Extraction of soil solution by drainage centrifugation-effects of centrifugal force and time of centrifugation on soil moisture recovery and solute concentration in soil moisture of loess subsoils.

The solute concentration in the subsoil beneath the root zone is an important parameter for leaching assessment. Drainage centrifugation is considered a simple and straightforward method of determining soil solution chemistry. Although several studies have been carried out to determine whether this method is robust, hardly any results are available for loess subsoils. To study the effect of centrifugation conditions on soil moisture recovery and solute concentration, we sampled the subsoil (1.5-3.0 m depth) at commercial farms in the loess region of the Netherlands. The effect of time (20, 35, 60, 120 and 240 min) on recovery was studied at two levels of the relative centrifugal force (733 and 6597g). The effect of force on recovery was studied by centrifugation for 35 min at 117, 264, 733, 2932, 6597 and 14,191g. All soil moisture samples were chemically analysed. This study shows that drainage centrifugation offers a robust, reproducible and standardised way for determining solute concentrations in mobile soil moisture in silt loam subsoils. The centrifugal force, rather than centrifugation time, has a major effect on recovery. The maximum recovery for silt loams at field capacity is about 40%. Concentrations of most solutes are fairly constant with an increasing recovery, as most solutes, including nitrate, did not show a change in concentration with an increasing recovery

The pontine micturition center projects to sacral cord GABA immunoreactive neurons in the cat

Stimulation of the pontine micturition center (PMC) results in micturition, i.e. an immediate relaxation of the bladder sphincter and a contraction of the detrusor muscle of the bladder. Earlier studies have shown that the bladder contraction is brought about by a direct excitatory pathway from the PMC to the parasympathetic bladder motoneurons in the sacral cord. How the PMC produces the inhibition of the bladder sphincter is not known. The present study in two adult male cats demonstrates at the ultrastructural level a direct pathway from the PMC to the dorsal gray commissure of the sacral cord. More than half (55%) of these terminals made contact with gamma amino butyric acid (GABA) immunoreactive neurons or somata, the others with non-GABA immunoreactive profiles. The PMC terminals contained many round vesicles, some dense cored vesicles and exclusively asymmetric synaptic clefts, which correspond with an excitatory pathway. A concept is put forward in which this pathway produces the relaxation of the bladder sphincter during micturition. (C) 1997 Elsevier Science Ireland Ltd

Natural Formation of Chlorinated Phenols, Dibenzo-P-Dioxins and Dibenzofurans in Soil of a Douglas Fir Forest.

Abstract not availableJRC.(EI)-Environment Institut

Ultrastructural Evidence For Direct Projections From The Pontine Micturition Center To Glycine-immunoreactive Neurons In The Sacral Dorsal Gray Commissure In The Cat

During micturition, according to the concept of Blok, Holstege, and colleagues ([1997] Neurosci. Lett. 233:109–112), the pontine micturition center (PMC) elicits bladder contraction by way of direct excitation of the parasympathetic bladder motoneurons. At the same time, the PMC elicits relaxation of the external urethral sphincter (EUS) by excitation of g-aminobutyric acid (GABA)-ergic interneurons in the sacral dorsal gray commissure (DGC), which, in turn, inhibit EUS motoneurons. The question is whether the inhibitory neurotransmitter glycine is also involved in this system. The present study investigated, first, whether there are glycine immunoreactive interneurons in the sacral DGC and, second, whether they receive direct PMC afferents. Finally, it was determined whether glycine and GABA are colocalized in DGC interneurons. In two adult male cats, the PMC was identified by electrical stimulation. Subsequently, the identified region was injected with the anterograde tracer WGA-HRP. Sections of sacral cord segments were processed for light and electron microscopic detection of anterograde labeling, as well as for glycine and GABA, using postembedding immunogold labeling with antibodies. In total 128 labeled PMC terminals were found in the DGC, which contained many round vesicles and asymmetric synapses. About 31.3% (40 of 128) made contact with glycine-immunoreactive dendrites. Eleven of them were selected for serial sectioning, which showed that 54.6% (6 of 11) of the glycine-immunoreactive dendrites were also immunoreactive for GABA. The results demonstrate that the PMC projects directly to dendrites of interneurons in the sacral DGC, which are immunoreactive for both glycine and GABA. These interneurons are thought to inhibit the EUS motoneurons during micturition.

