Synaptic connections of the cuticular stress detectors in crayfish: mono- and polysynaptic reflexes and the entrainment of fictive locomotion in an in vitro preparation

The reflex connections made by Cuticular Stress Detector afferents (CSD1 and CSD2) with motorneurones of the four proximal muscle groups in the 5th walking legs of crayfish (Procambarus clarkii, Pacifastacus leniusculus) have been studied in an in vitro preparation. Reflex responses to mechanical stimulation of the CSDs were studied in single neurones by means of intracellular techniques. Within each motorneurone pool, both excitatory and inhibitory reflex responses occurred, although sometimes no reflex connections were found. When present, they could be classified into levation and depression reflexes, corresponding to negative and positive feedback effects respectively. Each motorneurone receives input from a number of different CSD afferents (mean values between 3.0 and 5.8). Using electrophysiological and pharmacological tests, it was demonstrated that at least 32% of all connections were monosynaptic. In preparations showing fictive locomotion, phasic CSD stimulation was shown to be able to entrain anterior levator and depressor motorneurone activity in 95% of cases. The results thus demonstrate the importance of sensory feedback from the CSDs in shaping the final motor output.Abbreviations CPG Central pattern generator - CSDs (CSD1 and CSD2) Cuticular stress detector organs     

A role for cyclic AMP in entrainment of the circadian oscillator in Xenopus retinal photoreceptors by dopamine but not by light

The circadian oscillator in Xenopus retinal photoreceptor layers can be reset in similar ways by light and agonists of D2-like dopamine receptors. Treatments that increase cyclic AMP levels act on this oscillator in an opposite fashion, mimicking darkness in the induction of phase shifts. Light and dopamine have each been reported to inhibit adenylate cyclase in photoreceptors. Together, these data suggest that the transduction pathways for entrainment by dopamine and/or light include suppression of cyclic AMP or a cyclic AMP-sensitive step. In these studies, we examined this hypothesis by measuring the effects of treatment with a cyclic AMP analogue on the phase shifts induced in photoreceptor melatonin rhythms by light or a D2 receptor agonist (quinpirole). When photoreceptor layers were treated simultaneously with 8-(4-chlorophenylthio)cyclic AMP (8-CPT-cAMP) and quinpirole at any of three different phases of the circadian cycle, the resulting phase shifts of the melatonin rhythm were always the same as those caused by 8-CPT-cAMP alone. This indicates that there is a cyclic AMP-sensitive step in the dopamine entrainment pathway. In contrast, light pulses did reset the oscillator in the presence of elevated cyclic AMP. This suggests a separate cyclic AMP-insensitive transduction pathway for entrainment by light. Quinpirole reduced basal levels of cyclic AMP in photoreceptors, but light did not. These data suggest that cyclic AMP plays a role in the entrainment pathway activated by dopamine but not in the entrainment pathway activated by light.     

The diurnal modulation of the circatidal activity rhythm by feeding in the isopod eurydice pulchra

The diurnal modulation of circatidal activity was studied in freshly caught Eurydice pulchra of different feeding states. Apparently fully fed specimens displayed definite circadian modulation, with greatest tidal activity at the time of expected night‐time high tides, and apparently starved animals showed no circadian variation. Circatidal activity was also entrained in the laboratory using cycles of artificial agitation and the subsequent pattern of free‐running rhythmicity was studied. Animals fed prior to entrainment displayed definite diurnal modulation of the pattern of ciractidal swimming activity. Those fed after the entrainment regime, or not at all, displayed no apparent diurnal inequality of tidal activity peaks. No relationship between diurnal inequality and phototactic behaviour of freshly collected specimens was detected.     

Effect of cyclic AMP on the excitation and response of command neurons responsible for the snail defensive behavior caused by sensory stimulation]

Extraneuronal application of db-cAMP or intraneuronal injection of cAMP were found to increase the neural membrane excitability and synaptic facilitation in neural responses to sensory stimulation of Lpl1 and Rpl1 neurones. The db-cAMP exerted no effects on neural responses to tactile stimulation of the snail foot or mantle. The intraneuronal injection of cAMP produced synaptic facilitation only in neural responses to quinine application to the snail head. The findings suggest the cAMP selective involvement in postsynaptic mechanisms of inducing the long-term facilitation transient stage.     

