Thomas A. Kent

Neocortical neural sprouting, synaptogenesis, and behavioral recovery after neocortical infarction in rats.

BACKGROUND AND PURPOSEnNeuroanatomical plasticity is well described in lesions of the hippocampus but remains a subject of some controversy in the neocortex. The purpose of the present study was to measure the neocortical distribution and density of expression of proteins known to be involved in neurite growth or synaptogenesis and to correlate the neocortical expression with behavioral recovery after a focal neocortical infarction. Focal neocortical infarction creates a circumscribed lesion in the neocortex that provides a denervation stimulus for neurite growth and synaptogenesis.nnnMETHODSnUnilateral neocortical ischemia was induced in male spontaneously hypertensive Wistar rats (n = 4 per time point) by permanent occlusion of the distal middle cerebral artery and ipsilateral common carotid artery. To determine the spatial and temporal distribution of neurite growth and/or synaptogenesis, GAP-43, a growth-associated protein expressed on axonal growth cones, and synaptophysin, a calcium-binding protein found on synaptic vesicles, were examined by immunohistochemical techniques. The reaction product was measured, and the distribution was recorded. Since the resulting infarction included a portion of the forelimb neocortex, behavioral assessments of forelimb function that used the foot-fault test of Hernandez and Schallert were performed on the same rats used for immunohistochemical studies. Recovery times were 3, 7, 14, 30, and 60 days after surgery.nnnRESULTSnBoth GAP-43 and synaptophysin proteins demonstrated statistically significant increases in the density of immunoreaction product as determined by optical density measurements in the neocortex of infarcted rats compared with sham controls. The GAP-43 was elevated to statistically significant levels in forelimb, hindlimb, and parietal neocortical regions medial and lateral to the infarction only at days 3, 7, and 14. In contrast, synaptophysin demonstrated no statistically significant changes in expression at 3 or 7 days but demonstrated statistically significant increases at 14, 30, and 60 days in the forelimb, hindlimb, and parietal neocortical regions medial and lateral to the infarction as well as in the contralateral parietal neocortex. Behavioral assessment of forelimb function indicated impairment of forelimb placement on the side contralateral to the infarction that trended toward control values at 14 days and was not significantly different from controls by 30 days.nnnCONCLUSIONSnThese data support the occurrence of neurite growth followed by synaptogenesis in the neocortex, ipsilateral and contralateral to neocortical ischemia, in a pattern that corresponds both spatially and temporally with behavioral recovery. Thus, neuroanatomical remodeling in the neocortex provides a mechanism for recovery of function.

Enhanced Neocortical Neural Sprouting, Synaptogenesis, and Behavioral Recovery With d-Amphetamine Therapy After Neocortical Infarction in Rats

