Pretreatment with the NMDA antagonist dextrorphan reduces cerebral injury following transient focal ischemia in rabbits

Changes in NMDA Receptor Function in Rapid Ischemic Tolerance: A Potential Role for Tri-Heteromeric NMDA Receptors

In this study, we characterize biophysical changes in NMDA receptor function in response to brief non-injurious ischemic stress (ischemic preconditioning). Electrophysiological studies show NMDA receptor function is reduced following preconditioning in cultured rat cortical neurons. This functional change is not due to changes in the reversal potential of the receptor, but an increase in desensitization. We performed concentration-response analysis of NMDA-evoked currents, and demonstrate that preconditioned neurons show a reduced potency of NMDA to evoke currents, an increase in Mg2+ sensitivity, but no change in glycine sensitivity. Antagonists studies show a reduced inhibition of GluN2B antagonists that have an allosteric mode of action (ifenprodil and R-25-6981), but competitive antagonists at the GluR2A and 2B receptor (NVP-AMM077 and conantokin-G) appear to have similar potency to block currents. Biochemical studies show a reduction in membrane surface GluN2B subunits, and an increased co-immunoprecipitation of GluN2A with GluN2B subunits, suggestive of tri-heteromeric receptor formation. Finally, we show that blocking actin remodeling with jasplakinolide, a mechanism of rapid ischemic tolerance, prevents NMDA receptor functional changes and co-immunoprecipitation of GluN2A and 2B subunits. Together, this study shows that alterations in NMDA receptor function following preconditioning ischemia are associated with neuroprotection in rapid ischemic tolerance.

Ion channels involved in stroke

Ion channels are membrane proteins that flicker open and shut to regulate the flow of ions down their electrochemical gradient across the membrane and consequently regulate cellular excitability. Every living cell expresses ion channels, as they are critical life-sustaining proteins. Ion channels are generally either activated by voltage or by ligand interaction. For each group of ion channels the channels' molecular biology and biophysics will be introduced and the pharmacology of that group of channels will be reviewed. The in vitro and in vivo literature will be reviewed and, for ion channel groups in which clinical trials have been conducted, the efficacy and therapeutic potential of the neuroprotective compounds will be reviewed. A large part of this article will deal with glutamate receptors, focusing specifically on N-methyl-D-aspartate (NMDA) receptors. Although the outcome of clinical trials for NMDA receptor antagonists as therapeutics for acute stroke is disappointing, the culmination of these failed trials was preceded by a decade of efforts to develop these agents. Sodium and calcium channel antagonists will be reviewed and the newly emerging efforts to develop therapeutics targeting potassium channels will be discussed. The future development of stroke therapeutics targeting ion channels will be discussed in the context of the failures of the last decade in hopes that this decade will yield successful stroke therapeutics.

NMDA receptor antagonists and glycine site NMDA antagonists

Extracellular concentrations of excitatory amino acids increase substantially within cerebral tissue beds exposed to ischaemic conditions. This leads to excessive stimulation of N-methyl-D-aspartate (NMDA) receptors, a major cerebral excitatory neurotransmitter receptor that likely plays a critical role in the propagation of ischaemic injury in neurons. Pharmacological blockade of these receptors has proven to be an effective neuroprotective therapy by a number of animal models of central nervous system ischaemia. Clinical trials of these drugs were begun with high expectations for successful therapy of human stroke. These putative neuroprotective drugs included competitive or non-competitive inhibitors of the NMDA receptor itself, as well as inhibitors of a co-modulatory glycine site. Thus far, all clinical trials of NMDA antagonists have been unsuccessful in establishing benefit for human stroke.

