Adaptation in Helix pomatia neurons

• 1.1. Spike frequency adaptation has been studied on neurons of Helix pomatia subesophageal ganglia and interpreted by means of a behavioural model describing the phenomenon in neurons either silent or autorhythmic at rest.
• 2.2. At low stimulating currents the initial discharge frequency F(0) is linearly related to the current strength G.
• 3.3. In the linearity range F(0)/G each neuron was characterized by means of four model parameters: the proportionality constant between F(0) and G, the decay constant of the frequency, the inhibitory current from a single nerve impulse and the decay time constant of the inhibitory current.
• 4.4. The four parameters varied in different cells with a range of 0.18–4.98 Hz/nA, 1.02–3.85 sec, 0.05–0.95 nA and 1.74–22.33 see, respectively.
• 5.5. Experimental results have been analyzed considering inhibitory current, electrogenie sodium pump and other proposed adaptation parameters.

     

A behavioural and neuronal analysis of the locomotory system of Lymnaea stagnalis

• 1.1. During locomotion the pond snail Lymnaea stagnalis (L.) exhibits recurrent cyclical movements; in water this behaviour consists of anteriorly and posteriorly directed shell movements and on land these same movements are coupled with longitudinal contractions and extensions of the foot.
• 2.2. Motoneurones innervating the foot, body wall and column have been identified. The activity of some of these neurones is correlated with shell movements during spontaneous locomotor discharges in reduced preparations.
• 3.3. The structure of these motoneurones has been determined by intracellular injection of the fluorescent dye Lucifer Yellow CH.

     

Mechanism of long lasting synaptic inhibition of a silent neuron of Helix pomatia

• 1.1. Long lasting synaptic inhibitions (LLI) were recorded in the silent cells LPL1 and RPL1 of Helix pomatia.
• 2.2. During LLI the excitability of the cell was strongly reduced.
• 3.3. The membrane conductance changes during LLI were characterized using the voltage-clamp technique.
• 4.4. LLI in the silent cell LPL1 is mediated by a synaptically induced inhibition of the voltage-dependent inward Ca²⁺ -current.

     

Osmotically-induced volume changes in isolated cells of a pond snail

• 1.1. To assess whether the stretch-activated (SA) channels in snail cells could contribute to osmoregulation, information is needed about the behaviour of the cells under anisosmotic conditions.
• 2.2. Cells of Lymnaea stagnalis were therefore examined during acute hyposmotic stress (HOS).
• 3.3. Kidney, heart and neuronal cells (monitored photographically) swelled less than expected for strictly semipermeable cells, but exhibited no regulatory volume decrease.
• 4.4. Long-term viability of the cells was not compromised following acute hyposmotic stress.
• 5.5. Quinidine, which blocks SA channels in Lymnaea, intensified stress-induced swelling most markedly in kidney cells.
• 6.6. The data can, however, be explained without invoking recruitment of SA channels.

     

Glycogen and galactogen in the albumen gland of the freshwater snail Lymnaea stagnalis: Effects of egg laying,photoperiod and starvation

• 1.1. Glycogen and galactogen contents of the albumen gland of the freshwater snail Lymnaea stagnalis were determined under different conditions, known to influence these polysaccharides viz egg laying, photoperiod and starvation.
• 2.2. After oviposition, the galactogen content is restored within 32 hr, whereas glycogen remains constant during this period. Short-day photoperiods favour accumulation, long-day photoperiods induce depletion of glycogen. In contrast, the galactogen content is not affected by the photoperiod.
• 3.3. Since glycogen and galactogen are present in the same cells of the albumen gland, the independent variation of these polysaccharides would imply the presence of separate intracellular regulation mechanisms.

     

Electrotonic coupling within a cluster of neurosecretory endogenous oscillators in Lymnaea stagnalis (L.)

• 1.1. Double intracellular and extracellular recordings from cell bodies and axons were made to study the interactions between the neurosecretory “Light Yellow” bursting pacemaker cells (LYC) in the right parietal ganglion of Lymnaea stagnalis.
• 2.2. The LYC are interconnected by low efficiency, non-rectifying electrotonic junctions, transmitting low frequencies only.
• 3.3. Often bursts in different cells coincide; apparently the junctions are responsible for this coherence.
• 4.4. It is inferred that the coupling serves to bring about a pulse-wise release of the cluster's secretory product.

