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To evaluate the efficacy and safety of pramipexole in patients with moderate to severe restless legs syndrome (RLS)

In the abdominal ganglion of Aplysia californica, seven motoneurons have been described which modulate the myogenic heart beat and vasomotor tone (28). These neurons mediate their motor effects by chemical transmission. In this paper we have attempted to specify the transmitters of six of these motoneurons. We have 1) studied the effects of several common transmitters on the innervated structures and compared these effects with the effects of firing the motoneurons, 2) examined whether blocking agents influence similarly the effect of a putative transmitter applied to the innervated structure and the effect of firing a motoneuron, and 3) tested the capability of the motoneurons to synthesize the putative transmitters from precursors. The positive inotropic and chronotropic effects of firing the excitor motoneuron RB(HE) were mimicked by perfusion of the heart with serotonin at a low concentration. Cinanserin blocked both the effects of motoneuron excitation and serotonin perfusion. RB(HE) was also shown to synthesize [3H]serotonin from L-[3H]tryptophan injected directly into the cell body. The effects of firing the two LD(HI) heart-inhibitory motoneurons were mimicked by perfusion of the heart with acetylcholine. Benzoquinonium blocked the effects of the inhibitory motoneuron and acetylcholine perfusion. Perfusion with arecoline also inhibited the heart beat. Acetylcholine applied to the arteries mimicked the vasoconstriction caused by the LB(VC) motoneurons. Aortic constriction in response to activity in LB(VC) cells or to acetylcholine was blocked by hexamethonium and curare. The heart inhibitor and vasoconstrictor motoneurons synthesized [3H] acetylcholine from [3H] choline injected into their cell bodies. Thus, as in vertebrates, acetylcholine mediates inhibition to the heart. Unlike vertebrates, however, serotonin mediates excitation to the heart and acetylcholine mediates peripheral vasoconstriction.

Previously, we described the isolation of a cDNA clone and the gene encoding a protective antigen of the protozoan parasite Entamoeba histolytica, the serine-rich Entamoeba histolytica protein (SREHP). The derived amino acid sequence of the SREHP cDNA clone was remarkable for a high serine content (52/233 amino acids), a putative signal sequence, multiple hydrophilic dodecapeptide and octapeptide tandem repeats, and a hydrophobic C-terminal putative membrane-spanning region. Here, we show that SREHP is modified by the addition of phosphate at serine residues, O-linked terminal N-acetylglucosamine residues, and by acylation. When the SREHP gene is expressed in baculovirus transformed Sf-9 cells, the product is also phosphorylated and glycosylated and is localized to the plasma membrane of the insect cells. The native SREHP molecule also serves as a potent chemoattractant for amebic trophozoites. The data presented here suggest that SREHP is a unique membrane protein with phosphorylation and glycosylation patterns usually associated with nuclear or cytoplasmic proteins.

Five types of bursting neurons have been described in Aplysia: three types of individual bursters--the LUQ cells, L10, and R15, plus two types of population bursters--the bag cells and the R25/L25 cells. Individual bursters can burst without any synaptic input, while bursts generated by the population bursters are shaped largely by their synaptic interactions. In this paper we review what is known about the burst mechanisms of these five classes of neurons and attempt to relate them to the roles of the five cell types in the control of autonomic function.