Effects of the novel NMDA antagonists CP-98,113, CP-101,581 and CP-101,606 on cognitive function and regional cerebral edema following experimental brain injury in the rat

The present study evaluated the effects of two novel N-methyl-D-aspartate (NMDA) receptor blockers and ifenprodil derivatives, CP-101,606 and CP-101,581, and their racemic mixture CP-98,113, on spatial memory and regional cerebral edema following experimental fluid-percussion (FP) brain injury in the rat (n = 66). Fifteen minutes after brain injury (2.5 atm), animals received either (1) CP-98,113 (5 mg/kg, i.p., n = 11), (2) CP-101,581 (5 mg/kg, i.p., n = 13), (3) CP-101,606 (6.5 mg/kg, i.p., n = 12), or (4) DMSO vehicle (equal volume, n = 12); followed by a continuous 24-h subcutaneous infusion of drug at a rate of 1.5 mg/kg/h by means of miniature osmotic (Alzet) pumps implanted subcutaneously. Control (uninjured) animals were subjected to identical anesthesia and surgery without injury and received DMSO vehicle (n = 8); CP-98,113 (5 mg/kg, i.p., n = 3); CP-101,581 (5 mg/kg, i.p., n = 3); or CP-101,606 (6.5 mg/kg, i.p., n = 3). FP brain injury produced a significant cognitive impairment assessed at 2 days postinjury using a well-characterized testing paradigm of visuospatial memory in the Morris Water Maze (MWM) (p < 0.001). Administration of either CP-98,113, CP-101,581, or CP-101,606 had no effect on sham (uninjured) animals, but significant attenuated spatial memory impairment assessed at 2 days postinjury (p = 0.004, p = 0.02, or p = 0.02, respectively). Administration of CP-89,113 but not CP-101,581 or CP-101,606 significantly reduced the extent of regional cerebral edema in the cortex adjacent to the site of injury (p < 0.05) and in the ipsilateral hippocampus (p < 0.05) and thalamus (p < 0.05). These results suggest that excitatory neurotransmission may play a pivotal role in the pathogenesis of memory dysfunction following traumatic brain injury (TBI) and that blockade of the NMDA receptor may significantly attenuate cognitive deficits associated with TBI.

CGS 19755 (Selfotel): A Novel Neuroprotective Agent Against CNS Injury

The hypothesis that excitoxicity is a mechanism of damage following different types of cerebral injury including global and focal ischemia (34), and head and spinal cord trauma (6,7,9,25) has been supported by numerous findings. During ischemia for example, glutamate neurotoxicity is mediated in part through N-methyl-D-aspartate (NMDA) receptors, since selective antagonists to this receptor protect against hypoxic-ischemic injury (10,35,41). In the last few years, different NMDA antagonists have been developed and tested; they can be divided into competitive and noncompetitive antagonists. Noncompetitive NMDA antagonists are extremely lipophilic and reach high levels in the brain after systemic administration. Various studies have demonstrated that these agents provide neuroprotection against hypoxic-ischemic injury (for review see ref. 29). Many competitive NMDA antagonists are hydrophilic and require direct cerebral administration to obtain high brain levels. Newer competitive NMDA blockers, such as cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755, selfotel), provide neuroprotection against global ischemia, focal ischemia, and trauma when given systemically (2,3,32,33). Selfotel is currently being studied in multicenter safety and efficacy trials for stroke (17) and head trauma (6).

Marked hemodilution increases neurologic injury after focal cerebral ischemia in rabbits

Moderate hemodilution (hematocrit approximately 30%) reduces neurologic injury after focal cerebral ischemia. In contrast, both clinical and experimental studies suggest that marked hemodilution (hematocrit < 30%) may exacerbate neurologic injury. We compared the effect of marked versus minimal hemodilution on cerebral infarct volume after focal cerebral ischemia in rabbits. Anesthetized New Zealand White rabbits underwent hemodilution by exchange of arterial blood with 6% high molecular weight hydroxyethyl starch. In the marked hemodilution group (n = 15) the target hemoglobin concentration was 6 g/100 mL. In the minimal hemodilution group (n = 15) the target hemoglobin concentration was 11 g/100 mL. After hemodilution, middle cerebral artery occlusion was achieved by embolizing an autologous blood clot via the internal carotid artery. Four hours after embolization, the animals were killed and their brains removed. Brains were sectioned, stained with 2,3,5-triphenyltetrazolium chloride, and infarct volumes determined via quantitative image analysis. Systemic physiologic variables were similar between groups, except for arterial hemoglobin concentration. The percentage of hemispheric infarct was significantly larger in the marked hemodilution group as compared to the minimal hemodilution group, 70% +/- 19% vs 51% +/- 23%, respectively (mean +/- SD); P = 0.02. Similarly, the percentage of infarct was greater in the hemodilution group as compared to the minimal hemodilution group in both cortex (73% +/- 18% vs 54% +/- 23%, respectively; P = 0.02) and subcortex (62% +/- 25% vs 44% +/- 23%, respectively; P = 0.04). These findings indicate that marked hemodilution exacerbates neurologic injury resulting from permanent focal ischemia. Although some degree of hemodilution may improve neurologic outcome, the advantage is lost at an extreme level of therapy.