     

Degradation of bacterial lipopolysaccharides by digestive-gland extracts of marine bivalve molluscs

• 1.1. Crude digestive gland extract (DGE) of 5 species of marine bivalve mollusc had glycosidase activity against lipopolysaccharides (LPS) of gram-negative bacteria.
• 2.2. Most of these extracts, after ammonium sulphate precipitation, had higher glycosidase activity than commercial Helix pomatia gut juice.
• 3.3. Inorganic phosphate was also released from LPS by the various DGE but the lipid moiety of LPS appeared to be resistant to attack except by a DGE from Cerastoderma edule, which released small quantities of only non-hydroxylated fatty acids.

     

Fructose-bisphosphate aldolase from Helix pomatia—II. Chemical and physical properties

• 1.1. Fructose-bisphosphate aldolase from Helix pomatia is a tetramer of 40,000 mol. wt. sub-units like mammalian aldolases.
• 2.2. The snail enzyme differs slightly in amino acid composition from mammalian aldolases and has glycine as its amino terminus rather than proline.
• 3.3. Spectroscopic measurements (u.v., fluorescence, ORD, CD) show small yet definite differences in secondary structure between the snail and mammalian aldolases but indicate thaT no major structural changes have occurred during evolution.

     

Effect of acute temperature change on lung respiration of the mollusc Lymnaea stagnalis

• 1.Temperature-dependent effects on respiratory behaviour as well as the corresponding temperature-dependent activities of identified neurons within the respiratory network of the pulmonate snail Lymnaea stagnalis were investigated.
• 2.Lymnaea lung ventilation terminated at low temperatures (under 10 °C) while temperature elevation increased ventilation rates. The respiratory central pattern generator (CPG) functioning was relatively quiescent at temperatures under 12.5±0.44 °C.
• 3.Identified CPG neurons (RPeD1, VD4, VD1/RPaD2) and the respiratory network motor neurons (Vi- and RPa-cells) were found to exhibit varied temperature-dependent electrophysiological parameters (action potential frequency and amplitude, resting potential value) between cell types.
• 4.The observed alterations in the electrical activity of the Lymnaea respiratory network neurons underlie the marked changes of respiratory behaviour observed in the intact animal during temperature changes.

     

FMRFamide immunoreactive neurons in the central nervous system of the snail,Achatin a fulica

• 1.1. FMRFamide immunoreactive neurons were detected in the central nervous system of the snail, Achatina fulica.
• 2.2. FMRFamide immunoreactive neurons were found in all the ganglia comprising the central nervous system. In particular, the immunoreactivity was recognized in both the ordinary and giant neurons of the visceral and right parietal ganglia.
• 3.3. In the cerebral and pleural ganglia, FMRFamide immunoreactive neurons were found only in the ordinary neurons. The immunoreactivity was shown to have a tendency to form a group in the cerebral and pedal ganglia.

     

Behavioural modification of the optic tentacle of Helix pom atia; effect of puromycin,activity of S-100

• 1.1. A long-term learning phenomenon in the tentacle of Helix pomatia has been observed.
• 2.2. Repeated mechanical stimulation of the optic tentacle led to habituation of the associated withdrawal-extension action pattern whereas repeated combined mechanical and electrical stimulation potentiated the reflex.
• 3.3. The potentiation was present 40 days after four sessions of stimulations. Sessions spaced with proportionally increasing intervals were more effective than massed training. Puromycin (125 mg/ml) blocked 80% of protein synthesis as well as the long-term but not the short-term retention of potentiation.
• 4.4. Contrary to observations in other preparations, the amount of water soluble proteins, notably S-100, was not affected by learning. Injections in vivo of and exposure of brain in vitro to S-100 had no effect on learning or a variety of brain potentials.

