Plasticity, of neurons

A therapeutic decrement may be inherent in the repeated application of antidepressant treatments. In this context, patients who are repeatedly treated with antidepressants appear to become increasingly more resistant to subsequent treatment strategies, including ECT [Amsterdam et al. 1994b]. A number of clinical and biochemical factors, including progressive virulence of recurrent depressive episodes, reduced plasticity of neuronal receptor regulatory mechanisms, and the development of secondary (and even tertiary de-... 

Plasticity of neuronal tissue is generally divided into two types reversible changes in the nerve programming... 

Neurotrophins are peptides or protein molecules that regulate both cell survival and cell death of specific neuronal phenotypes and thus serve to influence development, maintenance, function, and plasticity of the nervous system. 

Thus the neurotransmitter role of ATP is well established in the periphary and also in sensory systems but its importance in the CNS remains to be elucidated (see Burnstock 1996). That requires the development of more specific antagonists and methods of mapping its location. The strong linkage of its P2x receptors to calcium currents may also provide a role for ATP in more long-term effects such as plasticity and neuronal development and death. 

So if ACh is involved in memory function, what does it do Any attempt to answer that question has to follow some consideration of how memory is thought to be processed. Many neuroscientists believe that memory is achieved by changes in the strength of synaptic connections (activation) between neurons and that increases in such synaptic activity somehow reinforce the pattern of neuronal activity during the memorising of an event so that it can be more easily restored later. One form of such plasticity is longterm potentiation (LTP), which has been mostly studied in the hippocampus where, as in other areas associated with memory, there is the appropriate complex synaptic morphology. 

The nervous system is one of the two regulatory systems in the human body that influences the activity of all the other organ systems. It consists of literally billions of neurons interconnected in a highly organized manner to form circuits. The number of neurons and the manner in which they are interconnected in a given circuit distinguishes one region of the brain from another and the brain of one individual from that of another. In addition, plasticity, the ability to alter circuit connections and function in response to... 

A variety of different types of tissue preparation are used to study neurosecretion and synaptic transmission. A classical preparation is the frog NMJ (discussed below). The brain slice has been used for many years for biochemical studies of CNS metabolism and is a useful preparation for electrophysiological studies of synaptic transmission in the CNS. Slices can be oriented to maintain the local neuronal circuitry and can be thin, 0.3 mm, to minimize anoxia. The transverse hippocampal slice is widely used as an electrophysiological preparation to study synaptic plasticity (see Ch. 53). Primary cultures of neurons from selected CNS areas and sympathetic ganglia are also frequently used. They permit excellent visual identification of individual neurons and control of the extracellular milieu, but the normal neuronal connections are disrupted. 

The synthesis of 5-HT can increase markedly under conditions requiring more neurotransmitter. Plasticity is an important concept in neurobiology. In general, this refers to the ability of neuronal systems to conform to either short- or long-term demands placed upon their activity or function (see Plasticity in Ch. 53). One of the processes contributing to neuronal plasticity is the ability to increase the rate of neurotransmitter synthesis and release in response to increased neuronal activity. Serotonergic neurons have this capability the synthesis of 5-HT from tryptophan is increased in a frequency-dependent manner in response to electrical stimulation of serotonergic soma [7]. The increase in synthesis results from the enhanced conversion of tryptophan to 5-HTP and is dependent on extracellular calcium ion. It is likely that the increased 5-HT synthesis results in part from alterations in the kinetic properties of tryptophan hydroxylase, perhaps due to calcium-dependent phosphorylation of the enzyme by calmodulin-dependent protein kinase II or cAMP-dependent protein kinase (PKA see Ch. 23). 

Curtis, J. and Finkbeiner, S. Sending signals from the synapse to the nucleus possible roles for CaMK, Ras/ERK, and SAPK pathways in the regulation of synaptic plasticity and neuronal growth. /. Neurosci. Res. 58 88-95,1999. 

Neonatal brain damage results in compensatory plasticity. Although, without intervention, axonal growth in the injured adult CNS is limited, the immature CNS responds to injury with a remarkable rerouting of neuronal pathways from undamaged areas to re-innervate... 

Benowitz, L. I. and Routtenberg, A. GAP-43 an intrinsic determinant of neuronal development and plasticity. Trends Neurosci. 20 84-91,1997. 

AA metabolites and PAF have initially been studied in terms of their roles in the inflammatory response, such as increased vascular permeability and the activation of and infiltration by inflammatory cells. It is now becoming apparent, however, that these bioactive lipids have significant neurobiological actions in ion channel functions, receptors, neurotransmitter release, synaptic plasticity and neuronal gene expression. 

So far, the best understood examples of genomic regulation of neuronal function stem from the actions of gonadal and adrenal steroids and thyroid hormone, and many of these actions are involved in the plasticity of behavior that results from hormonal secretion, such as changes in aggressive and reproductive behavior and... 

Matsumoto, A., Arai, Y., Urano, A. and Hyodo, S. Molecular basis of neuronal plasticity to gonadal steroids. Functional Neurol 10 59-76,1995. 

Robust decreases in the expression of the various proteasome subunits and ubiquitin-conjugating enzymes have been described in prefrontal cortex in schizophrenia. Neuronal ubiquitin and proteasomes play an important role in the assembly, function and plasticity of the synapse. Structural proteins including tubulin and a-spectrin also show decreased expression in prefrontal cortex. 

Addiction may result from inappropriate neuronal plasticity. As discussed in earlier sections of this chapter, drugs of abuse activate the same neuronal pathways as natural reinforcers. However, they do so in a strong and unregulated manner that is hypothesized to lead to abnormal engagement of learning and memory mechanisms, ultimately producing abnormal plasticity in neuronal circuits involved in motivation and decision-making. As a result, the addict becomes narrowly focused on compulsive, habitual behaviors associated with the addictive... 

McCallum SE, Parameswaran N, Bordia T, Fan H, McIntosh JM, Quik M (2006) Differential regulation of mesolimbic alpha 3/alpha 6 beta 2 and alpha 4 beta 2 nicotinic acetylchohne receptor sites, function after long-term oral nicotine to monkeys. J Pharmacol Exp Ther318 381-388 McKay BE, Placzek AN, Dani JA (2007) Regulation of synaptic transmission and plasticity by neuronal nicotinic acetylchohne receptors. Biochem Pharmacol 74 1120-1133 Mena-Segovia J, Winn P, Bolam JP (2008) Chohnergic modulation of midbrain dopaminergic systems. Brain Res Rev 58 265-271... 

Neuronal plasticity is an essential component of neuronal adaptability and there is increasing evidence that this is primarily a biochemical rather than a morphological process. The neuron is not a fixed entity in terms of the quantity of transmitter it releases, and transmitters which are co-localized in a nerve terminal may be differentially secreted under different conditions. This, together with the repeated firing of some neurons that appear to have "leaky" membranes, may underlie the rhythmicity of neuronal activity within the brain. 

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