5HT leech

Noxious stimuli can elicit stress in animals that produce a variety of adaptations including changes in responses to nociceptive and non-nociceptive sensory input. One example is stress-induced analgesia that may be mediated, in part, by the endocannabinoid system. However, endocannabinoids can also have pro-nociceptive effects. In this study, the effects of electroshock, one experimental approach for producing acute stress, were examined on responses to non-nociceptive mechanical stimuli and nociceptive thermal stimuli in the medicinal leech (Hirudo verbana)...

Incomplete spinal cord injury (iSCI) often results in significant motor impairments that lead to decreased functional mobility. Loss of descending serotonergic (5HT) input to spinal circuits is thought to contribute to motor impairments, with enhanced motor function demonstrated through augmentation of 5HT signaling. However, the presence of spastic motor behaviors in SCI is attributed, in part, to changes in spinal 5HT receptors that augment their activity in the absence of 5HT, although data demonstrating motor effects of 5HT agents that deactivate these receptors are conflicting...

Several studies suggest that acetyl-l-carnitine (ALC) might influence learning processes. Along this line of investigation, we have previously shown that ALC impaired sensitization and dishabituation induced by nociceptive stimulation of the dorsal skin of the leech Hirudo medicinalis, in the behavioural paradigm of the swim induction (SI). In previous works we showed that 5HT was involved in both sensitization and dishabituation of SI acting through the second messenger cAMP. In this work, we have reported that for given doses and temporal ranges ALC was able to block sensitization and to impair dishabituation mimicked by the injection of 5-HT or 8Br-cAMP, a membrane permeable analogue of cAMP...

Increasing evidence indicates that modulation of Na(+)/K(+) ATPase activity is involved in forms of neuronal and synaptic plasticity. In tactile (T) neurons of the leech Hirudo medicinalis, Na(+)/K(+) ATPase is the main determinant of the afterhyperpolarization (AHP), which characterizes the firing of these mechanosensory neurons. Previously, it has been reported that cAMP (3',5'-cyclic adenosine monophosphate), which mediates the effects of serotonin (5HT) in some forms of learning in the leech, negatively modulates Na(+)/K(+) ATPase activity, thereby reducing the AHP amplitude in T neurons...

In this paper the role of serotonin (5HT) and cyclic AMP (cAMP) in sensitization and dishabituation of swim induction (SI) has been investigated in the leech Hirudo medicinalis. Electrical stimulation of the body wall evokes swimming activity with a constant latency. In animals with a disconnection between head ganglion and segmental ganglia, repetitive stimulation induces habituation of swimming whereas brushing on the dorsal skin provokes sensitization of a naïve response or dishabituation of a previously habituated response...

We identified a new form of activity-dependent modulation of the afterhyperpolarization (AHP) in tactile (T) sensory neurons of the leech Hirudo medicinalis. Repetitive intracellular stimulation with 30 trains of depolarizing impulses at 15-s inter-stimulus interval (ISI) led to an increase of the AHP amplitude (~60% of the control). The enhancement of AHP lasted for >/=15 min. The AHP increase was also elicited when a T neuron was activated by repetitive stimulation of its receptive field. The ISI was a critical parameter for the induction and maintenance of AHP enhancement...

Networks of electrically coupled neurons play an important role in coordinating activity among widely distributed neurons in the CNS. Such networks are sensitive to neuromodulation; but how modulation of individual cells affects activity of the entire network is not well understood. In the CNS of the medicinal leech, the S interneuron (S-cell) forms a network of electrically coupled neurons where each S-cell is linked to its two neighboring S-cells by electrical synapses. An action potential initiated in one cell is carried the length of the animal along this S-cell chain...

In studies of the cellular basis of learning, much attention has focused on plasticity in synaptic transmission in terms of transmitter release and the number or responsiveness of neurotransmitter receptors. However, changes in postsynaptic excitability independent of receptors may also play an important role. Changes in excitability of a single interneuron in the leech, the S-cell, were measured during non-associative learning of the whole-body shortening reflex. This interneuron was chosen because it is known to be necessary for sensitization and full dishabituation of the shortening response...

1. In this paper the authors tested the effect of caulerpenyne (CYN), a sesquiterpene synthesized by the green alga Caulerpa taxifolia onto the central nervous system of the leech Hirudo medicinalis. Investigations have been performed with three different approaches: neuroethological, electrophysiological and neurochemical techniques. 2. CYN application mimics the effect of a nociceptive stimulation (brushing), eliciting a clear-cut potentiation of the animal swim response to the test stimulus (non associative learning process such as sensitization)...

The biochemical characterization of a serotonin (5HT) receptor and the cloning of a dopamine (DA) receptor in the central nervous system (CNS) of the leech, Theromyzon tessulatum, is presented. Additionally, DA and 5HT binding sites were examined in the CNS by Scatchard analysis which showed a single, relatively high-affinity binding site with a Kd 1.1 nM and a Bmax 126+18 fmol/mg protein for [3H]DA and a Kd 2.1 nM and a Bmax 225 fmol/mg protein for [3H]5HT. The first 88 amino acids of the 5HT receptor, isolated by a 5HT-affinity column followed by anion exchange chromatography and C3 reverse-phase HPLC exhibited a 43% sequence homology with Lymnaea stagnalis 5HT-receptor...

An increasing flow of evidences collected on elementary forms of learning processes in selected animal models evidentiates some mechanisms which can represent the basic cellular principles underlying plastic changes: 1. 5HT and second messengers of nucleotide type (like cAMP) have a pivotal role in the learning process. 2. In almost all short-term learning processes the modifications are subserved by a mechanism of protein phosphorylation. 3. In various animal models the modulation of K+ and Ca2+ channels is the molecular mechanism for learning...

1. 5-Hydroxytryptamine (5-HT) receptors in the Retzius neurones (R cells) and longitudinal body wall muscle strips of the leech H. medicinalis were studied using a range of selective agonists developed for mammalian receptors. 2. All agonists induced hyperpolarisation of R cells: the order of their potency was 5-HT > 5-CT > 2-Me 5HT > alpha-Me-5-HT > > CGS-12066B = 5MeOT > PAPP > Buspirone. This receptor is most like a mammalian 5-HT1C/2 receptor. 3. 5-HT induces relaxation of body wall strips, preceded at higher doses by contraction or an increase in spontaneous contractions...

The goal of these experiments was to test the role of serotonin (5HT) in classical conditioning of the touch-elicited shortening reflex in the leech (Hirudo medicinalis). The toxin 5,7-dihydroxytryptamine (5,7-DHT) was used to deplete serotonin. The results indicated that 5HT depletion significantly impairs the expression of conditioned responding; however, depleted leeches experiencing conditioned stimulus-unconditioned stimulus (CS-US) pairings still performed significantly better than depleted leeches experiencing unpaired CS-US presentations, suggesting that a 5HT-dependent mechanism does not account fully for learning in this preparation...

Serotonin (5HT) is the neurotransmitter involved in some forms of short-term memory in the leech. Behavioral experiments have demonstrated that long-term memory requires new protein synthesis. With the aim of studying the molecular mechanism underlying memory processes in the leech, we have analyzed the effect of 5HT on protein synthesis and protein phosphorylation. Segmental ganglia of the leech central nervous system have been labeled, proteins have been separated by two-dimensional-electrophoresis and labeled proteins detected by autoradiography...

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