Biomedical subjects

A Ter Maat

Publications and source records attributed to A Ter Maat.

13 recordsLinked to original sources

PubMed2000

A conserved location for the central nervous system control of mating behaviour in gastropod molluscs: evidence from a terrestrial snail.

We have investigated the role of the right mesocerebrum in the expression of mating behaviour in the garden snail Helix aspersa. Using an in vivo stimulation and recording technique, we provide evidence for both sensory and motor functions in the mesocerebral neuronal population. Some neurones were specifically sensitive to tactile stimuli delivered to the skin on the superior tentacles and around the genital pore. Electrical stimulation of the right mesocerebrum evoked genital eversion and, in combination with tactile stimulation, dart-shooting and penial eversion. Genital eversions were also elicited by injections of APGWamide. During courtship, one recorded unit increased its activity only in correlation with penial eversion, while six other units increased their activity only during dart-shooting. Three additional units increased their activity during both types of behaviour. In addition, most of the recorded units showed increased neuronal activity during times of contact with a partner. Comparison of our results with available data from other molluscs leads us to conclude that the right anteromedial region of the cerebral ganglion is an evolutionarily conserved region of the gastropod brain specialised for the control of male mating behaviour. It is striking to find such functional conservation in the central nervous system of phylogenetically distant gastropods given the large differences in behaviour during mating.

Animals↗

PubMed1999

Parasites flicking the NPY gene on the host's switchboard: why NPY?

It was investigated whether up-regulation of the NPY gene by the schistosome Trichobilharzia ocellata in its snail host Lymnaea stagnalis redirects the host's energy flows. We cloned the cDNA encoding Lymnaea NPY (LyNPY), purified and sequenced the peptide, and used synthesized peptide for physiological and morphological studies. Increasing the LyNPY titer in nonparasitized snails (mimicking parasitosis) by 1) implantation of slow-release pellets and 2) injections suppressed reproductive activity and reduced growth in a dose- and time-dependent manner without affecting food intake. When the LyNPY titer was back to normal, reproduction and growth were resumed, coinciding with a transient increase of food intake serving to replenish glycogen stores. Observations on double-immunostained whole mount preparations of brains support these data. A close association was found between LyNPY-positive axons and axons both from ovulation hormone-producing neurons and molluscan insulin-like peptide-producing neurons involved in regulation of growth. As no synaptic(-like) contacts were observed, it is supposed that LyNPY acts nonsynaptically. No morphological interaction was found between LyNPY-positive axons and motoneurons innervating the feeding apparatus. Our data explain why it is an advantageous strategy for endoparasites to up-regulate the highly conserved NPY gene in their host.

Amino Acid Sequence↗

PubMed1997

Functional role of peptidergic anterior lobe neurons in male sexual behavior of the snail Lymnaea stagnalis.

A morphologically defined group of peptidergic neurons in the CNS of the hermaphroditic snail, Lymnaea stagnalis, is concerned with the control of a very specific element of male sexual behavior. These neurons are located in the anterior lobe of the right cerebral ganglion (rAL). By using chronically implanted electrodes, we show that the rAL neurons are selectively active during eversion of the penis-carrying structure, the preputium. The preputium is normally contained inside the body cavity and is everted during copulation in the male role. Electrical stimulation of the rAL neurons through the implanted electrodes, induced eversion of the preputium in vivo. Injection of APGWamide (Ala-Pro-Gly-Try-NH2), a small neuropeptide that is present in all rAL neurons, induced eversion of the preputium. Application of APGWamide to in vitro preparations of the preputium caused relaxation of this organ. In contrast, injection of the neuropeptide conopressin, which is co-localized with APGWamide in 60% of the rAL neurons, did not induce any behavior associated with male sexual activities. These results show that the neurons of the rAL can induce an eversion of the preputium as occurs during male copulation by release of APGWamide during a period of electrical activity.

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PubMed1994

Modulatory role for the serotonergic cerebral giant cells in the feeding system of the snail, Lymnaea. I. Fine wire recording in the intact animal and pharmacology.

