Vasopressin and oxytocin as neuromediators

Vasopressin and oxytocin are peptide hormones which act on a variety of target organs, including kidney, smooth muscle, liver, and anterior pituitary. During the last decade, it has become apparent that these two neuropeptides may in addition act as neurotransmitters. We review a number of arguments which support this conjecture: 1) Vasopressin and oxytocin are not only synthesized in hypothalamoneurohypophysial neurones, but also in other--hypothalamic and extrahypothalamic--cell bodies whose axon projects to the limbic system, the brainstem and the spinal cord. 2) Vasopressin and oxytocin can be shed from central axons by the same secretory mechanism as are classical neurotransmitters. 3) Specific binding sites having a high affinity for vasopressin and/or oxytocin are present in the central nervous system. These binding sites represent functional receptors, because agonist binding leads to an increase in membrane phosphatidylinositol turnover. 4) Receptors, or at least part of them, are localized on neurones, since application of exogenous vasopressin and oxytocin alters the rate of firing of single neurones present in regions where binding sites have been detected autoradiographically. 5) Central vasopressin and oxytocin may play a role in brain functions, since in situ injection of antagonists interferes with physiological regulations.     

Functions of neuromediators in plants

In plants, neurotransmitters play a major biological role in chemo-signaling, as regulating agents of growth and development, membrane permeability, etc. In the plant cells, there are also main elements of cholinergic and aminergic systems including the enzymes as well as functional analogues of cholino- and aminoreceptors. It is important that the systems should be taken into consideration in fertilizing and chemical interaction of the plant cells. Acetylcholine and cholinesterase were shown to be secreted in male sexual cells (the pollen). Depression of cholinesterase on the gene level correlates with male sterility. Preliminary treatment of a female gametophyte with antagonists of acetylcholine and histamine, prior to pollination, blocked the normal process of fertilizing. Cholinesterase was also found in secrets released from the pollen surface and pistil.     

Memory,language, and ageing.

This overview provides both theoretical and empirical reasons for emphasizing practice and familiar skills as a practical strategy for enhancing cognitive functioning in old age. Our review of empirical research on age-related changes in memory and language reveals a consistent pattern of spared and impaired abilities in normal old age. Relatively preserved in old age is memory performance involving highly practised skills and familiar information, including factual, semantic and autobiographical information. Relatively impaired in old age is memory performance that requires the formation of new connections, for example, recall of recent autobiographical experiences, new facts or the source of newly acquired facts. This pattern of impaired new learning versus preserved old learning cuts across distinctions between semantic memory, episodic memory, explicit memory and perhaps also implicit memory. However, familiar verbal information is not completely preserved when accessed on the output side rather than the input side: aspects of language production, namely word finding and spelling, exhibit significant age-related declines. This emerging pattern of preserved and impaired abilities presents a fundamental challenge for theories of cognitive ageing, which must explain why some aspects of language and memory are more vulnerable to the effects of ageing than others. Information-universal theories, involving mechanisms such as general slowing that are independent of the type or structure of the information being processed, require additional mechanisms to account for this pattern of cognitive aging. Information-specific theories, where the type or structure of the postulated memory units can influence the effects of cognitive ageing, are able to account for this emerging pattern, but in some cases require further development to account for comprehensive cognitive changes such as general slowing.     

Memory,consciousness and neuroimaging.

Neuroimaging techniques that allow the assessment of memory performance in healthy human volunteers while simultaneously obtaining measurements of brain activity in vivo may offer new information on the neural correlates of particular forms of memory retrieval and their association with consciousness and intention. We consider evidence from studies with positron emission tomography and functional magnetic resonance imaging indicating that priming, a form of implicit retrieval, is associated with decreased activity in various cortical regions. We also consider evidence concerning the question of whether two components of explicit retrieval--intentional or effortful search and successful conscious recollection--are preferentially associated with increased activity in prefrontal and medial temporal regions, respectively. Last, we consider recent efforts to probe the relation between the phenomenological character of remembering and neural activity. In this instance we broaden our scope to include studies employing event-related potentials and consider evidence concerning the neural correlates of qualitatively different forms of memory, including memory that is specifically associated with a sense of self, and the recollection of particular temporal or perceptual features that might contribute to a rich and vivid experience of the past.     

Memory formation: sleep enough before learning

Is a full night of sleep a waste of time? No, numerous studies show dramatic performance impairments after sleep restriction, and a new study now indicates that sleep deprivation diminishes the brain's ability to form new memories.     

Molecular mechanisms of hormonal activity. I. receptors. neuromediators. systems with second messengers

Hormone signal transfer along all of the cell compartments including nucleus is powered by signal transduction systems. Characteristics and importance of hormone receptors, principal components, functional mechanisms, and biological role of different systems with second messengers are described. Considerable examples of the importance of these systems for medicine are adduced. The drugs modifying these systems comprise more than 65% of contemporary medicines.Translated from Biokhimiya, Vol. 70, No. 1, 2005, pp. 33–50.Original Russian Text Copyright © 2005 by Kulinsky, Kolesnichenko.     

