Brain research
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The secretion of prolactin (PRL) from the anterior lobe (AL) of the pituitary gland is tonically inhibited by dopamine (DA) of hypothalamic origin. While ovarian steroids play a role in the regulation of the secretion of PRL, their effect on all three populations of hypothalamic neuroendocrine dopaminergic neurons is not fully understood. In this study we describe the effects of ovarian steroids on regulation of the release of DA from tuberoinfundibular dopaminergic (TIDA), tuberohypophyseal dopaminergic (THDA) and periventricular-hypophyseal dopaminergic (PHDA) neurons. ⋯ The concentration of DA in the AL diminished prior to the estrogen-induced increase of PRL. Administration of progesterone, in concert with estrogen, delayed the increase of PRL in serum and the decrease of DA in the AL, compared to estrogen-treated rats, by 4 h. These data suggest a major role for ovarian steroids in controlling increases in the secretion of PRL by not only stimulating PRL release from lactotrophs, but also by inhibiting the activity of all three populations of hypothalamic neuroendocrine DAergic neurons.
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'Pre-emptive' analgesia is a controversial issue in both the clinical and experimental literature on pain. This paper investigates the effect of chronic (4 days) administration of morphine or ketoprofen initiated pre- or post-operatively on behavioral indicators of visceral pain and referred hyperalgesia in an animal model of artificial ureteric calculosis. In the morphine experiment, female Sprague-Dawley rats were treated i.p. with saline or morphine sulphate (2.5 or 5 mg/kg/day) starting either 45 min before or 45 min after surgery (pentobarbital anesthesia) for stone implantation in the left ureter, until the 4th day after intervention. ⋯ Vocalization thresholds to electrical stimulation of the left oblique musculature were measured daily for 3 days pre- and 4 days post-operatively. Muscle hyperalgesia (post-operative decrease in threshold with respect to pre-stone implantation) was significantly reduced in extent and duration in ketoprofen with respect to saline-injected animals but no difference was found between the pre- and post-operative treatment. It is concluded that pre-emptive administration of morphine or ketoprofen has no advantage in reducing behavioral indicators of visceral pain and referred hyperalgesia in this animal model.
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The intergeniculate leaflet (IGL) modulates photic and nonphotic entrainment of circadian rhythms in nocturnal species, but nothing is known about its role in diurnal species. We investigated the significance of the IGL for circadian rhythm function in the diurnal rodent, Octodon degus, by determining the effects of bilateral electrolytic IGL lesions (IGL(X)) on: (i) photic entrainment; (ii) reentrainment rates to photic cues following a 6-h phase advance of the light-dark (LD) cycle; (iii) reentrainment rates to nonphotic social and photic cues following a 6-h phase advance of the LD cycle; and (iv) the circadian period (tau) of the activity rhythm in constant darkness (DD). ⋯ Thus, the IGL modulates two parameters of photic entrainment, but is not necessary for reentrainment to either nonphotic social or photic cues. Our results contribute to the growing comparative database on the neural mechanisms controlling circadian rhythms and indicate that the role of the IGL varies across species with no apparent relationship between diurnality-nocturnality and circadian function.
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Substance P (SP) is an important neuromediator in the spinal processing of nociceptive afferent information. Our previous study has shown that spinal (intrathecal, IT) application of SP produces thermal hyperalgesia that is mediated by activation of the G-protein coupled NK1 receptor. The activation of some classes of the G-protein coupled receptors is known to produce diacylglycerol with consequent activation of protein kinase C (PKC). ⋯ Moreover, intrathecal treatment with GF (0.73 nmol) attenuated the formalin paw injection-induced flinching, preferentially at the 2nd phase, that is known to be associated with the release of endogenous SP at the spinal cord. These data suggest that activation of spinal PKC is involved in the SP-mediated hyperalgesia. Thus, SP, which is released in the spinal cord subsequent to persistent stimulation of small sensory afferents after tissue injury, may contribute to spinal hyperexcitability and persistent pain by enhancement of PKC-mediated phosphorylation of target molecules such as NMDA receptors.
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Previous work in our laboratory has shown that Urocortin (Ucn), a peptide related to corticotropin releasing factor (CRF), injected into the basolateral nucleus of the amygdala (BLA) in male Wistar rats would result in an anxiogenic response as measured in the social interaction (SI) test. In addition, it was found that repeated injections of subthreshold doses of Ucn would 'prime' the animal's response. This 'priming' effect induces a sensitivity to sodium lactate infusions that results in a panic-like reaction. ⋯ Autoradiographic studies, in Ucn primed and sham-primed animals indicated no significant changes in [(125)I]-Sauvagine binding to CRF(1) and CRF(2) receptors in several brain regions. Thus, a 60 pmole dose of Asn blocks the effects of an acute injection of Ucn (100 pmoles), while only partially blocking the behavioral effects after repeated injections of subthreshold doses of Ucn (6 pmoles) are given. Furthermore, Asn has no effect on anxiogenic responses due to sodium lactate infusions in 'primed' rats