1. The role of the paired serotonergic cerebral giant cells (CGCs) in the feeding system of Lymnaea was examined by electrophysiological and pharmacological techniques. 2. The firing characteristics of the CGCs were recorded by fine wires attached to their cell bodies in freely moving intact snails (in vivo recording) and their "physiological" rates of firing determined during feeding and other behaviors. 3. The mean CGC firing rates recorded in vivo varied between 1 and 20 spikes/min but never reached the average rates seen in the isolated CNS (60-120 spikes/min). Maximum rates of firing were seen during bouts of radula biting/rasping movements characteristic of the consummatory phase of feeding (15 +/- 1.69 spikes/min, mean +/- SE, range 7-20 spikes/min), with lower rates seen during locomotion (6.7 +/- 0.75 spikes/min; range 5-9 spikes/min. The cells were rarely active when the animal was quiescent (1.45 +/- 0.91 spikes/min; range 0-2 spikes/min). 4. In vivo recorded CGC firing was phase locked to the feeding movements of the animal, with spikes occurring just before the opening of the mouth, during the protraction phase of the feeding cycle. 5. Evoking firing rates on the CGCs in the isolated preparation similar to those seen in vivo during rasping movements (7-20 spikes/min) did not elicit a fictive feeding pattern in an inactive preparation. Neither did bath application of 10(-9) M serotonin (5-HT; the transmitter of the CGCs). 6. To allow the modulatory role of the CGCs to be examined during patterned activity, the fictive feeding pattern was evoked in the isolated preparation by injecting depolarizing current into a modulatory neuron, the slow oscillator (SO). 7. The tonic firing activity of the CGCs was accurately maintained by current injection in the isolated preparation at rates equivalent to that occurring during feeding, locomotion, and quiescence in the intact snail. This was possible where the CGCs became silent after 1-2 h. Only when the CGCs activity was maintained at a rate (approximately 15 spikes/min) similar to that occurring during rasping, was the SO able to drive a full, high-frequency fictive feeding pattern (15-20 cycles/min). At lower rates of CGC firing, the SO-driven rhythm was either of lower frequency or no rhythm occurred at all (CGCs silent). 8. In many isolated preparations (80%) the CGCs remained active, and it was difficult to maintain specific levels of tonic activity by current injection.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1992

Automatic wave form classification of extracellular multineuron recordings.

A PC-based method for the reconstruction of individual spike trains from extracellular multineuron recordings is described. Starting with virtually no knowledge about the wave forms in a record, a fully automatic template-finding algorithm extracts templates using the entire data set. In a second step, individual spike trains are reconstructed.

Algorithms↗

PubMed1990

Inhibitory modulation of neuronal voltage-dependent sodium current by Phe-Met-Arg-Phe-amide.

The tetrodotoxin (TTX)-sensitive, voltage-gated Na(+)-current (INa) in a cluster of peptidergic neurons, involved in egg laying, in the CNS of the mollusc Lymnaea stagnalis, is modulated by the neuropeptide FMRFa (Phe-Met-Arg-Phe-NH2). Application of FMRFa reversibly reduced the isolated INa in a dose-dependent fashion. The physiological consequence is that the threshold for action potential generation is increased, causing an arrest of ongoing firing activity. The inhibitory action of FMRFa reported here is the first known example of modulation of the voltage-gated INa by a putative neurotransmitter in intact nerve cells. This finding underlines the importance of modulation of ionic currents as a mechanism of regulation of neuronal excitability and includes the voltage dependent Na current in the range of currents subject to transmitter modulation.

Animals↗

PubMed1990

Discharge induction in molluscan peptidergic cells requires a specific set of autoexcitatory neuropeptides.