Acceleration of recovery from sciatic nerve damage by the ACTH(4–9) analog Org 2766: Different routes of administration

Functional recovery following a sciatic nerve crush in rats was investigated by measuring the reflex withdrawal of the hindpaw to a hot air stream. The ACTH(4–9) analog Org 2766 accelerated recovery when administered subcutaneously (two-daily injections: 10 μg/animal; minipumps: 20–40 μg/animal per 24 hr; biodegradable microspheres: 40 μg/animal per 24 hr), but oral administration (1.5–20 mg/animal daily, in the drinking water; 1.5–15 mg/animal daily, by gavage) was not effective.     

Photic induction of c-Fos in enkephalin neurons of the rat intergeniculate leaflet innervated by retinal PACAP fibres

The brain’s biological clock, located in the suprachiasmatic nucleus (SCN), is synchronised with the cyclic environment by photic and non-photic cues. Photic information to the SCN is mediated by pituitary adenylate-cyclase-activating polypeptide (PACAP)-containing retinal ganglion cells (RGCs), whereas non-photic input originates primarily from neuropeptide Y (NPY) cells in the ipsilateral thalamic intergeniculate leaflet (IGL). RGCs also seem to project to the IGL, indicating a role for this structure in the integration of photic and non-photic inputs related to the resetting of the biological clock. In the present study, we have used anterograde tracing from both eyes, bilateral eye enucleation, double-immunofluorescence histochemistry, high-resolution confocal laser scanning microscopy and three-dimensional computer analysis to show that (1) PACAP-containing RGCs project to the IGL and are the only source for the PACAP-immunoreactive fibres in the IGL; (2) a few NPY-containing neurons in the IGL are innervated by PACAP-containing retinal nerve fibres and the contacts are both axodendritic and axosomatic; (3) most enkephalin-immunoreactive neurons in the IGL are innervated by PACAP-containing retinal afferents and the contacts are mainly axodendritic; (4) light stimulation at various time points activates (as evidenced by c-Fos induction) enkephalin-positive neurons but not NPY-immunoreactive neurons. The findings suggest that PACAP-immunoreactive retinal afferents in the IGL primarily innervate enkephalin-immunoactive neurons and that the enkephalin-containing neurons, which project locally and to the contralateral IGL, are activated by light independent of diurnal time. This study was supported by the Danish Biotechnology Centre for Cellular Communication and The Danish Medical Research Council (no. 22-04-0667).     

The entrainment of sediments by the turbulent flow of water

This paper attempts to clarify the role of fluid turbulence in the entrainment process of particles from the flat bed of an alluvial channel. A 6 mm diameter sphere, placed in an array of similar particles on the bed of a laboratory flume, was connected to a 3-component force transducer. Dynamic measurements of longitudinal, lift and lateral force components were made with the particle at a number of positions above the bed. Detailed measurements of velocity and turbulence were also made. The velocity and force spectral measurements showed similarities in the longitudinal (streamwise) direction but the lift force component spectra were significantly different.An analytical model of the entrainment process is proposed, in which the impulse required to lift a sediment particle from the channel bed may be calculated. The experimental data has been used to evaluate the constants in the analytical expressions, and a relationship between the forces and turbulence intensity established. The analysis shows that the impulse required to entrain a particle may be expressed as a function of a dimensionless entrainment parameter, the turbulence intensity, and the initial angle of repose of the particle.     

Habituation of vasodilatation in the calf elicited by repeated sensory stimulation in man

In 28 subjects the cardiovascular response to repeated stimulation was monitored during six daily sessions. Calf blood flow was measured with mercury-in-silastic venous occlusion plethysmography, blood pressure with electronic sphygmomanometer. The stimuli used were: 1 kHz sound of 90 dB and 100 dB intensity and immersion of one foot for 60 s in water at 4 degrees C. Initially sounds induced large vasodilatation in the calf, immersion of one foot in the water induced in the contralateral calf vasodilatation in one group and vasoconstriction in another group of subjects. The blood pressure changes were less prominent and less consistent. After the first session of repeated stimulation the vascular response during the second session was significantly diminished. The reduction of the vasodilatation was the most rapid. During the remaining 5 days the responses were suppressed. It has been established that in the patients in the initial stage of hypertension the ability to habituate vascular response is impaired (Zbrozyna and Krebbel 1985). It is therefore suggested that the test of the ability for long-term vascular habituation could be used as a supplementary diagnostic test.     

