Brain Tissue Specific Gravity Research Articles

Effects of Aquaporin-4 on edema formation following intracerebral hemorrhage

Objective Intracerebral hemorrhage (ICH) constitutes 10% to 15% of all strokes and is associated with high morbidity and mortality. To date, little is known about the role of AQP4 (Aquaporin-4), which is abundantly expressed in pericapillary astrocyte foot processes and in edema formation after intracerebral hemorrhage. The purpose of this study was to examine the role of AQP4 in edema formation after ICH by using AQP4 −/− mice. Methods ICH was induced by microinjecting 5 µl autologous whole blood into the striatum of AQP4 +/+ and AQP4 −/− mice. We compared neurological deficits, brain edema contents of whole hemorrhagic ipsilateral hemisphere, specific gravity of brain tissue surrounding hematoma, Evans blue leakage and ultrastructure of brain microvessels between AQP4 +/+ and AQP4 −/− mice following ICH. Histological changes were also detected with Nissl's staining and TUNEL staining. Results Our experiments showed a significant increase of AQP4 expression following ICH in AQP4 +/+ mice. AQP4 deletion aggravated neurological deficits and brain edema contents of whole hemorrhagic ipsilateral hemisphere. Besides, it also reduced the specific gravity of brain tissue surrounding hematoma. Moreover, it enhanced Evans blue leakage and ultrastructure of brain microvessel damage. Histology also showed less Nissl's staining and more TUNEL staining in AQP4 −/− mice following ICH. Conclusions These results suggest that AQP4 deletion increases ICH damage, including edema formation, blood–brain barrier damage and neuronal death/TUNEL-positive cells. Further studies on the protective role of activated AQP4 expression following ICH may provide useful therapeutic target for ICH-induced brain injury.

Specific gravity of brain tissue during maturation.

The water content of the brain is closely related to the maturation and degree of myelination. In control rats studied from the day of birth to the age of 26 days, brain specific gravity increased in parallel to the decrease in water content (r = 1.00). Rats treated with 6-hydroxydopamine (6-OHDA) 100 microns/g daily during the first 2 or 4 days of life had significantly lower specific gravity than controls in all parts of the brain at the age of 2 weeks. With the smaller dose 6-OHDA, the specific gravity at the age of 1 month was lower than in controls in the occipital cortex; with the larger dose it was significantly reduced in all cortical regions as well as in the pons and the diencephalon. 2-months old 6-OHDA treated rats did not differ from controls. Rats pretreated with desipramine 30 min before administration of 6-OHDA to prevent uptake of 6-OHDA into catecholaminergic neurons did not differ from controls. Neonatal 6-OHDA treatment affects predominantly noradrenergic terminals in the cerebral cortex with cell bodies in the locus coeruleus. The present results are consistent with the hypothesis that these neurons have a trophic influence on the brain development during the postnatal maturation.

Effect of magnesium sulfate administration on blood–brain barrier in a rat model of intraperitoneal sepsis: a randomized controlled experimental study

IntroductionPermeability changes in the blood–brain barrier (BBB) and their possible contribution to brain edema formation have a crucial role in the pathophysiology of septic encephalopathy. Magnesium sulfate has been shown to have a protective effect on BBB integrity in multiple experimental models. In this study we determine whether magnesium sulfate administration could have any protective effects on BBB derangement in a rat model of sepsis.MethodsThis randomized controlled experimental study was performed on adult male Sprague–Dawley rats. Intraperitoneal sepsis was induced by using the infected fibrin–thrombin clot model. To examine the effect of magnesium in septic and sham-operated rats, a dose of 750 μmol/kg magnesium sulfate was given intramuscularly immediately after surgery. Control groups for both infected and sham-operated rats were injected with equal volume of saline. Those rats surviving for 24 hours were anesthetized and decapitated for the investigation of brain tissue specific gravity and BBB integrity by the spectrophotometric assay of Evans blue dye extravasations. Another set of experiments was performed for hemodynamic measurements and plasma magnesium level analysis. Rats were allocated into four parallel groups undergoing identical procedures.ResultsSepsis significantly increased BBB permeability to Evans blue. The dye content of each hemisphere was significantly lower in the magnesium-treated septic rats (left hemisphere, 0.00218 ± 0.0005; right hemisphere, 0.00199 ± 0.0007 [all results are means ± standard deviation]) than in control septic animals (left hemisphere, 0.00466 ± 0.0002; right hemisphere, 0.00641 ± 0.0003). In septic animals treated with magnesium sulfate, specific gravity was higher (left hemisphere, 1.0438 ± 0.0007; right hemisphere, 1.0439 ± 0.0004) than in the untreated septic animals (left hemisphere, 1.0429 ± 0.0009; right hemisphere, 1.0424 ± 0.0012), indicating less edema formation with the administration of magnesium. A significant decrease in plasma magnesium levels was observed 24 hours after the induction of sepsis. The dose of magnesium that we used maintained the baseline plasma magnesium levels in magnesium-treated septic rats.ConclusionsMagnesium administration attenuated the increased BBB permeability defect and caused a reduction in brain edema formation in our rat model of intraperitoneal sepsis.

