Supracallosal longitudinal fiber bundle: heterotopic cingulum, dorsal fornix or Probst bundle?

A thick longitudinal fiber bundle found within the dorsal corpus callosum in two unrelated adults (in a micrencephalic female patient and incidentally in another male patient) is considered to be a congenital aberrant cingulum. Agenesis or apparent hypoplasia of the indusium griseum of the limbic-cingular system as an accompanying finding in the present cases may support this hypothesis. The dorsal fornix and Probst bundle are discussed in terms of differential diagnosis, although there was no further support for this possibility. The hyperplastic dorsocallosal gray substance is excluded.

Effects of testosterone on hippocampal CA1 spine synaptic density in the male rat are inhibited by fimbria/fornix transection

This study investigated the contribution of sub-cortical afferent input to the effects of testosterone (T) on spine synapse density in the CA1 subfield of the hippocampus, in adult male rats. Gonadectomized (GDX) male rats exhibited a considerably lower density of spine synapses in the CA1 region than control, intact males. The effects of GDX were reversed by treatment with testosterone propionate (TP; 500 microg/day, for 2 days). Transection of the fimbria/fornix (FF) had no significant effect on the synaptic density in non-GDX males. However, FF transection partially inhibited the responses to TP in GDX animals. These data suggest that the effects of T on spine synapse density in the CA1 region of the male rat hippocampus are partially, but not completely, dependent on afferent sub-cortical input.

Gene expression profiling reveals multiple novel intrinsic and extrinsic factors associated with axonal regeneration failure

In contrast to the regeneration-competent peripheral nervous system (PNS), lesions of nerve tracts within the central nervous system (CNS) lead to chronically impaired neuronal connections. We have analysed changes in gene expression patterns occurring as a consequence of postcommissural fornix transection at a time when spontaneous axonal growth has ceased at the lesion site. This was done in order to describe both extrinsic and intrinsic determinants of regeneration failure. Using a genomic approach we have identified a number of so far undetected factors such as bamacan and semaphorin 6B, which relate to chronic axonal growth arrest and therefore are promising candidates for lesion-induced axonal growth inhibitors. In addition, we observed that within the subiculum, where the fornix axons originate, neuronal Oct-6 was induced and NG2 was down-regulated, indicating that axotomized neurons as well as glial cells react at the level of gene expression to remote axotomy.

[Tractography of the visual pathways: routine examination in magnetic resonance imaging]

Water diffusion analysis in magnetic resonance imaging (MRI) provides an elective visualization of fiber tract orientations in cerebral white matter, especially for optic tracts. We explored 25 patients from 18 to 45 years of age, with normal MRI in 20 subjects, and radiological anomalies in five. On a 1.5 Tesla MRI apparatus, diffusion tensor acquisitions were performed in 5 minutes 58 seconds with an EPI Single Shot sequence covering the entire brain. Image displacements were precluded by patient information and adequate fixation, then digitally corrected on workstations. Volume merging and fiber tract extraction were achieved using dedicated software (Volume-One and dTV). A directional depiction was obtained for all areas in the white matter, in particular for white matter junctions. Coming from the lateral geniculate body, the optic tracts were directed posteriorly toward the occipital cortex, with numerous connections to extrastriate associative areas, and through the corpus callosum and the fornix. Diffusion tractography requires optimization of volume displacements, before and secondary to MRI acquisitions. Our diffusion tensor acquisition, with image optimization in a short-duration sequence can be routinely applied to all patients, for a specific analysis of functional connections between cortical areas of cerebral white matter.

[Comparative study of bilateral lesions in the entorhinal cortex and in the fimbria fornix]

INTRODUCTION

Numerous reports show that lesions to hippocampus afferents, such as the entorhinal cortex (EC) and the fimbria fornix (FF), exert an effect on memory in rodents. There are, however, no long term comparative studies that show which of these lesions could be most useful as a model for studies into neuroplasticity.

MATERIAL AND METHODS

Young male Sprague Dawley rats were used. Bilateral electrolytic lesion was caused to the EC or the FF was damaged by transection. One, four or 12 weeks later the animals were evaluated in a Morris water maze, first with an invisible platform and then with the platform within view. The results from the two groups were compared to each other and to those obtained from healthy controls and subjects with false lesions by means of a variance analysis.

RESULTS

In the test with an invisible platform, both types of lesion gave rise to serious, irreparable involvement of the spatial memory of the animals, at least up to 12 weeks after the lesion. The test with the visible platform revealed significant differences between animals with lesion to the EC evaluated at 12 weeks, which suggests the development of some visual or motor deterioration in these animals.

CONCLUSIONS

Although both lesions gave rise to behavioural deterioration that was irreversible in the long term in rodents, the lesion to the FF seems to be a better model for evaluating specific effects on learning and memory, since the lesion to the EC apparently triggers additional sensory and motor involvement.

Significance of fornix atrophy in temporal lobe epilepsy surgery outcome

BACKGROUND

Previous magnetic resonance imaging (MRI) studies have shown concurrent fornix atrophy in a large proportion of patients with hippocampal atrophy. The contribution of the fornix as an independent preoperative determinant of surgical outcome is unknown.

OBJECTIVE

To evaluate the contribution of the fornix as a determinant of surgical outcome in patients with preoperatively determined temporal lobe epilepsy.

METHODS

We selected 78 patients who had undergone anterior temporal lobectomy for intractable temporal lobe epilepsy at the University of Alabama at Birmingham Epilepsy Center during a 24-month period. All patients underwent standard presurgical investigations and intracranial investigations when needed. Magnetic resonance imaging volumetric studies were performed prior to surgery using previously published techniques. Patients were assessed regularly for postoperative seizure control. Outcome after at least 3 years was evaluated using Engel's classification for epilepsy. The chi2 test was used to compare categorical data.