The effect of a vasopressin analog on the reaction of the command neurons in the defensive behavior of the edible snail during nerve stimulation

On the level of snail command neurones of the defensive behaviour an increase was revealed of the amplitude of summary EPSP recorded in command neurones in response to nerve stimulation, an increase of probability of appearance of action potential in the reaction and, under certain conditions, a significant decrease of habituation speed at rhythmic (0.1 Hz) nerve stimulation against the background of peptide. The latter effect was found during comparison of groups of neurones--control neurones and those to which the peptide was presented before the first series of stimulation in the test, i. e. without preliminary elaboration of habituation. The decrease of the speed of habituation concerned both the amplitude of summary EPSP and the probability of action potential appearance in the reaction. All these changes against the background of vasopressin analogue may be the basis of the increase of spike reactions of command neurones of the defensive behaviour and thus the basis of the initiation or the increase of behavioural defensive reactions. The obtained effects were not protracted and took place only in the presence of the peptide in the extracellular medium.     

The structure of the cereal sensory system and ventral nerve cord of Grylloblatta

Summary The structure of cereal sensilla, the cereal nerve and the central projections of the cereal sensory nerve of a notopteran (Grylloblatta sp.) are described and compared with other orthopteroid insects in which the cereal sensory system and central connections are well known. The cereal sensilla are similar to those of gryllids and blattids, but the gross structure of the cerci and distribution of cereal sensilla more closely resemble those of the Thysanura. The elements of the cereal sensory nerves and the central nervous system are similar to those of other orthopteroid insects, but extracellular material is present in greater quantity, and more extensive glial bundling of axons occurs in both the cereal nerve and central connectives. Glial structure, extracellular material and large multicristate mitochondria may be adaptations to life near 0° C. The form of central projections of the cereal nerve and the configuration of the largest abdominal interneurons are unlike those of gryllids and Dictyoptera; they are similar to those of Dermaptera.     

The generation of DPOAEs in the locust ear is contingent upon the sensory neurons

Tympanal organs of insects emit distortion-product otoacoustic emissions (DPOAEs) that are indicative of nonlinear ear mechanics. Our study sought (1) to define constraints of DPOAE generation in the ear of Locusta migratoria, and (2) to identify the sensory structures involved. We selectively destroyed the connection between the (peripheral) sensory ganglion and the tympanal attachment points of the “d-cell” dendrites; d-cells are most sensitive to sound frequencies above 12 kHz. This led to a decrease of DPOAEs that were evoked by f ₂ frequencies above 15 kHz (decrease of 15–40 dB; mean 28 dB; n = 12 organs). DPOAEs elicited by lower frequencies remained unchanged. Such frequency-specific changes following the exclusion of one scolopidial sub-population suggest that these auditory scolopidia are in fact the source of DPOAEs in insects. Electrical stimulation of the auditory nerve (with short current pulses of 4–10 μA or DC-currents of 0.5 μA) reversibly reduced DPOAEs by as much as 30 dB. We assume that retrograde electrical stimulation primarily affected the neuronal part of the scolopidia. Severing the auditory nerve from the central nervous system (CNS) did not alter the DPOAE amplitudes nor the effects of electrical stimulation.     

Human cerebrocortical potentials evoked by stimulation of the dorsal nerve of the penis

Cortical evoked potentials resulting from stimulation of the dorsal nerve of the penis (DNP) provide a unique opportunity to document the cortical localization of sexual sensory representation in man. The DNP supplies sensory axons to the major portion of the human phallus, including the penile shaft and glans. Animal and human studies indicate that this nerve plays a crucial role in erection and ejaculation. Direct cortical evoked responses to DNP electrical stimulation were recorded in patients undergoing preoperative evaluation for resection of epileptic foci. These studies provided evidence that the primary sensory cortex contains a large area of cortex devoted to the afferent fibers of the DNP and that the sensory field is in a different location than previously described. The location and distribution of this response indicated the need for revision of the traditional concept of the sensory cortical homunculus.     