BACKGROUND AND PURPOSEnD-Amphetamine administration increases behavioral recovery after various cortical lesions including cortical ablations, contusions, and focal ischemia in animals and after stroke in humans. The purpose of the present study was to test the enhanced behavioral recovery and increased expression of proteins involved in neurite growth and synaptogenesis in D-amphetamine-treated rats compared with vehicle-treated controls after a focal neocortical infarct.nnnMETHODSnUnilateral neocortical ischemia was induced in male spontaneously hypertensive Wistar rats (n=8 per time point per group) by permanently occluding the distal middle cerebral artery and ipsilateral common carotid artery in 2 groups of rats: D-amphetamine treated (2 mg/kg IP injections) and vehicle treated (saline IP injections). To determine the spatial and temporal distribution of neurite growth and/or synaptogenesis, growth-associated protein (GAP-43), a protein expressed on axonal growth cones, and synaptophysin, a calcium-binding protein found on synaptic vesicles, were examined by immunohistochemical techniques, and both density and distribution of reaction product were measured. Since the resulting infarction included a portion of the forelimb neocortex, behavioral assessments of forelimb function using the foot-fault test of Hernandez and Schallert were performed on the same rats used for immunohistochemical studies during the period of drug action and 24 hours later. A Morris water maze and other indices of behavioral assays were also measured similarly. Recovery times were 3, 7, 14, 30, and 60 days postoperatively.nnnRESULTSnBoth GAP-43 and synaptophysin proteins demonstrated statistically significant increases in density and distribution of immunoreaction product as determined by optical density measurements in the neocortex of the infarcted group treated with D-amphetamines compared with vehicle-treated infarcted controls. The GAP-43 was elevated to statistically significant levels in forelimb, hindlimb, and parietal neocortical regions ipsilateral to the infarction only at days 3, 7, and 14. By contrast, the synaptophysin demonstrated no statistically significant changes in expression at 3 or 7 days but demonstrated statistically significant increases at 14, 30, and 60 days in the forelimb, hindlimb, and parietal neocortical regions ipsilateral to the infarction as well as increased distribution in the contralateral parietal neocortex. Behavioral assessment of forelimb function indicated that improved recovery of forelimb placement on the side contralateral to the infarction was statistically significant in the D-amphetamine-treated group compared with the vehicle-treated group (P<0.025). Spatial memory, as measured with the Morris water maze, worsened in the vehicle-treated group compared with the D-amphetamine-treated group at 60 days (P<0.025).nnnCONCLUSIONSnThese data support the occurrence of neurite growth followed by synaptogenesis in the neocortex in a pattern that corresponds both spatially and temporally with behavioral recovery that is accelerated by D-amphetamine treatment. While the specific mechanisms responsible for D-amphetamine-promoted expression of proteins involved in neurite growth and synaptogenesis and of enhanced behavioral recovery are not known, it is suggested that protein upregulation occurs as a result of functional activation of pathways able to remodel in response to active behavioral performance.

Neuropsychological and cognitive psychophysiological substrates of impulsive aggression

The purpose of this study was to test whether subjects who commit impulsive vs non-impulsive aggression differ on measurements of personality, neuropsychology, and cognitive psychophysiology, and whether these differences can yield information regarding the etiology of impulsive aggression. Subjects were two groups of prison inmates, distinguished by their committal of impulsive or nonimpulsive aggression, and matched noninmate controls. All inmates met DSM III-R criteria for an antisocial personality disorder but for no other disorder. Impulsiveness, anger, and peak P300 latencies did not differ between the inmate groups, but verbal symbol decoding and peak P300 amplitudes did. Impulsiveness and verbal skills were inversely correlated. Impulsiveness was inversely correlated with, and verbal skills positively correlated with P300 amplitudes. The results indicate that aggression is not homogenous, even among antisocial persons, and that impulsive aggression is related to neuropsychological and cognitive psychophysiological measures of information processing beyond those factors related to criminality alone.

Impulsive and premeditated aggression: a factor analysis of self-reported acts.

Although aggression research in general has been hampered by a lack of objective measurements of aggressive acts, two types of aggressive acts, impulsive vs. premeditated, have been studied extensively in recent years. These two types of aggression have been primarily measured by structured or semi-structured interviews. The current study was designed to assess the construct validity of these two types of aggression using a self-report questionnaire which included items gleaned from the content of interviews used in past studies. For this study, 216 college students assessed their own aggressive acts rather than answering general questions about aggression. The students were not significantly different from normative sample groups on self-report measures of impulsiveness, aggression, and anger/hostility. A PCA factor analysis with a promax rotation of the items on the self-report questionnaire identified four factors: impulsive aggression; mood on the day the act occurred; premeditated aggression; and agitation. Thus, impulsive and premeditated aggression are independent constructs which exist in varying degrees among these normal persons in a non-clinical sample. Impulsive aggression was characterized in part by feelings of remorse following the acts and by thought confusion. Premeditated aggression was related to social gain and dominance.

