Biomedical subjects

K Lukowiak

Publications and source records attributed to K Lukowiak.

At least 19 recordsLinked to original sources

PubMed1992

Localization of vasopressin-like immunoreactivity in the CNS of Aplysia californica.

Chromatographic and immunological evidence indicates that a vasopressin-like peptide might be present in the CNS of Aplysia californica, and that this peptide may be involved in modulating the behaviour of the gill. Immunocytochemical techniques using antisera raised against various vasopressin-like peptides were used to localize the sites containing these peptides in the CNS of Aplysia. Vasopressin-like immunoreactivity was found to be restricted to one single neuron in the abdominal ganglion and two small neurons located bilaterally in each pedal ganglion. Immunoreactive fibres were present in the neuropile of the abdominal, pedal, pleural and cerebral ganglia, but not in the buccal ganglion. The identification of these neurons provides a morphological localization for vasopressin-like substances detected previously in CNS extracts of Aplysia californica. In addition, the possibility of electrophysiological studies involving the immunoreactive neurons identified in the present paper will allow a more direct approach to study the physiological role of vasopressin-like peptides in Aplysia.

Amino Acid Sequence↗

PubMed1992

Transplantation and functional integration of an identified respiratory interneuron in Lymnaea stagnalis.

The possibility that damaged neural circuitries can be repaired through grafting has raised questions regarding the cellular mechanisms required for functional integration of transplanted neurons. Invertebrate models offer the potential to examine such mechanisms at the resolution of single identified neurons within well-characterized neural networks. Here it is reported that a specific deficit in the respiratory behavior of a pulmonate mollusc, caused by the ablation of a solitary interneuron, can be restored by grafting an identical donor interneuron. The transplanted interneuron not only survives and extends neurites within the host nervous system, but under specific conditions forms synapses with appropriate target neurons and is physiologically integrated into the host's circuitry, thereby restoring normal behavior.

Action Potentials↗

PubMed1992

Specific in vitro synaptogenesis between identified Lymnaea and Helisoma neurons.

We tested the ability of identified neurons from two different families of pulmonate molluscs to form specific connections in vitro. The presynaptic neuron chosen for this study was the giant dopamine cell of Lymnaea stagnalis and Helisoma trivolvis which is known to synapse upon specific visceral and parietal ganglion neurons in both species. Here we show that the giant dopamine cells can reform specific connections in vitro on follower neurons from both species. Thus the mechanisms that determine synapse specificity are conserved between two different families of molluscs.

Animals↗

PubMed1992

Conopressin G, a molluscan vasopressin-like peptide, alters gill behaviors in Aplysia.

Superfusion of an invertebrate vasopressin structural analogue, conopressin G, over the abdominal ganglion of an in vitro preparation of Aplysia californica has significant neurophysiological and behavioral effects. Both the amplitude of the siphon-evoked gill withdrawal reflux and concomitant activity in gill motor neurons are reduced in the presence of conopressin G. Moreover, the frequency of spontaneous gill movements and their neural correlate, interneuron II activity, are increased. These behavioral modifications strongly resemble those that occur during the food-aroused behavioral state in intact Aplysia. In addition, conopressin G superfusion reduces both the excitability of gill motor neurons and the strength of gill contractions in response to gill motor neuron discharges elicited by direct depolarizing current. A role for conopressin G or a similar peptide in the modulation of gill behaviors associated with the food-aroused state is suggested.

Amino Acid Sequence↗

PubMed1992

The Aplysia gill-withdrawal reflex revisited: components of the network.

Attempts to understand how changes at identified synapses contribute to the behavioral changes that constitute learning in the GWR have been complicated by the complexity of gill innervation. In addition to the well-studied circuit between siphon sensory neurons and identified gill motor neurons of the PVG, both PNS and as yet unidentified CNS pathways are also involved in the control of gill movement. In this study we combine an anatomical study of the PNS with physiological and behavioral analyses of the CNS's contribution to the GWR. We tested the possibility that altering the activity of an identified gill motor neuron is sufficient to alter the GWR. The results show that altering activity of GMNs has no demonstrable effect on the GWR in the suppressed behavioral state. Furthermore, activity in identified MNs may vary in response to a uniform stimulus and is not a good predictor of gill behavior. Immunohistochemical staining in gill and siphon showed discrete and well localized serotonin and SCPB-like reactivity. This is the first report of serotonin and SCPB-like immunoreactivity in the PNS of Aplysia siphon.

