Contribution of Brain Processes to Tissue Loss After Spinal Cord Injury: Does a Pain-Induced Rise in Blood Pressure Fuel Hemorrhage?

Pain (nociceptive) input soon after spinal cord injury (SCI) expands the area of tissue loss (secondary injury) and impairs long-term recovery. Evidence suggests that nociceptive stimulation has this effect because it promotes acute hemorrhage. Disrupting communication with the brain blocks this effect. The current study examined whether rostral systems exacerbate tissue loss because pain input drives an increase in systolic blood pressure (BP) and flow that fuels blood infiltration. Rats received a moderate contusion injury to the lower thoracic (T12) spinal cord. Communication with rostral processes was disrupted by cutting the spinal cord 18 h later at T2. Noxious electrical stimulation (shock) applied to the tail (Experiment 1), or application of the irritant capsaicin to one hind paw (Experiment 2), increased hemorrhage at the site of injury. Shock, but not capsaicin, increased systolic BP and tail blood flow in sham-operated rats. Cutting communication with the brain blocked the shock-induced increase in systolic BP and tail blood flow. Experiment 3 examined the effect of artificially driving a rise in BP with norepinephrine (NE) in animals that received shock. Spinal transection attenuated hemorrhage in vehicle-treated rats. Treatment with NE drove a robust increase in BP and tail blood flow but did not increase the extent of hemorrhage. The results suggest pain input after SCI can engage rostral processes that fuel hemorrhage and drive sustained cardiovascular output. An increase in BP was not, however, necessary or sufficient to drive hemorrhage, implicating other brain-dependent processes.

Systemic application of the TRPV4 antagonist GSK2193874 induces tail vasodilation in a mouse model of thermoregulation

In humans the skin is a primary thermoregulatory organ, with vasodilation leading to rapid body cooling, whereas in rodents the tail performs an analogous function. TRPV4 is a widely distributed ion channel with both mechanical and thermosensitive properties. Previous studies have shown that TRPV4 can act as vasodilator by local action in blood vessels, and in this study we investigated whether there was a constitutive role for TRPV4 in mouse tail vascular tone and thermoregulation. We measured tail blood flow by pressure plethysmography in lightly sedated mice at a range of ambient temperatures, with and without intraperitoneal administration of the blood brain barrier crossing TRPV4 antagonist GSK2193874. We also measured heart rate and blood pressure with and without GSK2193874. As predicted, we found that tail blood flow increased with temperature. However, unexpectedly we found that the TRPV4 antagonist GSK2193874 increased tail blood flow at all temperatures. There were few detectable differences in heart rate, blood pressure or short-range heart rate variability. Since arterial TRPV4 activation is known to cause vasodilation that would increase tail blood flow, these data suggest that increases in tail blood flow resulting from the TRPV4 antagonist must arise from a site other than the blood vessels themselves, perhaps in central cardiovascular control centres such as the paraventricular nucleus of the hypothalamus.

Effect of six bis-THTT derivatives in the control of parasitaemia in two rodent malaria species

Malaria is a life-threatening disease caused by parasites of the genus Plasmodium and is transmitted to humans by the bite of female mosquitoes of the genus Anopheles. WHO has reported 219 million cases of malaria and 435,000 deaths were estimated in 2017. The anti-malarial treatment more frequently used is based on Chloroquine, which has been used for several decades. This prolonged application has caused the parasite to develop resistance to the use of the mentioned drug, so it becomes necessary to search for new treatments. In addition, some tetrahydro-(2H)-1,3,5-thiadiazine-2-thione (THTT) derivatives have been previously studied as possible trypanosomicides, obtaining satisfactory results in the treatment to Trypanosoma cruzi; Trichomonas vaginalis and T. b. rhodesiense, although no studies against malaria have been reported. In the present work, six bis-THTT derivatives were evaluated as potential anti-malarial drugs (JH1, JH2, JH3, JH4, JH5, and JH6) with BALB/c mice, which were inoculated with Plasmodium berghei ANKA strain and Plasmodium yoelii 17XL strain. The percentages of parasitemia were determined for each tested compound, which was assessed daily on smears from tail blood, stained with Giemsa’s reagent and observed under light microscopy as evidence of cure. Our results showed that JH2 and JH4 presented effective parasitemia control similar to chloroquine in P. berghei. Besides, JH5 and JH6 exhibited better results than Chloroquine with P. yoelii infection. In summary, four of the six bis-THTT derivatives tested, could be considerate as potential new drugs to infection malaria rodent control. Immune response essays should be realized in order to confirm our preliminary results.

Teknik Penanganan Kendali Hewan Sesuai Kaidah Kesejahteraan Hewan Meningkatkan Akurasi Pengukuran Profil Hemodinamika Tikus Laboratorium

Chronic discomfort potentially occurred during a hemodynamic measurements in a rat-tail blood pressure chamber due to the animal is restrained in restricted space for a long period – it took 10 repetitions each at approximately 1.5 minutes for a session of hemodynamic measure. Procedures related to the animal welfare methods are required to improve the accuracy of the measurement which would altered from the discomfort to comfort state of the animal. Welfare procedures are represented by humane handling and habituation of the subject (rats) to the operator and the hemodynamic apparatus. Seven rats were subjected in this study and measured for hemodynamic value in three times point: before (T0), after humane handling (T1) and after human handling and habituation to the measurement apparatus (T2), respectively. Six out of seven subjects showed a significant lowering deviation for all variables of hemodynamic measurements, and that deviation followed by a declining trend from T0 to T2, i.e T0>T1>T2. The results indicated that welfare-based approach would benefit the animals from feeling discomfort and yet improving the accuracy and quality of the outcomes.