Moclobemide in social phobia: A controlled dose-response trial

Although the monoamine oxidase inhibitor phenelzine has proven efficacious in social phobia, the risk of hypertensive crises has reduced its acceptability. The reversible monoamine oxidase inhibitor moclobemide has less potential for such reactions, but its efficacy in this disorder remains unproven. A double-blind, placebo-controlled study was undertaken to assess the efficacy and safety of fixed doses of moclobemide. After a 1-week placebo run-in, subjects with social phobia were randomly assigned to placebo or one of five doses (75 mg, 150 mg, 300 mg, 600 mg, or 900 mg daily) of moclobemide for 12 weeks. Although a trend toward greater efficacy of higher doses of moclobemide was observed at 8 weeks, no differences in response to various doses of the drug and placebo were observed at 12 weeks. At 12 weeks, 35% of subjects on 900 mg of moclobemide and 33% of those on placebo were at least much improved. Moclobemide was well tolerated, insomnia being the only dose-related adverse event observed with the drug. In this dose-response trial, moclobemide did not demonstrate efficacy at 12 weeks. Some other controlled studies have found moclobemide and brofaromine, another reversible monoamine oxidase inhibitor, efficacious in social phobia. Possible reasons for inconsistent findings are discussed.

The evolution of acute stroke recorded by multimodal magnetic resonance imaging

Events associated with an evolving cerebral infarction were studied using multiple magnetic resonance imaging (MRI) techniques at 4.7 T in a rat model of middle cerebral artery occlusion. High resolution perfusion images revealed a core of absent perfusion surrounded by a zone of slow, but measurable perfusion. Only the core of severest perfusion deficit demonstrated restricted water diffusion as early as 1 hr, consistent with cytotoxic cellular edema in the most vulnerable region. Within 24 hours, the area of restricted diffusion encompassed the entire region destined to become infarcted. In spin-echo images, hypointensity, likely reflecting deoxygenated hemoglobin, was visible in the ischemic hemisphere. Edema accumulated over 72 hr primarily in the surrounding slowly perfused rim, consistent with the concept of vasogenic edema. These studies demonstrate that multimodal MRI can visualize events which define the ischemic penumbra--deoxygenation, maintenance of transmembrane ionic gradients, reduced flow, and delayed cell death. These experiments noninvasively visualized differential hemodynamic and biochemical processes within the core and perifocal penumbra and will allow quantitation over time of the relationship between blood flow, cytotoxicity and edema in stroke.

Perfusion Deficit Parallels Exacerbation of Cerebral Ischemia/Reperfusion Injury in Hyperglycemic Rats

Magnetic resonance imaging (MRI) techniques were used to determine the effect of preexisting hyperglycemia on the extent of cerebral ischemia/reperfusion injury and the level of cerebral perfusion. Middle cerebral artery occlusion (MCAO) was induced by a suture insertion technique. Forty one rats were divided into hyperglycemic and normoglycemic groups with either 4 hours of continuous MCAO or 2 hours of MCAO followed by 2 hours of reperfusion. Diffusion-weighted imaging (DWI) was performed at 4 hours after MCAO to quantify the degree of injury in 6 brain regions. Relative cerebral blood flow (CBF) and cerebral blood volume (CBV) were estimated using gradient echo (GE) bolus tracking and steady-state spin echo (SE) imaging techniques, respectively. Brain injury correlated with the perfusion level measured in both SE CBV and dynamic GE CBF images. In the temporary MCAO model, mean lesion size in DWI was 118% larger and hemispheric CBV was reduced by 37% in hyperglycemic compared with normoglycemic rats. Hyperglycemia did not significantly exacerbate brain injury or CBV deficit in permanent MCAO models. We conclude that preexisting hyperglycemia increases acute postischemic MRI-measurable brain cellular injury in proportion to an associated increased microvascular ischemia.

