Binocular visual integration in the crustacean nervous system

Although the behavioral repertoire of crustaceans is largely guided by visual information their visual nervous system has been little explored. In search for central mechanisms of visual integration, this study was aimed at identifying and characterizing brain neurons in the crab involved in binocular visual processing. The study was performed in the intact animal, by recording intracellularly the response to visual stimuli of neurons from one of the two optic lobes. Identified neurons recorded from the medulla (second optic neuropil), which include sustaining neurons, dimming neurons, depolarizing and hyperpolarizing tonic neurons and on-off neurons, all presented exclusively monocular (ipsilateral) responses. In contrast, all wide field movement detector neurons recorded from the lobula (third optic neuropil) responded to moving stimuli presented to the ipsilateral and to the contralateral eye. In these cells, the responses evoked by ipsilateral or contralateral stimulation were almost identical, as revealed by analysing the number and amplitude of the elicited postsynaptic potentials and spikes, and the ability to habituate upon repeated visual stimulation. The results demonstrate that in crustaceans important binocular processing takes place at the level of the lobula.     

Anatomy and in vivo activity of neurons connecting the crustacean stomatogastric nervous system to the brain

In decapod crustaceans, the inferior ventricular nerve connects the cerebral ganglia (brain) with the stomatogastric nervous system (STNS). In the ivn of the crayfish, eight axons with diameters between 3.5 microm and 10 microm were found in close proximity to the oesophageal ganglion. Two of these axons terminate with their cell body within the ivn. The projections of the other six axons spread inside many neuropiles of the brain, mainly within the protocerebrum and the neuropils of the first and second antennae. Several fibers also send neurites via the circumoesophageal connectives toward the paired commissural ganglia and further down to the ventral nerve cord. The activity of motoneurons within the STNS and of axons in the ivn was recorded with implanted electrodes before, during and after times of feeding. At the beginning of feeding all tonically active ivn neurons accelerated their discharge rate and initially silent neurons also started to fire. Spike frequency was correlated with the quantity of food consumed. The ivn response was accompanied by a corresponding increase in pyloric frequency and an initiation of a gastric rhythm. The two motor rhythms showed a strong phasic interaction, but there was no phase coupling to the ivn activity.     

Electrophysiological analysis of potassium and sodium movements in crustacean nervous system.

1. An electrophysiological method was used to estimate the half-times for sodium and potassium entry to, and efflux from, the extra-axonal space in peripheral nerve and central nervous connectives of two species of crustacean. Results from crab (marine) and crayfish (fresh water) were qualitatively similar. 2. Peripheral nerve showed no evidence for diffusion barriers, potassium entry and efflux being rapid, and proceeding at comparable rates. 3. In connective, potassium entry was extremely slow, with a half-time greater than 100 min, while potassium efflux was relatively rapid (T 1/2 = 6 min). Sodium movements were less restricted, but sodium entry was more rapid than sodium efflux. 4. The potassium experiments were compared with the behaviour of a theoretical model system. Evidence is presented for diffusional restriction to potassium at the connective perineurial layer. The mechanism of restriction may involve changes in permeability or activation of an ion pump in the perineurial layer. 5. The physiological significance of these findings is discussed.     

Multimodal distribution and discontinuous variation in period of interacting oscillators in the crustacean stomatogastric nervous system

Summary In the stomatogastric ganglion (STG) of Homarus gammarus, pacemaker neurons of the pyloric central pattern generator are entrained by a network oscillator (CPO) contained in the commissural ganglion. A consequence of CPO's influence is that the spontaneous pyloric period can take one of several absolute values, most commonly displaying a bimodal distribution. These discrete values correspond to different coordination modes with the CPO rhythm. Moreover, the oscillation period of pyloric pacemaker neurons varies discontinuously with their membrane potential. This behavior persists when the mean pyloric period is modified by different perfusion salines but disappears when the STG is disconnected from the anterior ganglia. Under these conditions, pyloric pacemaker neurons are deprived of CPO inputs and behave like independent oscillators whose period varies continuously as a function of the membrane potential. The modulatory pyloric suppressor neurons (PS), which are known to decrease the oscillatory capabilities of the pyloric pacemakers, can change the coordination mode between these neurons and the CPO. PS can provoke discontinuous variations in the pyloric period as a function of their firing frequency. Finally, the nonlinear behavior of the pyloric pattern generator described in Homarus also occurs in Jasus lalandii, in which the existence of a CPO has not yet been demonstrated.Abbreviations AB anterior burster neuron - ASW artificial seawater - COG commissural ganglion - CP commissural pyloric neuron - CPG central pattern generator - CPO commissural pyloric oscillator - IC inferior cardiac neuron - ivn inferior ventricular nerve - LP lateral pyloric neuron - OG esophageal ganglion - PD pyloric dilator neuron - PDn pyloric dilator nerve - PS pyloric suppressor neuron - son superior esophageal nerve - PY pylonic neuron - STG stomatogastric ganglion - stn stomatogastric nerve - vlvn ventral branch of the lateral ventricular nerve Maître de conférence à l'U.E.R. de Médecine et de Pharmacie, 2 rue Dr Marcland, 87025 Limoges Cedex, France.     