RESULTS

Seventy-eight patients were included in this study. Eight patients were excluded because of inadequate follow-up. Thirty-five patients (44.9%) had unilateral isolated hippocampal atrophy exclusively on MRI volumetry, 29 (37.2%) had unilateral hippocampal atrophy with ipsilateral fornix atrophy, and 6 (7.7%) had isolated fornix atrophy without hippocampal atrophy. Twenty-eight patients (80%) in the unilateral hippocampal atrophy group were seizure free (ie, Engel class 1: patients who are completely seizure free with no aura and who do not receive antiepileptic drugs) compared with 21 patients (73%) in the fornix and hippocampal atrophy group (P =.57). All 6 patients with isolated fornix atrophy achieved an Engel's class 1 outcome.

CONCLUSIONS

These findings suggest that identification of fornix atrophy with or without associated hippocampal atrophy is not an important preoperative determinant of surgical outcome. However, in the presence of a normal hippocampus, fornix atrophy may be valuable in predicting seizure-free outcome.

Analysis of parahippocampal gyrus in 115 patients with hippocampal sclerosis

PURPOSE: Analysis of the parahippocampal gyrus (PHG) involvement in 115 patients with hippocampal sclerosis (HS) by MR imaging. The simultaneous occurrence of ipsilateral fornix (F) and mamillary body (MB) volume loss was checked also. These findings were correlated with the side of hippocampal involvement, the sex, patient´s age, and the symptoms onset. METHOD: The MR images of 115 patients with HS were studied retrospectively. All the examinations were performed on 1.5 T units (SIGNA, GE, Milwaukee, WI) and included high resolution coronal T2-weighted images (3 mm thickness, 0.6 mm gap). RESULTS: The patient's age ranged between 3.5 and 80 years (mean 34.1); 62 (53.9%) were female and 53 (46.1%) were male. There were HS on the left side in 53 (46.0%), on the right side in 51 (44.3%), and bilateral in 11 (9.7%). In 43 (37.3%) cases there were ipsilateral PHG volume loss and signal hyper intensity on T2-weighted imaging. In 29 (25.2%) cases there were ipsilateral fornix volume loss and in 10 (34.5%) of this there were also ipsilateral MB changes. In abnormal PHG, 23 (53.4%) were on the left side, 17 (39.5%) were on the right side, and 3 (7.1%) were bilateral. There were fornix changes in 15 (34.8%) cases and MB volume loss in 5 (11.6%) cases. Pertinent clinical data were obtained in only 18 (41.8%) of the PHG lesion cases and 11 (61.1%) of these patients had epileptic attacks for more than 20 years before the examination. CONCLUSION: PHG involvement must be investigated in patients with HS and we suggest that the term mesial temporal sclerosis should be used only if there are also changes at this anatomical site.

The Mechanism of Fornix Lesions in 3rdVentriculostomy

Fornix lesions as a complication of 3rd ventriculostomy are rare and almost not reported. However, in our series of 94 procedures we observed 5 fornix lesions. Although we did not find any clinical deterioration, we were alarmed by these unexpected incidences and analysed the mechanism. All fornix lesions occurred using an endoscope sheath with separated channels for the endoscope itself, the instruments and for rinsing and suction. The limited field of view suggests the surgeon to be already inside the 3rd ventricle while the tip of the scope is still in the lateral ventricle just before the foramen of Monro. The instrument enters the optic field--depending on the used optic--as lately as 2 to 3 mm. The analysis showed that the lesions happened when the instruments were in the blind angle of the endoscope's optic which itself was outside of the foramen of Monro. Being aware of this mechanism with its potential risks it did not occurred again.

Involuntary, unreinforced (pure) spatial learning is impaired by fimbria-fornix but not by dorsal hippocampus lesions

Pure spatial learning occurs when rats acquire information about an environment while exploring it in the absence of reinforcers. We previously reported that voluntary, unreinforced exploration of a radial maze retards subsequent reinforced conditioned cue preference (CCP) learning in the same maze. In the present experiment, we examined the effects of involuntary, unreinforced pre-exposure to a radial maze. During pre-exposure, rats were moved by an experimenter between the ends of two arms of a radial maze five times in 30 min. This form of pre-exposure retarded CCP learning, whereas rats that were not pre-exposed and rats that were pre-exposed to a maze in a different room displayed normal CCP learning. These findings suggest that some information specific to the maze environment was acquired during involuntary unreinforced pre-exposure to it. In experiment 2, the retardation of reinforced CCP learning by involuntary unreinforced pre-exposure was eliminated by fimbria-fornix lesions made before pre-exposure but was unaffected by fimbria-fornix lesions made after pre-exposure but before training. Large neurotoxic lesions of the dorsal hippocampus made before pre-exposure had no effect on the retardation of CCP learning, but the rats with these lesions were impaired on a standard test of reinforced spatial learning in a water maze. The lesion effects in experiment 2 are similar to those previously reported for voluntary exploration and suggest that pure spatial learning may occur during both voluntary exploration of and involuntary exposure to an environment in the absence of reinforcers. Pure spatial learning can apparently occur with exposure to two different locations within an environment, but the rats do not have to move between the locations voluntarily. An intact fimbria-fornix is required for acquisition but not expression of this form of learning. The hippocampus is not involved in this form of learning.

