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Neurogenesis has been the subject of active research in recent years. Although the majority of neurons form during the embryonic period, neurogenesis continues in restricted regions of the mammalian brain well into adulthood. In rodent brains, neuronal migration is present in the rostral migratory stream (RMS), connecting the subventricular zone to the olfactory bulb (OB). The migration in the RMS is characterised by a lack of dispersion of neuroblasts into the surrounding tissues and a highly directed motion towards the OB. This study uses a simple mathematical model to investigate several theories of migration of neuroblasts through the RMS proposed in the literature, including chemo-attraction, chemorepulsion, general inhibition and the presence of a migration-inducing protein. Apart from the general inhibition model, all the models were able to provide results in good qualitative correspondence with the experimental observations. [ABSTRACT FROM AUTHOR]

Composting of beef cattle (Bos Taurus) manure may increase the soluble salt (Ca, Mg, Na, K) and total sulfur (S) content and increase transport through the soil. Little research has been conducted on comparing transport of these chemicals through soil amended with composted (CM) manure versus fresh feedlot manure stockpiled for up to two months (FM). Our objective was to determine if the transport of these chemicals was greater for CM compared to FM when annually applied at 77Mg ha-1 dry wt. for nine years to a clay loam soil. Intact soil cores were taken from a field experiment in the spring of 2007. Deionized water was applied to the soil cores in the laboratory under steady-state (4.9 cm d-1) and unsaturated conditions. Residual chemical concentrations in effluent were measured and breakthrough curves and cumulative mass loss curves obtained. The peak concentrations of K and total S; flow-weighted mean concentration (FWMC) and mass loss for Na, K, and total S; and recovery of Mg, Na, K, and total S were significantly (P ≤ 0.05) greater for CM compared to FM. However, peak concentrations, FWMCs, and mass loss of Ca and Mg were similar for both manure types. Treatment effects on these two soluble salts were likely masked by high natural Ca and Mg already in the soil. Analysis of co-variance also suggested greater cumulative mass loss of most chemicals (except Ca) for CM than FM at pore volumes between 0.25 and 2.5. However, our findings could not be explained by the differences in chemical content of the amendments or soil, or greater cation exchange capacity for CM than FM. The greater unsaturated hydraulic conductivity (at 7 mBar) of soil amended with CM compared to FM was the likely cause of greater transport of Na, K, and total S; and may be related to a physical effect of finer particles increasing water flow for composted manure. [ABSTRACT FROM AUTHOR]

Effects of composting manure on viability of Giardia cysts (GC) and Cryptosporidium oocysts (CO) were determined in a two-year study with manure from feedlot cattle bedded on barley straw or woodchips. Each year, manure was deposited in 8 m × 2.5 m 7times; 2 m windrows (one per bedding type) on a sheltered concrete pad. On day 0, porous bags containing 100 g of feces from confirmed Giardia- and Cryptosporidium-positive cattle (9 bags per retrieval day in Year 1; 3 per day in Year 2) were implanted in the windrows. Replicate bags were placed on the concrete pads as uncomposted contrails. Windrow temperature and water content were measured and compost was turned mechanically twice each week. Fecal bags were retrieved and subsampled for enumerations of total and viable cysts and oocysts after 1, 2, 3, 7, 10, 17, 24 and 31 days in 1998 and after 1, 2, 3, 7, 9, 16, 23, 30, 42, 56, 70 and 98 days in 1999. Windrow temperatures (TEMP) exceeded 557deg;C during the fourth week of composting, and remained above 50°C for 4 wk thereafter in 1999. Bedding material did not affect overall mean temperature in either year, but TEMP was higher with straw than with woodchip from day 10 to day 17 in 1998 (P < 0.05) and on day 16 and day 42 in 1999 (P < 0.10). In 1998, moisture content decreased from 62.2 to 43.2% during composting of woodchip manure and from 67.3 to 39.3% during composting of straw manure. In 1999, moisture content decreased from 61.0 to 31.8% for woodchip and from 64.5 to 86.6% for straw compost. Percentage of viable CO declined gradually over the 31 days in 1998. The following year revealed a rapid decline in viability of GC and CO once compost temperature exceeded 55°C and viabilities of GC and CO were reduced to zero after 42 days (straw compost) and after 56 days (woodchip compost). Exposure of CO and GC to temperatures > 55°C for a period of 15 days appears to be an effective method of inactivating Giardia cysts and Cryptosporidium oocysts in feedlot manure. [ABSTRACT FROM AUTHOR]

A three‐year study was conducted at Lethbridge, on a 1‐ha field (clay loam soil) with a history of previous herbicide applications, to determine herbicide levels in shallow (0.3–5.8 m) groundwater and the effect of seasonal events such as herbicide application and rainfall/irrigation. A mass‐selective detector, gas chromatographic method was used to analyze for seven different herbicides. Samples were collected from 6‐m monitoring wells at various intervals (9–32 d) after herbicide applications made in 1991–1993. 2, 4‐D (0.05–5.2 ppb), bromoxynil (0.03–8.4 ppb), diclofop (0.1 ‐11 ppb), MCPA (0.2–0.3 ppb) and triallate (0.1 ‐0.5 ppb) were detected in 17–61% of the wells sampled. Herbicide levels depended upon the interval and the timing and amounts of rainfall/irrigation after spraying. All levels were below the Canadian drinking water guidelines except for one detection of bromoxynil (8.4 ppb) and diclofop (11 ppb). We concluded there are large seasonal and spatial variations in herbicide levels in shallow Alberta groundwater. Levels are highest when the first moisture event after a herbicide application is a heavy rainfall/irrigation ('worst case’ scenario). Levels are lower when the applied herbicides are first ‘set‐in’ by gentle rains, then a drying period occurs and the residues adsorb to the soil. Subsequent heavy rainfall/irrigation does not flush large amounts of these adsorbed residues into the groundwater. This latter ‘best case’ scenario probably occurs more often than the former ‘worst case’ scenario. [ABSTRACT FROM AUTHOR]