Correlation of CGS 19755 neuroprotection against in vitro excitotoxicity and focal cerebral ischemia

The in vivo neuroprotective effect and brain levels of cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755), a competitive N-methyl-D-aspartate (NMDA) antagonist, were compared with its in vitro neuroprotective effects. The dose-response for in vitro neuroprotection against both NMDA toxicity and combined oxygen-glucose deprivation (OGD) was determined in murine neocortical cultures. Primary cultures of neocortical cells from feta mice were injured by exposure to 500 microM NMDA for 10 min or to OGD for 45 min. The effect of CGS 19755 in both injury paradigms was assessed morphologically and quantitated by determination of lactate dehydrogenase release. Near complete neuroprotection was found at high doses of CGS 19755. The ED50 for protection against NMDA toxicity was 25.4 micro M, and against OGD the ED50 was 15.2 microM. For the in vivo paradigm rabbits underwent 2 h of left internal carotid, anterior cerebral, and middle cerebral artery occlusion followed by 4 h reperfusion; ischemic injury was assessed by magnetic resonance imaging and histopathology. The rabbits were treated with 40 mg/kg i.v. CGS 19755 or saline 10 min after arterial occlusion. CSF and brain levels of CGS 19755 were 12 microM and 5 microM, respectively, at 1 h, 6 microM and 5 microM at 2 h, and 13 microM and 7 microM at 4 h. These levels were neuroprotective in this model, reducing cortical ischemic edema by 48% and ischemic neuronal damage by 76%. These results suggest that a single i.v. dose penetrates the blood-brain barrier, attaining sustained neuroprotective levels that are in the range for in vitro neuroprotection.

In vivo models of cerebral ischemia: effects of parenterally administered NMDA receptor glycine site antagonists

Both in vitro and in vivo experiments have implicated extracellular glycine in the pathogenesis of ischemic brain damage. Recently, halogenated derivatives of quinoxaline-2,3-dione have been synthesized that possess bioavailability when parenterally administered and minimal psychotomimetic properties. Such compounds have allowed investigation into the efficacy of glycine receptor antagonism as a strategy for protection against cerebral ischemic insults. Rats underwent either 90 min of middle cerebral artery filament occlusion or 10 min of forebrain ischemia with recovery while receiving intraperitoneal injections of either a glycine receptor antagonist (ACEA-1021, ACEA-1031, or ACEA-1011) or vehicle (dimethyl sulfoxide). Both ACEA-1021 and ACEA-1031 reduced cerebral infarct volumes and were associated with a reduced incidence of hemiparesis resulting from MCA occlusion. ACEA-1011, administered in a smaller dose had no effect. In the forebrain ischemia model, glycine receptor antagonism had no effect on delayed neuronal necrosis in the hippocampal CA1 sector, neocortex, or caudoputamen. We conclude that pharmacologic antagonism of glycine at the strychnine-insensitive glycine receptor presents a neuroprotective profile similar to that previously observed for antagonists of glutamate at the N-methyl-D-aspartate complex with a potential for fewer side effects.

Dextrorphan inhibits the release of excitatory amino acids during spinal cord ischemia