Effect of Neuregen nutrient medium on survival of cortical neurons after aspiration lesion in rats

OBJECT

During brain surgery, it would be beneficial to irrigate the surgical cavity with a solution that promotes neuronal growth and survival. The authors find that incubation of cultured neurons with normal saline, also known as buffered salts, which are often used in brain surgery in humans, does not support neuron survival. Neuregen is an optimized serum-free culture medium that promotes regeneration of adult rat and human central nervous system neurons in vitro. It includes balanced salts, glucose, amino acids, vitamins, essential fatty acids, hormones, antioxidants, and other ingredients. The authors hypothesize that brain lesions irrigated and soaked in Neuregen nutrients will have better neuron survival rates in deafferented regions than lesions irrigated with saline.

METHODS

Lesioning of the rat fimbria-fornix area was achieved by aspiration through the cortex; animals were killed 4 weeks later. Brain sections were stained with cresyl violet for neuron counts in the medial septum and cortex. Treatment of the lesion cavity with Neuregen resulted in a 55% increase in neuron density in the septum compared with saline treatment (p = 0.02). Cortical lesions treated with Neuregen showed a 27% increase in neuron density compared with saline-treated lesions (p = 0.015); the neuron density in Neuregen-treated rat brains was equivalent to that seen with sham treatment. Efficacy of Neuregen with basic fibroblast growth factor (bFGF) was significantly better than with Dulbecco modified Eagle medium bFGF, but not better than Neuregen alone. Neuregen produced a coincidental fourfold reduction in glial fibrillary acidic protein immunoreactivity at 4 weeks compared with saline (p = 0.002), to levels equivalent to those found in sham lesions.

CONCLUSIONS

These results indicate that a highly optimized nutrient medium promotes neuron survival after brain surgery.

Suprasellar arachnoidal cyst as a cause of precocious puberty--report of three patients and literature overview

The authors present three boys--3 years old, 5.8 years old and 10.4 years old--who were diagnosed with isosexual precocious puberty (IPP) triggered by a rare developmental disorder of suprasellar arachnoid cyst (SAC) accompanied by corpus callosum and fornix dysgenesis as well as anterior commissura magna agenesis (patient 1) and empty sella (patients 2, 3). The reason for diagnostic management recommendation was a rapid progression of IPP signs over one year (patients 1, 2) or 6 months (patient 3) prior to hospitalization, these signs having been present but less intense since infancy (patient 1), 4th year of life (patient 2) and approximately 8 years of age (patient 3). Neurological signs (spastic paresis in patient 1, postural tremor in patient 2 and head bobbing and behavioral changes in patient 3), as well as slowly progressing increased head circumference were observed since neonatal period (patient 1), 1 year old (patient 2) and approximately 4 years old (patient 3). None of the patients manifested hypophyseal-hypothalamic axis dysfunction other than IPP prior to and after surgical management. Shunt implantation resulted in gradual resolution of neurological signs in all patients and in patient 3 also in partial normalization of serum testosterone levels and growth rate. Regression of IPP in patients 1 and 2 was achieved by administration of a long-acting GnRH analogue. Our observations are in accord with data reported by other investigators and confirm the often slow, insidious development of subsequent SAC signs, the type and intensity of which differ from patient to patient. We suggest that some of the neuroanatomical anomalies coexisting with SAC may have a common genesis, or they could under certain conditions be an additional trigger for IPP and possibly other hypothalamopituitary dysfunction.

Malformations of the midline commissures: MRI findings in different forms of callosal dysgenesis

Malformations of the corpus callosum (CC) may occur in many different syndromes. Various forms have been observed. We report seven cases of malformation of the CC. Special attention is directed towards the development of the fornix and hippocampus as a hippocampal commissure is a prerequisite of normal hippocampal development. The clinical disability of the patients presented here differed significantly, which may in part be due to the different extent of this cerebral malformation. The relevance of the concomitant aplasia of the limbic system has not been addressed in detail previously in the literature.

Memory Implications of a “Fornix White Line” in HIV Infection

The "fornix white line" (FWL) is a brain abnormality detected on magnetic resonance imaging (MRI) in some people with human immunodeficiency virus (HIV) infection. This finding has previously been associated with clinical findings of cognitive disturbance, particularly regarding memory. The current study provides preliminary substantiation of the previously reported clinical finding of FWL-associated memory disturbance through formal psychometric evaluation over time. Specifically, despite comparable baseline performances, 8-10 months later subjects without the FWL improved performance on neuropsychological verbal memory testing, while subjects with the FWL declined; the magnitude of this dissociation on follow-up was 1.5 to 2.2 standard deviations. In contrast, general cognitive status, as assessed through performance on the Mini-Mental State Exam, remained comparable between groups and stable over time. Further, the comparable CD4 count and Karnofsky scores at baseline counters the argument that the FWL is simply a marker of HIV disease progression. These preliminary findings suggest the need for future research of the hypotheses raised thereby; particularly salient is the hypothesis that the FWL may serve as an earlier marker indicating anti-CMV treatment before memory impairment is clinically apparent.

Selective impairments in rats on an odor-guided continuous delayed nonmatching-to-sample (cDNMS) task after fornix transection

The two experiments reported in this article examined recognition of simple and complex olfactory stimuli. In Experiment 1, three groups of control rats were trained to criterion without delay then, tested with delays on a continuous delayed nonmatching-to-sample (cDNMS) task using one of three kinds of odor pairs: replicates of the same odor (S), different odors that were each common with another pair (O), different odors with no overlap between pairs (NO). Results showed that initial learning and performance with delays were both poorer for O pairs than for S and NO pairs. Experiment 2 used a within-subject design to study the effects of fornix transection on recognition of the same three kinds of odor pairs as those described for Experiment 1. Sham-operated controls and rats (SH) with fornix transection were trained to criterion prior to the test with delays first on S, then on O and, finally, on NO pairs. During training, numbers of sessions to criterion did not differ in lesioned and SH rats on any of the three kinds of pairs. During testing, the level of performance was delay-dependent in both groups. However, lesioned rats were significantly impaired when tested with S and O pairs, but did not differ from sham-operated controls when tested with NO pairs. This selective impairment can be interpreted as evidence that fornix lesions impair recognition memory of stimuli that provide few and/or confusing retrieval cues. It might also suggest that postlesional performance on DNMS procedures depends on task difficulty.