Blood platelet uptake of serotonin in episodic aggression

Blood platelet uptake of 3H-serotonin (5HT uptake), a potential marker of serotonergic function, was determined in male outpatients with episodic aggression (n = 15) and in age- and sex-matched nonaggressive controls (n = 15). Correlations with rating scales of impulsivity (Barratt Impulsivity Scale, 10th revision) and anger (Spielberger Anger Expression Scale) were performed. Mean 5HT uptake was 18% lower in patients with episodic aggression. A significant negative correlation between % difference in platelet 5HT uptake and impulsivity score was observed, but the correlation between 5HT uptake and anger was not significant. These results support the hypothesis of disturbed serotonergic function in aggression and suggest that the primary relationship is in the control of aggression. The blood platelet may be useful in identifying impulsive subtypes.

Acute increase in expression of growth associated protein GAP-43 following cortical ischemia in rat

Focal cerebral ischemia creates an area of infarction that is surrounded by neuronal tissue that may respond to nearby damage by creating neurite growth. To determine if axonal sprouting occurs after infarction, antibodies to growth associated protein MW 43,000 (GAP-43), a protein expressed on axonal growth cones, were used to assess the level of GAP-43 immunoreactivity as a measure of sprouting. Cerebral ischemia was induced in spontaneously hypertensive rats by permanently occluding the distal middle cerebral artery and ipsilateral common carotid artery. After 1 week of recovery, the animals were perfused, the brains removed, processed, and optical densities of the immunoreaction were measured. The cortex surrounding the infarcted area had increased optical densities (mean +/- S.D. = 14.2% +/- 5.5) compared to the optical density values measured in similar areas in the contralateral hemisphere (mean +/- S.D. = 6.0% +/- 3.3), a 136% increase that is statistically significant, P < 0.05 Students t-test. We hypothesize that this increase in GAP-43 reaction product is due to axonal sprouting in the cortex surrounding an area of infarction. These data, coupled with previous work examining synaptophysin levels after cortical infarction, support the hypothesis of sprouting and synaptogenesis in the cortex following cerebral infarction.

Differential NF-κB regulation of bcl-x gene expression in hippocampus and basal forebrain in response to hypoxia

Cell death often occurs after hypoxic/ischemic injury to the central nervous system. Changes in levels of the anti‐apoptotic Bcl‐XL protein may be a determining factor in hypoxia‐induced neuronal apoptosis. The transcription factor NF‐κB regulates bcl‐x gene expression. In this study, we examined the role of NF‐κB in the regulation of bcl‐x in hypoxia‐induced cell death. Rat hippocampus and basal forebrain tissues were collected at different time points after hypoxia (7%O2, 93% N2 for 10 or 20 min). We found that 1) hypoxia induced apoptosis in the hippocampus and basal forebrain; 2) the NF‐κB dimers c‐Rel/p50 and p50/p50 bound to the bcl‐x promoter NF‐κB sequence (CS4) in the hippocampus, but only p50/p50 bound to the CS4 sequence in the basal forebrain and hypoxia‐induced differential binding patterns of c‐Rel/p50 and p50/p50 correlated with the bcl‐x expression pattern in the hippocampus; 3) the hypoxia‐induced patterns of binding of c‐Rel/p50 to the bcl‐x promoter CS4 sequence were different from those to the IgG‐κB enhancer sequence, whereas those of p50/p50 were similar to both sequences; 4) nuclear protein levels of c‐Rel, but not p50, correlated with the c‐Rel/p50 DNA binding patterns to the bcl‐x CS4 site; and 5) there were differential responses to hypoxia among the different NF‐κB protein subunits. These results suggest that there is a tissue‐specific regulation of bcl‐x gene expression by NF‐κB in hypoxia‐induced cell death in the hippocampus. The absence of these regulating features in the basal forebrain may account for the early appearance of apoptosis in response to hypoxia as compared with that in hippocampus. J. Neurosci. Res. 64:223–234, 2001.