The release of excitatory amino acids, particularly glutamate, into the extracellular space plays a causal role in irreversible neuronal damage after central nervous system ischemia. Dextrorphan, a noncompetitive N-methyl-D-aspartate receptor antagonist, has been shown to provide significant protection against cerebral damage after focal ischemia. We investigated the changes in extracellular neurotransmitter amino acid concentrations using in vivo microdialysis in a swine model of spinal cord ischemia. After lumbar laminectomies were performed, all animals underwent left thoracotomy and right atrial-femoral cardiopulmonary bypass with additional aortic arch perfusion. Microdialysis probes were then inserted stereotactically into the lumbar spinal cord. The probes were perfused with artificial cerebrospinal fluid and 15-minute samples were assayed using high-performance liquid chromatography. Group 1 animals (n = 9) underwent aortic clamping distal to the left subclavian and proximal to the renal arteries for 60 minutes. Group 2 animals (n = 7) were treated with dextrorphan before application of aortic clamps, and during aortic occlusion and reperfusion. Five amino acids were studied, including two excitatory neurotransmitters (glutamate and aspartate) and three putative inhibitory neurotransmitters (glycine, gamma-amino-butyric acid, and serine). Somatosensory-evoked potentials and motor-evoked potentials were monitored. Glutamate exhibited a threefold increase in extracellular concentration during normothermic ischemia compared with baseline values and remained elevated until 60 minutes after reperfusion. In animals treated with dextrorphan, glutamate concentrations decreased to one-third of baseline levels before aortic clamping and remained unchanged during ischemia and reperfusion. There was early loss of somatosensory-evoked potentials and motor-evoked potentials during ischemia in group 1 animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamate-mediated injury in focal cerebral ischemia: the excitotoxin hypothesis revised

Neuronal injury following focal cerebral ischemia is widely attributed to the excitotoxic effects of glutamate. However, critical analysis of published data on glutamate toxicity in vitro and the comparison of these data with in vivo release of glutamate and the therapeutic effect of glutamate antagonists raises doubts about a neurotoxic mechanism. An alternative explanation for glutamate-mediated injury is hypoxia due to peri-infarct spreading depression-like depolarizations. These depolarizations are triggered in the core of the ischemic infarct and spread at irregular intervals into the peri-infarct surrounding. In ischemically uncompromised tissue, the metabolic workload associated with spreading depression is coupled to an increase in blood flow and oxygen supply, assuring maintenance of oxidative respiration. In the penumbra region of focal ischemia, the hemodynamic constraints of collateral blood circulation prevail the adequate adjustment of oxygen delivery, leading to transient episodes of relative tissue hypoxia. The hypoxic episodes cause a suppression of protein synthesis, a gradual deterioration of energy metabolism and a progression of irreversibly damaged tissue into the penumbra zone. The generation of peri-infarct spreading depressions and the associated metabolic workload can be suppressed by NMDA and non-NMDA antagonists. As a result, the penumbral inhibition of protein synthesis and the progressing energy failure is also prevented, and the volume of ischemic infarct decreases. Interventions to improve ischemic resistance should therefore aim at improving the oxygen supply or reducing the metabolic workload in the penumbra region.

Pharmacologic management of neonatal cerebral ischemia and hemorrhage: old and new directions

New developments in pharmacologic management of cerebral ischemia and hemorrhage are reviewed. A number of agents with diverse modes of action have now been shown to be neuroprotective in adult and neonatal animal models when administered either before or after a hypoxic-ischemic insult. As experience improves with these agents in hypoxic-ischemic injury and periventricular-intraventricular hemorrhage in human neonates, there is reason to be optimistic that effective neuroprotective strategies will soon be clinically available.

Inhibitory influence of morphinans on ictal and interictal EEG changes induced by cortical application of penicillin in rabbits: a comparative study with NMDA antagonists and pentobarbitone

The effects of dextrorphan (DX) and dextromethorphan (DM) were tested using the electroencephalogram (EEG) and behavioral effects induced by topical cortical application of penicillin in rabbits. For comparison, the influence of the NMDA antagonists, dizocilpine (MK 801) and 3-((+-(-)2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP), and of pentobarbitone was investigated. Intracortical injection of 500 IU of penicillin produced an EEG spiking followed by a repeated generalization of the electrical and behavioral symptoms. Within a few minutes, DX (5-15 mg/kg, IV) or pentobarbitone (5-10 mg/kg, IV) reduced dose dependently and significantly (p less than 0.01) the interictal and ictal EEG and behavioral effects elicited by cortical injection of 500 IU of penicillin. Higher doses of pentobarbitone (20 mg/kg, IV) but not of DX (20 mg/kg, IV) completely blocked the ictal behavioral and EEG effects elicited by cortical injection of 500 IU of penicillin. Within a few minutes, MK 801 (0.1-0.2 mg/kg, IV) or CPP (10-20 mg/kg, IV) reduced dose dependently and significantly (p less than 0.01) the ictal EEG and behavioral effects elicited by cortical injection of 500 IU of penicillin, while they did not affect the penicillin-induced interictal EEG changes. Higher doses of MK 801 (0.3 mg/kg, IV) completely blocked the ictal behavioral and EEG effects elicited by cortical injection of 500 IU of penicillin. Within a few minutes, DM (10-20 mg/kg, IV) blocked the behavioral effects, but failed to affect either the interictal or the ictal EEG effects induced by cortical injection of 500 IU of penicillin.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection after transient focal cerebral ischemia by the N-methyl-D-aspartate antagonist dextrorphan is dependent upon plasma and brain levels