Ruptured pericallosal aneurysm causing hemorrhage along the fornix

We present a 57 year-old man with a pericallosal aneurysm causing parenchymal hemorrhage in the preseptal region of the frontal lobe with extension into the fornix. We briefly discuss the literature pertaining to ruptured pericallosal aneurysms and their bleeding patterns.

Fimbria-fornix lesions disrupt the dead reckoning (homing) component of exploratory behavior in mice

Exploration is the primary way in which rodents gather information about their spatial surroundings. Thus, spatial theories propose that damage to the hippocampus, a structure thought to play a fundamental role in spatial behavior, should disrupt exploration. Exploration in rats is organized. The animals create home bases that are central to exploratory excursions and returns, and hippocampal formation damage alters the organization of exploration by disrupting returns. Mice do not appear to readily establish home bases in novel environments, thus, for this species, it is more difficult to establish the contribution of the hippocampus to exploration. The purpose of the present study was threefold: develop a task in which mice center their exploration from a home base, determine whether the exploratory behavior is organized, and evaluate the role of fimbria-fornix lesions on exploration. Mice were given a novel exploratory task in which their nesting material was placed on a large circular table. Video records of control and fimbria-fornix mice were made in both light and dark (infrared light) conditions. Exploration patterns (outward trips, stops, and homeward trips) were reconstructed from the video records. Control mice centered their activity on their bedding, from which they made circuitous outward trips marked by many stops, and periodic direct returns. The bedding-centered behavior and outward trips of the fimbria-fornix mice were similar to those of the control mice, but significantly fewer direct return trips occurred. The direct homeward trips observed under light and dark conditions were consistent with a dead-reckoning strategy, in which an animal computes its present position and homeward trajectory from self-movement cues generated on the outward trip. Because the fimbria-fornix lesions disrupted the homeward component of exploratory trips, we conclude that the fimbria-fornix may contribute to dead reckoning in mice. The results also show that the home-bedding methodology facilitates the establishment of a home base by mice, thus providing a useful methodology for studies with mice.

Akinetic mutism caused by bilateral infiltration of the fornix in a patient with astrocytoma

In a 59-year-old female patient, a World Health Organization (WHO) grade II astrocytoma had been diagnosed 16 years ago, which finally progressed into WHO grade III. Several right frontal neurosurgical resections, local radiation and a local radioimplant had been applied. Despite this long record, she was reported alert with a Karnofsky index of 90% until admission. Within a few weeks she rapidly developed akinetic mutism. Upon admission, computed tomography (CT) scan showed a large cystic right frontal defect and a suggested small tumor recurrence. White matter of the frontal lobe appeared to be translucent and compatible with previous radiation. The severe mental changes were initially attributed to a delayed radiation encephalopathy. Neuropathologically, the white matter of the frontal lobe showed mild elevated cell density consistent with gliosis; however, a tumor recurrence invading the tip of the corpus callosum and invading the entire length both fornices appeared. From the neuropathological findings of massive local tumor recurrence in both fornices, together with the acute clinical onset, it seems unlikely that the sequel of radiotherapy caused akinetic mutism, but the symmetric and severe involvement of the limbic system. We conclude that the rapid progression from a state of alertness to a full clinical picture of akinetic mutism was because of infiltration of both fornices.

Diagnostic imaging and clinical findings in rhombencephalosynapsis: case report and literature review

Rhombencephalosynapsis is a rare condition in which most cases are found in newborns and infants. Morphological findings are predominantly characterized by fusion of the cerebellar hemispheres and absence of the vermis with often associated supratentorial anomalies. We review the literature with emphasis on diagnostic imaging of this condition and present a case of a 2-year-old girl.

Heavily T2 weighted MR assessment of fornical injury after anterior interhemispheric approach for large suprasellar tumors

Fornical injury in transforaminal approach is well known. Its injury in the anterior interhemispheric approach (AIA) has been rarely highlighted. We report 2 cases with a large suprasellar tumor who underwent AIA. Postoperative heavily T2 weighted reversed (T2R) MR images demonstrated its unilateral injury. The clinical significance of symptom-free fornical injury after AIA is discussed. Cases 1 and 2 were a 15 year-old girl with a meningioma and a 49-year-old woman with a craniopharyngioma, respectively. They underwent AIA. Postoperative T2R images revealed unilateral fornical crus atrophy. They did not present associated memory deficits. Case 1 had the injury of both fornical column and anterior commissure. They were speculatively torn by intra-operative lateral retraction of the frontal lobes. Case 2 had unilateral atrophy of the mammillary body and postcommissural fornix, which were probably caused by ischemic damage related to surgical manipulation, since case 2 had an associated anterior thalamic infarct. During the operation for large suprasellar tumors, excessive laterally directed brain retraction should be avoided, since such manipulation may easily tear the overstretched anterior commissure and fornical column. Once we notice or suspect fornical injury on MR studies in cases of re-operation, we have to choose a surgical approach and operative manipulation to preserve an intact fornix. The MR evaluation of fornix should be included in the perioperative radiological assessment, since patients with unilateral fornical injury were free of memory disturbance, and T2R imaging is a useful MR sequence for depicting the anatomy related to the fornix.

