Memory impairment in aged primates is associated with region-specific network dysfunction.

Age-related deficits in episodic memory result, in part, from declines in the integrity of medial temporal lobe structures, such as the hippocampus, but are not thought to be due to widespread loss of principal neurons. Studies in rodents suggest, however, that inhibitory interneurons may be particularly vulnerable in advanced age. Optimal encoding and retrieval of information depend on a balance of excitatory and inhibitory transmission. It is not known whether a disruption of this balance is observed in aging non-human primates, and whether such changes affect network function and behavior. To examine this question, we combine large-scale electrophysiological recordings with cell-type-specific imaging in the medial temporal lobe of cognitively assessed, aged rhesus macaques. We found that neuron excitability in the hippocampal region CA3 is negatively correlated with the density of somatostatin-expressing inhibitory interneurons in the vicinity of the recording electrodes in the stratum oriens. By contrast, no hyperexcitability or interneuron loss was observed in the perirhinal cortex of these aged, memory-impaired monkeys. These data provide a link, for the first time, between selective increases in principal cell excitability and declines in a molecularly defined population of interneurons that regulate network inhibition.

Embryonic fibroblast motility and orientation can be influenced by physiological electric fields.

Epithelial layers in developing embryos are known to drive ion currents through themselves that will, in turn, generate small electric fields within the embryo. We hypothesized that the movement of migratory embryonic cells might be guided by such fields, and report here that embryonic quail somite fibroblast motility can be strongly influenced by small DC electric fields. These cells responded to such fields in three ways: (a) The cells migrated towards the cathodal end of the field by extending lamellipodia in that direction. The threshold field strength for this galvanotaxis was between 1 and 10 mV/mm when the cells were cultured in plasma. (b) The cells oriented their long axes perpendicular to the field lines. The threshold field strength for this response for a 90-min interval in the field was 150 mV/mm in F12 medium and between 50 and 100 mV/mm in plasma. (c) The cells elongated under the influence of field strengths of 400 mV/mm and greater. These fibroblasts were therefore able to detect a voltage gradient at least as low as 0.2 mV across their width. Electric fields of at least 10-fold larger in magnitude than this threshold field have been detected in vivo in at least one vertebrate thus far, so we believe that these field effects encompass a physiological range.

Changes in the fibronectin-specific integrin expression pattern modify the migratory behavior of sarcoma S180 cells in vitro and in the embryonic environment.

The molecules that mediate cell-matrix recognition, such as fibronectins (FN) and integrins, modulate cell behavior. We have previously demonstrated that FN and the beta 1-integrins are used during neural crest cell (NCC) migration in vitro as well as in vivo, and that the FN cell-binding domains I and II exhibit functional specificity in controlling either NCC attachment, spreading, or motility in vitro. In the present study, we have analyzed the effect of changes in the integrin expression patterns on migratory cell behavior in vivo. We have generated, after stable transfection, S180 cells expressing different levels of alpha 4 beta 1 or alpha 5 beta 1 integrins, two integrins that recognize distinct FN cell-binding domains. Murine S180 cells were chosen because they behave similarly to NCC after they are grafted into the NCC embryonic pathways in the chicken embryo. Thus, they provide a model system with which to investigate the mechanisms controlling in vitro and in vivo migratory cell behavior. We have observed that either the overexpression of alpha 5 beta 1 integrin or the induction of alpha 4 beta 1 expression in transfected S180 cells enhances their motility on FN in vitro. These genetically modified S180 cells also exhibit different migratory properties when grafted into the early trunk NCC migratory pathways. We observe that alpha 5 and low alpha 4 expressors migrate in both the ventral and dorsolateral paths simultaneously, in contrast to the parental S180 cells or the host NCC, which are delayed by 24 h in their invasion of the dorsolateral path. Moreover, the alpha 4 expressors exhibit different migratory properties according to their level of alpha 4 expression at the cell surface. Cells of the low alpha 4 expressor line invade both the ventral and dorsolateral pathways. In contrast, the high expressors remain as an aggregate at the graft site, possibly the result of alpha 4 beta 1-dependent homotypic aggregation. Thus, changes in the repertoire of FN-specific integrins enable the S180 cells to exploit different pathways in the embryo and regulate the speed with which they disperse in vivo and in culture. Our studies correlate well with known changes in integrin expression during neural crest morphogenesis and strongly suggest that neural crest cells that migrate into the dorsolateral path, i.e., melanoblasts, do so only after they have upregulated the expression of FN receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Clustering of perirhinal neurons with similar properties following visual experience in adult monkeys.