Effects of magnesium administration on brain edema and blood-brain barrier breakdown after experimental traumatic brain injury in rats.

In this study, we examined the effects of magnesium sulfate administration on brain edema and blood-brain barrier breakdown after experimental traumatic brain injury in rats. Seventy-one adult male Sprague-Dawley rats were anesthetized, and experimental closed head trauma was induced by allowing a 450-g weight to fall from a 2-m height onto a metallic disk fixed to the intact skull. Sixty-eight surviving rats were randomly assigned to receive an intraperitoneal bolus of either 750 micromol/kg magnesium sulfate (group 4; n = 30) or 1 mL of saline (group 2; n = 30) 30 minutes after induction of traumatic brain injury; 39 nontraumatized animals received saline (group 1; n = 21) or magnesium sulfate (group 3; n = 18) with an identical protocol of administration. Brain water content and brain tissue specific gravity, as indicators of brain edema, were measured 24 hours after traumatic brain injury. Blood-brain barrier integrity was evaluated quantitatively 24 hours after injury by spectrophotometric assay of Evans blue dye extravasations. In the magnesium-treated injured group, brain water content was significantly reduced (left hemisphere: group 2, 83.2 +/- 0.8; group 4, 78.4 +/- 0.7 [P <.05]; right hemisphere: group 2, 83.1 +/- 0.7; group 4, 78.4 +/- 0.5. [P <.05]) and brain tissue specific gravity was significantly increased (left hemisphere: group 2, 1.0391 +/- 0.0008; group 4, 1.0437 +/- 0.001 [P <.05]; right hemisphere, group 2, 1.0384 +/- 0.001; group 4, 1.0442 +/- 0.005 [P <.05]) compared with the saline-treated injured group. Evans blue dye content in the brain tissue was significantly decreased in the magnesium-treated injured group (left hemisphere: group 2, 0.0204 +/- 0.03; group 4, 0.0013 +/- 0.0002 [P <.05]; right hemisphere: group 2, 0.0064 +/- 0.0009; group 4, 0.0013 +/- 0.0003 [P <.05]) compared with the saline-treated injured group. The findings of the present study support that beneficial effects of magnesium sulfate exist after severe traumatic brain injury in rats. These results also indicate that a blood-brain barrier permeability defect occurs after this model of diffuse traumatic brain injury, and magnesium seems to attenuate this defect.

Treatments to Support Blood Pressure Increases Bleeding and/or Decreases Survival in a Rat Model of Closed Head Trauma Combined with Uncontrolled Hemorrhage

Hemorrhagic hypotension may aggravate the detrimental effects of head trauma on neurologic outcome. Our study examined whether using phenylephrine or large volumes of saline IV to increase mean arterial blood pressure (MAP) to 70, 80, or 90 mm Hg during the combination of head trauma and uncontrolled hemorrhage would improve neurologic outcome. Rats were assigned to one of 17 groups. In Groups 1–5, the variables were head trauma (yes/no), hemorrhage (yes/no), 0 or 3 mL saline per milliliter of blood lost, and no target MAP. In Groups 6–11, hemorrhage was or was not combined with head trauma, and large volumes of saline were given IV to achieve target MAPs of 70, 80, or 90 mm Hg. Groups 12–17 were similar to Groups 6–11 except that phenylephrine was used rather than saline to achieve target MAPs. Saline increased blood loss at 2 h to approximately 16 and 25 mL at a MAP of 80 and 90 mm Hg respectively, increased (worsened) the neurodeficit score but not cerebral edema at 24 h, and decreased survival rate at 2 and 24 h. Because phenylephrine was fatal for 62 of 63 rats, group mean values for blood loss, neurodeficit score, and brain tissue specific gravity could not be calculated. We conclude that supporting MAP with either phenylephrine or large volumes of saline worsened the neurodeficit score and/or survival and did not affect cerebral edema formation in our rat model of head trauma combined with hemorrhage. Implications The results of this study indicate that maintaining mean arterial blood pressure at 70, 80, or 90 mm Hg with either phenylephrine or large volumes of saline worsened the neurodeficit score and/or survival and did not affect cerebral edema formation in our rat model of head trauma combined with hemorrhage.

