V. V. Sherstnev

Serotonin imitates several of the neuronal effects of nociceptive sensitization in the common snail.

Experiments on defensive behavior command neurons in common snails showed that synaptic facilitation in the responses of nerve cells to sensory stimulation occurs 50–60 min after the onset of application of serotonin (10 μM) to the CNS. The properties of neuron electrogenic membranes (membrane potential, membrane excitability) did not change after exposure to serotonin. Along with synaptic facilitation, serotonin (100 μM) increased the excitability and produced minimal depolarization of the membranes of command neurons. Serotonin had selective effects on the reactions of neurons to different sensory stimuli: facilitation of neuron responses to tactile stimulation of the head lasted 1 h, while responses to application of dilute quinine solution lasted 2–3 h; serotonin facilitated neuron responses to tactile stimulation only of the snail’s head, and did not alter the responses to stimulation of the foot or the mantle ridge. The time course of the electrophysiological effects of serotonin coincided with changes in bound calcium (Cab) levels in command neurons. This set of serotonin-induced neurophysiological effects is simular to the effects resulting from the development of nociceptive sensitization. It is suggested that serotonin is involved in the mechanisms of transient changes and consolidation of long-term plastic rearrangements in command neurons which underlie sensitization.

Effects of protein synthesis inhibitors during reactivation of associative memory in the common snail induces reversible and irreversible amnesia.

The effects of protein synthesis inhibitors on the reactivation of an associative skill consisting of refusing a particular food by common snails were studied. Animals were given single injections of a protein synthesis inhibitor (cycloheximide at 0.6 mg/snail or anisomycin at 0.4 mg) 24 h after three days of training, and were then presented with a “reminding” stimulus (the “conditioned reflex” food-banana) and tested for retention of the skill. Observations revealed an impairment of reproduction of the acquired skill 2.5 h after the “reminder, ” with spontaneous restoration at 4.5–5.5 h. Other snails were given single 1.8-mg doses of cycloheximide or three 0.6-mg doses with intervals of 2 h. “Reminders” were presented after each injection. In these conditions, impairment of reproduction of the conditioned reflex also appeared 2.5 h after the first “reminder, ” though amnesia lasted at least 30 days and repeat training of the animals produced only partial recovery of the skill. Thus, we have provided the first demonstration that recovery of a long-term memory “trace” on exposure to relatively low doses of protein synthesis inhibitors produces transient and short-lived amnesia, lasting 2–3 h, while long-term, irreversible amnesia occurrs after longer-lasting or more profound suppression of protein synthesis. These results suggest that the “reminding” process induces reconsolidation of the “ initial” memory, suppression of which by protein synthesis inhibitors leads to “erasure” of the memory “trace” and impairs consolidation on repeat training.

Neurogenesis enhancer RO 25-6981 facilitates repeated spatial learning in adult rats.

The effects of Ro 25-6981 (selective NMDA receptor blocker) in a dose stimulating neurogenesis on repeated learning, reversal learning, and memory reconsolidation were studied in adult rats in Morris water maze. Ro 25-6981 facilitated repeated learning 13 days after injection, but did not influence reversal learning. The blocker injected directly before reminder did not disturb repeated learning and reversal learning in Morris water maze. These effects of Ro 25-6981 on the dynamics of repeated learning seemed to be due to its effects on neurogenesis processes in adult brain.

Regional Features of the Expression of Genes Involved in Neurogenesis and Apoptosis in the Brain of Adult Rats

The expression of mRNA of genes involved in neurogenesis and apoptosis (Apaf1, Ascl1, Bax, Bcl2, Casp3, Casp8, Casp9, Dffb, Myh10, Naip2, Napa, Notch2, Numb, Pura, S100a6, Tnf) in the prefrontal cortex, hippocampus, and cerebellum was studied in adult rats. The content of mRNA of these genes (except Apaf1) was several-fold higher in the cerebellum than in the hippocampus and brain cortex. In the hippocampus, the expression of Apaf1 was significantly lower than in the prefrontal cortex, while the expression of Ascl1, Pura, S100b, and Tnf was higher. Regional differences in the direction, strength, and numbers of significant correlations between the expression of the studied genes were detected. Documented differences in gene expression were regarded as validation of the structural and functional cooperation of neurogenesis and apoptosis at the molecular genetic level.

Hexapeptides HLDF-6 and PEDF-6 restore memory in rats after chronic intracerebroventricular treatment with β-amyloid peptide Aβ(25–35)

Effects of homologous peptides HLDF-6 and PEDF-6 on behavior of animals with experimental Alzheimer’s disease induced by chronic intracerebroventricular administration of β-amyloid peptide Aβ(25–35) were studied in the zoosocial recognition test and Morris water maze. Peptides HLDF-6 and PEDF-6 possessed neuroprotective activity and counteracted the toxic effect of Aβ(25–35). Peptides HLDF-6 and PEDF-6 mainly improved long-term memory and working memory, respectively.

