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Biomedical subjects

M Moghaddam

Publications and source records attributed to M Moghaddam.

11 recordsLinked to original sources
PubMed1997

Rotation of water in the Morris water maze interferes with path integration mechanisms of place navigation.

The idea that place navigation in the Morris water maze is implemented by path integration between locations determined by landmark sighting was investigated in a 200-cm-diameter pool in which circular (7.2 degrees/s) motion of water could be induced by tangentially arranged water jets. The rats were trained at 8 trials per day to navigate to an erectable platform which was raised after the rat had spent a criterion time in the target annulus (30 cm in diameter) in the midpoint of the NW quadrant. Asymptotic escape latency of 7 s was reached after 9 days in moving water (n = 8) and after 6 days in stationary water (n = 8). The group overtrained for 13 days in stable water performed well even after it was transferred to moving water. Changing the sense of rotation of water from counterclockwise to clockwise did not affect the asymptotic performance. The above findings show that overtrained rats rely on landmark sighting rather than on path integration. The influence of water movement reappeared when place navigation to a new target (SW) was examined in alternating 2-s periods of light (L) and darkness (D). On the first day, the latencies were 15.2 +/- 1.2 and 22.8 +/- 1.9 s in stable and moving water, respectively, but dropped to 10 s on the following day. The tracks generated in the L period were more tortuous than those generated in the D period and this difference was more pronounced in moving than in stable water. It is concluded that path integration mechanisms supporting navigation during intervals of darkness are impaired in moving water but that this impairment disappears in overtrained animals.

Animals↗
PubMed1996

Novel metabolic pathways for linoleic and arachidonic acid metabolism.

Mouse liver microsomes oxidized linoleic acid to form 9,10- or 12,13-epoxyoctadecenoate. These monoepoxides were subsequently hydrolyzed to their corresponding diols in the absence of the microsomal epoxide hydrolase inhibitor, 1,2-epoxy-3,3,3-trichloropropane. Furthermore, both 9,10- and 12,13-epoxyoctadecenoates were oxidized to diepoxyoctadecanoate at apparently identical rates by mouse liver microsomal P-450 epoxidation. Both epoxyoctadecanoates and diepoxyoctadecanoates were converted to tetrahydrofuran-diols by microsomes. Tetrahydroxides of linoleate were produced as minor metabolites. Arachidonic acid was metabolized to epoxyeicosatrienoates, dihydroxyeicosatrienoates, and monohydroxyeicosatetraenoates by the microsomes. Microsomes prepared from clofibrate (but not phenobarbital) -treated mice exhibited much higher production rates for epoxyeicosatrienoates and vic-dihydroxyeicosatrienoates. This indicated an induction of P-450 epoxygenase(s) and microsomal epoxide hydrolase in mice by clofibrate and not by phenobarbital. Incubation of synthetic epoxyeicosatrienoates with microsomes led to the production of diepoxyeicosadienoates. Among chemically generated diepoxyeicosadienoate isomers, three of them possessing adjacent diepoxides were hydrolyzed to their diol epoxides which cyclized to the corresponding tetrahydrofuran-diols by microsomes as well as soluble epoxide hydrolase at a much higher rate. Larger cyclic products from non-adjacent diepoxides were not observed. The results of our in vitro experiments suggest that linoleic and arachidonic acid can be metabolized to their tetrahydrofuran-diols by two consecutive microsomal cytochrome P-450 epoxidations followed by microsomal or soluble epoxide hydrolase catalyzed hydrolysis of the epoxides. Incubation experiments with the S-9 fractions indicate that the soluble epoxide hydrolase is more important in this conversion. This manuscript is the first report of techniques for the separation and identification of regio and geometrical isomer of an interesting class of oxylipins and their metabolism by liver microsomes and S-9 fractions to THF-diols.

Animals↗
PubMed1996

Vestibular navigation directed by the slope of terrain.

Slope of terrain is an important orienting gradient affecting the goal-directed locomotion of animals. Its significance was assessed in experiment 1 by training rats to find in darkness a feeder on the top of a low cone (80-cm base, 0- to 4-cm high). A computerized infrared tracking system monitoring the rat's position in darkness showed that the path length on the cone surface was inversely proportional to cone height. A device allowing continuous generation of slope-guided locomotion was used in experiment 2. This device consists of a 1-m arena, the floor of which can be supported at a point corresponding to the position of one of three equidistant feeders located 17 cm from its center. The arena is inclined by the locomotion of the rat to a plane passing through the elevated (2- or 4-cm) feeder, the rat's center of gravity, and a point at the edge of the arena resting on the floor. The multitude of such planes generated by the rat's locomotion forms the surface of a virtual cone, the top of which is formed by the feeder. Additional path (difference between distance traveled and shortest distance of the animal from the goal at the onset of inclination) is inversely related to the incline of the arena and is a sensitive measure of performance in this type of vestibular navigation.

Animals↗
PubMed1996

Contribution of egocentric spatial memory to place navigation of rats in the Morris water maze.