1. We have identified putative histaminergic neurons in the central nervous system of Aplysia californica by light-microscopic autoradiography after uptake of [3H]histamine and by immunohistochemistry with the use of an antibody specific for histamine. 2. In the cerebral ganglion cells previously shown to contain histamine (C2 and 2 large neighboring cells in the E cluster and a group of smaller cells in the L cluster) were identified both by uptake of [3H]histamine and by histamine immunoreactivity. The identification of C2 was confirmed by experiments in which individual C2s were characterized electrophysiologically and injected with Lucifer yellow before processing for immunohistochemistry. The giant serotonergic neuron did not take up [3H]histamine and was not immunoreactive. 3. In the abdominal ganglion two clusters of cells--one in the left hemiganglion and the other in the right--took up [3H]histamine and were histamine immunoreactive. These clusters are located in the regions occupied by the 30 identified respiratory interneurons, R25 and L25. Individual cells in the R25 and L25 clusters were identified electrophysiologically, marked by injection of Lucifer yellow, and processed for immunocytochemistry. Eleven of the 30 L25 cells examined (from 7 ganglia) and 2 of the 25 R25 cells (from 6 ganglia) that had been marked with Lucifer yellow were also histamine immunoreactive. 4. Also in the abdominal ganglion, identified cells in the L32 cluster were not histamine immunoreactive and did not take up [3H]histamine. These interneurons, which mediate presynaptic inhibition, had previously been considered histaminergic. Neurons in the ganglion known to use transmitters other than histamine (L10, R2, RB cells, and bag cells) were not histamine immunoreactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Previous studies have demonstrated that heart rate and blood pressure increase in Aplysia during an arousal state elicited by food stimuli. In addition, during biting, blood flow is routed alternately to the head (during protraction of the buccal mass) and to the digestive system (during retraction). In this study, cutting the pleuroabdominal connectives eliminated 75% of the heart rate response during food arousal, and cutting the pleuroabdominal connectives eliminated 20-50% of the pressor response. Recording in the abdominal ganglion from the RBHE heart excitor and the three LBVC vasoconstrictor motor neurons in a reduced preparation showed that activity in these neurons was increased 50 and 100%, respectively, during food arousal. Activity of the LBVC cells was maximal during the protraction phase of biting. The LBVC vasoconstrictor motor neurons, when fired at the rates recorded during food arousal, can occlude the abdominal aorta completely. We conclude that the RBHE and LBVC neurons mediate, in part, the heart rate and pressor responses recorded during food arousal and that cyclic activity in LBVC contributes significantly to the cyclic alternation of blood flow between the head and the gut during rhythmic biting behavior.

1. The cardiovascular system of Aplysia has proven to be a useful preparation for study of the neural control of circulation. To better understand the neural integration of function in this system, we have attempted to gain a more complete picture of its morphology and innervation patterns, with particular emphasis on the abdominal aorta and heart. 2. The vasoconstrictor muscle fibers of the abdominal aorta were found by dye injection to be extensively branched, with many processes that are less than 1 micron in diameter. Because of the wide spacing between individual muscle fibers, these fine processes, which have relatively few contractile filaments, may be required to mediate the electrical coupling that is observed between muscle cells. 3. L7, an identified cell in the abdominal ganglion, had been shown by others to be an excitatory motoneuron for the gill, the siphon, and the sheath-contracting muscles of the pleuroabdominal connectives, and also to excite the gill motoneurons in the branchial ganglion (5, 43, 56). We have found that this multimodal motoneuron also directly excites the auricle of the heart and the vasoconstrictor muscle of the abdominal aorta. 4. The excitatory effect of L7 on the abdominal aorta interacts synergistically with that produced by the other known excitatory inputs to that structure, the LBVc vasoconstrictor motoneurons. 5. The abdominal aorta is also richly innervated by axons immunoreactive for serotonin and for the neuropeptide FMRFamide. Serotonin inhibits the contractions of the aorta elicited by firing either L7 or the LBVC cells. In contrast, FMRFamide selectively inhibits the contractions elicited by the LBVC cells. 6. Our results suggest that a significant amount of the functional integration of the cardiovascular and respiratory systems is achieved by the use of a motoneuron common to both systems, and that there is likely to be extensive peripheral inhibitory modulation of the vasoconstrictor inputs to the abdominal aorta.