Glutaminase activity in the chick central nervous system during postnatal growth.

1. Glutaminase activity was evaluated in the chick cerebral hemispheres, optic lobes and cerebellum between the 1st and 30th day of postnatal growth. 2. Glutaminase activity is higher in the cerebral hemispheres than in the optic lobes and is lowest in the cerebellum. 3. It seems to be inversely related to the magnitude of the variations of glutamine concentration in the three areas. 4. No direct relation exists between enzyme activity and glutamate concentration in the three tissues.     

Identity of the cells recruited to a lesion in the central nervous system of a decapod crustacean

In a previous study, we analyzed and described the features of the degeneration of the protocerebral tract (PCT) of the crustacean Ucides cordatus, after the extirpation of the eyestalk. In that study, among axons with axoplasmic degeneration, cells with granules resembling blood cells (hemocytes) were seen. Therefore, in the present study, we characterized the circulating hemocytes and compared them with the cells recruited to a lesion, which was produced as in the former study. Using histochemistry, immunohistochemistry, and electron microscopy (transmission and scanning), we confirmed that circulating and recruited cells display a similar morphology. Therefore, in the crab, hemocytes were attracted to the lesion site in the acute stage of degeneration, appearing near local glial cells that showed signs of being responsive. Some of the attracted hemocytes displayed a morphology that was considered to be possibly activated blood cells. Also, the cells that migrated to the injured PCT displayed features, such as the presence of hydrolytic enzymes and an ability to phagocytize neural debris, similar to those of vertebrates. In summary, our results indicate that hemocytes were not only phagocytizing neural debris together with glial cells but also that they may be concerned with creating a favorable environment for regenerating events.     

Central nervous system depressant activity of Russelia equisetiformis.

The central nervous system depressant activity of the crude methanol extract (REC) and fractions (RE1, RE2, and RE3) of Russelia equisetiformis were evaluated in mice using the following models: amphetamine-induced stereotypy, picrotoxin-induced convulsion and phenobarbitone sleeping time. At 200-400 mg/kg, REC significantly increased phenobarbitone-sleeping time [P < 0.05] in a dose- dependent manner and also reduced the sleep latency significantly [P < 0.05]. The fractions, at doses 1.5 mg/kg for RE1 and 20 mg/kg for RE2 and RE3 also significantly prolonged Phenobarbitone sleeping time and sleep latency [P < 0.05]. Picrotoxin-induced convulsion was not prevented by 100-400 mg/kg of REC but this dose range significantly prolonged seizure latency. A significant reduction [P < 0.05] in amphetamine-induced stereotype behavior was observed with 200 mg/kg REC, but there was no protection against amphetamine-induced mortality. The results of this study suggest that Russelia equisetiformis methanol extract possesses central nervous system depressant activities.     

Central nervous system activity of Leucas inflata Benth. in mice.

The analgesic activity of the methanol and acetone extracts of Leucas inflata L. (family Labiatae) was evaluated in mice using different experimental models. The effect of the two extracts on pentobarbitone-sleeping time, motor activity, sensorimotor coordination, carrageen induced inflammation, and brewer's yeast-induced pyrexia has also been investigated. The two crude extracts have been phytochemically analyzed and some constituents isolated and characterized. These included stigmasterols, a chromone and coumarins. Extracts of L. inflata L., given at single oral doses of 0.25, 0.5, 1.0 or 2.0 g/kg, significantly and dose-dependently, reduced formalin-induced pain, acetic acid induced abdominal constrictions and increased the reaction time in the hot-plate test. Both extracts caused significant and dose-related impairment in the sensorimotor control and ambulatory and total motor activity of treated mice. Both extracts exhibited anti-inflammatory action by reducing paw edema of treated mice. The extracts did not significantly affect the rectal temperature of normothermic mice. However, they were effective in preventing Brewers yeast induced pyrexia. It is concluded that the crude methanol and acetone extract of L. inflata has CNS depressant properties, manifested as antinociception and sedation. Both extracts have anti-inflammatory and antipyretic actions.     

Sildenafil acts on the central nervous system increasing sympathetic activity.