Treatments to support blood pressure increases bleeding and/or decreases survival in a rat model of closed head trauma combined with uncontrolled hemorrhage.

Hemorrhagic hypotension may aggravate the detrimental effects of head trauma on neurologic outcome. Our study examined whether using phenylephrine or large volumes of saline IV to increase mean arterial blood pressure (MAP) to 70, 80, or 90 mm Hg during the combination of head trauma and uncontrolled hemorrhage would improve neurologic outcome. Rats were assigned to one of 17 groups. In Groups 1-5, the variables were head trauma (yes/no), hemorrhage (yes/no), 0 or 3 mL saline per milliliter of blood lost, and no target MAP. In Groups 6-11, hemorrhage was or was not combined with head trauma, and large volumes of saline were given IV to achieve target MAPs of 70, 80, or 90 mm Hg. Groups 12-17 were similar to Groups 6-11 except that phenylephrine was used rather than saline to achieve target MAPs. Saline increased blood loss at 2 h to approximately 16 and 25 mL at a MAP of 80 and 90 mm Hg respectively, increased (worsened) the neurodeficit score but not cerebral edema at 24 h, and decreased survival rate at 2 and 24 h. Because phenylephrine was fatal for 62 of 63 rats, group mean values for blood loss, neurodeficit score, and brain tissue specific gravity could not be calculated. We conclude that supporting MAP with either phenylephrine or large volumes of saline worsened the neurodeficit score and/or survival and did not affect cerebral edema formation in our rat model of head trauma combined with hemorrhage. The results of this study indicate that maintaining mean arterial blood pressure at 70, 80, or 90 mm Hg with either phenylephrine or large volumes of saline worsened the neurodeficit score and/or survival and did not affect cerebral edema formation in our rat model of head trauma combined with hemorrhage.

Protective effect of the N-methyl-D-aspartate receptor antagonists, MK-801 and CPP on cold-induced brain oedema.

Cold injury model in rat was used to determine the effect of treatment with the competitive NMDA antagonists CPP and the non-competitive NMDA antagonist MK-801 in cerebral oedema. MK-801 was applied in doses of 1 mg/kg and CPP of 10 mg/kg, 15 min. after injury. Control animals received 1 ml saline at the same time interval after injury. Tissue samples from the core and periphery of the lesion of the injured hemisphere and from the symmetrical location of the undamaged contralateral hemisphere were removed 24 hours after injury. Blood brain barrier permeability, brain water content and tissue specific gravity values were determined. MK-801 was found beneficial for reducing the oedema and restore the blood brain barrier permeability at the penumbral zone of the lesion, whereas both MK-801 and CPP were found ineffective for prevention of oedema accumulation at the core of the lesion.

Phenylephrine-induced hypertension does not improve outcome after closed head trauma in rats.

Phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) is reported to increase cerebral perfusion pressure and collateral flow to ischemic areas of the brain in a rat model of focal cerebral ischemia. In the present study, we examined whether phenylephrine-induced hypertension of similar magnitude and duration was beneficial in a rat model of closed head trauma (CHT). Forty-eight rats were randomized into four experimental conditions: CHT at time 0 min (yes/no), plus phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) at 65 min (yes/no). CHT was delivered using a weight-drop device (0.5 J). Outcome measures were neurological severity score (NSS) at 1, 4, and 24 h, and brain tissue specific gravity (microgravimetry) and injury volume (2,3,5-triphenyltetrazoium chloride) at 24 h. After CHT, NSS at 24 h (median +/- range) and brain tissue specific gravity (mean +/- SD, injured hemisphere) were 7+/-2 and 1.033+/-0.007 without phenylephrine and 8+/-2 and 1.035+/-0.005 with phenylephrine (P = 0.43), respectively. Tissue injury volume (mean +/- SD) was 335+/-92 mm3 without phenylephrine and 357+/-154 mm3 with phenylephrine (P > 0.62). The results of our study indicate that postinjury treatment with 15 min of phenylephrine-induced hypertension does not attenuate brain edema, reduce tissue injury volume, or improve neurological outcome after CHT in rats. Phenylephrine-induced hypertension is reported to increase cerebral perfusion pressure and blood flow in a rat model of focal cerebral ischemia. In our study, phenylephrine-induced hypertension did not decrease brain edema or tissue injury volume or improve neurological outcome in a rat model of closed head trauma.