Animals↗

PubMed1992

The respiratory central pattern generator (CPG) of Lymnaea reconstructed in vitro.

We have recently developed a model system for testing the necessity, appropriateness and sufficiency of individual components of the respiratory central pattern generator (CPG) in Lymnaea stagnalis. In order to examine the intrinsic and network properties of the three CPG interneurons (R.Pe.D1, V.D4 and Ip.3.I), these cells were isolated and cultured in vitro. All of these cells exhibited extensive neurite outgrowth within 18-24 h of plating in conditioned medium. These isolated neurons maintained their intrinsic properties in culture and also formed specific synapses with each other similar to those observed in vivo. However, only when all three interneurons were plated together was it possible to initiate the alternating rhythm characteristic of the respiratory activity observed in semi-intact or isolated brain preparations.

Animals↗

PubMed1992

Regeneration of an interneuronal network in Helisoma: re-establishment of synaptic contacts.

We have identified a network of three interneurons located in the central ring ganglia of Helisoma. Two of these interneurons, designated Left Pedal Dorsal 1 (LPeD1) and Right Pedal Dorsal 1 (RPeD1), are the largest neurons of the pedal ganglia and appear to contain dopamine and serotonin, respectively. A third interneuron, identified as Visceral Dorsal 4 (VD4), is a small FMRFamide immunoreactive cell located on the dorsal surface of the visceral ganglion. Monosynaptic chemical connections exist between all these interneurons. For instance, a reciprocal inhibitory connection exists between LPeD1 and RPeD1, whereas VD4 has inhibitory effects on both LPeD1 and RPeD1. Furthermore, LPeD1, but not RPeD1, has an excitatory connection with VD4. We demonstrate that following axotomy these interneurons not only regenerate their axons but re-establish their appropriate synaptic connections.

Animals↗

PubMed1991

Evidence for the presence, synthesis, immunoreactivity, and uptake of GABA in the nervous system of the snail Helisoma trivolvis.

In the present study several techniques were employed to test the hypothesis that gamma-aminobutyric acid (GABA) is a neurotransmitter in the central nervous system (CNS) of the pond snail Helisoma trivolvis (Mollusca, Pulmonata). First, by using chromatographic techniques, the presence of GABA and its differential distribution among the ganglia constituting the CNS was demonstrated. Second, de novo synthesis of 3H-GABA from 3H-glutamate was shown by the CNS. Levels of both endogenous and newly synthesized GABA were greatest in the buccal, cerebral, and pedal ganglia. Third, indirect immunohistochemistry of wholemounts revealed a central network of GABA-like immunoreactive neurons. With the possible exceptions of two pairs of fibers in nerve trunks, all projections from GABA-immunoreactive neurons were confined to the CNS, suggesting a predominantly central role for GABA. Stained neurons were found on the dorsal surface of the buccal ganglia and throughout the cerebral and pedal ganglia. No GABA-immunoreactive cell bodies were observed in the parietal, pleural, or visceral ganglia. Finally, uptake of 3H-GABA was examined autoradiographically in sectioned ganglia. A pattern of radiolabelled cells was observed that closely resembled the distribution of GABA-immunoreactive neurons. The data described above fulfill several criteria necessary to establish GABA as a transmitter in the nervous system of Helisoma. Taken together with previously obtained pharmacological evidence demonstrating that GABA acts on Helisoma central neurons, GABA is considered to be a strong candidate for a neurotransmitter in Helisoma.

Animals↗

PubMed1991

Nerve growth factor (NGF) induces sprouting of specific neurons of the snail, Lymnaea stagnalis.