     

The association of changes in cerebral ganglion dopamine metabolism with ootheca development in Periplaneta americana

• 1.1. Dopamine levels and DOPA-decarboxylase activity were measured in cerebral ganglia and haemolymph of female Periplaneta americana.
• 2.2. Measurements were made at four points in the oothecal cycle of cockroaches known to drop oothecae at regular three day intervals.
• 3.3. Dopamine levels and DOPA-decarboxylase activity in haemocytes and plasma cycle in phase with ootheca formation; their levels in haemolymph are maximal when a half visible, untanned ootheca is present.
• 4.4. In the cerebral ganglia dopamine levels and DOPA-decarboxylase also cycle in phase with ootheca formation suggesting that cerebral ganglion dopamine metabolism is under the same controls as dopamine metabolism associated with oothecal tanning.

     

The UDP-galactose 4-epimerase of the albumen gland of Lymnaea stagnalis and the effects of photoperiod,starvation and trematode infection of its activity

• 1.1. Kinetic aspects of the enzyme UDP-galactose 4-epimerase in crude homogenates of the albumen gland of the snail Lymnae stagnalis were estimated. The mean values of the Km for UDP-galactose and for NAD are 0.343 and 0.097 mM, respectively. The enzyme is inhibited by NADH. It is inactivated by freezing and raised temperature (25°C), but it can be reactivated by NAD.
• 2.2. In the albumen gland the epimerase activity is 10–100 times higher than in other tissues, reflecting the high turnover of glucose to galactose, essential for the synthesis of galactogen in this organ.
• 3.3. In fed snails long day conditions stimulates albumen gland epimerase activity, coinciding with high egg production.
• 4.4. In starved snails a fairly high residual activity of the enzyme is maintained, irrespective of photoperiod or egg production.
• 5.5. Trematode infection leads to a considerable reduction of the epimerase activity.
• 6.6. The results indicate that the epimerase activity in fed snails, when the gland shows a regular release, reflects long-term adaptations (photoperiod). In starved and parasitized snails, when no regular release or product occurs, a basic epimerase activity is maintained. This might be important for a rapid restoration of egg production after the termination of adverse conditions.

     

The effects of extracellular-and intracellular-pH on transmitter mobilization and fractional release in Helix pomatia

• 1.1. Transmitter mobilization and fractional release were studied in Helix pomatia. The right palliai nerve was stimulated and a synaptic potential was recorded in cell F76 in the right parietal ganglion.
• 2.2. The extra- and intra-cellular pH were changed with Tris-maleate, CO₂ or (NH₄)₂SO₄.
• 3.3. The time constant for the monoexponential part of mobilization decreased with reduced intracellular pH. Only a fraction of this effect could be related to an increase in the intracellular Ca-activity.
• 4.4. Fractional release was reduced in low external pH, but was increased in low intracellular pH. Fractional release is affected more by changes in internal pH than external pH.

     

Electrophoretic identification of bird species involved in collisions with aircraft

• 1.1. The utility of biochemical genetic methods of bird identification was investigated for some common species which create a hazard for commercial aviation in Ireland.
• 2.2. Sixteen enzyme loci were assayed in eight species, using starch gel electrophoresis; three larids, three corvids and two columbids.
• 3.3. Genera were distinguishable using all but two loci.
• 4.4. Differences within genera were small, but all species except for the gulls Larus argentatus and L. marinus, could be identified using one or more loci.
• 5.5. Arising from the success of the method using fresh specimens, a protocol for the electrophoretic identification of traumatized remains of strikes is suggested.

     

IDentification of a microsomal retinoic acid synthase as a microsomal cytochrome P-450-linked monooxygenase system

• 1.1. To characterize an enzyme which metabolizes retinal in liver microsomes, several properties of the enzymatic reaction from retinal to retinoic acid were investigated using rabbit liver microsomes.
• 2.2. The maximum pH of the reaction in the liver microsomes was 7.6.
• 3.3. The K_m and V_max values for all-trans, 9-cis and 13-cis-retinals were determined.
• 4.4. The reaction proceeded in the presence of NADPH and molecular oxygen.
• 5.5. The incorporation of one atom of molecular oxygen into retinal was confirmed by using oxygen-18, showing that the reaction comprised monooxygenation, not dehydrogenation.
• 6.6. The monooxygenase activity was inhibited by carbon monoxide, phenylisocyanide and antiNADPH-cytochrome P-450 reductase IgG, but not by anti-cytochrome b₅ IgG.
• 7.7. The enzymatic activity inhibited by carbon monoxide was photoreversibly restored by light of a wavelength of around 450 nm.
• 8.8. The retinal-induced spectra of liver microsomes with three isomeric retinals were type I spectra.
• 9.9. The microsomal monooxygenase activity induced by phenobarbital or ethanol were more effective than that by 3-methylcholanthrene, clotrimazole or β-naphthoflavone.
• 10.10. These results showed that the monooxygenase reaction from retinal to retinoic acid in liver microsomes is catalyzed by a cytochrome P-450-linked monooxygenase system.