Place navigation in the Morris water maze can be directed by memory of the target coordinates relative to remote landmarks (allocentric) or by the memory of the start-goal route (egocentric). When the start and goal positions remain constant and visual cues are eliminated by darkness, memory of the route may become decisive. This assumption was tested in 10 male hooded rats using an infrared television tracking system allowing navigation training in the dark. In Expt. 1, these animals were trained to swim in the dark from the start at the S rim of the pool to the goal position in the center of the NW quadrant of the pool. Mean escape latencies decreased from 47 s initially to 16 s during the 24 daily sessions. Another group of 10 male hooded rats learned the same task in the light. Mean escape latencies decreased from 20 s initially to 5 s during 4 daily sessions. In Expt. 2, possible allocentric location of the target was tested in the same rats by rotating both the start and goal positions by 90 degrees counterclockwise (i.e., to E-SW and later to N-SE). Mean escape latency during 5 days after the first rotation increased to 24 s, but returned back to the asymptotic level of 18 s after the second rotation. The same change of the start and goal position (from S-NW to E-SW) in the light only increased escape latency in the first session. In Expt. 3, both the goal position and route direction were changed to N-SW. Surprisingly, the animals rapidly acquired a new heading angle at the start and mean escape latencies were not significantly changed. It is concluded that overtrained place navigation in darkness can be easily changed to a new direction.

Animals↗
PubMed1996

Effects of lesions of the associative parietal cortex on the acquisition and use of spatial memory in egocentric and allocentric navigation tasks in the rat.

It has been hypothesized that the rat associative parietal cortex (APC) is involved in the association between visuospatial and locomotion-generated (kinesthetic) information. To study the kinesthetic component, APC-lesioned and control rats were trained in total darkness to reach a submerged platform in the Morris water maze. In the egocentric task, the relative position of the starting point and the platform was constant all over training. Parietal rats have been found impaired in acquisition and to a less extent in retention of this task. In the allocentric task, rats were then trained in the standard version of the navigation task. A mild deficit was observed in acquisition of this task because the APC-lesioned rats displayed longer escape latencies but control-like search patterns. These results suggest that the APC is involved in the coding of kinesthetic information that plays an important role in place navigation.

Animals↗
PubMed1993

Variable density linear acoustic inverse problem.

The linear acoustic inverse problem is solved simultaneously for density (rho) and compressibility (kappa) using the basic ideas of diffraction tomography (DT). The key to solving this problem is to utilize frequency diversity to obtain the required independent measurements. The receivers are assumed to be in the far field of the object, and plane wave incidence is also assumed. The Born approximation is used to arrive at a relationship between the measured pressure field and two terms related to the spatial Fourier transform of the two unknowns, rho and kappa. The term involving compressibility corresponds to monopole scattering and that for density to dipole scattering. Measurements at several frequencies are used and a least squares problem is solved to reconstruct rho and kappa at the same time. It is observed that the low spatial frequencies in the spectra of rho and kappa produce inaccuracies in the results. Hence, a regularization method is devised to remove this problem. Several results are shown. Low contrast objects for which the above analysis holds are used to show that good reconstructions are obtained for both density and compressibility after regularization is applied.

Acoustics↗
PubMed1991

Oxylipin metabolism in the red alga Gracilariopsis lemaneiformis: mechanism of formation of vicinal dihydroxy fatty acids.

Conversion of arachidonic acid into the vicinal diol fatty acid 12R,13S-dihydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid using an acetone powder of the marine red alga, Gracilariopsis lemaneiformis, occurred via intermediate formation of 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid. Incubations of the linoleic acid-derived 13S- and 13R-hydroperoxy-9Z,11E-octadecadienoic acids led to the formation of 13R,14S-dihydroxy-9Z,11E-octadecadienoic acid and 13S,14S-dihydroxy-9Z,11E-octadecadienoic acid, respectively, whereas incubation of 9S-hydroperoxy-10E,12Z-octadecadienoic acid resulted in the formation of 8S,9R-dihydroxy-10E,12Z-octadecadienoic acid. Experiments with 18O2-labeled 13S-hydroperoxyoctadecadienoic acid demonstrated that the oxygens of the two hydroxyl groups of 13R,14S-dihydroxy-9Z,11E-octadecadienoic acid originated in the hydroperoxy group of the substrate. Furthermore, experiments with mixtures of unlabeled and 18O2-labeled 13S-hydroperoxyoctadecadienoic acid showed that conversion into 13R,14S-dihydroxyoctadecadienoic acid occurred by a reaction involving an intramolecular hydroxylation at C-14 by the distal hydroperoxide oxygen. The existence of a hydroperoxide isomerase in G. lemaneiformis which catalyzes the conversion of fatty acid hydroperoxides into vicinal diol fatty acids is postulated.

Arachidonic Acids↗
PubMed1987

Mechanical slicing of frozen brain tissue: a reappraisal of catecholamine loss.

Catecholamine levels in mechanically sliced frozen bovine brain tissue were compared with those found in hand-cut, unfrozen tissue. Hemispheric content of catecholamines in small regions of cortex, caudate, nucleus accumbens, thalamus, and hippocampus in bovine brain was no different from that seen in the homologous area of the contralateral hemisphere, despite selective slicing of opposing hemispheres with the two techniques. Brodmann area 25 in human brain (previously suspected to be highly vulnerable to degradative loss of catecholamines by mechanical slicing) is shown to be a restricted area of dense catecholamine concentration when compared to surrounding cortical tissue. The usage of Brodmann area 25 for technique comparisons without precise control of cortical delineation is questioned.

Animals↗