Nerve growth factor (NGF) was examined for its ability to elicit sprouting by adult molluscan neurons. Motoneurons and interneurons (but not neurosecretory cells) from Lymnaea exhibited a sprouting response to murine 2.5S NGF in defined medium with a half-maximal response at about 150 ng/mL. Furthermore, an NGF antiserum blocked sprouting by all normally responsive neurons. We tested whether an NGF-like molecule is a component of conditioned medium (CM) by attempting to preabsorb its sprout-inducing activity with NGF antiserum. Treatment of CM with immune (but not nonimmune) serum largely blocked the response of motoneurons, but not that of neurosecretory cells, to CM. We conclude that NGF exerts neurotrophic activity on specific adult Lymnaea neurons, and suggest the possibility that an NGF-like molecule may exist in the molluscan nervous system.

Absorption↗

PubMed1991

Electrophysiological studies of the gill ganglion in Aplysia californica.

1. An electrophysiological analysis was made of gill ganglion neurons in Aplysia californica. 2. Gill ganglion neurons behave similarly to neurons in the abdominal ganglion (the central nervous systems; CNS) that are involved with gill withdrawal behaviors. 3. Some gill ganglion neurons are motor neurons much like those in the CNS. 4. Neurons in the gill ganglion are electronically and dye-coupled. In addition, they receive common chemical synaptic inputs from the Int-II network in the CNS. 5. Tactile stimulation of the gill or siphon evokes synaptic activity in gill ganglion neurons whether or not the CNS is present. 6. Pedal nerve stimulation results in synaptic activity in gill ganglion neurons and facilitates synaptic input evoked by tactile stimulation of the gill or siphon. 7. Antibody staining reveals serotonin-like fibers in the branchial nerve close to the gill ganglion but no cell bodies in the ganglion. 8. The gill ganglion may play a role in the mediation of adaptive gill reflex behaviors. It may be one of the loci where the CNS and peripheral nervous system (PNS) interact and form an integrated circuit to mediate gill withdrawal reflex (GWR) behaviors.

Animals↗

PubMed1991

Experimental reconstruction of neuronal pattern generators.

It has recently become possible to reconstruct a central pattern generator in tissue culture. This accomplishment will allow investigators to design and interpret experiments at a level not possible in in vivo preparations and enhance our understanding of the mechanisms that underlie the generation of rhythmic behaviour.

Animals↗

PubMed1991

Central pattern generators: some principles learned from invertebrate model systems.

1. Central pattern generators (CPGs) underlie a wide variety of rhythmic behaviours such as locomotion and respiration in most multi-cellular organisms. 2. The CPG's are capable of generating a patterned output without phasic sensory input. 3. The organization of the CPG is due to both intrinsic properties of the individual neurons and their network interactions. 4. To gain an understanding of the mechanisms which underlie rhythmicity a CPG has been reconstructed in culture. This will allow investigators to test directly the mechanisms underlying the generation of rhythmic output and will allow the direct testing of the mechanisms by which various modulators affect the CPG.

Animals↗

PubMed1990

In vitro reconstruction of the respiratory central pattern generator of the mollusk Lymnaea.

Most rhythmic behaviors such as respiration, locomotion, and feeding are under the control of networks of neurons in the central nervous system known as central pattern generators (CPGs). The respiratory rhythm of the pond snail Lymnaea stagnalis is a relatively simple, CPG-based behavior for which the underlying neural elements have been identified. A three-neuron network capable of generating the respiratory rhythm of this air-breathing mollusk has been reconstructed in culture. The intrinsic and network properties of this neural ensemble have been studied, and the mechanism of postinhibitory rebound excitation was found to be important for the rhythm generation. This in vitro model system enables a better understanding of the neural basis of rhythm generation.

Animals↗

PubMed1990

Dopamine and FMRFamide act directly on isolated gill muscle fibers in culture.