Dextrorphan is a dextrorotatory morphinan and a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist. We studied the dose response characteristics of dextrorphan's neuroprotective efficacy and side effects, correlating these beneficial and adverse responses with plasma and brain levels in a rabbit model of transient focal cerebral ischemia. Thirty-three rabbits, anesthetized with halothane, underwent occlusion of the left internal carotid and anterior cerebral arteries for 1 h, followed by 4.5 h of reperfusion. One hour after the onset of ischemia, they were treated with an i.v. infusion of varying dextrorphan doses or normal saline. After killing, the brains were analyzed for ischemic high signal intensity using magnetic resonance imaging (MRI) and for ischemic neuronal damage with histopathology. A separate group of 12 anesthetized ischemic rabbits received similar doses of dextrorphan, correlating plasma with brain dextrorphan levels. Twenty-six additional dextrorphan unanesthetized, nonischemic rabbits received infusions of dextrorphan to correlate behavioral side effects with dextrorphan dose and levels. Compared with controls, dextrorphan 15 mg/kg group had significantly less cortical ischemic neuronal damage (5.3 versus 33.2%, p = 0.01) and a reduction in cortical MRI high signal area (9.1 versus 41.2%, p = 0.02). The dextrorphan 10 mg/kg rabbits showed less cortical ischemic neuronal damage (27.2%) and less MRI high signal (34.8%) but this was not statistically significant (p = 0.6). Dextrorphan 5 mg/kg had no benefit on either neocortical ischemic neuronal damage (35.8%) or MRI high signal (42.9%). The protective effect of dextrorphan was correlated with plasma free dextrorphan levels (r = -0.50, p less than 0.02 for ischemic neuronal damage; r = -0.66, p less than 0.001 for ischemic MRI high signal). All the rabbits with plasma levels greater than 2,000 ng/ml had less than 12% cortical ischemic neuronal damage and less than 34% MRI high signal. All rabbits with plasma levels greater than 3,000 ng/ml showed less than 7% ischemic neuronal damage and less than 11% MRI high signal. Plasma levels of approximately 2,500 ng/ml correlated with brain dextrorphan levels of approximately 6,000 ng/g. Unanesthetized rabbits with plasma levels of approximately 2,500 ng/ml demonstrated loss of the righting reflex. These results demonstrate that systemic treatment with dextrorphan after 1 h focal ischemia can significantly protect against cerebral damage if adequate plasma and brain levels of dextrorphan are achieved. The brain levels necessary to obtain in vivo protection are similar to concentrations that prevent glutamate or NMDA-induced injury in neuronal culture.

Regionally selective effects of NMDA receptor antagonists against ischemic brain damage in the gerbil

