Conditioned defensive reflex in the edible snail (molecular-genetic aspects)

The proliferation of glioma cells requires cholesterol, which could be provided by synthesis within the cells or by uptake of cholesterol esters in particles of Low Density Lipoprotein (LDL). Cholesterol esters and cholesterol were therefore analysed in human glioma tissue, its surrounding areas and serum from 40 patients. The analyses revealed an increased concentration of cholesterol esters up to 100 times (0.1-10 mumol/g) in both tumour-tissue and surrounding areas compared with control material (< 0.1 mumol/g). The analyses also demonstrated that cholesterol esters in tumour tissue eminated mainly from serum. The cholesterol concentrations were significantly lower in tumour tissue compared with surrounding areas as expected. These results indicate that tumour cell proliferation utilises serum derived cholesterol esters presumably carried by LDL particles.     

Conditioning of cortical neurons in cats with antidromic activation as the unconditioned stimulus

Single-cell activity was recorded from the postcruciate cortex of acutely prepared cats during a differential classical conditioning procedure. The conditioned stimuli (CS) were hind paw stimuli, and the unconditioned stimulus (US) was pyramidal tract stimulation that produced an antidromic response in the recorded cortical neuron. A control group was also examined in which the pyramidal stimulus was set below the threshold to produce an antidromic response. Clear differential conditioning was found for the experimental group, with antidromic activation of the neuron as the US. There was no evidence of differential conditioning in the control group without antidromic activation. Any activation of orthodromic pathways should have been the same in the control and experimental groups. The absence of conditioning in the control group demonstrated that orthodromic pathways were not contributing to the differential conditioning observed in the experimental group. This indicates that it was activation of the neuron produced by antidromic firing which was important for conditioning. All the evidence suggests that the site of learning was in the cortex. It is concluded that the the role of the US in conditioning may be simply to activate the neuron at an appropriate interval following the CS.     

An associative process maintains reflex facilitation of the unconditioned nictitating membrane response during the early stages of training.

The presentation of a neutral or conditioned stimulus (CS) at an appropriate interval prior to the presentation of a corneal airpuff or a paraorbital shock (unconditioned stimulus, US) can facilitate the amplitude of the unconditioned nictitating membrane (NM) response in rabbits. In two experiments, it was demonstrated that an associative process mediates the maintenance of that facilitation during repeated CS–US pairings. Although CS-alone presentations produced a substantial decrease in the amount of reflex facilitation in animals not pretrained with the CS, pretraining that consisted of paired CS–US presentations prevented that decrease when CS-alone presentations were subsequently given. Conditioned facilitation of the unconditioned response occurred very rapidly (within 5–22 trials in these experiments) and long before the appearance of overt conditioned responses to the CS. In addition, it was demonstrated that conditioned facilitation can be relatively specific to the tonal frequency of the CS. These results indicate the first sign of conditioning of the NM response is exhibited in the amplitude of the unconditioned response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Met-enkephalin Arg-Phe-immunoreactive neurons in the central nervous system of the pond snail Lymnaea stagnalis

The distribution of an opioid peptide related to YGGFMRF was determined in the CNS and other organs of the pond snail, Lymnaea stagnalis, by RIA and immunocytochemistry. RIA revealed the highest levels in the CNS (1 pmol/organ) and penis (400 fmol/organ). There were also significant levels in the haemolymph, most of which was not associated with haemocytes (580 fmol/ml). Both serial section and whole-mount immunocytochemistry of the CNS revealed immunoreactive cells in every ganglion with the majority in the cerebral and pedal ganglia. In the pedal ganglia some of the immunoreactive cells were close to the cells of the A-cluster, which are known to respond to opioids, and could innervate them. In the cerebral ganglia the immunoreactive cells included a group of neurosecretory cells, the caudo dorsal cells (CDCs) and the terminals of these cells in the cerebral commissure were also stained. The CDCs secrete peptides into the haemolymph and so could be the source of the YGGFMRF immunoreactivity. Immunoreactivity (including the CDCs) was observed in locations that correspond to those reported for other fragments of proenkephalin, such as Met- and Leu-enkephalin, suggesting that they may share a common precursor, a Lymnaea proenkephalin. A map of the 358 YGGFMRF-immunoreactive cells in the CNS is presented, many of which have not been previously identified.     