The peripheral nervous system (PNS) in the gill of Aplysia plays an important role in the mediation of adaptive gill withdrawal reflex (GWR) behaviors. It has proven difficult to determine whether or not neuronally active agents work directly on PNS neurons, the muscle or both. We have now been able to isolate individual gill muscle fibers in culture and thus begin an analysis of how endogenous neurotransmitters and/or neuromodulators act. We report here that both dopamine and FMRF-amide act directly on gill muscle fibers to cause contractions.

Animals↗

PubMed1990

Suppression of gill withdrawal reflex behaviours in Aplysia: the role of acetylcholine.

Acetylcholine (ACh) dissolved in seawater and perfused through the isolated gill of the Aplysia californica produced suppression of the gill withdrawal reflex (GWR) evoked by tactile stimulation of the gill. This suppression was reversible upon washout and was blocked by co-perfusion of curare and alpha-bungarotoxin. Co-perfusion of atropine did not block the suppression of the GWR produced by ACh. We concluded that the suppressive effects produced by perfusion of ACh through the gill occur as a result of the action of ACh at the nicotinic-like receptors. The role of ACh suppression in the mediation of gill reflex behaviours is discussed.

Acetylcholine↗

PubMed1989

A neuromodulator of synaptic transmission acts on the secretory apparatus as well as on ion channels.

The mechanisms that underlie synaptic plasticity have been largely inferred from electrophysiological studies performed at sites remote from synaptic terminals. Thus the mechanisms involved in plasticity at the secretory sites have remained ill-defined. We have now used somatic synapses of cultured Helisoma neurones to directly assess presynaptic ion conductances and study the secretory apparatus. At these synapses we determined the actions of a modulatory neuropeptide, Phe-Met-Arg-Phe-NH2 (FMRFa), on the release of the neurotransmitter acetylcholine (ACh). Using voltage- and calcium-clamp techniques, we have demonstrated that FMRFa causes a presynaptic inhibition of ACh release by (1) reducing the magnitude of the voltage-dependent calcium current, and (2) regulating the secretory apparatus. The photolabile calcium cage, nitr-5 (refs 3-8), was dialysed into the presynaptic cell. In response to ultraviolet light, calcium was released from nitr-5 and ACh secretion was stimulated. Under conditions of constant internal calcium, FMRFa reduced the rate of ACh release. Thus we conclude that FMRFa reduces the influx of calcium during the action potential and decreases the sensitivity of the secretory apparatus to elevated internal calcium, thereby contributing to a presynaptic inhibition of transmitter release.

Acetylcholine↗

PubMed1989

Regeneration of frog sympathetic neurons is accompanied by sprouting and retraction of intraganglionic neurites.

Regeneration of frog sympathetic neurons (B-cells) was found to be accompanied by sprouting of neurites within the ganglion. Neurons whose axons had been crushed and allowed to regenerate exhibited sprouts that arose mainly from the axon hillock and initial segment of the axon. Sprouting was apparent by 5-7 days and reached maximal values by 14-21 days, but had decreased to control levels by 42-49 days after injury. In contrast, neurons whose axons were prevented from regenerating (by cut and proximal ligation of nerves) exhibited sprouts which did not retract by 42-49 days. These results suggest that successful regeneration to targets may dictate the recovery of normal B-cell morphology in bullfrog sympathetic ganglia.

Animals↗

PubMed1989

Reexamination of the gill withdrawal reflex of Aplysia californica Cooper (Gastropoda; Opisthobranchia).

The gill withdrawal reflex (GWR), an important model system for neural mechanisms of learning, varies in form and amplitude within as well as between preparations and is therefore a heterogeneous collection of action patterns, not a reflex. At least 4 action patterns occur in response to mechanical stimulation of the siphon. It is often impossible to categorize a particular movement unambiguously. All may occur spontaneously. Gill movements may be described as combinations of 10 actions; 4 involving vein movements are described here. All actions and action patterns can occur in preparations lacking the central nervous system. Some vein movements may generate considerable force without markedly altering gill area. It is suggested that this explains why some early studies failed to identify the important role of the peripheral nervous system in the GWR. Studies based on the assumption that the GWR involves a single type of movement controlled by cells of the parietovisceral ganglion require reevaluation.

Animals↗