarily delayed.

Report of the National Commission on Nurse Anesthesia Education. The impact of the national nursing shortage on applicants for nurse anesthesia educational programs.

The serious nursing shortage of the late 1980s is reviewed in relation to the impact it has had on the recruitment and training of nurse anesthetists. A rapid expansion of the nurse anesthesia educational system and improved practice conditions for all nurses are advocated.

Profile of nurse anesthesia programs.

Over time, the Council on Accreditation of Nurse Anesthesia Educational Programs (COA) and the AANA Education and Research Department have recognized the need to gather information significant to nurse anesthesia programs. The need to create a formalized mechanism to gather and analyze information has also been identified as the profession has grown. COA and the Education and Research Department have responded to this need by creating a database and a reporting mechanism in order to present information to the Assembly of School Faculty at its annual meeting. The information will be summarized in this article, which is the first formal vehicle of disseminating the data.