Three types of reticular neurons involved in the spino-bulbo-spinal reflex of cats

Reticular neuron activity was recorded in 28 chloralosed cats in order to analyze the reflex arc of the spino-bulbo-spinal (SBS) reflex. Three types of reticular neurons, types I (input), II(output) and III (relay), were identified by unit discharges in response to stimulation of the sural nerve. (1) Type I (input) neurons received spinal ascending volleys monosynaptically and responded to stimulation of the sural nerve with spikes of low amplitude and short latency. Unit spikes, however, were not produced by stimulation of the superficial radial nerve and the sensorimotor cortex. These input neurons were located in the dorsocaudal part of the medial bulbar reticular formation. (2) Type II (output) neurons were part of the reticulospinal tract, which sends axons to the spinal cord, since these neurons exhibited antidromic spikes following stimulation of the ventrolateral funiculus of the spinal cord. Unit spikes were evoked by stimulation either to the sural or superficial radial nerves. These neurons were located in the ventrocaudal part of the medial bulbar reticular formation. (3) Type III neurons included relay neurons. Unit spikes were evoked by stimulation of the sural nerve, superficial radial nerve and sensorimotor cortex. However, unit discharges were not obtained by antidromic stimulation to the reticulospinal tract. These neurons were distributed widely in the brain stem, both in the bulb and pons. (4) Latency difference of unit discharges between input and output neurons was 3.5--5 msec, indicating the presence of interneurons (relays) between input and output neurons. Spikes of output neurons with 3.8--4.2 msec latency were observed following stimulation of the region where input neuron activity was found. We may conclude that three kinds of reticular neurons, input, relay and output, were involved in pathways of the SBS reflex.     

Membrane potential at the low pH in neurons from the snail, Lymnaea stagnalis L

In the snail, the pH 6.7-6.8 decreased the neuron membrane potential in 10% of cases and increased it in 30%. The hyperpolarisation was equal to 9(5 mV, the effect being abolished by addition of 5-10 M strophantidine. The findings suggest that low pH activates sodium conduction, the hyperpolarisation being caused by activation of the K+/Na(+)-pump.     

Mathematical model of pacemaker activity in bursting neurons of snail, Helix pomatia

On the basis of experimental data we have developed a mathematical model of pacemaker activity in bursting neurons of snail Helix pomatia which includes a minimal model of membrane potential oscillation, spike-generating mechanism, voltage- and time-dependent inward calcium current, intracellular calcium ions, [Ca2+]in, their fast buffering and accumulation, stationary voltage-dependent [Ca2+]in-inhibited calcium current. A resulting model of bursting pacemaker activity reproduces all experimental phenomena which were mimicked on the minimal model for membrane potential oscillation including (a) the effect of polarizing current on bursting activity, (b) an increase of input resistance during depolarizing phase, (c) induced hyperpolarization, etc. This model demonstrates adaptation of bursting activity to both the polarizing current and changes in the stationary sodium or potassium conductances. The model also reproduces the behavior of the transmembrane ionic current at membrane potentials clamped in different phases of slow-wave development; the calculated current-voltage relationships of the model neuronal membrane using a slow ramp potential clamp demonstrate hysteresis properties. Relationships between the model of bursting activity and the properties if intact bursting neurons are discussed.     

Classical conditioning and conditioning-specific reflex modification of rabbit heart rate as a function of unconditioned stimulus location.

Heart rate conditioning is used as an index of conditioned fear and is important for understanding disorders of anxiety and stress, including post traumatic stress disorder (PTSD). One important feature of PTSD is that patients generalize conditioned fear from danger signals to safety signals especially when the two signals have overlapping features. What has not been determined is whether generalization occurs between unconditioned stimuli with overlapping features. In the current experiment, heart rate conditioning and conditioning-specific reflex modification of rabbit heart rate were examined as a function of two different unconditioned stimulus locations. Heart rate conditioning occurred at identical terminal levels whether electrical stimulation was presented near the eye or on the back. Despite different heart rate response topographies to electrical stimulation at the two locations, conditioning-specific reflex modification was detected near the eye and on the back and appeared to generalize between the locations. Interestingly, only conditioning-specific reflex modification detected on the back persisted for a week after heart rate conditioning. This persistence may be a model for some features of post traumatic stress disorder. Overgeneralization of unconditioned responses to unconditioned stimuli similar to the trauma may also be an important aspect of PTSD modeled here. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Spatial-temporal organization of the functions of cortical neurons in a conditioned reflex to time

The impulse activity of neurons in the motor cortex of cats during the development of a conditioned food-procuring reflex in relation to a time interval of 2 min (CRT) was analyzed. It was demonstrated, by comparing the behavioral and neurophysiological correlates of the formation of the conditioned food-procuring reaction, that its formation is accompanied by extremely complex systemic transformations which are different for neuronal micro- and macrostructures. The systemic processes in the micro- and macrostructures differed with respect to the specific characteristics of spatial distribution, and with respect to the number, strength, and stability of the manifestation of the functional connections. The capacity of the neurons for functional orientation even at the initial levels of the formation of the reaction, an increase in the per cent of incidence of functional connections in the second half of the conditioned reflex interval, and the substantial destabilization of all neuronal units at the last, highest level of formation of the conditioned reflex food-procuring reaction were common to the micro- and macrostructures in this form of learning.     