1. Respiratory pumping in Aplysia consists of synchronous, brief contractions of the mantle organs that can occur spontaneously and also can be triggered by tactile or noxious stimulation. It has been shown previously to be driven in part by a cluster of electrically coupled interneurons, called the L25 cells, located in the left hemiabdominal ganglion. This paper describes a second class of interneurons, the R25 cells, that also plays an important role in the control of respiratory pumping. 2. The R25 cells are a cluster of approximately 14 interneurons located in the right hemiabdominal ganglion, roughly symmetrical to the L25 cells. The R25 cells are electrically coupled to each other and to the L25 cells. Some R25 and L25 cells also produce chemically mediated fast excitation and slow inhibition of other neurons in the R25/L25 network. 3. Three lines of evidence demonstrate that the R25 cells play a role in mediating respiratory pumping: 1) They fire in a synchronous burst each time the behavior occurs. 2) They make direct chemical synaptic connections to motoneurons that mediate the behavior; and 3) Firing a single R25 cell can trigger the entire behavior, by recruiting synchronous bursts of activity in all of the other R25 and L25 neurons. Individual R25 and L25 cells can act both as trigger cells (exciting the other interneurons) and as relay cells (projecting directly to motoneurons). 4. Burst initiation within the R25/L25 network appears to have two phases: 1) There is an initial phase when the R25 and L25 cells fire at a relatively low frequency. This phase can be driven either by endogenous pacemaker activity of the R25/L25 cells or by afferent synaptic input from sensory pathways; and 2) The late, high-frequency phase of the burst results largely from reverberation within the network, as activity in each cell contributes positive feedback via the excitatory chemical and electrical connections between R25 and L25 cells. 5. Synchronization of the different motor outputs that make up the pumping behavior is achieved by three mechanisms: 1) When pumping occurs spontaneously, the electrical coupling between the cells of the R25/L25 network ensures that these cells will all be near spike threshold at the end of each interburst period.(ABSTRACT TRUNCATED AT 400 WORDS)

1. To account for the similarity in the kinetics of habituation between the central and peripheral components of siphon withdrawal, we have tested the idea (52) that each centrally located mechanoreceptor sensory neuron sends two branches to siphon motor neurons; one to centrally located siphon motor neurons and a collateral branch that remains in the periphery and innervates the peripheral siphon motor neurons. 2. We have found a group of peripheral siphon motor neurons and tested the connection onto these cells by central mechanoreceptors. In addition, we have defined by various electrophysiological and morphological criteria two general classes of peripheral neurons that lie along the course of the siphon nerve. 3. One class (type I) consists of only a single cell in each animal. This peripheral neuron typically has the largest cell body found lying along the siphon nerve and is the only peripheral nerve cell that appears white when viewed under epi-illumination. The type I neuron often has a highly regular firing pattern, which occurs in the absence of spontaneous synaptic input. The three-dimensional morphology of this neuron suggests a paucity of fine processes, most of which do not arborize and may terminate in the connective tissue sheath. Fine structural observations of the peripheral white cell have revealed the presence of large densecore granules. The peripheral type I neuron is similar in most of its electrophysiological and morphological properties to central neurons postulated to be neurosecretory. The peripheral white cell is, at present, the only peripheral neuron we can identify with certainty as a unique individual. 4. The second class (type II) of peripheral neurons are siphon motor neurons for the peripheral component of the siphon-withdrawal reflex. In contrast to the type I neurons, members of the second class of peripheral neurons possess smaller, more spherical cell bodies that have varying amounts of orange pigmentation and which give rise to a relatively well-developed and arborized dendritic tree. Type II neurons feature an irregular spontaneous firing pattern that is occasionally modulated by a rich spontaneous synaptic input. Peripheral siphon motor neurons have restricted motor fields that produce contraction of the mantle floor and the base of the siphon. Most of the type II neurons were found to be electrically coupled to one another. 5. The peripheral siphon motor neurons resemble the central siphon motor neurons in that they receive a collateral synapse from centrally located mechanoreceptor sensory neurons. This peripheral sensory-to-motor synapse exhibits the same kinetics of decrement as its central counterpart, both of which parallel behavioral habituation. 6. The rich mechanoreceptor input onto the relatively isolated dendritic trees of the peripheral siphon motor neurons provide a uniquely restricted neuropil to study the sensory-to-motor synapse. The peripheral motor neurons may, therefore, be a useful simple preparation for the cellular study of behavioral plasticity.