Phenylephrine-Induced Hypertension Does Not Improve Outcome After Closed Head Trauma in Rats

Phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) is reported to increase cerebral perfusion pressure and collateral flow to ischemic areas of the brain in a rat model of focal cerebral ischemia. In the present study, we examined whether phenylephrine-induced hypertension of similar magnitude and duration was beneficial in a rat model of closed head trauma (CHT). Forty-eight rats were randomized into four experimental conditions: CHT at time 0 min (yes/no), plus phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) at 65 min (yes/no). CHT was delivered using a weight-drop device (0.5 J). Outcome measures were neurological severity score (NSS) at 1, 4, and 24 h, and brain tissue specific gravity (microgravimetry) and injury volume (2,3,5-triphenyltetrazoium chloride) at 24 h. After CHT, NSS at 24 h (median +/- range) and brain tissue specific gravity (mean +/- SD, injured hemisphere) were 7 +/- 2 and 1.033 +/- 0.007 without phenylephrine and 8 +/- 2 and 1.035 +/- 0.005 with phenylephrine (P = 0.43), respectively. Tissue injury volume (mean +/- SD) was 335 +/- 92 mm3 without phenylephrine and 357 +/- 154 mm3 with phenylephrine (P > 0.62). The results of our study indicate that postinjury treatment with 15 min of phenylephrine-induced hypertension does not attenuate brain edema, reduce tissue injury volume, or improve neurological outcome after CHT in rats. Implications: Phenylephrine-induced hypertension is reported to increase cerebral perfusion pressure and blood flow in a rat model of focal cerebral ischemia. In our study, phenylephrine-induced hypertension did not decrease brain edema or tissue injury volume or improve neurological outcome in a rat model of closed head trauma. (Anesth Analg 1998;87:574-8)

0.45% saline and 5% dextrose in water, but not 0.9% saline or 5% dextrose in 0.9% saline, worsen brain edema two hours after closed head trauma in rats.

In this study, we examined the effect of four i.v. fluids (250 mL/kg) on blood glucose and osmolality and brain tissue specific gravity after closed head trauma (CHT) in rats. CHT was delivered at Time 0; blood was sampled at 60 min; fluid infusion began at 75 min and ended at 105 min. Blood was again sampled at 105 and 120 min, and brain tissue specific gravity was determined at 120 min. Five groups (one control and four fluid-treated groups) received CHT, and five other groups (one control and four fluid-treated) did not (n = 9 in each group). 0.45% saline (1/2 NS) and 5% dextrose in water (D5W) accentuated the decrease of brain tissue specific gravity (1.0366 +/- 0.0025 and 1.0368 +/- 0.0028, respectively; mean +/- SD) caused by CHT (1.0395 +/- 0.0036), but 5% dextrose in 0.9% saline (D5NS) and 0.9% saline (NS) did not (1.0431 +/- 0.0042 and 1.0389 +/- 0.0049, respectively). In addition, 1/2 NS decreased blood osmolality (248 +/- 6 mOsm/L), D5W increased blood glucose (1095 +/- 173 mg/dL), D5NS increased blood osmolality (350 +/- 5 mOsm/L) and glucose (1695 +/- 76 mg/dL), and NS caused no significant change. We conclude that administering hypoosmolar i.v. fluids after CHT causes a significant worsening of cerebral edema 2 h after CHT. We previously reported worse neurological outcome and/or mortality after closed head trauma in rats when 5% dextrose in water or 0.45% saline was given i.v. compared with 0.9% saline or 5% dextrose in 0.9% saline. The present results and our previous findings indicate that worsening of outcome after closed head trauma in rats may be caused more by edema formation than by hyperglycemia.

Effect of magnesium given 1 hour after head trauma on brain edema and neurological outcome.