The peptidergic caudodorsal cells of the pond snail Lymnaea stagnalis generate long lasting discharges of synchronous spiking activity to release their products. During caudodorsal cell discharges a peptide factor is released which induces similar discharges in silent caudodorsal cells [Ter Maat A. et al. (1988) Brain Res. 438, 77-82]. To identify this factor, the electrophysiological effects of putative caudodorsal cell gene products, calfluxin, caudodorsal cell hormone, four alpha caudodorsal cell peptides and three beta caudodorsal cell peptides, were tested individually and in various combinations. Calfluxin, alpha caudodorsal cell peptide and beta 1 caudodorsal cell peptide each had no effect on membrane potential or excitability of the caudodorsal cells. All other caudodorsal cell peptides caused excitatory responses, but did not induce discharges. Instead, only a specific combination of four caudodorsal cell peptides, caudodorsal cell hormone and alpha caudodorsal cell peptide (1-11, 3-11 and 3-10), evoked caudodorsal cell discharges with similar characteristics to electrically evoked discharges. Incomplete versions of this combination failed to cause a discharge. In addition, antibodies to caudodorsal cell hormone or alpha caudodorsal cell peptide reduced caudodorsal cell excitability and prevented the generation of discharges by electrical stimulation. These results suggest that excitatory autotransmission caused by four caudodorsal cell peptides provides a means to amplify excitatory inputs, thus leading to the generation of the all-or-nothing caudodorsal cell discharge.

Amino Acid Sequence↗

PubMed1989

Egg laying in Aplysia. I. Behavioral patterns and muscle activity of freely behaving animals after selectively elicited bag cell discharges.

Aplysia egg laying is a complex sequence of head and neck movements initiated by the release of ovulatory and neuroactive hormones from the neurosecretory bag cells. This behavioral pattern is difficult to study in reduced preparations, because they do not show ovulation or egg laying behaviors. This paper describes the use of chronically implanted electrodes to elicit normal neurosecretory activity and provides an analysis of egg laying behaviors and the underlying muscle activity in intact, freely behaving A. californica and A. brasiliana. 1. Bag cell discharges elicited with a fine wire electrode implanted in the connective tissue sheath above the cell bodies were typically without noxious behavioral side effects. 2. Following selectively elicited bag cell discharges, egg laying consisted of four rhythmic head and neck movements that were separated functionally into appetitive behaviors ('waves' and 'undulations') used to explore and prepare the substrate and consummatory behaviors ('weaves' and 'tamps') used to distribute and attach the egg string. The amount of time an animal performed consummatory behaviors was positively related to the amount of eggs deposited. By contrast, the appetitive phase of egg laying was independent of the size of the egg mass. 3. The individual behaviors and their temporal sequence were similar following selectively elicited bag cell discharges, spontaneous discharges of animals with implanted electrodes and during normal egg laying of unoperated animals. 4. Three longitudinal muscle systems occurred within the head and neck. Following a selectively elicited bag cell discharge, spatially and temporally coordinated patterns of EJP bursts of different durations were recorded chronically from each muscle group. These EJP patterns were characteristic for specific head and neck movements used in appetitive and consummatory egg laying behaviors.

Animals↗

PubMed1989

Egg laying in Aplysia. II. Organization of central and peripheral pathways for initiating neurosecretory activity and behavioral patterns.

1. Central pathways for bag cell activation were identified by examining the frequency of spontaneous egg laying episodes in animals with central connective lesions. Bilateral lesions of the cerebropleural (but not the cerebropedal) connectives abolished spontaneous egg laying. In contrast, bilateral lesions of all cerebral ganglion peripheral nerves did not abolish spontaneous egg laying, suggesting that sensory input to the cerebral ganglion is not necessary for activating the bag cells. 2. Backfilling either pleuroabdominal connective labelled cell bodies in the cerebral ganglia (via the ipsilateral cerebropleural connective) that could project to the bag cells. Focal extracellular stimulation of these stained clusters activated the bag cells in isolated brains. 3. Central pathways for initiating egg laying behaviors were identified by selectively eliciting bag cell discharges in animals with central connective lesions. Bilateral lesions of the cerebropedal (but not the cerebropleural) connectives completely abolished elicited egg laying behaviors. 4. Pathways for motor output during rhythmic head and neck movements were identified by eliciting bag cell discharges in animals with peripheral nerve lesions. Bilateral lesions of the four tegumentary nerves in combination with the anterior pedal nerve completely abolished elicited egg laying behaviors, indicating that these nerves are necessary for normal motor output. A normal pattern of egg laying behaviors occurred when the four tegumentary and the anterior pedal nerves were left intact and all other pedal ganglion nerves were lesioned bilaterally, indicating that these nerves are also sufficient for normal motor output.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Dual inhibitory action of FMRFamide on neurosecretory cells controlling egg laying behavior in the pond snail.