     

The ionic mechanism responsible for L-glutamate excitation of leech Retzius cells

• 1.1. Intracellular recordings were made from the Retzius cells in the segmental ganglia of the leech, Hirudo medicinalis. L-Glutamate has a direct excitatory action on the neurons.
• 2.2. L-Glutamate causes an increase in the membrane conductance.
• 3.3. L-Glutamate causes conductance increase at the Retzius cell to both sodium and potassium ions but not to chloride ions.

     

Morphology and electrophysiological characteristics of caudodorsal cells of Lymnaea stagnalis in dissociated cell culture

• 1.1. The neuroendocrine caudodorsal cells (CDCs) of Lymnaea stagnalis are a network of about 100 electrotonically coupled neurones. The CDCs release multiple peptides, including an ovulation hormone, during a period of electrical activity, the CDC-discharge.
• 2.2. In isolated brains, a similar period of electrical activity (the afterdischarge) can be induced in all CDCs by a period of intracellular repetitive suprathreshold stimulation of one CDC.
• 3.3. In order to study the regulation of this electrical behaviour in the absence of electrical interactions and in a controlled environment, experiments were performed on CDCs in dissociated cell culture.
• 4.4. Methods for isolation and cell culture are described. Cell cultures had long-term viability and outgrowth of neurities occurred under serum-free conditions.
• 5.5. CDCs in cell culture maintained their capability of producing afterdischarges upon electrical stimulation. Cells in culture appeared more excitable than cells in the intact isolated brain.
• 6.6. The characteristic responses of CDCs in intact isolated brains to acetylcholine and FMRFamide were preserved in cultured CDCs. Both agents induced a transient hyperpolarization of the membrane, inexcitability and inhibition of an ongoing discharge.
• 7.7. In experiments where isolated CDCs were closely apposed, but physically separate, it was found that an afterdischarge in one CDC could induce a discharge in the other CDC.
• 8.8. These results confirm previous results which showed that an excitatory factor is released from the brain during the afterdischarge (Ter Maat et al., 1988, Brain Res., 43, 77–82), and demonstrate that this excitatory factor is released from the CDCs themselves.

     

Morphology of leech retzius cells demonstrated by intracellular injection of horseradish peroxidase

• 1.1. The neuronal geometry of Retzius (R) cells in two species of leech (Hirudo medicinalis and Haemopis sanguisuga) was investigated by intracellular injection of horseradish peroxidase.
• 2.2. Each R cell sends major branches into the ipsilateral segmental nerves and, via the ipsilateral connectives, into the anterior and posterior adjacent ganglia.
• 3.3. No structural connection between the proximal axons of the two R cells could be detected, although numerous dendrites were demonstrated, some of which extended across the midline of the ganglion.
• 4.4. No major differences were found between the R cell morphology of the two species.

     

The influence of optic nerve section on blood metabolite levels in Carcinus maenas (Crustacea: Brachyura)

• 1.1. Blood metabolite levels were assayed in Carcinus maenas as an indicator of the functioning of the hyperglycemic hormone, HGH, secreted by the crab's eyestalk neuroendocrine tissue.
• 2.2. Bilateral eyestalk ablation eventually resulted in a hypoglycemic response after 2–3 days.
• 3.3. Bilateral optic nerve section produced a significant, long-term hypoglycemic response suggesting that release of HGH from the eyestalk sinus gland is controlled, via a promotive neural pathway, by the CNS and probably by the cerebral ganglia.
• 4.4. Injection of eyestalk extract into operated crabs consistently produced significant, short-term hyperglycemia.