Antibody formation to morphine and neuromediators in morphinized rats]

The paper demonstrates induction of antibodies to morphine and neurotransmitters (dopamine, norepinephrine, serotonin) in rats treated with intraperitoneal injections of morphine hydrochloride during 2 and 4 weeks in increasing doses. A contribution of such antibodies to the mechanisms of morphine tolerance and formation of physical dependence is considered.     

Effect of neuromediators on acid-base status]

A relationship between the state of adrenergic, cholinergic, and serotoninergic systems, on the one hand, and the acid-alkaline balance of the organism, on the other hand, was revealed in sharp and chronic experiments on dogs. A surplus of each of the mediators was accompanied by respiratory alkalosis, and its deficiency--by combined respiratory and metabolic acidosis.     

Effects of amiridin and tacrine, drugs effective in Alzheimer's disease, on synaptosomal uptake of neuromediators]

The study of the drugs effective in the treatment of cognitive deficits and memory loss associated with senile dementia of the Alzheimer's type--tacrine and amiridin, acetylcholinesterase inhibitor physostigmine and nootrop piracetam on uptake of 3H-serotonin (3H-5-HT), 3H-adrenaline (3H-AD), 3H-noradrenaline (3H-HA), 2H-dopamine (3H-DA), 3H-gamma-aminobutyric acid (3H-GABA), 3H-glutamic acid (3H-GLU), 3H-aspartic acid (3H-ASP) and 3H-glycine (3H-GLI) showed that tacrine and amiridin (5 x 10(-5) M) statistically significantly (P less than 0.05) inhibited the uptake of 3H-DA and 3H-5-HT. Physostigmine at concentration 5 x 10(-4) M statistically significantly (P less than 0.05) inhibited uptake of 3H-5-HT only. Piracetam at concentration range 1-5 x 10(-3) M had no effect on uptake of all investigated neurotransmitters. The above finding suggest that the uptake of neurotransmitter in nerve terminals is not the main target of amiridin and tacrine.     

Synaptic and nonsynaptic release of neuromediators in the central nervous system

Different types of release site were studied ultrastructurally with tannic acid and immunohistochemical techniques in the central nervous system (CNS) of the invertebrate pond snail Lymnaea stagnalis and in two neuromediator rich core regions in the CNS of the rat, viz., the median eminence (ME) and the mesencephalic central grey substance (MCG). In the CNS of the snail, release of the contents of the secretory granules could be clearly demonstrated in (1) neurohaemal axonterminals, (2) synapses and (3) in nonsynaptic release sites: neuronal processes without morphological synaptic specializations. In the ME, release of secretory products by exocytosis was found in neurohaemal axonterminals in the external part of the palisade layer and in nonsynaptic release sites in all other layers of the median eminence. It was found that oxytocine and vasopressin were released by exocytosis into the extracellular space from such (preterminal) nonsynaptic release sites. Serial section analysis revealed three types of fibre in the MCG, viz. (1) varicose fibres that made synaptic contacts with MCG dendrites on every varicosity, (2) fibres with two types of varicosity, viz. synapse-bearing varicosities and varicosities without synaptic specializations, and (3) varicose fibres without any synaptic specializations. It has been discussed that the nonsynaptic release sites in the CNS of the snail Lymnaea stagnalis, and the nonsynaptic varicosities in the rat brain are the morphological correlates of nonsynaptic communication in the CNS. The results further indicate that particular peptidergic neuromediators are released from such nonsynaptic varicosities, and may reach via the extracellular space receptors located at some distance.     

The role of carrier ATPases and neuromediators in neurological disorders

Physiological and biochemical processes which take place in the nervous system at stroke and neurotrauma are reviewed, and the experience of using low doses of steroid derivatives with piridamole in the treatment of central nervous system (CNS) disorders is summarized. ATPases (including Na,K-ATPase) are reported to play an important role in CNS functioning, the correlation between Na,K-ATPase activity and the extent of CNS injury is revealed. The use of NMR-spectroscopy method for investigation of brain and spinal cord condition in vivo is suggested.     

Memory.

The key interrelated issues in the neurobiology of memory are to identify the neural circuitries essential for memory formation, localize sites of memory storage and analyze mechanisms of memory formation, storage and retrieval. Several circuits have now been identified in vertebrates and researchers are investigating their properties, in particular the role of glutamate receptors and long-term potentiation, in memory formation. Invertebrate preparations continue to be of value and recent studies suggest that changes in gene expression and protein synthesis may be important in long-term sensitization.     

Effect of hypothermia on reuptake of neuromediators by synaptosomes

Cranio-cerebral hypothermia (temperature of the body 32-30 degrees C, of the brain 29-27 degrees C) was studied for its effect on the reuptake of neuromediators (3H-noradrenaline and [14C]GABA) by the cortex and hypothalamus synaptosomes of the rat brain. It was found that the reuptake of [3H]noradrenaline by the cortex synaptosomes under narcosis and cranio-cerebral hypothermia was inhibited much stronger than that by the hypothalamus synaptosomes. At the same time GABA-ergic synapses of the cortex and hypothalamus were not sensitive to narcosis. Cranio-cerebral hypothermia essentially inhibited the reuptake of [14C] GABA by synaptosomes and hypothalamus.