Excitatory amino acids (EAA), mainly glutamate and aspartate, are released in excessive amounts from terminals of ischemic or traumatically injured neurons. These excessive levels of EAAs initiate a cascade of events believed to lead to secondary delayed damage to the surrounding brain. The N-methyl-D-aspartate receptor antagonists MK-801 and ketamine are reported to suppress excessive EAA release and to attenuate the development of focal brain edema following neuronal injury. Magnesium is also reported to work at the postsynaptic receptor to reduce the neurotoxic effect of glutamate. The present study was undertaken to examine the effect of postinjury treatment with Mg++ on brain edema and neurological outcome after traumatic brain injury. Sixty-nine rats that survived halothane anesthesia and closed head trauma (CHT) were randomly assigned to one of seven experimental groups: sham, CHT, and CHT with administration of Mg++ 1 hour postinjury. At 48 hours, brain tissue Mg++ concentration (calculated from optical density using a standard curve) was significantly increased compared to baseline levels (10.06 +/- 2.44 mg/g vs. 6.83 +/- 0.81 mg/g, p < 0.01 calculated by one-way analysis of variance). Also at 48 hours postinjury, brain tissue specific gravity in the contused hemisphere of Mg(++)-treated rats was significantly greater than that in the contused hemisphere of untreated rats, indicating attenuation of brain edema formation by Mg++. The neurological severity score (NSS) of rats treated with Mg++ improved significantly at both 18 and 48 hours, compared to baseline values obtained 1 hour after CHT but prior to administration of Mg++ (11.2 +/- 2.5 vs. 15.2 +/- 4.1, p = 0.03; and 12.3 +/- 6.1 vs. 17.3 +/- 3.6, p = 0.004, respectively). In the untreated groups, the NSS at 18 and 48 hours was not significantly different from baseline values (that is, no neurological improvement). The present study indicates that postinjury treatment with Mg++ attenuates brain edema formation and improves neurological outcome after experimental CHT.

Brain edema and neurological status with rapid infusion of lactated Ringer's or 5% dextrose solution following head trauma.

Rapid infusion of 0.25 ml/g of 0.9% saline over 30 minutes has been shown to have no effect on electrolyte balance, neurological severity score (NSS), or brain edema, following closed head trauma (CHT). Rapid infusion of the same volume of 5% dextrose solution decreased blood sodium concentration, increased edema, and decreased NSS following CHT. In the present study the authors examined the effect of rapid infusion (30 minutes) of smaller volumes of 5% dextrose (0.08 ml/g and 0.16 ml/g) and of 0.25 ml/g lactated Ringer's solution on blood electrolyte concentrations, plasma osmolality, brain edema, and NSS. The purposes of this study were to determine whether rapid infusion of a large volume of lactated Ringer's solution could be given after CHT without increasing mortality or brain edema or producing electrolyte disturbances, and whether small volumes of 5% dextrose could be infused with few or none of the deleterious effects expected from large volumes of 5% dextrose. One hundred eighteen rats, which survived halothane anesthesia and CHT, were randomly assigned to one of 15 experimental groups. Fluids were administered beginning 1 hour after scalp incision or CHT. The NSS, extent of edema, blood electrolyte concentrations, and plasma osmolality in the groups treated with lactated Ringer's solution were not significantly different from those values in the nontreated groups. In addition, the mortality rate after CHT was not increased by administration of lactated Ringer's solution. The groups treated with 5% dextrose solution showed a significantly higher mortality rate, but the NSSs of the surviving rats were not different from controls. None of the groups treated with 0.16 ml/g 5% dextrose solution survived 24 hours. Although blood glucose concentration increased to 1126 +/- 102 g% (mean +/- standard deviation) and 1568 +/- 283 g% and blood sodium concentration decreased to 110.4 +/- 4.6 mEq/L and 92.0 +/- 5.2 mEq/L in the groups treated with 0.08 ml/g and 0.16 ml/g of 5% dextrose solution, respectively, plasma osmolality was normal and no significant difference could be found between the brain tissue specific gravity of animals in the nontreated and 5% dextrose treatment groups. It is concluded that in the CHT model used in this study, the large volume of lactated Ringer's solution did not affect blood electrolyte concentration, neurological outcome, or formation of brain edema, whereas smaller volumes of 5% dextrose solution increased blood glucose and decreased blood sodium concentrations, did not affect plasma osmolality, and had a deleterious effect on neurological outcome.