The functional organization of early visual areas seems to be largely determined during development. However, the organization of areas important for learning and memory, such as perirhinal cortex, may be modifiable in adults. To test this hypothesis, we recorded from pairs of neurons in perirhinal cortex of macaques while they viewed multiple complex stimuli. For novel stimuli, neuronal response preferences for pairs of nearby neurons and far-apart neurons were uncorrelated. However, after one day of experience with the stimuli, response preferences of nearby neurons became more similar. We conclude that specific visual experience induces development of clusters of perirhinal neurons with similar stimulus preferences.

The neurobiology of memory changes in normal aging.

Cognitive alterations occur over the lifespan of every species studied and have been quantified carefully in humans, other primates and rodents. Correspondingly, changes in hippocampal function have been associated with a number of observed memory impairments across species. It appears that humans, alone, show Alzheimer's disease-like cognitive and neural pathology spontaneously. Thus, a comparison of normal age-related changes in cognition in other animals can help disambiguate the boundary between normal and pathological states of aging in humans. Another important contribution made from studying aging in non-human species is the ability to examine, in more detail, the basic neural mechanisms that may be responsible for brain aging in these species. So far, most of the functional neurobiological studies have been conducted in the aged rat. We propose that the link between rodent and human work can be made much stronger by combining neurophysiological and behavioral investigation of normal aging in the non-human primate.

Morphogenesis of the avian trunk neural crest: use of morphological techniques in elucidating the process.

Morphological data generated from light and electron microscopy form the basis of our understanding of avian morphogenesis. Because chicken embryos are readily and cheaply obtained and are easily accessible for experimental manipulation, morphogenetic processes have been studied extensively in this species. Such studies have allowed us to identify the cells involved during morphogenesis, observe the shape changes or cellular translocations that accompany a morphogenetic process, and determine the timing of these events. Elucidation of the molecular basis of morphogenesis has awaited the integration of several additional approaches. Among these are experimental embryology, which has allowed us to understand cellular behavior associated with morphogenesis; immunocytochemistry, which has identified the macromolecular cues that regulate cell movements and the environmental factors that control them; and molecular techniques, which will permit us eventually to clarify the genetic regulation of morphogenesis. Although current research in development is heavily biased towards molecular biology, morphological studies continue to frame the questions that are now being addressed using molecular techniques. This review focuses on the cells of the neural crest as a model system where questions of avian morphogenesis have been profitably addressed.

Treatment of irradiation injury to the ureter by ileal substitution.

Ureteral obstruction following radiotherapy for cervical cancer is most often due to recurrent tumor. However, in a few patients ureteral stricture is secondary to radiation damage. Surgical treatment of this obstruction requires special consideration since many procedures for urinary diversion may be contraindicated in an irradiated pelvis. Ileal substitution (uretero-ileoneocystostomy) preserves renal function without resorting to external diversion of urine. A discussion of the method together with a report of 6 patients treated in this manner is presented. Results were excellent, with followup ranging from 11/2 to 4 years. A brief history of irradiation damage to the ureter and the use of small bowel as substitute ureter is discussed. Patient acceptance of this surgical approach was gratifying.

Prognostic significance of carcinoembryonic antigen in colorectal carcinoma. Serum levels before and after resection and before recurrence.

The use of carcinoembryonic antigen was evaluated in 425 patients with a mean follow-up of 48 months. The preoperative and postoperative carcinoembryonic antigen levels were predictive of recurrence and survival independent of the tumor stage. In a multivariate regression analysis of age, location, tumor stage, and preoperative and postoperative carcinoembryonic antigen levels, the latter three factors were significant prognostic variables with respect to the adjusted survival. Recurrent disease was found in 42% of patients, excluding patients with stage IV disease. The carcinoembryonic antigen level at recurrence was greater than 5 ng/mL in 79% of the patients and in 89% of the intra-abdominal recurrences. Carcinoembryonic antigen level at recurrence was not predictive of postrecurrence survival except in the subgroup of locoregional disease. The life span in patients with liver and lung metastases was not influenced by carcinoembryonic antigen level at recurrence. Preoperative and postoperative carcinoembryonic antigen levels can indicate a poorer prognostic group of patients with colorectal cancer who may benefit from adjuvant treatment. The carcinoembryonic antigen at recurrence can be used effectively to diagnose intra-abdominal recurrences and project survival after development of local/regional disease.

Comparison of long-term enhancement and short-term exploratory modulation of perforant path synaptic transmission.