Locus coeruleus noradrenergic innervation of the amygdala facilitates alerting-induced constriction of the rat tail artery

The amygdala, innervated by the noradrenergic locus coeruleus, processes salient environmental events. α2-adrenoceptor-stimulating drugs (clonidine-like agents) suppress the behavioral and physiological components of the response to salient events. Activation of sympathetic outflow to the cutaneous vascular bed is part of the physiological response to salience-mediated activation of the amygdala. We have determined whether acute systemic and intra-amygdala administration of clonidine, and chronic immunotoxin-mediated destruction of the noradrenergic innervation of the amygdala, impairs salience-related vasoconstrictor episodes in the tail artery of conscious freely moving Sprague-Dawley rats. After acute intraperitoneal injection of clonidine (10, 50, and 100 μg/kg), there was a dose-related decrease in the reduction in tail blood flow elicited by alerting stimuli, an effect prevented by prior administration of the α2-adrenergic blocking drug idazoxan (1 mg/kg ip or 75 nmol bilateral intra-amygdala). A dose-related decrease in alerting-induced tail artery vasoconstriction was also observed after bilateral intra-amygdala injection of clonidine (5, 10, and 20 nmol in 200 nl), an effect substantially prevented by prior bilateral intra-amygdala injection of idazoxan. Intra-amygdala injection of idazoxan by itself did not alter tail artery vasoconstriction elicited by alerting stimuli. Intra-amygdala injection of saporin coupled to antibodies to dopamine-β-hydroxylase (immunotoxin) destroyed the noradrenergic innervation of the amygdala and the parent noradrenergic neurons in the locus coeruleus. The reduction in tail blood flow elicited by standardized alerting stimuli was substantially reduced in immunotoxin-treated rats. Thus, inhibiting the release of noradrenaline within the amygdala reduces activation of the sympathetic outflow to the vascular beds elicited by salient events.

Effects of fasting on thermoregulatory processes and the daily oscillations in rats

To investigate the mechanism involved in the reduction of body core temperature (Tcore) during fasting in rats, which is selective in the light phase, we measured Tcore, surface temperature, and oxygen consumption rate in fed control animals and in fasted animals on day 3 of fasting and day 4 of recovery at an ambient temperature (Ta) of 23°C by biotelemetry, infrared thermography, and indirect calorimetry, respectively. On the fasting day, 1) Tcore in the light phase decreased ( P < 0.05) from the control; however, Tcore in the dark phase was unchanged, 2) tail temperature fell from the control ( P < 0.05, from 30.7 ± 0.1 to 23.9 ± 0.1°C in the dark phase and from 29.4 ± 0.1 to 25.2 ± 0.2°C in the light phase), 3) oxygen consumption rate decreased from the control ( P < 0.05, from 24.37 ± 1.06 to 16.24 ± 0.69 ml · min−1 · kg body wt−0.75 in the dark phase and from 18.91 ± 0.64 to 14.00 ± 0.41 ml · min−1 · kg body wt−0.75 in the light phase). All these values returned to the control levels on the recovery day. The results suggest that, in the fasting condition, Tcore in the dark phase was maintained by suppression of the heat loss mechanism, despite the reduction of metabolic heat production. In contrast, the response was weakened in the light phase, decreasing Tcore greatly. Moreover, the change in the regulation of tail blood flow was a likely mechanism to suppress heat loss.

Heat acclimation and hypohydration: involvement of central angiotensin II receptors in thermoregulation

This investigation attempted to confirm the involvement of central ANG II-ergic signals in thermoregulation. Experiments were conducted on rats undergoing short (STHA)- and long (LTHA)-term heat acclimation, with and without superimposed hypohydration. Vasodilatation (VTsh) and salivation (STsh) temperature thresholds, tail blood flow, and heat endurance were measured in conscious rats during heat stress (40°C) before and after losartan (Los), an ANG II AT1-selective receptor antagonist, administration either to the lateral ventricle or intravenously. Heat acclimation alone resulted in decreased VTsh. STsh decreased during STHA and resumed the preacclimation value, together with markedly increased heat endurance on LTHA. Hypohydration did not affect this biphasic response, although STsh was elevated in all groups. The enhanced heat endurance attained by LTHA was blunted. Neither Los treatment affected the nonacclimated rats. In the heat-acclimated, euhydrated rats, intracerebroventricular Los resulted in decreased VTsh, whereas intravenous Los resulted in elevated STsh. Both intracerebroventricular and intravenous Los led to markedly enhanced heat endurance of the LTHA hypohydrated rats. It is concluded that the LTHA group showed a loss of the benefits acquired by acclimation on hypohydration, whereas the STHA rats, which show an accelerated autonomic excitability in that phase, gained some benefit. It is suggested that ANG II modulates thermoregulation in conditions of chronic adjustments. Central ANG II signals may lead to VTsh upshift, whereas circumventricular structures, activated via circulating ANG II, decrease STsh. On hypohydration these responses seem to be desensitized.