Use of Anisotropy, 3D Segmented Atlas, and Computational Analysis to Identify Gray Matter Subcortical Lesions Common to Concussive Injury from Different Sites on the Cortex.

Traumatic brain injury (TBI) can occur anywhere along the cortical mantel. While the cortical contusions may be random and disparate in their locations, the clinical outcomes are often similar and difficult to explain. Thus a question that arises is, do concussions at different sites on the cortex affect similar subcortical brain regions? To address this question we used a fluid percussion model to concuss the right caudal or rostral cortices in rats. Five days later, diffusion tensor MRI data were acquired for indices of anisotropy (IA) for use in a novel method of analysis to detect changes in gray matter microarchitecture. IA values from over 20,000 voxels were registered into a 3D segmented, annotated rat atlas covering 150 brain areas. Comparisons between left and right hemispheres revealed a small population of subcortical sites with altered IA values. Rostral and caudal concussions were of striking similarity in the impacted subcortical locations, particularly the central nucleus of the amygdala, laterodorsal thalamus, and hippocampal complex. Subsequent immunohistochemical analysis of these sites showed significant neuroinflammation. This study presents three significant findings that advance our understanding and evaluation of TBI: 1) the introduction of a new method to identify highly localized disturbances in discrete gray matter, subcortical brain nuclei without postmortem histology, 2) the use of this method to demonstrate that separate injuries to the rostral and caudal cortex produce the same subcortical, disturbances, and 3) the central nucleus of the amygdala, critical in the regulation of emotion, is vulnerable to concussion.

Imaging the neural circuitry and chemical control of aggressive motivation.

BACKGROUND: With the advent of functional magnetic resonance imaging (fMRI) in awake animals it is possible to resolve patterns of neuronal activity across the entire brain with high spatial and temporal resolution. Synchronized changes in neuronal activity across multiple brain areas can be viewed as functional neuroanatomical circuits coordinating the thoughts, memories and emotions for particular behaviors. To this end, fMRI in conscious rats combined with 3D computational analysis was used to identifying the putative distributed neural circuit involved in aggressive motivation and how this circuit is affected by drugs that block aggressive behavior. RESULTS: To trigger aggressive motivation, male rats were presented with their female cage mate plus a novel male intruder in the bore of the magnet during image acquisition. As expected, brain areas previously identified as critical in the organization and expression of aggressive behavior were activated, e.g., lateral hypothalamus, medial basal amygdala. Unexpected was the intense activation of the forebrain cortex and anterior thalamic nuclei. Oral administration of a selective vasopressin V1a receptor antagonist SRX251 or the selective serotonin reuptake inhibitor fluoxetine, drugs that block aggressive behavior, both caused a general suppression of the distributed neural circuit involved in aggressive motivation. However, the effect of SRX251, but not fluoxetine, was specific to aggression as brain activation in response to a novel sexually receptive female was unaffected. CONCLUSION: The putative neural circuit of aggressive motivation identified with fMRI includes neural substrates contributing to emotional expression (i.e. cortical and medial amygdala, BNST, lateral hypothalamus), emotional experience (i.e. hippocampus, forebrain cortex, anterior cingulate, retrosplenial cortex) and the anterior thalamic nuclei that bridge the motor and cognitive components of aggressive responding. Drugs that block vasopressin neurotransmission or enhance serotonin activity suppress activity in this putative neural circuit of aggressive motivation, particularly the anterior thalamic nuclei.

Imaging the neural substrates involved in the genesis of pentylenetetrazol-induced seizures.

PURPOSE: Functional imaging of animal models makes it possible to map the functional neuroanatomy contributing to the genesis of seizures. Pentylenetetrazol (PTZ)-induced seizure in rats, a relevant model of human absence and of generalized tonic-clonic epilepsy, was used to stimulate seizure activity within 30 s of administration while collecting continuous, high-resolution, multislice images at subsecond intervals. METHODS: Pilot studies were conducted to establish a quick and effective PTZ model for the imaging experiments. PTZ was then used to stimulate seizure activity in rats while collecting multislice functional MRI (fMRI) images from the entire forebrain at 4.7 Tesla. Ethosuximide (ESM) also was used to block seizure activity. RESULTS: Within 2-4 s of PTZ administration, a rapid increase in blood oxygen level-dependent (BOLD) signal intensity was noted in the thalamus, especially the anterior thalamic nuclei. Activity in the anterior thalamus peaked approximately 15 s before seizure onset and was more than twofold greater than that in all other thalamic areas. The retrosplenial cortex showed a twofold greater increase in activity as compared with other cortical areas, also peaking at approximately 15 s. The dentate gyrus was twice as active as other hippocampal areas but peaked just before seizure onset. Treatment with ESM blocked seizures, decreasing PTZ-induced activation in most forebrain areas. The anterior thalamus and retrosplenial cortex were essentially blocked by pretreatment with ESM. CONCLUSIONS: The anterior thalamus, retrosplenial cortex, and dentate gyrus show the greatest increases in BOLD signal activity before seizure onset. Neurons in these areas may contribute to the neural network controlling the initiation of generalized tonic-clonic seizure.

