In order to study the morphological characteristics and terminating patterns of the neurons of the trigeminal mesencephalic nucleus (Vme), 55 masseteric neurons in Vme in the rat were stained by intracellular injection of horseradish peroxidase (HRP). Labeled cells were distributed throughout the nucleus. These neurons were divided into three types: uni- or pseudounipolar (type A, n = 43), bipolar (type B, n = 5), and multipolar cells (type C, n = 7). Each type was further divided into two subtypes according to the largest diameter of the perikarya (type a greater than or equal to 30 microns, type b less than 30 microns). The central processes of type Aa neurons projected to the following three groups of target nuclei: 1) nuclei functioning as interneurons, including supratrigeminal nucleus (Vsup), intertrigeminal nucleus (Vint), juxta-trigeminal region (Vjux), and parvicellular nucleus of the pontomedullary reticular formation (PcRF); 2) motor nuclei, including the trigeminal motor nucleus (Vmo), accessory facial nucleus (NVIIacs), accessory abducens nucleus (NVIacs), and a small number of labeled axons in the oculomotor nucleus and trochlear nucleus; 3) sensory nuclei, including the dorsomedial part of the principal trigeminal sensory nucleus (Vpdm) and the dorsomedial part of subnucleus oralis of the trigeminal spinal nucleus (Vodm). Labeled processes were dense in the Vsup, Vmo, and Vpdm. The proprioceptive pathway of the fifth nerve is discussed. Direct projections from type Aa neurons of Vme to the Vpdm and dorsolateral part of the Vsup contribute to conduction of the proprioceptive information from spindles of masticatory muscle to the contralateral thalamus in the rat. Different axon morphology, distribution, terminal branch density, and terminating patterns of type Aa neurons were noted in different functional groups of the projecting nuclei, especially in the Vsup, Vmo, and Vpdm. The highest terminal branching density, the most extensive distribution, and two different types of branching patterns (claw-like and comb-like) were observed in Vsup. Selective distribution and single-beaded or "Y"-shaped terminal branches were observed in Vmo. In the Vppdm the axonal branches were sparser than in the Vsup or Vmo, and had an arrangement like the branches of a weeping willow tree. These characteristics of anatomical organization might be related to the function of each projecting nucleus.
Field experiments in calcareous and acidic field soils were conducted to study the effects of copper (Cu) and nickel (Ni) added to soils on maize growth and metal accumulation in maize plants. The results revealed that the critical concentrations of Cu added to soils that decreased maize grain yield by 10% (EC 10 ) were 711 mg kg −1 for calcareous soil with a pH of 8.9, and 23 mg kg −1 for acidic soil with a pH of 5.3. The toxicity thresholds of EC 10 did not differ significantly for Cu and Ni. A different pattern of Cu and Ni accumulation in maize plants was also found. The accumulation of Cu in above-ground parts of the plants increased initially as the concentrations of Cu added to soils increased, after which they decreased to a constant level. As the concentrations of Ni added to soils increased, the accumulation of Ni in stems and leaves increased linearly, but the accumulation of Ni in the grains was nonlinear. Additionally, the results revealed that Ni was transported to grains more easily than Cu. The results also showed that the concentrations of Cu and Ni in soil solutions as toxicity predictors and the critical concentrations of Cu and Ni in maize were all soil-dependent.
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