Brain Edema and Neurologic Status with Rapid Infusion of 0.9% Saline or 5% Dextrose After Head Trauma

We previously reported that intravenous (i.v.) administration of large volumes (0.2 ml/g) of either an isotonic dextrose-free solution or 5% dextrose solution given over 18 h after closed head trauma (CHT) in rats did not significantly affect neurological severity score or brain tissue specific gravity. However, it is possible that with more rapid administration, isotonic or 5% dextrose i.v. solutions may alter neurological outcome after CHT. Our study examined whether neurological severity score, brain tissue specific gravity and water content, and blood composition were significantly altered when 0.25 ml/g of either 0.9% saline or 5% dextrose was given i.v. over 0.5 h (rather than over 18 h) after CHT. Eight-four rats that survived ether anesthesia and CHT were randomly assigned to one of 11 experimental groups. Saline- and dextrose-treated rats were evaluated at 4 and 48 h after CHT and were compared to rats without CHT and to untreated rats at 4 and 48 h after CHT. There were no statistically significant differences in neurologic outcome and brain edema between the untreated and the saline-treated groups. However, 5% dextrose i.v. increased mortality (group 6 and 11, 50 and 0% survivors, respectively), decreased specific gravity in the noncontused hemisphere, and worsened neurologic outcome with and without CHT. Blood osmolality remained stable in comparison to the baseline value of 291.9 +/- 7.4 mOsm/kg (mean +/- SD).(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutic time window and dose response of the beneficial effects of ketamine in experimental head injury.

The aim of this study was to determine the time and dose response of the therapeutic effects of the N-methyl-D-aspartate receptor antagonist ketamine in experimental head injury. Sixty-six male Sprague-Dawley rats were divided into eight groups. Groups A, B, and C were surgically prepared but received no trauma. Groups D through H received a nonpenetrating impact to the left cranium. Group A (n = 7) received no treatment. Groups B (n = 4) and C (n = 5) received 60 and 120 mg/kg IP ketamine, respectively. Group D (n = 8) received no treatment. Groups E (n = 8) and F (n = 7) received 120 and 180 mg/kg IP ketamine, respectively, 1 hour after head trauma. Groups G (n = 7) and H (n = 9) were treated with 180 mg/kg IP ketamine 2 and 4 hours after head trauma, respectively. Neurological severity score (NSS, 0 through 25 from no injury to severe injury) was determined at 1, 24, and 48 hours after head trauma. After death at 48 hours, cortical slices were taken adjacent to the lesion on the traumatized hemisphere and from comparable sites in the contralateral hemisphere for determination of tissue specific gravity and water content. Brains were then placed in 4% formaldehyde, and the volume of hemorrhagic necrosis was measured 4 days later. NSS was compared within and between groups using the Kruskal-Wallis test for repeated measurements and Mann-Whitney U test for post hoc testing. Water content, specific gravity, and hemorrhagic necrosis were compared within and between groups using two-way ANOVA followed by Fisher's protected least significant difference procedure. A value of P < .05 was considered statistically significant. Head trauma alone increased NSS, decreased specific gravity, increased water content, and caused cerebral infarction in the injured hemisphere. Ketamine given in two time-dose regimens, 180 mg/kg IP at 2 hours (group G) and 120 mg/kg IP at 1 hour (group F) after trauma, improved NSS from 11.6 +/- 1.7 and 14.4 +/- 0.8 at 1 hour to 4.4 +/- 1.3 and 8.0 +/- 1.4 (mean +/- SEM) at 48 hours, respectively (P < .03). Compared with the untreated group (group D), 180 mg/kg IP ketamine given at 2 and 4 hours after head trauma decreased the volume of hemorrhagic necrosis from 37.1 +/- 9.5 mm3 to 10.1 +/- 3.8 and 15.3 +/- 3.6 mm3, respectively (P < .05). Brain tissue specific gravity and water content at 48 hours were not significantly different between treated and untreated groups. There was no difference in rectal and temporalis muscle temperature between groups. We conclude that 180 mg/kg IP ketamine was effective in ameliorating neurological dysfunction after head trauma in rats when the administration time was delayed for 1 hour to 2 hours but not after 4 hours. When given at 1 hour after head trauma, ketamine at 120 mg/kg but not 60 mg/kg is effective in reducing neurological damage after head trauma.

