Neurons electrical properties

The availability of genetically modified mice has advanced our understanding of several neurodegenerative processes. Cellular neurobiology experiments have informed us about mechanisms of neuronal dysfunction in AD and PD mouse models. For instance, recent studies have identified that synaptic transmission is one of the earliest events in the cognitive abnormalities that characterize AD and PD. The integration of this information with data-based circuits modeling, in which neuronal electrical properties, synaptic transmission parameters, and brain oscillations can now be evaluated and it has been recently addressed in PD and AD. 

The values of circuit elements can be readily calculated from the geometry of the neurons and the specific values of neuron electrical properties. Consider a cylindrical representation of a segment of... 

An excellent description of the discovery of neurotransmitters is provided by Valenstein (2005). Only the essentials of neurotransmitter metabolism are covered here for more detailed information the reader is directed to textbooks of neurochemistry, e.g. Siegel et al. (1994). For a more advanced coverage of the topics discussed here as well as information on the electrical properties of the neurons involved, the interested reader is directed to Steriade McCarley (2005). 

In this chapter we will focus on two basic principles of neurotransmission that may help to understand normal brain function on the one hand, and the current practice of clinical psychopharmacology on the other. First, the anatomic organization of neurotransmitter systems determines their behavioral affiliation. Second, neurotransmitter receptors modulate the electrical properties (via ion channels) or the biochemical properties (via second messenger systems) of neurons. We will then review these two basic principles for some of the neurotransmitter systems relevant to the practice of neuropsychopharmacology. 

Information is conveyed within individual neurons by electrical means - generating nerve impulses which can be recorded and displayed on an oscilloscope. In the twentieth century it was shown that information is conveyed between neurons by chemical means. When a nerve impulse (an action potential) travelling along the long extension or axon of a neuron arrives at a junction (or synapse) with another neuron, it causes the release of a neurotransmitter chemical from the presynaptic cell. This chemical affects the electrical properties of the postsynaptic neuron through its interaction with specialized receptor proteins embedded in the surface membrane of the postsynaptic cell. It has been shown that there are numerous kinds of neurotransmitter chemical which, depending on the specific... 

Electrical properties of neurons are measured by a variety of techniques. A review of these methodologies is beyond the purview of this chapter. However, it is important to note that changes in the electrochemical potential, ionic diffusion or current, and membrane conductance or permeability can be determined experimentally by intracellular and extracellular recording techniques that can be performed in vitro and in vivo. Hubbard et al. (1969) describe in detail a variety of intracellular techniques, such as voltage clamping, and extracellular techniques, such as sucrose-gap recording. 

Colmers, W.F. Bleakman, D. (1994) Effects of neuropeptide Y on the electrical properties of neurons. Trends Neurosci. 17, 373-379. 

A final word of warning concerning the identification of isolated cells. The neuronal nature of a dissociated cell can be confirmed by its electrical properties. Identifying the specific neuronal type, however, may prove more difficult and require the use of other techniques. For example, immunohistochemical methods were used to establish that the dorsal raphe neurons isolated in this laboratory were those that contain 5-HT (8),... 

ScHOLFiELD, C. N., 1978fl, Electrical properties of neurones in the olfactory cortex slice in vitro,]. Physiol. 275 535-546. 

More detailed analysis has been conducted regarding the influence of capsaicin on the electrical properties of various types of neurons. God-fraind et al. (1980), recording from rat and chick sensory neurons in culture, found that capsaicin prolongs the duration of action potentials evoked by intracellular current injection. Salt and Hill (1980) investigated the effect of microiontophoretically applied capsaicin on trigeminal nucleus caudalis and cerebellar neurons in the rat and cat. The predominant response in the trigeminal nucleus was one of excitation or potentiation of amino acid-induced excitation while cerebellar neurons were either inhibited or unaffected. 

More recently, successful reinnervation of carotid body glomus cells, changes in the electrical properties, pharmacological sensitivity, and reappearance of hypoxic chemosensitivity in petrosal ganglion cells have been reported when explants of both organs are cultured together (31-35). Petrosal ganghon neurons acutely disconnected from the carotid body and superfused in vitro are not excited by hypoxic hypoxia (36). 

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