Axonal transection in adult rat brain induces transsynaptic apoptosis and persistent atrophy of target neurons

We used the fimbria-fornix (FF) transection model of axonal injury to test the hypothesis that transneuronal degeneration occurs in the adult central nervous system in response to deafferentation. The medial mammillary nucleus, pars medialis (MMNm) was analyzed by light and electron microscopy at 3, 7, 14, and 30 days, and 6 months after unilateral FF transection in adult rat to identify the time course of neuronal responses in a remote target. Presynaptic terminals and neuronal cell bodies degenerated in the MMNm ipsilateral to FF transection. Terminal degeneration occurred predominantly at 3 and 7 days postlesion. Between 14 and 30 days postlesion, neuronal number in the MMNm decreased (approximately 20%). Two forms of neuronal degeneration were found in the MMNm after deafferentation. Some neurons died apoptotically. Other neurons underwent vacuolar degeneration. In these latter neurons, somatodendritic pathology occurred at 14 and 30 days and 6 months postlesion. The ultrastructure of this vacuolar degeneration was characterized by disorganization of the cytoplasm, formation of membrane-bound vacuolar cisternae and membranous inclusions, loss of organelles, cytoplasmic pallor, and chromatin alterations. This study shows that both anterograde axonal degeneration and transneuronal degeneration occur in a fornical target after FF axon transection. This transneuronal degeneration can be classified as sustained neuronal atrophy or transsynaptic apoptosis.

Heavily T2-weighted MR imaging of white matter tracts in the hypothalamus: normal and pathologic demonstrations

BACKGROUND AND PURPOSE

The MR appearance of white matter tracts in the hypothalamus and the role of the hypothalamus as a memory mechanism have not been sufficiently described in clinical settings. Heavily T2-weighted black-and-white reversed (T2R) images were assessed to reveal their visualization and clinical significance.

METHODS

One hundred healthy subjects and three patients with hypothalamic lesions underwent fast spin-echo MR imaging to reveal the postcommissural fornix (PF) and mammillothalamic tract (MT).

RESULTS

The PF was identifiable in axial and/or coronal sections in all healthy subjects. No remarkable asymmetry of its size or course was evident. Both anteroposterior and vertical dimensions ranged from 10.5 to 14 mm. The MT was visible in one or two axial sections above the mammillary body in 64% of healthy subjects and in a coronal section in 36%. Two patients with glioblastoma multiforme and lacunar infarct at the hypothalamus presented with anterograde amnesia; T2R imaging revealed involvement of both the PF and MT. The third patient had a suprasellar craniopharyngioma with PF injury sparing the MT resulting from surgical manipulation and was free of memory deficit. Anterograde amnesia was evident only when both the PF and MT were injured.

CONCLUSION

T2R images have made a high rate of detection of the PF and MT possible and could provide a more detailed correlation of hypothalamic neuroanatomy and memory mechanism in clinical settings.

Reduced corpus callosum, fornix and hippocampus in PDAPP transgenic mouse model of Alzheimer's disease

Persons with Alzheimer's disease (AD) have progressive reductions in the relative sizes of the corpus callosum and hippocampus. Homozygotic PDAPP transgenic mice over-expressing a mutant form of the human amyloid precursor protein have more pronounced reductions in these regions, which are apparent prior to the deposition of amyloid plaques and do not progress with advancing age. The length of the corpus callosum was reduced by two-thirds, the fornix commissure was negligible, and the hippocampal volume was reduced by one-third, suggesting a massive disconnection between the cerebral hemispheres and the hippocampi in PDAPP mice. These findings, which might account for the early, nonprogressive behavioral abnormalities observed in these animals, have implications for the study of AD.

Verbal memory deficits associated with fornix atrophy in carbon monoxide poisoning

Magnetic resonance (MR) images and neuropsychological testing data of 69 carbon monoxide (CO) poisoned patients were prospectively obtained within 1 day of CO poisoning, two weeks and six months. CO patients' Day 1 cross-sectional fornix surface area measurements, corrected for head size by using a fornix-to-brain ratio (FBR), were compared to normal age and gender-matched controls. Additionally, a within-subjects analysis was performed comparing the mean areas between CO patients' Day 1, 2 weeks and 6-month FBR. The FBR was correlated with patients' neuropsychological data. There were no significant differences between CO patients' Day 1 fornix measurements compared to normal control subjects. However, significant atrophic changes in the fornix of CO poisoned patients occurred at two weeks with no progressive atrophy at 6 months. By 6 months, CO patients showed significant decline on tests of verbal memory (when practice effects were taken into account), whereas visual memory, processing speed and attention/concentration did not decline. This study indicates that CO results in brain damage and cognitive impairments in the absence of lesions and other neuroanatomic markers.

Electrically evoked release of glutamate in rat hippocampal slices: effects of various drugs and fimbria-fornix lesions