1. The release of ink from the ink gland of Aplysia californica in response to noxious stimuli is mediated by three electrically coupled motor neurons, L14A, L14B, L14C, whose cell bodies are located in the abdominal ganglion. The initial synaptic input to the ink motor neurons is relatively ineffective in firing the cells. As a result, a pause of 1--3 s often occurs before the cells attain their maximum firing frequency and cause the release of ink. Using current and voltage-clamp techniques we have analyzed the mechanisms underlying the firing pattern of these cells. 2. The presence of a fast transient K+ current appears to play an important role in mediating the firing pattern of the ink motor neurons. Their high resting potential (-75 mV) ensures that the steady-state level of inactivation of the conductance channels for the fast K+ current will normally be low. Thus a train of EPSPs or a depolarizing current pulse can activate this current maximally, thereby reducing the initial effectiveness of the excitatory input. 3. In addition to the fast transient K+ current, four other currents were identified: 1) a fast transient tetrodotoxin-sensitive inward current, presumed to be carried by Na+; 2) a slower tetrodotoxin-insensitive inward current, presumed to be carried by Ca2+; 3) a slow transient outward tetraethylammonium- (TEA) sensitive current; and 4) a very slow TEA-insensitive outward current. 4. A decreased conductance EPSP, which turns on over a several-second period, contributes to a late acceleration of spike discharge in the L14 cells. 5. The results suggest that a unique combination of biophysical properties of the L14 cells and the features of the synaptic input cause them to act as a low-pass filter in the reflex pathway for inking. Their high resting potential, which ensures minimal inactivation of the fast transient K+ current channel, makes these cells preferentially responsive to strong and long-lasting stimuli. The delayed recruitment of a decreased conductance EPSP augments the tendency of the L14 cells to fire in an accelerating burst pattern.

1. A behavioral and electrophysiological analysis of defensive ink release in Aplysia californica was performed to examine the response of this behavior and its underlying neural circuit to various-duration noxious stimuli. 2. Three separate behavioral protocols were employed using electrical shocks to the head as noxious stimuli to elicit ink release. Ink release was found to be selectively responsive to longer duration stimuli, and to increase in a steeply graded fashion as duration is increased. 3. Intracellular stimulation of ink motor neurons revealed that ink release is a linear function of motor neuron spike train duration, indicating that the selective sensitivity of the behavior to long-duration stimuli is not due to a nonlinearity in the glandular secretory process. 4. In contrast, electrophysiological examination of ink motor neuron activity in response to sustained head shock revealed an accelerating spike train. During the later part of the spike train, compound excitatory synaptic potentials show a positive shift in reversal potential. 5. Our results suggest a central locus for the mechanisms that determine sensitivity of inking behavior to stimulus duration. 6. In contrast to ink release, defensive gill withdrawal was found to be extremely sensitive to short-duration stimuli.

The neural network that controls the cardiovascular system ofAplysiaadapts cardiovascular function to a variety of different physiological and behavioral situations. It (1) coordinates the cardiovascular system with the renal and respiratory systems; (2) modifies both systemic and regional blood flow during food-elicited arousal and feeding; and (3) changes the tension of longitudinal vascular muscle to adapt the arterial tree to changes in body shape. Indirect evidence suggests that the cardiovascular control circuit may also play a role in maintaining homeostasis during egg laying. Several putative neurotransmitters, including acetylcholine, serotonin, R15α1 and R15α2 peptides, have been localized to identified neurons in this circuit.

Bivalve and gastropod molluscs undergo large changes in external environmental conditions, as well as in internal state. Cardiac responses to these changing conditions have been recorded in a variety of species. There is a general tendency for heart rate, and presumably cardiac output, to increase in response to situations that would increase the load on respiratory and excretory systems. Changes in molluscan heart function in many cases appear not to be mediated directly by cardiac nerves, but rather by such indirect mechanisms as changes in blood constituents or mechanical, hemodynamic effects on heart muscle. Three types of cardiac response in Aplysia have been shown to be mediated, at least in part, by the heart regulator nerves. The neural circuits that regulate heart rate in Aplysia and in Helix have been partially described in cellular detail. In Mercenaria, Aplysia and other molluscan species there is evidence that cyclic adenosine monophosphate has a role in mediating the excitatory effects of serotonin on heart muscle. There appears to be, in fact, a general tendency in the Aplysia nervous system for neurons that exert tonic, modulatory effects within neural networks that control a variety of behaviors to use serotonin for a transmitter. In each case there is evidence to suggest that changes in cyclic adenosine monophosphate levels may mediate some of the modulatory effects of serotonin.