oxytocin 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

The olfactory epithelium (OE) is composed of olfactory sensory neurons (OSNs) and sustentacular cells; it lies in the nasal cavity where it is protected by a thin mucus layer. The finely regulated composition of this mucus provides OSN with a suitable ionic environment. To maintain the functional integrity of the epithelium despite permanent physical, chemical and microbial aggressions, both OSNs and surrounding sustentacular cells are continuously renewed from globose basal cells. Moreover, the sense of smell is involved in so numerous behaviours (feeding, reproduction, etc.) that it has to cross-talk with the endocrine and neuroendocrine systems. Thus, besides its sensory function, the olfactory epithelium is thought to undergo a lot of complex regulatory processes. We therefore studied the effects of various neuropeptides on primary cultures of Sprague-Dawley rat olfactory epithelium cells. We found that arginine-vasopressin (AVP) triggered a robust, dose-dependent calcium increase in these cells. The cell response was essentially ascribed to the V1a AVP receptor, whose presence was confirmed by RT-PCR and immunolabelling. In the culture, V1a but not V1b receptors were present, mainly localized in neurons. In the epithelium, both subtypes were found differentially distributed. V1a-R were localized mainly in globose basal cells and at the apical side of the epithelium, in the area of the dendritic knobs of OSNs. V1b-R were strongly associated with Bowman's gland cells and globose basal cells. These localizations suggested potential multifaceted roles of a hormone, AVP, in the olfactory epithelium.

Topics: Animals; Animals, Newborn; Arginine Vasopressin; Boron Compounds; Cadmium Chloride; Calcium; Calcium Channel Blockers; Cells, Cultured; Chelating Agents; Dose-Response Relationship, Drug; Drug Interactions; Egtazic Acid; Enzyme Inhibitors; Estrenes; Extracellular Space; Fura-2; Immunohistochemistry; Male; Neurons; Olfactory Mucosa; Oxytocin; Pyrrolidinones; Rats; Rats, Sprague-Dawley; Receptors, Oxytocin; Receptors, Vasopressin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Thapsigargin; Time Factors; Verapamil