Temporal characterisation of pro- and anti-apoptotic mechanisms following diffuse traumatic brain injury in rats.

Few studies have characterised apoptosis in a brain injury model that causes a significant degree of diffuse axonal injury. Such characterisation is essential from a clinical viewpoint since diffuse axonal injury is a major component of human head injury. The present study therefore, examines the expression of active and proactive caspase-3, and the bax, bcl-2 and bcl-x members of the bcl-2 family, to characterise the temporal profile of apoptosis in a model of traumatic brain injury in rats that produces significant diffuse axonal injury. Pentobarbital anaesthetised male Sprague-Dawley rats were injured using the 2m impact-acceleration model of diffuse traumatic brain injury. After injury, diffuse trauma resulted in an increased bax expression followed by induction of caspase-3. The increase in caspase-3 was simultaneous with an increase in anti-apoptotic bcl-2 expression. Bcl-x levels were increased after induction of caspase-3 and the increased levels of bcl-x were sustained to the end of the 5-day observation period. Increased active caspase-3 expression was associated with the appearance of TUNEL positive cells. These cells were detected in different brain regions at different times, with some regions showing no apoptotic cells until 3 days after injury. No TUNEL positive cells were detected at 7 and 14 days after injury. DNA electrophoresis confirmed that DNA fragmentation was maximal at 3 days after injury. Increased active caspase-3 levels were also significantly correlated with increased bcl-2 levels (r=0.80; P<0.001) suggesting that the apoptotic cascade after diffuse traumatic brain injury is a carefully controlled cellular homeostatic response. Pharmacological manipulation of this balance may offer a therapeutic approach for preventing cell death and improving outcome after diffuse traumatic brain injury.

Estrogen-dependent regulation of neurokinin 3 receptor-mediated uterine contractility in the rat.

The receptors for neurokinin 1 (NK1-R), neurokinin 2 (NK2-R), and neurokinin 3 (NK3-R) are expressed and functionally active in the uterus, promoting strong contractions of the myometrium. Previously, we demonstrated that myometrial contractility activated by the NK-Rs is regulated by estrogen. In the current study, we furthered our investigations of the role of estrogen in the regulation of NK3-R-mediated myometrial contractility. Estrogen promotes both heterologous and homologous desensitization of NK3-R-mediated uterine contractility. In tissue obtained from estrogen-dominated rats (ovariectomized estrogen-treated rats and rats in estrus), the magnitude of uterine contractions decreased in response to consecutive additions of the NK3-R-selective agonist senktide. By addition of the fourth dose of agonist, the contractile response was routinely barely above baseline. In contrast, in tissue obtained from non-estrogen-dominated rats consecutive doses of senktide resulted in contractions of identical magnitude. The homologous desensitization was specific to the NK3-R, and the desensitization of the NK3-R-mediated response did not affect the magnitude or nature of uterine contractions in response to NK1-R or NK2-R activation. Furthermore, heterologous and homologous desensitization of NK3-R-mediated contractility is dependent upon the duration of exposure to estrogen. This complex mechanism appears to be important in intact tissue; capsaicin-mediated release of endogenous neuropeptides resulted in a desensitization of response to subsequent stimulation with senktide in estrogen-dominated uterine tissue.