We describe here the electrophysiological characterization of a dual inhibitory action of FMRFamide (FMRFa, Phe-Met-Arg-Phe-NH2) on the caudodorsal cells (CDCs) of the pond snail Lymnaea stagnalis: (i) a transient hyperpolarizing response (H-response) and (ii) a suppression of the excitability of the cells, which lasted as long as the peptide was present. Both effects of FMRFa occurred in silent, excitable cells as well as discharging cells. The effects were reversible and dose-dependent in the range of 10(-9) to 10(-5) M. The H-response was not blocked by any of the antagonists to classical neurotransmitters that were tested. The reversal potential of the H-response was dependent on the [K+]o, which suggests that K+ is the major charge carrier in this response. 4-Aminopyridine (4-AP) blocked the H-response but did not affect the suppression of the excitability by FMRFa. This indicates that the effects of the peptide on these cells are independent. Experiments on the mechanism of the inhibition of the excitability indicated that FMRFa blocks the cAMP-dependent activation of the pacemaking mechanism of the CDCs. In experiments with isolated cells it was demonstrated that the actions of FMRFa are mediated directly through receptors on CDCs (H-response: ED50 = 10(-8) M). Finally, anti-FMRFa-positive varicosities and axons close to the somata, the axons and the neurohaemal endings of the CDCs were demonstrated immunocytochemically. The duality of the action of FMRFa on the neural activity of CDCs indicates its role of high priority in the regulation of egg laying behavior.

Animals↗

PubMed1982

Suppression of egg-laying during starvation in the snail Lymnaea stagnalis by inhibition of the ovulation hormone producing caudo-dorsal cells.

Starvation inhibits egg-laying in the snail, Lymnaea stagnalis. In starved animals the neurosecretory Caudo-Dorsal Cells (CDC), which produce the egg-laying hormone, are hyperpolarized as compared to the CDC of controls. However, they are more responsive to repetitive intracellular stimulation, which induces the hormone releasing discharge. Hyperpolarization is not found in the non-neurosecretory Cerebral Giant Cells, which indicates that the effect is specific for the CDC. It is also a characteristic effect of starvation as compared to another treatment (dirty water) inhibiting egg-laying.

Animals↗

PubMedDate not supplied

Peripheral injection of DNS-RFa, a FMRFa agonist, suppresses morphine-induced analgesia in rats.

The present results demonstrate an antagonistic effect of DNS-RFa on morphine-induced analgesia in rats. This confirms previous evidence presented by others on the effects of FMRFa-related peptides when applied centrally. Unlike these peptides, however, it is shown here that DNS-RFa is effective upon peripheral injection. The effects of DNS-RFa on morphine-induced analgesia were dose-dependent (ED50 = 0.5 mg/kg). DNS-RFa alone (5 mg/kg) did not affect the control level of nociception. Peripheral injection of FMRFa (5 mg/kg) did not affect morphine-induced analgesia. DNS-RFa defines the minimal configuration to activate neuronal FMRFa receptors in the pond snail. The present report suggests also that in vertebrates the Arg-Phe-NH2 sequence is essential and that DNS-RFa readily penetrates the blood-brain barrier.

Analgesia↗

PubMedDate not supplied

Molluscan ovulation hormone containing neurons and age-related reproductive decline.

Behavioural and neurophysiological experiments were conducted to examine the state of the neurosecretory caudodorsal cells (CDCs) during female reproductive decline in the freshwater snail Lymnaea stagnalis. Old animals that had ceased egg laying do not respond to an oviposition-inducing stimulus. Female reproductive organs in such animals are still intact, though less sensitive to CDC-hormone. The CDC contents of old nonlaying snails are still effective in producing ovulation in young animals. The electrophysiological properties of the CDCs of old nonlaying snails only differ from those of egg-laying snails in one respect; the duration of the afterdischarge is longer. This difference is not directly related to age but to egg-laying activity of the snails since the afterdischarge in old layers did not differ significantly from that in young layers. It is concluded that the CDCs of old nonlaying animals are in principle still intact. Female reproductive decline and subsequent cessation of female reproduction in Lymnaea may result from impairment of input to the CDCs.

Age Factors↗