Microvascular changes in estrogen-α sensitive brainstem structures of aging female hamsters

Structural neuronal plasticity is present in the nucleus para-retroambiguus (NPRA) and the commissural nucleus of the solitary tract/A2 group (NTScom/A2) in female hamsters. Both brainstem nuclei play a role in estrous cycle related autonomic adaptations. We investigated how aging affects the capillary condition in these adaptive brainstem regions. Senescent female hamsters (±95 weeks) were tested weekly for their 4-day estrous cycle. Subsequently morphological changes of NPRA and NTScom/A2 were compared with those of young (±20 weeks) females in an ultrastructural study. The medial tegmental field served as control area. In 841 capillaries (n = 319 capillaries, young females (N = 3); n = 522 capillaries, aged females (N = 4)) vascular aberrations were classified into 3 categories: endothelial and tight junction, basement membrane and pericyte aberrations. In old animals, capillaries showed marked endothelial changes, disrupted tight junctions, and thickening and splitting of basement membranes. Aberrations were found in 40–60% of all capillaries. About 70% of the pericytes contained degenerative inclusions. Despite this generalized vascular degeneration, the reproductive cycle of female hamsters was unaffected by vascular senescence. Perivascular fibrosis as reported in aging rats was never observed, which suggests the existence of species differences.

Spumiform capillary basement membrane swelling:a new type of microvascular degeneration in senescent hamster

<p>Brain microvasculature plays a critical role in the regulation of homeostasis of neural tissues. The present study focuses on characteristic microvascular basement membrane (bm) aberrations in the midbrain periaqueductal gray matter (PAG) and their relation to aging. The PAG can be considered a caudal extension of the limbic system and is a key structure in the regulation of a myriad of autonomic and motor control functions. In an ultrastructural study, morphologic changes in mesencephalic PAG capillaries were assessed in aged and young hamster and compared with those in caudal brainstem areas. Bm aberrations were studied in 1200 capillaries (n = 600 young hamsters; n = 600 aged hamsters). A new, never reported variant of bm degeneration was found that presented itself as foamy-like structures accumulating within the lamina densa of notably PAG capillaries. We classified these foamy structures as 'spumiform basement membrane degenerations' (sbmd) in which we could distinguish 4 stages depending on the size and intramembranous localization, ranging from split bm (stage I), intermediate stages II and III, to extensive stage IV, affecting almost the complete capillary bm outline. In the PAG of senescent animals various stages of sbmd were observed in 92 +/- 3% of all capillaries. Stage II was most prominently present (59%), followed by stage III (20%), and stage IV (13%). These bm aberrations were clearly age-dependent because in young animals, only 5% of the PAG capillaries showed characteristics of sbmd. For comparison, in the pontine reticular formation at the PAG-level, 41% of the capillaries showed a form of sbmd, but these defects were significantly less severe (stages I-II, 98%), and caudal brainstem structures displayed no sbmd at all. In addition to sbmd, diffuse endothelial changes, disrupted tight junctions, thickening of the bm, pericyte degeneration, and gliosis were observed in PAG capillaries. It is hypothesized that selective bm permeability of PAG capillaries results in a sequence of bm damage events that start with split bm, gradually changing into more and more extensive sbmd accumulations that eventually almost completely surround the capillary. Progressive sbmd in PAG capillaries might lead to a loss of blood-brain barrier function and consequently to impairment of autonomic and motor control functions exerted by the PAG. (C) 2013 Elsevier Inc. All rights reserved.</p>