This study compared the ability of three N-methyl-D-aspartate (NMDA) receptor antagonists to prevent neuronal degeneration in an animal model of global cerebral ischemia. The model employed is characterized by damage to the striatum, hippocampus, and neocortex. Antagonists were administered to gerbils either before or after a 5-min bilateral carotid occlusion. The intraischemic rectal temperature was either maintained at 36-37 degrees C or allowed to fall passively to 28-32 degrees C. Antagonists and doses tested were 1 and 10 mg/kg of MK-801 (pre- or postischemia), 30 mg/kg of CGS 19755 preischemia, four 25 mg/kg doses of CGS 19755 administered between 0.5 and 6.5 h postischemia, and 40 mg/kg of MDL 27,266 (pre- or postischemia). All three NMDA receptor antagonists exhibited some degree of neuroprotective activity when the carotid occlusion was performed under normothermic conditions. Most of the treatments with antagonist markedly reduced striatal damage. CA1 hippocampal and neocortical pyramidal cells were spared by only three of the treatments, however, and the extent of neuroprotection varied widely from case to case. Toxic doses of antagonist were required to protect CA1 pyramidal cells from ischemic damage. Ischemic damage to hippocampal areas CA2-CA3a and CA4 appeared to be resistant to all of these treatments. Most CA1 pyramidal cells that were protected from degeneration by an NMDA receptor antagonist were histologically abnormal. The neuroprotective effects of MK-801 and intraischemic hypothermia appeared to be additive. MK-801 (10 mg/kg) consistently reduced the postischemic brain temperature, but only the magnitude of hypothermia produced soon after reperfusion correlated with its neuroprotective action. These results suggest that NMDA receptor antagonists are relatively poor neuroprotective agents against a moderately severe ischemic insult.

Appearance of NMDA receptors triggered by anoxia independent of voltage in vivo and in vitro

Using rat hippocampus we have studied the pattern of neuronal death, abnormal discharge and loss of electrical excitability in slices prepared from animals subjected to bilateral, four-vessel cerebral anoxia and in slices prepared from normal animals that are subjected to anoxia in the recording chamber. As others have reported, pyramidal neurons in area CA1 are lost first after anoxia, while CA3 neurons have an intermediate sensitivity, and those in dentate are relatively anoxia-resistant. After anoxic damage to the intact animal, neurons in both CA1 and CA3 show abnormal bursting discharges in response to synaptic activation for several days, and then the response in CA1 decreases in amplitude and finally the area become unexcitable. While antagonists for N-methyl-D-aspartate (NMDA) receptors have essentially no effect on synaptic responses in control animals, they reduce the bursting responses and greatly depress the small responses in CA1 as neurons are becoming unexcitable after anoxia. With intracellular recording CA1 neurons from animals made transiently anoxic, in contrast to controls, show prolonged synaptic responses, the later components of which are blocked by NMDA antagonists. When slices from normal animals are subjected to anoxia such that excitability is totally lost over a period of about 10 min, there is no significant membrane depolarization during the anoxic episode and recovery of excitability occurs with reoxygenation. However, a period of hyperexcitability and bursting follows and electrical excitability is lost in CA1 but not CA3 neurons after about 90 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Diversified electrophysiological properties of morphinan drugs in rats

1. In in vivo and in vitro studies in rats, the effects of dextromethorphan (DM), dextrorphan (DX), and levorphanol (LV) were compared with those induced by kappa and sigma opiate agonists. 2. In rat hippocampal slices all the morphinans were able to pertubate the CAI hippocampal synaptic transmission, while only DX and LV affected the N-methyl-D-aspartate excitability through a possible interaction at sigma opiate receptors. 3. On the other hand EEG studies show that only DX appears to act as a full agonist at sigma opiate receptors. 4. Present data demonstrate diversified electrophysiological properties of morphinans both in in vitro and in vivo studies.

Correlation between amino acid release and neuropathologic outcome in rat brain following middle cerebral artery occlusion

Using in vivo brain microdialysis, we studied amino acid release in the striatum and cortex of eight rats following permanent middle cerebral artery occlusion. We then processed all brains for histopathologic assessment of the volume of ischemic damage 4 hours after occlusion. Ischemic damage was varied by occlusion of the middle cerebral artery at a point either proximal (n = 4) or distal (n = 4) to the lenticulostriate vessels. Proximal occlusion elevated the dialysate contents of all amino acids. The largest increases occurred for the potentially neurotoxic amino acids aspartate and glutamate and for taurine (800-2,800% of basal efflux). We observed smaller increases for the "metabolic" amino acids (280-580% of basal efflux). Distal occlusion did not affect amino acid efflux in the striatum, and release in the cortex was significantly lower than that following proximal occlusion. We compared release data with acute histopathologic outcome. Proximal occlusion resulted in a large volume of ischemic damage in the cortex and striatum (25-48% of hemispheric volume). A smaller volume of ischemic damage was noted following distal occlusion (0-21% of hemispheric volume). The volume of ischemic damage and the amount of amino acid release were significantly correlated (p less than 0.05).