Long-term enhancement (LTE/LTP) is an artificially induced form of synaptic change that may underlie memory storage in the hippocampus; however, there is as yet no evidence that this process occurs naturally as a result of normal neural activity. In the dentate gyrus, synaptic change does occur in conjunction with an animal's recent history of exploratory behavior. This change, which persists for a short time (ca. 30 min) following cessation of exploration, has been called short-term exploratory modulation (STEM). This experiment examined the relationship between LTE and STEM by comparing the magnitude of STEM before and after induction of LTE in rats with chronically implanted stimulating electrodes in the perforant path and recording electrodes in the fascia dentata. The absolute magnitude of STEM was the same before and after LTE saturation, suggesting that the processes are independent of each other. Furthermore, quantitative and qualitative analyses of the types of changes seen in the evoked-potential waveforms reveal different types of alteration. LTE includes an increase in EPSP slope, whereas STEM reflects an increase in EPSP onset. These data suggest that it is unlikely that STEM and LTE reflect the same synaptic process, and are at least partly consistent with recent reports suggesting that STEM may be mediated by activity-dependent changes in brain temperature.

Effects of hyperbaric oxygenation therapy on cerebral metabolism and intracranial pressure in severely brain injured patients.

OBJECT: Hyperbaric oxygenation (HBO) therapy has been shown to reduce mortality by 50% in a prospective randomized trial of severely brain injured patients conducted at the authors' institution. The purpose of the present study was to determine the effects of HBO on cerebral blood flow (CBF), cerebral metabolism, and intracranial pressure (ICP), and to determine the optimal HBO treatment paradigm. METHODS: Oxygen (100% O2, 1.5 atm absolute) was delivered to 37 patients in a hyperbaric chamber for 60 minutes every 24 hours (maximum of seven treatments/patient). Cerebral blood flow, arteriovenous oxygen difference (AVDO2), cerebral metabolic rate of oxygen (CMRO2), ventricular cerebrospinal fluid (CSF) lactate, and ICP values were obtained 1 hour before and 1 hour and 6 hours after a session in an HBO chamber. Patients were assigned to one of three categories according to whether they had reduced, normal, or raised CBF before HBO. In patients in whom CBF levels were reduced before HBO sessions, both CBF and CMRO2 levels were raised 1 hour and 6 hours after HBO (p < 0.05). In patients in whom CBF levels were normal before HBO sessions, both CBF and CMRO2 levels were increased at 1 hour (p < 0.05), but were decreased by 6 hours after HBO. Cerebral blood flow was reduced 1 hour and 6 hours after HBO (p < 0.05), but CMRO2 was unchanged in patients who had exhibited a raised CBF before an HBO session. In all patients AVDO2 remained constant both before and after HBO. Levels of CSF lactate were consistently decreased 1 hour and 6 hours after HBO, regardless of the patient's CBF category before undergoing HBO (p < 0.05). Intracranial pressure values higher than 15 mm Hg before HBO were decreased 1 hour and 6 hours after HBO (p < 0.05). The effects of each HBO treatment did not last until the next session in the hyperbaric chamber. CONCLUSIONS: The increased CMRO2 and decreased CSF lactate levels after treatment indicate that HBO may improve aerobic metabolism in severely brain injured patients. This is the first study to demonstrate a prolonged effect of HBO treatment on CBF and cerebral metabolism. On the basis of their data the authors assert that shorter, more frequent exposure to HBO may optimize treatment.

Changes in mesenchymal cell-shape, matrix collagen and tenascin accompany bud formation in the early chick lung.

In the chick, lung branches arise as buds from the center of the pre-existing mesobronchial tube. Budding is known to be controlled by the mesenchyme. We have investigated mesenchymal properties in budding vs non-budding regions of the early chick lung, including sources of mesenchyme, cell shapes and densities, morphology and composition of the basement membrane, and distribution of the ECM components collagen, fibronectin and tenascin. We found that at points of outgrowth--the buds and the distal tip of the mesobronchus-mesenchymal cells adjacent to the lung epithelium are flattened, and the basement membrane is markedly thinned. In these basement membranes collagen is largely absent and tenascin redistributed into amorphous clumps. Of these characteristics only the cell-shape change, which results in the flattened mesenchymal cells at the bud tips, is correlated with initiation of the bud. We suggest that the cell-shape change leads to localized loss of collagen, which promotes emergence of buds, and that tenascin, which is found in the mesenchyme only in the budding region, promotes outgrowth and elongation of the bud.

Analyzing aversiveness of denatonium saccharide and quinine in rats.

Denatonium saccharide is reported to be the most bitter substance currently known. Two experiments comparing the suppressive capabilities of this compound and the more common bitter, quinine, are presented. Analysis indicated that rats preferred to consume denatonium rather than quinine when afforded a choice between the two. Exp. 2 also indicated that the pairing of quinine with vanilla and almond flavors resulted in subsequent refusal of these flavors. Pairing flavors with denatonium did not produce comparable refusals. Caution is expressed with regard to the use of denatonium saccharide as a rodent repellent.

Neural responses to facial expression and face identity in the monkey amygdala.

