Currents evoked by GABA and glycine in acutely dissociated neurons from the rat medial preoptic nucleus.
ABSTRACT The responses of acutely dissociated medial preoptic neurons to application of GABA, and glycine were studied using the perforated-patch whole-cell recording technique under voltage-clamp conditions. GABA, at a concentration of 1 mM, evoked outward currents in all cells (n = 33) when studied at potentials positive to -80 mV. The I-V relation was roughly linear. The currents evoked by GABA were partially blocked by 25-75 microM picrotoxin and were also partially or completely blocked by 100-200 microM bicuculline. Glycine, at a concentration of 1 mM, did also evoke outward currents in all cells (n = 12) when studied at potentials positive to -75 mV. The I-V relation was roughly linear. The currents evoked by glycine were largely blocked by 1 microM strychnine. In conclusion, the present work demonstrates that neurons from the medial preoptic nucleus of rat directly respond to the inhibitory transmitters GABA and glycine with currents that can be attributed to GABAA receptors and glycine receptors respectively.
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ABSTRACT: Pulsatile release of gonadotropin-releasing hormone (GnRH) is requisite for fertility. The rhythms generated by GnRH neurons, however, are not well characterized, nor are the interaction among GnRH neurons that result in secretory patterns. To describe the rhythmic output of GnRH neurons at the individual cell and network levels, extracellular recordings of firing patterns were made using two model systems. The first series of experiments utilized immortalized GnRH neurons (GT1 cells) grown onto multi-micro electrode arrays to observe artificial network activity among multiple cells. Results indicated that GT1-7 cells at several different locations within a culture displayed low frequency rhythms. When combined, these low frequency component rhythms produced an overall pattern that was consistent with previous reports of secretory pulse intervals, suggesting network interactions produce appropriate secretory patterns. For the second set of experiments, targeted extracellular recordings were made from green-fluorescent-protein-expressing GnRH neurons in coronal brain slices. Results demonstrated that GnRH neurons in display low frequency rhythms consistent with secretory patterns of the reproductive neuroendocrine axis in rodents. Blockade of the dominant ionotropic neurotransmitters gamma-aminobutyric acid and glutamate did not change patterns in neurons recorded from ovariectomized (OVX) mice. Blockade in OVX plus estradiol implanted mice, however, resulted in OVX-like patterns in 50% of GnRH neurons; these were located in the medial preoptic area. This suggests that estradiol effects can be conveyed to GnRH neurons by transmitters that gate ionotropic receptors. In addition, Fourier spectral analysis identified high frequency burst firing rhythms and low frequency rhythms in the range of secretory intervals. Peaks and nadirs in the low frequency rhythm formed from changes in the interval between bursts of action currents (high frequency rhythm), thus demonstrating a possible link between these rhythms. Collectively, these results suggest at least three types of rhythms in GnRH neurons: (1) a low frequency rhythm occurring at secretory intervals, (2) a high frequency burst firing rhythm, and (3) a rhythm that arises from the integrated activity of many GnRH neurons. The role of each of these rhythms in generating secretory patterns in GnRH neurons is discussed, and a model of rhythm interactions is presented.01/2003, Degree: Ph.D., Supervisor: Suzanne M. Moenter
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ABSTRACT: Maintenance of osmotic pressure is a primary regulatory process essential for normal cell function. The osmolarity of extracellular fluids is regulated by modifying the intake and excretion of salts and water. A major component of this regulatory process is the neuroendocrine hypothalamo-neurohypophysial system, which consists of neurons located in the paraventricular and supraoptic nuclei. These neurons synthesize the neurohormones vasopressin and oxytocin and release them in the blood circulation. We here review the mechanisms responsible for the osmoregulation of the activity of these neurons. Notably, the osmosensitivity of the supraoptic nucleus is described including the recent data that suggests an important participation of taurine in the transmission of the osmotic information. Taurine is an amino acid mainly known for its involvement in cell volume regulation, as it is one of the major inorganic osmolytes used by cells to compensate for changes in extracellular osmolarity. In the supraoptic nucleus, taurine is highly concentrated in astrocytes, and released in an osmodependent manner through volume-sensitive anion channels. Via its agonist action on neuronal glycine receptors, taurine is likely to contribute to the inhibition of neuronal activity induced by hypotonic stimuli. This inhibitory influence would complement the intrinsic osmosensitivity of supraoptic neurons, mediated by excitatory mechanoreceptors activated under hypertonic conditions. These observations extend the role of taurine from the regulation of cell volume to that of the whole body fluid balance. They also point to a new role of supraoptic glial cells as active components in a neuroendocrine regulatory loop.Progress in Neurobiology 11/2000; · 10.30 Impact Factor
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ABSTRACT: The preoptic area regulates body temperature. GABA-ergic terminals and receptors are present in this area. Local microinjection studies have shown that GABA, its agonist, and its antagonist in this area may modulate body temperature. However, there are warm and cold sensitive neurons, and they are known to be affected by local and peripheral temperatures. In order to understand the mechanism of action of GABA in temperature regulation at the cellular level it was necessary to study the effect of GABA on individual thermosensitive neurons in in vivo preparations. Hence, in this study the responses of preoptic area thermosensitive and insensitive neurons to microiontophoretic application of picrotoxin, a GABA-A antagonist, were studied in anaesthetized rats. It was observed that a majority of both the thermosensitive and insensitive neurons were affected by microiontophoretic application of picrotoxin. Although almost an equal number of cold and warm sensitive neurons were affected, a majority of the cold sensitive neurons were excited, while a majority of the warm sensitive neurons were inhibited by picrotoxin. The results suggested that in normal conditions GABA acts through GABA-A receptor in modulating the spontaneous activity of thermosensitive neurons in the preoptic area. Furthermore, the results of the present study taken together with other reports suggest that normally GABA exerts a direct inhibitory action on the cold sensitive neurons, while it acts on presynaptic heteroreceptors, possibly on norepinephrinergic afferent input terminals on the warm sensitive neurons, for mediating its action. © 2001 John Wiley & Sons, Inc. J Neurobiol 48: 291–300, 2001Journal of Neurobiology 09/2001; 48(4):291 - 300. · 3.05 Impact Factor