The ultimate goal of this research is to investigate mechanisms of action of dopamine and acetylcholine in the neostriatum. This research may have important clinical ramifications since dysfunction of these neurotransmitter systems is implicated in the pathophysiology of Parkinson's disease, Huntington's chorea and tardive dyskinesia. Previous electrophysiologic studies used voltage recording which cannot directly measure neuronal conductance. Also, most past studies recorded from unidentified neuronal type. Recent studies show that the mammalian striatum consists of a neuronal patch and matrix system, identified by a range of immunohistochemical markers. Retrograde labelling studies also show that patch and matrix neurons have different afferent and efferent connections. We propose to use single electrode voltage clamp to record ionic currents and characterize receptor-mediated responses on identified patch and matrix neurons. Brain slices will be used in vitro. Intrinsic membrane properties will be studied, and intrastriatal as well as cortical stimulation will be used to evoked synaptic activity. Drugs (receptor agonists and antagonists) will be added to the superfusing solution and their effects measured at steady-state concentrations. Schild plots will be constructed and dissociation constants will be estimated. Lucifer yellow will be injected intracellularly from the micropipette using iontophoresis. Slices will be subsequently fixed and immunohistochemically stained for calcium binding protein to identify the matrix. Neurons filled with Lucifer yellow will be identified and their presence in stained matrix or unstained patch will be noted. In further experiments, striatonigral projection neurons will be identified by prior injection of rhodamine- labelled microspheres into the zona compacta of the substantia nigra. Back-filled neurons will be identified by rhodamine fluorescence at the time of intracellular recording. Using these techniques we will investigate receptor-mediated effects of dopamine and acetylcholine and test the hypothesis that these neurotransmitters have opposite effects on conductances in identified striatal neurons. We will also study post- synaptic current generated by dopamine released synaptically in response to intrastriatal stimulation. Pre-synaptic effects of dopamine on neurotransmission in the corticostriatal pathway will also be studied.
| Grenhoff, J; North, R A; Johnson, S W (1995) Alpha 1-adrenergic effects on dopamine neurons recorded intracellularly in the rat midbrain slice. Eur J Neurosci 7:1707-13 |
| Seutin, V; Johnson, S W; North, R A (1994) Effect of dopamine and baclofen on N-methyl-D-aspartate-induced burst firing in rat ventral tegmental neurons. Neuroscience 58:201-6 |
| Seutin, V; Johnson, S W; North, R A (1993) Apamin increases NMDA-induced burst-firing of rat mesencephalic dopamine neurons. Brain Res 630:341-4 |
| Johnson, S W; North, R A (1992) Opioids excite dopamine neurons by hyperpolarization of local interneurons. J Neurosci 12:483-8 |
| Johnson, S W; North, R A (1992) Two types of neurone in the rat ventral tegmental area and their synaptic inputs. J Physiol 450:455-68 |
| Johnson, S W; Mercuri, N B; North, R A (1992) 5-hydroxytryptamine1B receptors block the GABAB synaptic potential in rat dopamine neurons. J Neurosci 12:2000-6 |