Brain ion and amino acid contents during edema development in hepatic encephalopathy.

Brain edema in hepatic encephalopathy has been associated with circulating ammonia that is metabolized to glutamine. We measured alterations in blood chemistry and brain regional specific gravity and ion and amino acid contents in models of simple hyperammonemia and liver failure induced by daily administrations of ammonium acetate (AAc) or thioacetamide (TAA), respectively. Serum and brain ammonia increased to similar levels (200 and 170% of control, respectively) in both experimental groups. Serum transaminase activities increased 10-fold in animals injected with TAA but were unchanged in animals given AAc injections. In both experimental groups glutamine was elevated in cerebral white matter, cerebral gray matter, and basal ganglia, whereas brain tissue specific gravity decreased in all brain regions, indicating edema formation. In the AAc group, we observed a decrease in glutamate and taurine contents concomitant with the development of brain edema. In these animals, cerebral gray matter specific gravity and taurine contents returned to control levels 24 h after the third AAc injection. TAA-injected animals demonstrated similar decreases in brain tissue specific gravity, whereas glutamine, glutamate, and taurine contents were all elevated. During hepatic encephalopathy, ammonia-induced changes in brain amino acid content may contribute to brain edema development.

Blood-brain barrier permeability, cerebral edema, and neurologic function after closed head injury in rats.

We previously described the time course of changes in neurologic status (as indicated by neurologic severity score [NSS]) and cerebral edema (as indicated by brain tissue specific gravity and water content) after closed head trauma in rats. The present study was designed to determine whether head trauma alters the integrity of the blood-brain barrier (BBB), the role of the BBB in edema formation and neurologic outcome, and the effect of MK-801 (a noncompetitive N-methyl-D-aspartate receptor antagonist) on BBB permeability. Rats in which cranial impact was delivered during ether anesthesia (n = 106) were killed at 15 min, 1, 2, 4, 10, and 24 h, and 2, 4, and 7 days. Control rats (n = 12) received no cranial impact. Subsets of head-injured rats killed at 4 and 24 h received MK-801 (3 mg/kg intraperitoneally) 1 h after injury. BBB permeability was assessed with intravenous injection of Evans Blue dye, cerebral edema was assessed by determining brain tissue specific gravity and water content, and neurologic status was assessed using NSS. Tissue extravasation of Evans Blue was maximal in the injured hemisphere 4 h after injury, but a residual BBB permeability defect was still evident as long as 4 days after the insult. In MK-801-treated rats, extravasation of Evans Blue in the injured hemisphere was not significantly different from that in the noninjured hemisphere.(ABSTRACT TRUNCATED AT 250 WORDS)

Ketamine Decreases Cerebral Infarct Volume and Improves Neurological Outcome Following Experimental Head Trauma in Rats

In brain injury, concentrations of extracellular excitatory amino acids are increased and stimulate glutamate receptors in general and the N-methyl-D-aspartate (NMDA)-preferring subtype in particular. That stimulation causes substantial calcium influx, which appears to initiate a cascade of events leading to neuronal death. Blockage of NMDA receptors with specific antagonists or noncompetitive ion channel blockers provides protection against excitatory amino acid-induced neurotoxicity. We previously reported that the NMDA receptor antagonist dizocilpine maleate improved the neurological severity score (NSS) after head trauma in rats. The present study was designed to determine whether ketamine, a NMDA receptor antagonist like dizocilpine maleate, improves neurological outcome following head trauma in rats. Thirty-two male Sprague-Dawley rats (235-250 g) were divided into four groups. Groups A and B were surgically prepared only. Groups C and D were surgically prepared and then a nonpenetrating impact was delivered to the cranium over the left hemisphere. Groups A and C received no treatment. Groups B and D were treated with ketamine, 180 mg/kg i.p., 1 h after head trauma. The NSS was determined at 1, 2, 4, 10, 24, and 48 h following head trauma. After killing at 48 h, cortical slices were taken adjacent to the lesion on the traumatized hemisphere and from comparable sites on the nontraumatized hemisphere to measure the tissue specific gravity and water content. Brains were then placed in 4% formaldehyde and the volume of hemorrhagic necrosis measured 4 days later. Head trauma increased the NSS and, in the traumatized hemisphere, decreased the specific gravity, increased the water content, and caused cerebral infarction. With ketamine, the NSS at 24 and 48 h following head trauma was 7.4 +/- 2.6 and 6.7 +/- 2.6 (mean +/- SEM), respectively, significantly improved compared to the NSS in the untreated group of 12.6 +/- 2.6 and 11.3 +/- 2.6, respectively (p <0.02, Mann-Whitney U test). With ketamine, the volume of hemorrhagic necrosis was 88.0 +/- 23.1 mm, significantly less than that in the untreated group (147.4 +/- 22.4 mm; p <0.05, unpaired t test). The brain tissue specific gravity and water content at 48 h and the rectal temperature at 4 and 48 h after head trauma were not significantly different between treated and untreated groups. It is concluded that in this model of closed cranial impact, ketamine improves neurological outcome and decreases the volume of hemorrhagic necrosis without altering brain edema.