A model of electrically evoked release of glutamate from rat hippocampus was developed and used to detect possible changes induced by lesions of hippocampal afferences. Neuronal glutamate in hippocampal slices was labelled by preincubation with [3H]glutamine. The slices were then superfused with physiological medium in the presence of the glutamate uptake inhibitor L-transpyrrolidine-2,4-dicarboxylic acid (100 microM or 3 microM) and stimulated twice electrically (S1, S2: 240 pulses, 3 Hz, 2 ms, 26-30 mA); various drugs were added before S2. In order to determine the basal and evoked outflow of [3H]glutamate only, the mixture of 3H-labelled compounds (glutamine, glutamate and GABA) was separated by ion exchange chromatography in superfusate fractions and slices. The electrically evoked overflow of [3H]glutamate was largely Ca2+-dependent and tetrodotoxin-sensitive and hence represented action potential-induced exocytotic release of [3H]glutamate. Evoked [3H]glutamate release was significantly increased by the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 microM), suggesting the presence of endogenous inhibitory adenosine, and reduced by the A1 receptor agonist N6-cyclopentyladenosine (1 microM, antagonized by DPCPX, 0.1 microM). There was no evidence for a cholinergic, serotonergic, or adrenergic modulation of the evoked release of [3H]glutamate: the corresponding selective agonists (or antagonists) were ineffective. After aspirative lesions of the septohippocampal pathways the hippocampal noradrenaline content was markedly increased, whereas cholinergic and serotonergic markers were reduced. The evoked release of [3H]glutamate in hippocampal slices of lesioned rats was significantly increased by a mechanism which still has to be determined, but which is not related to alterations in A1 receptor function. It is concluded that the present model was able to detect lesion-induced differences in electrically evoked release of [3H]glutamate, but the relationship of these differences to changes of noradrenergic, cholinergic or serotonergic hippocampal innervations remains to be established.

The time course of the hyperactivity that follows lesions or temporary inactivation of the fimbria-fornix

Lesions of the hippocampus or the fimbria-fornix produce a pronounced hyperactivity in rats. This effect is thought to be due to the loss of glutamatergic hippocampal inputs to the nucleus accumbens, although the mechanisms involved remain unclear. It has been suggested that the hyperactivity is due to changes in accumbens dopamine receptors, possibly involving the gradual development of denervation supersensitivity. Consistent with this possibility, the present study found that fimbria-fornix transection produced hyperactivity which, although undetectable immediately after surgery, gradually became apparent and then continued to increase over the course of several days. This does not, however, preclude the possibility that there is an immediate increase in activity which is masked by the after effects of surgery. To address this issue, local anaesthetic was infused into the fimbria-fornix via chronic indwelling cannulae, in order to silence the hippocampal inputs to the nucleus accumbens. This procedure impaired spatial working memory on the elevated T-maze and resulted in immediate hyperactivity, suggesting that there may be at least two components to fornix lesion-induced hyperactivity, and that the immediate effects of mechanical fornix lesions on activity levels may be masked by the after effects of surgery per se.

Enlargement of the fornix in early-onset schizophrenia: a quantitative MRI study

Abnormalities of temporal lobe structure and frontal lobe function occur in schizophrenia. There have been few studies of young people with schizophrenia and little is known about temporo-frontal connectivity in the disease. Therefore, the cross-sectional area of the body of the fornix was measured on MR images from 17 young people with schizophrenia, nine with other serious psychiatric illnesses and eight without illness. The mean age of each group was 16-17 years. The mean cross-sectional fornix area in subjects with schizophrenia was significantly larger than that in subjects without illness ( approximately 40%) and psychiatric controls ( approximately 26%). There was no such significant difference between subjects without illness and psychiatric controls. The nature of the larger fornix in early-onset schizophrenia, whether it persists and whether it occurs in schizophrenia presenting in adulthood, remain to be elucidated.

[Morphological abnormalities of limbic lobe structures in partial temporal lobe epilepsy]

PURPOSE

To evaluate lesions of the different structures of the Papez circuit in association with hippocampal sclerosis.

MATERIAL

and methods. 13 patients (32.1+/-8.2 y.o.) suffering from partial, temporal lobe, drug-resistant epilepsy and 20 normal volunteers (31.8+/-7.7 y.o.) were evaluated by MRI on a 1.5 T scanner (Philips): axial T1w 3D Gradient Echo acquisitions, thickness: 1.5mm. Hippocampus and cingulate gyrus volume were calculated after semi-automated segmentation of intrasulcal gray matter using the "Surgiscope Scopeplan" Elekta((R)). The thickness of the posterior column of the fornix and the thickness of the mamillary bodies were also measured.

RESULTS

We found 10 cases of ipsolateral hippocampal sclerosis, 6 cases of ipsolateral atrophy of the mamillary body and 4 cases of ipsolateral atrophy of the fornix. We did not find any atrophy of the cingulate gyrus.

CONCLUSION

Hippocampal sclerosis can be associated with lesions of limbic lobe structures (fornix and mamillary body), excluding the cingulate gyrus.

Long term modulation of the HPA axis by the hippocampus. Behavioral, biochemical and immunological endpoints in rats exposed to chronic mild stress

Mature rats were given lesions of the hippocampus (HIPPO), subiculum (SUBIC) or fimbria-fornix (FIFO) and then received the mild chronic stressors of food deprivation and isolation housing for ten months prior to testing. Group differences in circadian activity were investigated along with locomotion elicited by amphetamine (AMP 1.0-2.0 mg/kg i.p.) alone, and following the corticosterone (CORT) synthesis inhibitor, metyrapone (MET 10.0-25.0 mg/kg i.p.). Basal levels of plasma CORT, (ng/ml), plasma glucose (GLUC, mmol/l), thymic and splenic wet weights were subsequently determined along with complete blood counts (CBC). In comparison to age matched, unoperated controls, selective SUBIC lesions altered the circadian periodicity of locomotion, while rats with FIFO lesions were spontaneously hyperactive. Both HIPPO and FIFO animals showed significantly higher levels of amphetamine-induced locomotion. In all groups metyrapone significantly enhanced locomotion elicited by amphetamine, probably due to a pharmacokinetic interaction between these drugs. In comparison to controls, animals in the HIPPO group showed significant reductions in plasma glucose levels, decreased thymic wet weights and reductions in lymphocyte numbers, indicating lesion-related immuno-suppression. These findings highlight a functional difference among the effects of these specific hippocampal lesions on neural regulation of the HPA axis, under conditions of chronic mild stress, suggesting that the modulatory influence of the hippocampus on the stress axis is dependent on the neuroanatomical location and total extent of cell loss within this structure. They further suggest that the heightened response to amphetamine occurs independently of any lesion-induced changes in modulation of the HPA axis.