Sildenafil induces vasodilation and is used for treating erectile dysfunction. Although its influence on resting heart function appears to be minimal, recent studies suggest that sildenafil can increase sympathetic activity. We therefore tested whether sildenafil injected into the central nervous system alters the autonomic control of the cardiovascular system in conscious rats. The effect of sildenafil citrate injected into the lateral cerebral ventricle was evaluated in conscious rats by means of the recording of lumbar sympathetic nerve activity (LSNA), spectral analysis of systolic arterial pressure and heart rate variability, spontaneous baroreflex sensitivity, and baroreflex control of LSNA. Intracerebroventricular (ICV, 100 microg /5 microl) administration of sildenafil caused remarkable tachycardia without significant change in basal arterial pressure and was associated with a conspicuous increase (47 +/- 14%) in LSNA. Spectral analysis demonstrated that systolic arterial pressure oscillations in the low frequency (LF) range were increased (from 6.3 +/- 1.5 to 12.8 +/- 3.8 mmHg(2)), whereas the high frequency (HF) range was not affected by ICV administration of sildenafil. Sildenafil increased pulse interval oscillations at LF and decreased them at HF. The LF-HF ratio increased from 0.04 +/- 0.01 to 0.17 +/- 0.06. Spontaneous baroreflex sensitivity measured by the sequence method and the baroreflex relationship between mean arterial pressure and LSNA were not affected by ICV administration of sildenafil. In conclusion, sildenafil elicited an increase in sympathetic nerve activity that is not baroreflex mediated, suggesting that this drug is able to elicit an autonomic imbalance of central origin. This finding may have implications for understanding the cardiovascular outcomes associated with the clinical use of this drug.     

Autonomic nervous system activity in Macaca fascicularis

This study was performed to determine the contributions of the sympathetic and parasympathetic nervous systems to cardiovascular control. Hexamethonium was administered to block the autonomic ganglia, propranolol to block beta adrenergic receptors of the sympathetic nervous system, and methylatropine to block the parasympathetic nervous system. The results of this study indicate high sympathetic tone and low parasympathetic tone in resting Macaca fascicularis. These findings are different from those in man but are similar to other nonhuman primates.     

Pyridine alkaloids with activity in the central nervous system

This review discusses all pyridine alkaloids with CNS activity, their therapeutic potential, and the interesting array of sources whence they originate.     

Neural activity and survival in the developing nervous system

Recent evidence suggests that blockade of normal excitation in the immature nervous system may have profound effects on neuronal survival during the period of natural cell death. Cell loss following depression of electrical activity in the central nervous system (CNS) may explain the neuropsychiatric deficits in humans exposed to alcohol or other CNS depressants during development. Thus, understanding the role of electrical activity in the survival of young neurons is an important goal of modern basic and clinical neuroscience. Here we review the evidence from in vivo and in vitro model systems that electrical activity participates in promoting neuronal survival. We discuss the potential role of moderate elevations of intracellular calcium in promoting survival, and we address the possible ways in which activity and conventional trophic factors may interact.     

Evidence for a crustacean hyperglycemic hormone-like molecule in the nervous system of the stick insect,Carausius morosus

Summary Histological sections of the brain, suboesophageal ganglion, and the corpora cardiaca/corpora allata complex were examined for the presence of crustacean hyperglycemic hormone-like immunoreactive material. With the use of an antiserum directed against the hyperglycemic hormone of Carcinus maenas, immunofluorescence was found in the median portion of the pars intercerebralis, and the corpora cardiaca. Extracts of corpora cardiaca were examined by radioimmunoassay for competitive binding to the antiserum; one pair of corpora cardiaca contains at least 7 pg crustacean hyperglycemic hormone-like material.     

Form optical activity in crustacean cuticle

Some decalcified crustacean cuticle reflects left and transmits right circularly polarized light. The form optical rotatory dispersion is negative at lower and positive at higher wavelengths than that giving the interference colour for the system. The helicoidal structure deduced from the optics is supported by parabolic patterning in electron micrographs of oblique sections. The cuticle helicoid is anti-clockwise so that the right circularly polarized light transmitted through it rotates in the same sense as the helicoid from which it is produced.     

Occurrence of crustacean cardioactive peptide (CCAP) in the nervous system of an insect,Locusta migratoria

Summary Using a radioimmunoassay developed for the determination of crustacean cardioactive peptide (CCAP), immunoreactive material was detected in extracts of locust nervous tissue. Serial dilutions of a brain extract gave a displacement curve parallel to the CCAP standard curve. One locust nervous system was calculated to contain approximately 1.4 pmol CCAP-like material.In order to investigate whether the immunoreactive substance was similar or identical to the crustacean neuropeptide, isolation and complete characterization was carried out using 800 locust nervous systems. The isolation procedure consisted of pre-purification of the crude extract on a Sep-Pak cartridge, affinity chromatography on a column which was prepared by coupling of anti-CCAP antibody to CNBr-activated Sepharose, and reversed phase high performance liquid chromatography (HPLC). In the HPLC-profile immunoreactivity was confined to a single peak which co-chromatographed with authentic CCAP. The peptide was carboxymethylated and analyzed in an automated gas-phase sequencer. Its amino acid sequence, is identical to that of CCAP fromCarcinus maenas.Synthetic CCAP was tested on the isolated locust hindgut in vitro. The peptide proved to be a potent enhancer of gut contractions, with a significant effect being observable at concentrations of 10^–10 M. It is concluded that in the locust CCAP may function as a myotropic peptide.