Target specificity and size of avian sensory neurons supported in vitro by nerve growth factor,brain-derived neurotrophic factor,and neurotrophin-3

To obtain insight into which subpopulations of sensory neurons in dorsal root ganglia are supported by different neurotrophins, we retrogradely labeled cutaneous and muscle afferents in embryonic day 9 chick embryos and followed their survival in neuron-enriched cultures supplemented with either nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), or neurotrophin-3 (NT-3). We found that NGF is a wide survival factor for subpopulations of both cutaneous and muscle afferents, whereas the survival effects of BDNF and NT-3 are restricted primarily to muscle afferents. We also measured soma size in each neurotrophic factor. These new data show that BDNF- and NT-3–dependent cells appear to be a mixture of two populations of neurons: one small diameter and the other large diameter. In contrast, based on size alone, NGF-dependent cells appear to be a single population of only small-diameter neurons. Thus, BDNF and NT-3 may have some new, previously unreported effects on small-diameter afferent neurons. © 1994 John Wiley & Sons, Inc. 1994 John Wiley & Sons, Inc.     

Effects of capsaicin and nitric oxide synthase inhibitor on increase in cerebral blood flow induced by sensory and parasympathetic nerve stimulation in the rat.

Effects of electrical stimulation of the nerve bundles including sensory and parasympathetic nerves innervating cerebral arteries on cerebral blood flow (CBF) and mean arterial blood pressure (MABP) were investigated with a laser-Doppler flowmeter and a blood pressure monitoring system in anesthetized rats pretreated with and without capsaicin. The electrode was hooked on the nerve bundles including the distal nasociliary nerve from trigeminal nerve and parasympathetic nerve fibers from sphenopalatine ganglion. In control rats, the nerve stimulation for 30 s increased CBF in the ipsilateral side and MABP. Hexamethonium attenuated the increase in CBF and abolished that in MABP. Under treatment with hexamethonium, N(G)-nitro-L-arginine (L-NNA, 1 mg/kg) significantly attenuated the stimulation-induced increase in CBF, which was restored by the addition of L-arginine. Although the dose of L-NNA was raised up to 10 mg/kg, the stimulation-induced increase in CBF was not further inhibited and was never abolished. In capsaicin-pretreated rats, magnitudes of the stimulation-induced increases in CBF and MABP were lower than those in control rats. Hexamethonium attenuated the increase in CBF and abolished that in MABP. Under treatment with hexamethonium, L-NNA abolished the stimulation-induced increase in CBF in capsaicin-pretreated rats. In conclusion, nitric oxide released from parasympathetic nerves and neuropeptide(s) released antidromically from sensory nerves may be responsible for the increase in CBF in the rat. The afferent impulses by nerve stimulation may stimulate the trigeminal nerve and lead to the rapid increase in MABP, which partly contributes to the increase in CBF.     

The effects of sensory stimulation on the free amino acid pool of the developing brain

Developing chicks were subjected to three different paradigmata of sensory stimulation, and the effects on the free amino acid concentrations in the blood and in various brain regions were monitored. The free amino acid pool of individual brain regions was found to be affected in a treatment-and age-specific manner. The increased neuronal activity resulting from sensory stimulation seems to affect intrinsic factors involved in the regulation of the free amino acid pool, most likely via modulations of the rate of metabolization of individual amino acids and/or of the rate of synthesis and degradation of individual proteins in certain brain regions.Special Issue dedicated to Prof. Holger Hydén.     

Dynamics of calcium release and uptake by the internal calcium stores in rat sensory neurons

Calcium dynamics in the endoplasmic reticulum of dorsal root ganglion neurons of rats during Ca²⁺ release induced by caffeine and subsequent Ca²⁺ uptake were studied. Calcium release is shown to include two (a short transient and a prolonged slow) phases. We suggest that the transient phase reflects release of free Ca from the calcium store, while the slow phase reflects transition of Ca from a bound form to a free one. The process of Ca²⁺ uptake is characterized by exponential recovery of the calcium level in the store due to the SERCA activity. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 361–363, July–August, 2006.