A quantitative MR measure of the fornix in schizophrenia

Some cognitive disturbances accompanying schizophrenia may be due to abnormalities in the thalamus and components of the limbic system. The fornix is an important white-matter relay pathway connecting these structures and is likely to be affected in schizophrenia as well.Magnetic resonance images of the fornix were analyzed in 15 schizophrenic patients and 15 matched comparison group subjects. Fornix volume was compared between the two groups and was also correlated with the volumes of other neuroanatomical structures, as well as with illness presentation, clinical status, and cognitive/psychological measures. There was no significant difference in fornix volume between the two groups. Of note, fornix volume correlated significantly with the volumes of the hippocampus, parahippocampus, and the superior temporal gyrus in the schizophrenic subjects, but not in the controls. Moreover, the correlation between fornix and parahippocampal gyrus volumes differed significantly between the two groups. No association was found between fornix volume and illness presentation or between fornix and cognitive/clinical measures.Results suggest that there are no marked changes in fornix volume in schizophrenia by MRI. The fornix, however, may be part of a network of structures affected in schizophrenia, as indicated by correlated volumetric changes.

Impaired recognition memory in rats after damage to the hippocampus

Rats with radio-frequency or ibotenic acid lesions of the hippocampus and rats with radio-frequency lesions of the fornix were tested on the visual paired comparison task (VPC), a test of recognition memory. Memory was assessed at five different delay intervals ranging from 10 sec to 24 hr. All operated groups performed normally at the shorter delays (10 sec and 1 min). Across longer delays, the two groups with hippocampal damage were impaired. Rats with fornix lesions performed well on the VPC task but were impaired on a spatial task (spontaneous alternation). The results show that the hippocampus is essential for normal recognition memory. Moreover, fornix lesions need not mimic the effects of direct damage to hippocampal tissue. The findings are discussed in the context of the contribution of the hippocampus to recognition memory.

Using fos imaging in the rat to reveal the anatomical extent of the disruptive effects of fornix lesions

Activity of the immediate early gene c-fos was compared across hemispheres in rats with unilateral fornix lesions. To engage Fos production, rats first performed a radial arm maze task that is severely disrupted by bilateral fornix lesions. Using immunohistochemical techniques, Fos-positive cells were visualized and counted in 39 sites in both hemispheres. Fornix lesions led to a significant reduction in Fos in all ipsilateral hippocampal subfields, as well as the entorhinal cortex and most of the subicular complex. Other sites that showed reduced activity included the ipsilateral retrosplenial, anterior cingulate, and postrhinal cortices. Subcortical regions showing significant Fos decreases included the anterior thalamic nuclei, supramammillary nucleus, diagonal band of Broca, and lateral septum. Thus, the effects of fornix lesions extended beyond the hippocampal formation and included sites not directly innervated by the tract. These changes were nevertheless selective, as shown by the lack of hemispheric difference in any of the preselected control sites, the perirhinal cortex, or nucleus accumbens. Furthermore, there were no hemispheric differences in an additional group of animals with unilateral fornix lesions that were killed directly from the home cage. The location of Fos changes closely corresponded to those brain regions that when lesioned disrupt spatial working memory. Moreover, there was a correspondence between those brain regions that show increased Fos production in normal animals performing the radial arm maze task and those affected by fornix lesions. These results show that fornix transection has widespread, but selective, effects on a network of structures normally activated by spatial memory processes, with these effects extending beyond the hippocampal formation.

Fornix and hippocampal atrophy in traumatic brain injury

This study compared a fornix cross-sectional-area measurement and hippocampal volume in 86 traumatic brain injury (TBI) subjects with 46 normal controls. The TBI group showed a significant reduction in fornix area and hippocampal volume. It was also shown that initial injury severity was related to the degree of atrophy in both structures. Although fornix size and hippocampal volume correlated, such a modest correlation between these two structures suggests differential and potentially independent mechanisms of injury. The General Memory Index score from the Wechsler Memory Scale-Revised was shown to be significantly correlated with hippocampal volume following TBI.

Effects of fetal septal grafts on memory and learning performance with hippocampal acetylcholine and choline metabolism in fimbria transected rats

Female Sprague-Dawley rats underwent aspirative lesion of the fimbria to produce septohippocampal disconnection. Two weeks after the lesion surgery, fetal septal grafts prepared from ventral forebrain of 13-15 days old fetuses of the same outbred strain were placed into the lesion cavity (grafted group). Three months after grafting, all rats were tested for spontaneous motor activity (SMA), step through passive avoidance (STPA) and in Morris' water maze (MWM). Six months after grafting, both basal and stimulated acetylcholine (ACh) and choline (Ch) release and their tissue levels were measured in ipsilateral hippocampal slices. Septohippocampal disconnection caused a significant impairment in Morris' water maze tasks, but did not alter spontaneous motor activity and step through passive avoidance. Fimbrial lesion, moreover, also declined both stimulated ACh release and tissue ACh levels in hippocampal slices. While lesion-induced change in Morris' water maze was ameliorated partially, declines in both stimulated ACh release and tissue ACh levels were raised to the control levels by fetal septal graft placed into the lesion cavity. These data show that grafted cholinergic neurons can work biochemically which may not result with a complete behavioral amelioration which is, in fact something more complex.

