Brain slices properties

The immediate and reversible actions of dopamine are a combination of modulations of individual ion channels. The major ion channels expressed in spiny projection neurons are summarized in Table 2. Current understanding of the properties of these channels is mostly based on whole cell recordings from isolated cells, which have been recently reviewed by Nichola et al. (2000). The role of these channels in whole cell behavior has been studied using intracellular recordings in brain slices or anaesthetized animals. Many of the important cellular properties of spiny projection neurons can be accounted for in terms of ion channel activations occurring at different membrane potentials. 

The development of in vitro brain slice and isolated neuron techniques has greatly facilitated detailed studies of the electrophysiology of a wide range of neuronal types in the adult and neonatal vertebrate central nervous system (CNS). Particularly advantageous are the greater mechanical stability that these preparations provide over in vivo models and the control allowed over the composition of the extracellular environment. In addition, the development of the patch-clamp technique has opened up the possibility of direct access to the intracellular environment via internal patch pipet solutions. In combination, these approaches have enabled detailed investigations of neuronal membrane properties, the cellular actions of neurotransmitters, and synaptic mechanisms. 

When the effect of nitric oxide donors on cGMP-accumulation is studied, one must take into account the rate of NO-release from the donor compound The diffusion rate of NO is quite high, because of the small size and hpophihcity of this molecule (45), Sodium nitroprusside (SNP) is often used an NO-donor. This compound is inexpensive, which is an important asset. However, the byproduct after NO-release, [Fe(CN)5], is not devoid of pharmacological activity (46) In addition, SNP is light sensitive, although in most cases this property should not rule out use of this compound. In 10-min incubations with brain slices, SNP and the NO-donors S-nitroso-acetyl-penicillamine and streptozotocin were equally effective in raising cGMP levels (unpublished). 

HT has also the properties of a neurotransmitter at some synapses in the CNS of mammals (1) 5-HT neurons are located in specific areas 5-HT is found in nerve endings in subcellular fractions identical with synaptosomes (2) all the biosynthetic equipment for making 5-HT is present in the brain along with the inactivating machinery (uptake and MAO) (3) 5-HT is released from spinal-cord neurons and brain slices by electrical stimulation (4) 5-HT or iproniazid when applied by microelectrophoretic technique to isolated neurons alters the firing pattern (5) drugs which alter the metabolism of 5-HT in the brain (reserpine, p-chlorophenylalanine) produce pronounced behavioural effects. 

Chen WR, Shepherd GM. 1997. Membrane and synaptic properties of mitral cells in slices of rat olfactory bulb. Brain Res 745 189-196. 

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