Spinal reflexes and the concentrations of 5-HIAA, MHPG, and HVA in lumbar cereborspinal fluid after spinal lesions in man. (25/5249)

Descending bulbospinal pathways that employ specific neurotransmitter substances are known to be capable of modulating segmental reflex activity in the experimental animal. To determine whether this might also occur in man correlations have been sought between the activity in spinal reflex pathways and the lumbar cerebrospinal fluid (CSF) concentrations of 5-hydroxyindolacetic acid (5-HIAA), 3 methoxy-4-hydroxyphenylglycol (MHPG), and homovanillic acid (HVA) in 12 patients with complete or virtually complete spinal lesions. The concentrations of 5-HIAA and MHPG in lumbar CSF ARE REDUCED AFTER COMPLETE OR VIRTUALLY COMPLETE SPINAL LESIONS IN MAN. This may occur within 18 days of the lesion. MHPG concentrations appear to be inversely related to the level of the lesion. The HVA concentration in lumbar CSF is reduced when there is obstruction of the CSF pathways. No relationship could be demonstrated between the concentrations of 5-HIAA or MHPG in lumbar CSF and the activity in the spinal monosynaptic pathway (estimated from the proportion of the motoneurone pool activated by the Achilles tendon reflex or H reflex) or the activity of a spinal inhibitory mechanism (estimated by the degree of vibratory inhibition of the monosynaptic reflex). Patients with a tonic vibration reflex (TVR) tended to have higher MHPG levels. There appeared to be an association between low CSF HVA and enhanced vibratory inhibition of the monosynaptic reflex in the nine patients whose spinal lesions were complete.  (+info)

Neuronal basis of a sensory analyser, the acridid movement detector system. III. Control of response amplitude by tonic lateral inhibition. (26/5249)

1. The Lobular Giant Movement Detector neurone (LGMD) of Schistocerca responds with spikes when small areas of the visual field change in luminance. Previous work has shown that changes of +/- 1 log 10 unit are enough to produce maximal ON and OFF responses. 2. Using a 5 degree test area, it is shown that the number of spikes generated by such a stimulus depends on the luminance of the surrounding area. When the surround is dark, the response is maximal; when it is brightly lit, the response is minimal. Intermediate intensities produce intermediate values of response. A X 2 change in response is produced by about 3 log 10 units change in surround intensity. 3. A bright annulus, with diameters of 10-5 degrees and 25-8 degrees, inhibits both ON and OFF responses when concentric with the 5 degree test area, but not when it is 30 degrees eccentric to the test area. The inhibitory effect shows no decrease after 4 min. 4. These results are interpreted to indicate a tonic lateral inhibitory network, sited peripherally in the optic lobe prior to the divergence of the separate ON and OFF channels found in the projection from the medulla to the LGMD. It is probably identical with that described for the lamina by previous workers.  (+info)

Primitive nervous systems: electrophysiology of the pharynx of the polyclad flatworm, Enchiridium punctatum. (27/5249)

1. Electrical activity accompanying motor activity can be recorded from the excised pharynx of Enchiridium punctatum. Multiple stimuli elicit behaviour which consists of an initial aperture closure followed by extension and then peristalsis. If the stimulus parameters are increased the preparation bends from side to side instead of proceeding through the behavioural sequence. Bending appears to inhibit other movements differentially. 2. The conduction involved with peristalsis is polarized and proceeds in a proximal direction. 3. With stimulus intensities greater than those needed to produce the behavioural response an initial muscle potential (IMP) is evoked. The IMP is frequency sensitive. Maximum facilitation occurs within 100 ms and drops to 50% of maximum within 250 ms. 4. Conduction velocities of the IMP range from 0-05 m s-1 to 1-9 m s-1. Conduction velocities appear to increase with facilitation.  (+info)

On the analysis of nerve signals deduced from metacontrast experiments with human observers. (28/5249)

1. This paper reviews Alpern, Rushton & Torii's (1970a-d) derivation of the size of the inhibitory nerve signal arising from after flashes in the metacontrast experiment. 2. Their geometric argument is recast in terms of simple functional equations. This form of argument clearly displays the role of their assumptions in obtaining their main conclusion: nerve signal is linear in intensity over a range of 3-4 log units. 3. Two disadvantages of their approach are discussed. First, it is noted that in the presence of the data the assumption they employ in their analysis is logically equivalent to their conclusion. 4. Secondly, accepting their claim that the nerve signal generated by the after flash is linear over a broad range of intensities, and that this inhibitory signal simply cancels the excitatory signal of the test flash, leads to the conslusion that over this same intensity range the excitatory nerve signal is a power function with an exponent of close to two. This is incompatible with the suggestion that photoreceptor signals have been measured.  (+info)

Receptive fields, geometry and conduction block of sensory neurones in the central nervous system of the leech. (29/5249)

1. In segmental ganglia of the leech, the cutaneous mechanosensory neurones responding to to touch innervated the skin of their own segment and of part of the anterior and posterior adjacent segments. Each touch receptive field could be divided into three non-overlapping areas: a central part innervated by the branches of the cell which ran in the nerve roots of the ganglion containing the cell body, and anterior and posterior parts innervated by its branches which ran in the nerve roots of the anterior and posterior adjacent ganglia. 2. Impulses originating from the anterior and posterior parts of the receptive fields were susceptible to conduction block within the central nervous system when the touch cells fired repetitively at frequencies that could readily be elicited with weak mechanical stimulation. In contrast, impulses originating from the central part of the receptive fields were less susceptible to block. 3. The morphology of touch cells revealed by intracellular injection of horseradish peroxidase suggested that conduction block occurred at specific bifurcation points where small cell processes joined the main process. Different physiological experiments supported this conclusion. 4. In some touch cells, bifurcation points with particularly low safety margins of conduction operated as low-pass filters, limiting the frequency of impulses capable of invading certain branches. 5. The results suggest that mechanical stimuli which would likely be encountered by the animal can lead to conduction block within its central nervous system and as a result modify its integrative activities.  (+info)