Amnesia due to fornix infarction

Background and Purpose-The fornix connects various structures involved in memory. We report a patient with anterograde amnesia after an acute ischemic infarct in the anterior fornix. Case Description-A 71-year-old female with acute-onset amnesia had neuroimaging studies showing ischemic infarction of both columns and the body of the fornix and the genu of the corpus callosum. Neuropsychological evaluation revealed anterograde amnesia without evidence of callosal disconnection. The patient showed marked improvement in her memory function on the follow-up visit. Conclusions-Amnesia in this case is likely due to infarction of the anterior fornix structures.

An analysis of atrophy in the medial mammillary nucleus following hippocampal and fornix lesions in humans and nonhuman primates

Lesions of the hippocampal formation or transections of the fornix are followed by shrinkage of the medial mammillary nucleus (MMN). We determined whether the shrinkage of this nucleus was due to loss and/or shrinkage of neurons in addition to the loss of neuropil. We examined the MMN in a patient (KB) with an infarct that led to marked atrophy of the left hippocampus and subiculum, leaving the right MMN intact. Unbiased, stereological measurement techniques were used to compare the total cell number and individual neuronal cross-sectional areas in both left and right MMN in this patient and in two control human brains. We also analyzed the MMN in four macaque monkeys that underwent experimental unilateral transections of the fornix. The volume of the MMN on the lesioned side in KB was 55% of the unlesioned side (2.8 mm(3) vs 5.1 mm(3)); the MMN in the monkey cases were reduced to 47-58% of the volume of the nonlesioned side. Neurons in the deafferented MMN of KB and of the monkey subjects were decreased in cross-sectional area (16-20%, P < 0.0001). There was a trend toward decreased cell numbers (11-15%) on the lesioned side in all cases. We have estimated that the loss in cell number and shrinkage of remaining cells contribute negligibly to the 45% reduction in MMN volume. Therefore, the loss of neuropil (dendrites and afferent and efferent axons) appears to be the major contributor to the change in MMN volume.

Differential expression of small heat shock protein 27 in the rat hippocampus and septum after fimbria-fornix lesion

mRNA, Western analysis and immunohistochemistry were used to study the expression of the small heat shock protein (HSP) 27 in the rat septum and hippocampus following fimbria-fornix lesions, a model of neurodegeneration and regeneration. (HSP) 27 mRNA level was increased 2.5-fold in the medial septum 3 days after lesion and this increase persisted for 10 days. In the hippocampus, after an initial 15-fold increase at 3 days post-injury, HSP27 mRNA returned to basal levels 10 days after the lesion. Three and 10 days after lesion, HSP27 protein levels were increased in the septum (4.5 and 5-fold, respectively) and hippocampus (65 and 10-fold, respectively). The morphology of the HSP27 positive cells was indistinguishable from that of GFAP-immunoreactive cells. In addition, in the septum of injured rats, occasional neurons were heavily labelled with anti-HSP27 antibodies. Thus, up-regulation of HSP27, particularly in glial cells, may be a component of glial input in the processes on degeneration/regeneration which occur in this model.

Up-regulation of genes involved in cellular stress and apoptosis in a rat model of hippocampal degeneration

Changes in gene expression within the hippocampus induced by denervation after electrolytic fimbria-fornix lesion in rat were compared to morphological and biochemical alterations. Fimbria-fornix lesion results in degeneration of hippocampal cholinergic terminals as evidenced by a sustained (2 days to 1 month) decrease in cholineacetyltransferase (ChAT) activity (50%). These changes were accompanied by a decrease in growth associated protein 43 (GAP-43) immunoreactivity in all hippocampal layers 4 days after lesion followed by a subsequent increase and return to normal levels by 20 days postinjury. This increase in GAP-43 expression in the hippocampus between 7 to 20 days after lesion may reflect heterotypic sprouting. TUNEL-positive cells were revealed by in situ assay within the hippocampus at 10 days, but not at 3 days, after lesion. Two subtracted cDNA libraries from the dorsal hippocampus of control and injured rats (at 3 and 10 days postlesion) were constructed in order to search for new genes potentially implicated in degeneration/regeneration phenomena. We analysed 1,536 clones from each library by differential screening and found a total of 46 up-regulated genes. Among the 15 known genes, 6 coded for proteins involved in signal transduction pathways. The upregulation of growth arrest DNA damage induced gene (GADD153), brain-specific RING finger protein, JNK interacting protein (JIP-1), protein kinase A (PKA), and Na+K+ ATPase was studied by quantitative polymerase chain reaction (PCR). Two of these genes, GADD153 and JIP-1, have been previously shown to participate in cell modifications induced by stress and apoptosis.

[A comparative study of lesion of the fimbria-fornix by aspiration and by transsection]

INTRODUCTION

Lesion of the fimbria-fornix causes dysfunction of learning processes and has been used in animal models for the study of Alzheimer's disease.

MATERIAL AND METHODS

With the objective of comparing the efficacy of two methods of producing a lesion of the fimbria-fornix, 40 young male Sprague-Dawley rats were distributed in four experimental groups: control (6), falsely lesioned (8), lesion due to aspiration (12) and lesion due to transection (14).

RESULTS

The results showed that whilst with both techniques, in rats, serious cognitive defects were produced, as expressed by the high latencies of escape and small number of crossings of Morris's aquatic labyrinth, the aspiration lesion led to greater mortality than the transection lesion did. Similarly, the aspiration technique in rats induced hyperactivity, aggressiveness and tigmotaxia, while in the rats with lesions due to transection tigmotaxia ceased after their first attempts and hyperactivity on the second day of training.

CONCLUSION

These results would suggest that a bilateral lesion due to transection of the fimbria-fornix is an effective alternative to an aspiration lesion to interrupt this pathway.