The Effects of Antibodies Against Proteins of the s100 Group on Neuron Plasticity in Sensitized and Non-Sensitized Snails

The effects of antibodies to a total fraction of s100 proteins and protein s100b on the activity of defensive behavior command neurons LPl1 and RPl1 were studied in common snails, using non-sensitized animals and animals which had acquired nociceptive sensitization. In non-sensitized snails, application of antibodies against s100 or s100b (0.1 mg/ml) induced membrane depolarization, increased membrane permeability, and suppressed slow excitatory postsynaptic potentials in the responses of neurons to sensory stimulation. Acquisition of sensitization in snails in the presence of antibodies to s100 or s100b (0.1 mg/ml) led to significantly less marked facilitation of synaptic transmission and smaller increases in neuron membrane excitability than in cells of control sensitized animals. The difference in synaptic facilitation in the neurons of control sensitized snails and neurons in sensitized snails given antibody was comparable with the magnitude of synaptic depression due to antibody in non-sensitized animals. At a dose of 0.01 mg/ml, antibody had no effect on these measures of neuron activity. It is suggested that s100 proteins, particularly s100b, are involved in the mechanisms regulating excitability, the membrane potential, and synaptic transmission in command neurons in untrained snails, as well as in the mechanism of plasticity of the electrogenic membranes of nerve cells during the acquisition of nociceptive sensitization.

Content of S100b Protein, HLDF24 Peptide and Autoantibodies to These Factors as Potential Biomarkers for Arterial Hypertension in Blood Serum of Healthy People

The content of S100b protein, HLDF24 peptide, and autoantibodies to these factors in blood serum was measured in healthy individuals (35-64-year-old men and women) with various levels of “normal” BP. Significant differences in the amount of these molecular factors were found in individuals with various categories of BP. We revealed age-related and gender differences in the content of molecular factors in the serum. Our results indicate that variations in the concentration of S100b, HLDF24, and autoantibodies to these factors in blood serum from adult people can serve as a reliable criterion for the risk of arterial hypertension.

Irreversible Amnesia in Rats and Edible Snails under Conditions of Associative Memory Reconsolidation Disturbance Caused by NMDA-Glutamate Receptor Antagonist

The effect of MK-801, an antagonist to NMDA-glutamate receptors, on reconsolidation of olfactory discrimination task in rats and taste discrimination in edible snails was examined. Twenty-four hours after conditioning, the animals received a single systemic injection of MK-801 followed by a reminding conditional stimulus. Disturbances in retrieval of the acquired task were observed 10 days after injection followed by a reminding procedure. Repeated conditioning of these animals did not restore the task. Injection of MK-801 without reminding stimulation had no effect on task retention. Thus, disturbances of NMDA-dependent reconsolidation of the associative memory in animals of different taxonomic groups irreversibly eliminated long-term memory.

The acoustic startle response and polymorphism of the gene for catechol-O-methyltransferase in the norm and in schizophrenia

Using 46 healthy subjects and 47 male patients with schizophrenia we studied the influence of the rs4680 polymorphism (Val158Met) in the gene for catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, on the level of catecholamines in the blood plasma and basic parameters and prepulse inhibition of the acoustic startle response (ASR), which are potential neurophysiological markers of the risk of the development of schizophrenia. An effect of the polymorphism of the COMT gene on the prepulse inhibition of ASR was observed only in healthy persons and consisted in a decrease in this index in carriers of the Val/Val genotype. In patients with schizophrenia, polymorphism of the COMT gene was associated with another potential endophenotype of schizophrenia, viz., the basic latent period of ASR; its largest increase, as compared to the norm, was found in homozygous carriers of Met at the 158th position. We found a positive correlation between prepulse inhibition and the ratio of dopamine metabolism in the blood plasma of healthy subjects and the adrenaline level in patients. Binary logistic regression showed that inclusion of the factor of the genotype considerably increases the validity of the diagnostic model, which is based on the evaluation of the neurophysiological indices.

Involvement of HLDF Protein and Anti-HLDF Antibodies in the Mechanisms of Blood Pressure Regulation in Healthy Individuals and Patients with Stable Hypertension and Hypertensive Crisis

We studied the relationships between the blood serum levels of human leukemia differentiation factor HLDF, idiotypic and anti-idiotypic antibodies to HLDF, and clinical indicators of cardiovascular function in apparently healthy individuals and patients with essential hypertension and cerebral hypertensive crisis. Markedly reduced HLDF levels and anti-HLDF antibody titers were found in the blood of the examined patients. Correlations between HLDF levels, duration of hypertension, and systolic and diastolic BP were revealed. These findings suggest that the studied molecular factors are involved in the mechanisms of BP regulation under normal conditions and during hypertension development. The protein HLDF and anti-HLDF antibodies can be considered as biomarkers for early diagnosis of hypertension and its cerebral complications.