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Fast neurotransmission in the rat medial preoptic nucleus.
Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
2005 (English)In: Brain Research, ISSN 0006-8993, Vol. 1040, no 1-2, 157-68 p.Article in journal (Refereed) Published
Abstract [en]

The functional properties of neurotransmission in the medial preoptic nucleus (MPN) were studied in a brain slice preparation from young male rats. The aims were to evaluate the thin slice preparation for studying evoked synaptic responses in MPN neurons, to characterize the fast responses triggered by activation of presynaptic nerve fibers in the MPN, and to identify the involved receptor types. Presynaptic stimulation within the MPN evoked postsynaptic voltage and current responses that were blocked by 200 microM Cd2+ or by 2.0 microM tetrodotoxin and were attributed to action potential-evoked transmitter release. The relation to stimulus strength and comparison with spontaneous synaptic currents suggested that in many cases only one presynaptic nerve fiber was excited by the stimulus. Furthermore, the transmission was probabilistic in nature, with frequent failures. Thus, response probability, most likely reflecting transmitter release probability, could be evaluated in the thin slice preparation. Evoked excitatory postsynaptic currents recorded under voltage-clamp conditions were, due to kinetics, I-V relation, and pharmacological properties, attributed to AMPA/kainate receptors and NMDA receptors, whereas inhibitory currents were attributed to GABAA receptors. No responses that could be attributed to glycine or other types of primary transmitters were detected. Although serotonin (5-HT) did not appear to function as a primary transmitter, glutamate- as well as GABA-mediated transmission was suppressed by 500 microM 5-HT, with a clear reduction in response probability observed. 5-HT also reduced the frequency, but not the amplitude, of spontaneous postsynaptic currents and was therefore ascribed a presynaptic site of action.

Place, publisher, year, edition, pages
2005. Vol. 1040, no 1-2, 157-68 p.
Keyword [en]
Animals, Dizocilpine Maleate/pharmacology, Preoptic Area/drug effects/*physiology, Quinoxalines/pharmacology, Rats, Rats; Sprague-Dawley, Synaptic Transmission/drug effects/*physiology
URN: urn:nbn:se:umu:diva-12595DOI: doi:10.1016/j.brainres.2005.01.094PubMedID: 15804437OAI: diva2:152266
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2011-01-12Bibliographically approved
In thesis
1. Neurotransmission and functional synaptic plasticity in the rat medial preoptic nucleus
Open this publication in new window or tab >>Neurotransmission and functional synaptic plasticity in the rat medial preoptic nucleus
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Brain function implies complex information processing in neuronal circuits, critically dependent on the molecular machinery that enables signal transmission across synaptic contacts between neurons. The types of ion channels and receptors in the neuronal membranes vary with neuron types and brain regions and determine whether neuronal responses will be excitatory or inhibitory and often allow for functional synaptic plasticity which is thought to be the basis for much of the adaptability of the nervous system and for our ability to learn and store memories. The present thesis is a study of synaptic transmission in the medial preoptic nucleus (MPN), a regulatory center for several homeostatic functions but with most clearly established roles in reproductive behaviour. The latter behaviour typically shows several distinct phases with dramatically varying neuronal impulse activity and is also subject to experience-dependent modifications. It seems likely that the synapses in the MPN contribute to the behaviour by means of activity-dependent functional plasticity. Synaptic transmission in the MPN, however, has not been extensively studied and is not well understood. The present work was initiated to clarify the synaptic properties in the MPN. The aim was to achieve a better understanding of the functional properties of the MPN, but also to obtain information on the functional roles of ion channel types for neurotransmission and its plastic properties in general. The studies were carried out using a brain slice preparation from rat as well as acutely isolated neurons with adhering nerve terminals. Presynaptic nerve fibres were stimulated electrically or, in a few cases, by raised external K+ concentration, and postsynaptic responses were recorded by tight-seal perforated-patch techniques, often combined with voltage-clamp control of the post-synaptic membrane potential. Glutamate receptors of α-amino-3-hydroxy-5-methyl-4-izoxazole propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) types were identified as mediating the main excitatory synaptic signals and γ-aminobutyric acid (GABA)A receptors as mediating the main inhibitory signals. Both types of signals were suppressed by serotonin. The efficacy of AMPA-receptor-mediated transmission displayed several types of short-term plasticity, including paired-pulse potentiation and paired-pulse depression, depending on the stimulus rate and pattern. The observed plasticity was attributed to mainly presynaptic mechanisms. To clarify some of the presynaptic factors controlling synaptic efficacy, the role of presynaptic L-type Ca2+ channels, usually assumed not to directly control transmitter release, was investigated. The analysis showed that (i) L-type channels are present in GABA-containing presynaptic terminals on MPN neurons, (ii) that these channels provide a means for differential control of spontaneous and impulse-evoked GABA release and (iii) that this differential control is prominent during short-term synaptic plasticity. A model where Ca2+ influx through L-type channels may lead to reduced GABA release via effects on Ca2+-activated K+ channels, membrane potential and other Ca2+-channel types explains the observed findings. In addition, massive Ca2+ influx through L-type channels during high-frequency stimulation may contribute to increased GABA release during post-tetanic potentiation. In conclusion, the findings obtained in the present study indicate that complex neurotransmission mechanisms and different forms of synaptic plasticity contribute to the specific functional properties of the MPN.

Place, publisher, year, edition, pages
Umeå: IMB, 2009. 57 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1286
medial preoptic nucleus, synaptic plasticity, GABA, glutamate, L-type Ca2+ channel
National Category
Research subject
urn:nbn:se:umu:diva-25874 (URN)978-91-7264-843-2 (ISBN)
Fysiologi, 901 87, Umeå
Public defence
2009-09-30, Hörsal KB3A9, Umeå Universitet, Umeå, 10:00 (English)
Available from: 2009-09-10 Created: 2009-09-08 Last updated: 2010-01-18Bibliographically approved

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