fMRI of generalized absence status epilepticus in conscious marmoset monkeys reveals corticothalamic activation.

PURPOSE: A nonhuman primate model of generalized absence status epilepticus was developed for use in functional magnetic resonance imaging (fMRI) experiments to elucidate the brain mechanisms underlying this disorder. METHODS: Adult male marmoset monkeys (Callithrix jacchus) were treated with gamma-butyrolactone (GBL) to induce prolonged absence seizures, and the resulting spike-wave discharges (SWDs) were analyzed to determine the similarity to the 3-Hz SWDs that characterize the disorder. In addition, blood-oxygenation-level-dependent (BOLD) fMRI was measured at 4.7 Tesla after absence seizure induction with GBL. RESULTS: Electroencephalographic recordings during imaging showed 3-Hz SWDs typical of human absence seizures. This synchronized EEG pattern started within 15 to 20 min of drug administration and persisted for >60 min. In addition, pretreatment with the antiepileptic drug, ethosuximide (ESM), blocked the behavioral and EEG changes caused by GBL. Changes in BOLD signal intensity in the thalamus and sensorimotor cortex correlated with the onset of 3-Hz SWDs. The change in BOLD signal intensity was bilateral but heterogeneous, affecting some brain areas more than others. No significant negative BOLD changes were seen. CONCLUSIONS: The BOLD fMRI data obtained in this marmoset monkey model of absence status epilepticus shows activation within the thalamus and cortex.

Corticothalamic modulation during absence seizures in rats: a functional MRI assessment.

PURPOSE: Functional magnetic resonance imaging (fMRI) was used to identify areas of brain activation during absence seizures in an awake animal model. METHODS: Blood-oxygenation-level-dependent (BOLD) fMRI in the brain was measured by using T2*-weighted echo planar imaging at 4.7 Tesla. BOLD imaging was performed before, during, and after absence seizure induction by using gamma-butyrolactone (GBL; 200 mg/kg, intraperitoneal). RESULTS: The corticothalamic circuitry, critical for spike-wave discharge (SWD) formation in absence seizure, showed robust BOLD signal changes after GBL administration, consistent with EEG recordings in the same animals. Predominantly positive BOLD changes occurred in the thalamus. Sensory and parietal cortices showed mixed positive and negative BOLD changes, whereas temporal and motor cortices showed only negative BOLD changes. CONCLUSIONS: With the BOLD fMRI technique, we demonstrated signal changes in brain areas that have been shown, with electrophysiology experiments, to be important for generating and maintaining the SWDs that characterize absence seizures. These results corroborate previous findings from lesion and electrophysiological experiments and show the technical feasibility of noninvasively imaging absence seizures in fully conscious rodents.

Seed finding in golden hamsters: a potential animal model for screening anxiolytic drugs.

Fasting hamsters overnight, followed by temporary isolation in a novel environment are stressful conditions that hamper their ability or motivation to find hidden sunflower seeds when returned to their home environment. Studies were done to test whether treatment with antianxiety drugs would reduce stress and shorten the latency to find the hidden seeds. Prior to testing, the animals were fasted for 18-20 h. Ninety minutes after intraperitoneal injection of test drugs (fluoxetine, buspirone, chlordiazepoxide, clozapine, desipramine, yohimbine), the animals were taken from their home cage and placed into a novel holding cage for 2 min. During their absence, 6 sunflower seeds were buried under the bedding in one corner of their home cage. The animals were placed back into their home cage and timed for their latency to find the seeds in a 5-min observation period. Treatment with anxiolytics caused a dose-dependent reduction in the latency to find the sunflower seed, while treatment with other psychotherapeutics were ineffective. Seed finding is an extremely sensitive bioassay, responding to anxiolytics given in doses as low as 1 microg/kg. These data provide evidence that seed finding in hamsters may serve as an animal model for screening potential anxiolytic drugs.