The amygdala is purported to play an important role in face processing, yet the specificity of its activation to face stimuli and the relative contribution of identity and expression to its activation are unknown. In the current study, neural activity in the amygdala was recorded as monkeys passively viewed images of monkey faces, human faces, and objects on a computer monitor. Comparable proportions of neurons responded selectively to images from each category. Neural responses to monkey faces were further examined to determine whether face identity or facial expression drove the face-selective responses. The majority of these neurons (64%) responded both to identity and facial expression, suggesting that these parameters are processed jointly in the amygdala. Large fractions of neurons, however, showed pure identity-selective or expression-selective responses. Neurons were selective for a particular facial expression by either increasing or decreasing their firing rate compared with the firing rates elicited by the other expressions. Responses to appeasing faces were often marked by significant decreases of firing rates, whereas responses to threatening faces were strongly associated with increased firing rate. Thus global activation in the amygdala might be larger to threatening faces than to neutral or appeasing faces.

Behavior of neural crest cells on embryonic basal laminae.

Neural crest cells separate from the neural epithelium in a region devoid of a basal lamina and migrate along pathways bordered by intact basal laminae. The distribution of basal laminae suggests that they might have an important role in the morphogenesis of the neural crest by acting as a barrier to migration. The experiments reported here have tested directly whether neural crest cells can penetrate a basal lamina. Isolated neural tubes, neural crest cells cultured for 24 hr, or pigmented neural crest cells were explanted onto human placental amnions from which the epithelium had been removed to expose the basal lamina. In no case did neural crest cells or crest derivatives penetrate the basal lamina to invade the underlying stroma. If crest cells were grown on the stromal side of the amnion, they invaded the connective tissue. Pigmented neural crest derivative and [3H]thymidine-labeled nonpigmented crest cells were also confronted with chick embryonic basal laminae by grafting the cells into the lumen of the neural tube at the axial levels where host crest migration had commenced. Most of the grafted cells invaded the neural epithelium and accumulated after 24 hr at the basal surface of the neural tube. A few crest cells escaped through the dorsal surface of the neural tube and entered the overlying ectoderm, presumably through the wound created during the grafting procedure. Some of these grafted cells, located initially by light microscopy, were examined at the higher magnification and resolution offered by the transmission electron microscope to determine the relationship of the grafted cells to the basal lamina. In 50% (14 total) of the cases, the crest cells never reached the basal lamina of the neural tube, but were trapped by cell junctions between the neural epithelial cells. Of the remaining grafted cells that were relocated in the TEM (50%, total 15) all were spread on the basal lamina, but were not seen penetrating it. Likewise, in the three cases where crest cells were found in the epidermal ectoderm, all were in contact with the basal lamina of the ectoderm but did not have any processes extending through it. In three cases, at the level of the light microscope, crest cells were found to extend through the basal surface of the neural tube. In all these instances, the cells followed the dorsal root nerve exiting through a region of the neural tube that is devoid of a basal lamina.(ABSTRACT TRUNCATED AT 400 WORDS)

Control of pathfinding by the avian trunk neural crest.

We have determined the pathways taken by the trunk neural crest of quail and examined the parameters that control these patterns of dispersion. Using antibodies that recognize migratory neural crest cells (HNK-1), we have found that the crest cells take three primary pathways: (1) between the ectoderm and somites, (2) within the intersomitic space and (3) through the anterior somite along the basal surface of the myotome. The parameters controlling dispersion patterns of neural crest cells are several. The pathways are filled with at least two adhesive molecules, laminin and fibronectin, to which neural crest cells adhere tenaciously in culture. The pattern of migration through the somite may be accounted for in part by the precocious development of the basal lamina of the dermamyotome in the anterior half of the somite; this basal lamina contains both fibronectin and laminin and the neural crest cells prefer to migrate on it. In contrast, the regions into which the crest cells do not invade are filled with relatively nonadhesive molecules such as chondroitin sulphate. Some of the pathways are filled with hyaluronic acid, which stimulates the migration of neural crest cells when they are cultured in three-dimensional gels, presumably by opening spaces. Neural crest cells are also constrained to stay within the pathways by basal laminae, which act as barriers and through which crest cells do not go. Therefore, crest pathways are probably defined by several redundant factors. The directionality of crest cell migration is probably due to contact inhibition, which can be demonstrated in tissue culture. Various grafting experiments have suggested that chemotaxis and haptotaxis do not play a role in controlling the dispersion of the crest cells away from the neural tube. We have documented the extraordinary ability of neural crest cells to disperse in the embryo, even when they are grafted into sites in which they would normally not migrate. We have evidence that the cells' production of plasminogen activator, a proteolytic enzyme, and also the minimal tractional force that crest cells exert on the substratum as they migrate, contribute to this migratory ability.