Nature of the reflex excitation of the spinal motor neurons in children with isiopathic scoliosis

In 32 girls from 12-14 years with expressed idiopathic scoliosis (III-IV stage) the authors studied H-reflexes, evoked from the soleus muscles. In 16 patients they established an expressed asymmetry in the expressivity of H-reflexes from the right and left sides. This asymmetry was found in a localization of the primary arch of spinal distortion in the sacral part. In a localization of the primary arch in the thoracal part, the asymmetry in the reflectory excitation of sacral motoneurons is not expressed. It is being assumed that changes in the motoneuron apparatus of the spinal cord are the reason of the appearance of a scoliotic deformation of the spine.     

The modulating action of serotonin on single calcium channels in the neurons of the snail Helix pomatia

The influence of a neurotransmitter serotonin (5-hydroxytriptamine, 5-HT) on single Ca2+ channel activity was studied on unidentified neurons of the snail Helix pomatia. Our findings showed that 5-HT influences the channel molecule in indirect manner, as it appeared effective at its application by adding to the bath solution, that had no contact with the tested membrane fragment. This finding excludes the possibility of direct binding of 5-HT to the channel molecule and shows that the effect is really mediated through a cytoplasmic messenger, cAMP-dependent cascade of phosphorylation. Also our investigations shows, that only one type of Ca2+ channel with the unitary conductance of 5 pS was identified in this kind of neurons.     

Analysis of a network of electrically coupled neurons producing rhythmic activity in the snail Helisoma trivolvis

Root tip mitosis in both Vinca rosea and the chosen control Lepidium sativum is susceptible to the effects of colchicine at and above 5X10(-4)M.--Root tip mitosis in L. sativum is susceptible to the effects of vinblastine at concentrations equal to and greater than 10(-4)M, while root tip mitosis in V. rosea, the plant which is the source of vinblastine, is unaffected by exogenously-applied VBL at concentrations up to and including 10(-2)M.--The possible mechanisms by which the resistance of V. rosea to vinblastine might be conferred are discussed.     

Atrophy and degeneration of peptidergic neurons and cessation of egg laying in the aging pond snail Lymnaea stagnalis

The morphology of the neuroendocrine caudodorsal cells (CDCs), which are involved in the regulation of female reproduction in the pond snail Lymnaea stagnalis, was studied in young (200 to 234 days of age) and old (400 to 500 days) animals. Lucifer Yellow fills of ventral CDCs showed that in young animals ventral CDCs branch ipsilaterally as well as contralaterally in the cerebral commissure. In old animals these branches were reduced at different degrees and in some cases even lacking completely, leaving only an axon crossing the commissure. Immunocytochemical stainings with antibodies against CDC peptides (CDCH-I and alpha CDCP) corroborated the finding that ventral CDCs degenerate. Among the other types of CDCs (dorsal, lateral), degeneration was found as well. The immunocytochemical findings showed that in old animals the axon terminals of the CDCs were strongly stained, indicating that they are packed with secretory vesicles containing peptides. It was also found that these darkly stained, peptide-containing axon terminals protruded into the perineurium. These findings suggest that accumulation of peptides in the terminals of the CDCs of old animals may be due to the impaired release. The relationship between atrophy and degeneration of CDCs and cessation of egg-laying activity in Lymnaea is discussed.     

On the involvement of tachykinin neurons in the secretory nervous reflex elicited by cholera toxin in the small intestine

Considering the fact that one of the indicators of effects of hypoxia in pilots could be an altered speech we have analysed changes in uttering a sound (A) in our examinees, pilot-students, aged 21-23, under effects of hypoxia only, the associated effects of hypoxia and mental loading and under conditions of normal barometric pressure. In the frequency and three dimensional representation of the selected sound, there have been analysed frequency components, intensity, duration and quality of the sound. It has been found that acute hypoxia causes deep structural and durational changes. During the stay at the simulated altitude the contributing factor to these changes which should be taken into account is the mental loading--performance of the test. It has been obvious that the same degree of hypoxia associated with mental activities during test performance causes deeper degradation of the voice structure both in the resistant subjects, and especially in individuals sensitive to the lack of oxygen compared to that under effects of hypoxia only and that under physiologic conditions.     

