6-cyano-7-nitroquinoxaline-2-3-dione and 2-aminoethoxydiphenyl-borate

Milk production in the nursing mother is induced by the hormone prolactin. Its release from the anterior pituitary is generally under tonic inhibition by neuroendocrine tuberoinfundibular dopamine (TIDA) neurons of the arcuate nucleus. Successful nursing, however, requires not only production but also ejection of breast milk. This function is supported by the hormone oxytocin. Here we explored the possibility that interaction between these functionally complementary hormones is mediated by TIDA neurons. First, whole-cell patch-clamp recordings were performed on prepubertal male rat hypothalamic slices, where TIDA neurons can be identified by a robust and rhythmic membrane potential oscillation. Oxytocin induced a switch of this rhythmic activity to tonic discharge through a depolarization involving direct actions on TIDA neurons. The depolarization is sensitive to blockade of the oxytocin receptor and is mediated by a voltage-dependent inward current. This inward current has two components: a canonical transient receptor potential-like conductance in the low-voltage range, and in the high-voltage range, a Ca(2+)-dependent component. Finally, whole-cell and loose-patch recordings were also performed on slices from virgin and lactating female rats to evaluate the relevance of these findings for nursing. In these preparations, oxytocin was found to excite TIDA neurons, identified by their expression of tyrosine hydroxylase. These findings suggest that oxytocin can modulate prolactin secretion by exciting TIDA neurons, and that this may serve as a feedforward inhibition of prolactin release.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Animals, Newborn; Arcuate Nucleus of Hypothalamus; Boron Compounds; Dopaminergic Neurons; Dose-Response Relationship, Drug; Electric Stimulation; Excitatory Amino Acid Antagonists; Female; In Vitro Techniques; Lactation; Oxytocics; Oxytocin; Rats; Rats, Sprague-Dawley; Sodium Channel Blockers; Tetrodotoxin; Tyrosine 3-Monooxygenase

Ca2+ and Na+ play important roles in neurons, such as in synaptic plasticity. Their concentrations in neurons change dynamically in response to synaptic inputs, but their kinetics have not been compared directly. Here, we show the mechanisms and dynamics of Ca2+ and Na+ transients by simultaneous monitoring in Purkinje cell dendrites in mouse cerebellar slices. High frequency parallel fibre stimulation (50 Hz, 3-50-times) depolarized Purkinje cells, and Ca2+ transients were observed at the anatomically expected sites. The magnitude of the Ca2+ transients increased linearly with increasing numbers of parallel fibre inputs. With 50 stimuli, Ca2+ transients lasted for seconds, and the peak [Ca2+] reached approximately 100 microm, which was much higher than that reported previously, although it was still confined to a part of the dendrite. In contrast, Na+ transients were sustained for tens of seconds and diffused away from the stimulated site. Pharmacological interventions revealed that Na+ influx through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and Ca2+ influx through P-type Ca channels were essential players, that AMPA receptors did not operate as a Ca2+ influx pathway and that Ca2+ release from intracellular stores through inositol trisphosphate receptors or ryanodine receptors did not contribute greatly to the large Ca2+ transients.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Anesthetics, Local; Animals; Animals, Newborn; Boron Compounds; Calcium; Calcium Channel Blockers; Cells, Cultured; Cerebellum; Dendrites; Dose-Response Relationship, Radiation; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Amino Acids; Female; Fluorescent Dyes; Glutamic Acid; Glycine; In Vitro Techniques; Iontophoresis; Male; Mice; omega-Conotoxin GVIA; Patch-Clamp Techniques; Purkinje Cells; Ryanodine; Sodium; Stimulation, Chemical; Tetrodotoxin; Time Factors