Specific alteration of spontaneous GABAergic inhibition in cerebellar purkinje cells in mice lacking the potassium channel Kv1. 1. (30/5249)

In the cerebellum, the basket cell innervation on Purkinje cells provides a major GABAergic inhibitory control of the single efferent output from the cerebellum. The Shaker-type K channel Kv1.1 is localized at the axon arborization preceding the terminal of the basket cells and is therefore a potential candidate for regulating the GABAergic inhibition. In this study, we directly assess this role of Kv1.1 by electrophysiological analysis of Kv1.1 null mutant mice. Whole-cell patch-clamp recordings of spontaneous IPSCs (sIPSCs) were made from Purkinje cells in thin cerebellar slices from postnatal day (P)10-15 Kv1.1-null mutants using wild-type littermates as controls. The null mutation confers a very specific change in the sIPSC: the frequency increases about twofold, without accompanying changes in the mean and variance of its amplitude distribution. The frequency and amplitude of the miniature IPSCs (mIPSCs) are unaffected. Spontaneous firing rate of the basket cells is unaltered. Evoked IPSC does not show multiple activity in the mutants. Motor skills tests show that Kv1.1 null mice display a compromised ability to maintain balance on a thin stationary rod. We conclude that the Kv1.1 null mutation results in a persistent elevation of the tonic inhibitory tone on the cerebellum Purkinje cell efferent and that this is not fully compensated for by residual Shaker-type channels. We further suggest that the increase in inhibitory tone in the mutants might underlie the behavioral deficits. At the cellular level, we propose that Kv1.1 deletion enhances excitability of the basket cells by selectively enhancing the likelihood of action potential propagation past axonal branch points.  (+info)

RVLM and raphe differentially regulate sympathetic outflows to splanchnic and brown adipose tissue. (31/5249)

To determine whether neurons in the rostral raphe pallidus (RPa) specifically control the sympathetic nerve activity to brown adipose tissue (BAT SNA), thereby regulating adipocyte metabolism and BAT thermogenesis, the responses in BAT SNA to disinhibition of RPa neurons and to disinhibition of neurons in the vasomotor region of the rostral ventrolateral medulla (RVLM) were compared with those in splanchnic (Spl) SNA, which primarily regulates visceral vasoconstriction. In urethan-chloralose-anesthetized ventilated rats, both acute hypothermia and microinjection of bicuculline into RPa produced significantly larger increases in BAT SNA (542 and 1,949% of control) than in Spl SNA (19 and 24% of control). The enhanced burst discharge in BAT SNA was not coherent with that in Spl SNA or with the arterial pressure (AP) at any frequency except the central respiratory frequency. Microinjections of bicuculline into RVLM evoked increases in Spl SNA (86% of control) and AP (32 mmHg), but reduced BAT SNA to low, normothermic levels. Microinjections of muscimol into RVLM reduced Spl SNA (-82% of control) and AP (-59 mmHg), but did not prevent the increase in BAT SNA after disinhibition of RPa neurons. These results indicate that the neural networks generating BAT SNA in response to disinhibition of RPa neurons are independent of those generating basal Spl SNA and support a model in which sympathetic outflow to tissues involved in thermoregulation and metabolism is regulated by central pathways, including neurons in RPa, that are distinct from those involved in the sympathetic control of the cardiovascular system.  (+info)

Midline medullary depressor responses are mediated by inhibition of RVLM sympathoexcitatory neurons in rats. (32/5249)

Mechanisms underlying the depressor and sympathoinhibitory responses evoked from the caudal medullary raphe (MR) region were investigated in pentobarbital sodium-anesthetized, paralyzed rats. Intermittent electrical stimulation (0.5 Hz, 0.5-ms pulses, 200 microA) of the MR elicited a mixed sympathetic response that consisted of a long-latency sympathoexcitatory (SE) peak (onset = 146 +/- 7 ms) superimposed on an inhibitory phase (onset = 59 +/- 10 ms). Chemical stimulation of the MR (glutamate; Glu) most frequently elicited depressor responses accompanied by inhibition of sympathetic nerve discharge. Occasionally, these responses were preceded by transient pressor and SE responses. We examined the influence of intermittent electrical stimulation (0.5 Hz, 0.5-ms pulses, 25-200 microA) and Glu stimulation of the MR on the discharge of rostral ventrolateral medulla (RVLM) premotor SE neurons. Peristimulus-time histograms of RVLM unit discharge featured a prominent inhibitory phase in response to MR stimulation (onset = 20 +/- 2 ms; duration = 42 +/- 4 ms; n = 12 units). Glu stimulation of the MR reduced blood pressure (-37 +/- 2 mmHg, n = 19) and inhibited the discharge of RVLM SE neurons (15 of 19 neurons). Depressor and sympathoinhibitory responses elicited by chemical and electrical stimulation of the MR region are mediated by inhibition of RVLM premotor SE neurons and withdrawal of sympathetic vasomotor discharge.  (+info)