On the respective contributions of awareness of unconditioned stimulus valence and unconditioned stimulus identity in attitude formation through evaluative conditioning.

Evaluative conditioning (EC) is a central mechanism for both classic and current theories of attitude formation. In contrast to Pavlovian conditioning, it is often conceptualized as a form of evaluative learning that occurs without awareness of the conditioned stimulus–unconditioned stimulus (CS-US) contingencies. In the present research, the authors directly address this point by assessing the respective roles of US valence awareness and US identity awareness in attitude formation through EC. Across 4 experiments, EC was assessed with evaluative ratings as well as evaluative priming measures, and the impact of valence and identity awareness on EC was evaluated. EC effects on priming and rating measures occurred only for CSs for which participants could report the associated US valence, and US identity awareness did not further contribute to EC. This finding was obtained both for semantically meaningless (i.e., nonword letter sequences) and meaningful (i.e., consumer products) CSs. These results provide further support for the critical role of contingency awareness in EC, albeit valence awareness, not identity awareness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial heterogeneity of caffeine- and inositol 1,4,5-trisphosphate-induced Ca2+ transients in isolated snail neurons

Inositol 1,4,5-trisphosphate- and caffeine-induced Ca2+ release was examined in neurons isolated from the mollusc Helix pomatia using Ca2+ indicator fura-2 and fluorescent digital-imaging microscopy technique. Extracellular application of caffeine caused a fast and pronounced augmentation of [Ca2+]i whose amplitude and kinetics differ in the centre of the cell and near its membrane. Mean values of caffeine-induced increase of [Ca2+]i were 0.97 +/- 0.11 microM at the periphery and 0.53 +/- 0.13 microM in the centre. The rates of rise and relaxation of caffeine-evoked [Ca2+]i transients were faster near the membrane. Pressure injection of inositol, 1,4,5-trisphosphate into the same neurons produced an abrupt and significant increase of [Ca2+]i in the centre (mean value of inositol 1,4,5-trisphosphate-induced elevation = 0.55 +/- 0.11 microM) while the response was smaller or even absent near the cellular membrane. Inositol 1,4,5-trisphosphate- and caffeine-induced Ca2+ transients did not affect each other. The data obtained indicate that in snail neurons these two calcium pools are not overlapping and at least some part of the caffeine-sensitive store is located close to the cellular membrane and that the inositol 1,4,5-trisphosphate-sensitive one is located in the centre of the cell.     

Inhibitors of NO-synthase and guanylate cyclase block the modulation of cholinoreceptor plasticity in snail neurons by 15-hydroxyeicosatetraenoic acid

Probable participation of two second messengers, NO and cGMP, in short- and long-latent effects of 15(S)-hydroxy-(5Z,8Z,11Z, 13E)-eicosatetraenoic acid (15-HETE, acyclic eicosanoid) on plasticity of somatic acetylcholine receptors on identified neurons of Helix lucorum was studied using two-electrode voltage clamp technique. It was shown that inhibitor of NO synthase N omega-Methyl-L-Arginine and inhibitors of soluble guanylate cyclase LY-83,583 and methylene blue disturbed short- and long-latent modulatory effects of 15-HETE on depression depth of the inward current evoked by rhythmic acetylcholine application on the neuron soma. We suppose that NO and cGMP participate in short- and long-latent effects of 15-HETE on plasticity of acetylcholine receptors.     

Conditioning the unconditioned response: Modification of the rabbit's (Oryctolagus cuniculus) unconditioned nictitating membrane response.

Conditioning-specific reflex modification (CRM) occurs when classical conditioning modifies responding to a unconditioned stimulus/stimuli (UCS) in the absence of a conditioned stimulus (CS). Three experiments monitored rabbit (Oryctolagus cuniculus) nictitating membrane unconditioned responses to 5 intensities and 4 durations of periorbital electrical stimulation before and after CS or UCS manipulation. CRM occurred after 12 days of CS-UCS pairings but not following unpaired CS/UCS presentations or restraint. CRM survived CS-alone and CS/UCS-unpaired extinction of the conditioned response (CR) but not presentations of the UCS alone, although CRs remained intact. Thus, CRs could be weakened without eliminating CRM and CRM could be weakened without eliminating CRs. Data indicate CRM is a reliable, associative effect that is more than a generalized CR and may not be explained by habituation, stimulus generalization, contextual conditioning, or bidirectional conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)