Measurement of brain tissue specific gravity using pycnometry

In this paper we introduce and characterize pycnometry, a method used to measure fluid density, for determining a tissue's specific gravity. It uses a 2-ml glass pycnometer filled with distilled water to determine a tissue sample's displacement volume. The tissue's density is determined when it's weight is divided by this volume and specific gravity is computed by dividing the tissue density by the density of water. Pycnometry was validated using pre-calibrated glass, specific gravity standards over the range 1.03–1.26, and compared to the density gradient method using rat brain tissue. We observed that the specific gravity values obtained using pycnometry were highly correlated with the specific gravity standards (slope = 1.0107, r = 0.996) and with the density gradient column when tissue volumes larger than 0.120 ml were used with the pycnometer (slope = 1.0707, r = 0.9826). Good correlation was also observed between percent water content values computed using the Nelson equation with pycnometry or density gradient specific gravity values versus the measured percent water content values obtained with the wet weight/dry weight method. Pycnometry is an accurate, reproducible technique to measure tissue specific gravity and brain edema and is best suited for use in a laboratory that engages sporadically in brain edema measurement.

Blood-brain barrier permeability to micromolecules and edema formation in the early phase of incomplete continuous ischemia

The distribution patterns of ionic Lanthanum (La3+; mol. wt. 139) were evaluated after 15, 30 and 60 min of middle cerebral artery occlusion in perfused-fixed rats. Blood-brain barrier (BBB) permeability to Evans blue (EB) and horseradish peroxidase (HRP; mol. wt. 40,000) in vivo was also evaluated. Brain tissue specific gravity was measured. An increase in brain water content was found as early as 30 min following occlusion. HRP and EB extravasation was not observed. La3+ crossed the interendothelial clefts of venules and capillaries at 30 and 60 min and was seen in both extracellular and intracellular brain compartments at 60 min. La3+ extravasation was seen in nonedematous areas bordering the regions of water accumulation. Our findings suggest that the early phase of incomplete continuous ischemia is accompanied by changes in BBB permeability and the interendothelial clefts of venules and capillaries seem to represent one of the early sites of ischemic damage.

The effect of hypoxia on traumatic head injury in rats: alterations in neurologic function, brain edema, and cerebral blood flow.

We evaluated the effects of early posttraumatic hypoxia on neurologic function, magnetic resonance images (MRI), brain tissue specific gravities, and cerebral blood flow (CBF) in head-injured rats. By itself, an hypoxic insult (PaO2 40 mm Hg for 30 min) had little effect on any measure of cerebral function. After temporal fluid-percussion impact injury, however, hypoxia significantly increased morbidity. Of rats subjected to impact (4.9 +/- 0.3 atm) plus hypoxia, 71% had motor weakness contralateral to the impact side 24 h after injury, while only 29% of rats subjected to impact alone had demonstrable weakness (p less than 0.05). Lesions observed on MR images 24 h after injury were restricted to the impact site in rats with impact injury alone, but extensive areas with longer T1 relaxation times were observed throughout the ipsilateral cortex in rats with impact injury and hypoxic insult. Brain tissue specific gravity measurements indicated that much more widespread and severe edema developed in rats with impact injury and hypoxia. [14C]Iodoantipyrine autoradiography performed 24 h after injury showed that there was extensive hypoperfusion of the entire ipsilateral cortex in rats with impact injury and hypoxia. These results show that large areas of impact-injured brain are extremely vulnerable to secondary insults that can irreparably damage neural tissue, and provide experimental evidence for the observed adverse effects of hypoxia on outcome after human head injury.