Lateralization and functional organization of the locus coeruleus projection to the trigeminal somatosensory pathway in rat.

The primary goals of this study were to (1) examine the distribution of locus coeruleus (LC) neurons, which project to cortical and subcortical sites along the trigeminal somatosensory pathway in rats, and (2) determine the extent to which different regions within this ascending sensory system receive collateral projections from the same LC neuron. Long-Evans hooded rats received unilateral pressure injections of different combinations of retrograde fluorescent tracers into whisker-related regions of primary (SI) and secondary (SII) somatosensory cortices, the ventrobasal (VB) and posterior group (POm) nuclei of the thalamus, and the principalis nucleus of the trigeminal complex (PrV). Coronal sections (40-100 microm) through the LC were examined by fluorescence microscopy, and the distribution of retrogradely labeled cells was recorded. The major finding was that whisker-related regions of the cortex receive efferent projections from neurons concentrated in the caudal portion of the ipsilateral LC, whereas subcortical trigeminal somatosensory structures receive bilateral input from both LC nuclei. Despite the bilateral nature of the LC projection to subcortical sites, the majority of LC efferents to VB and POm thalamus originate in the ipsilateral LC nucleus, whereas projections to PrV originate primarily from the contralateral LC. An additional finding was that a relatively large proportion of LC cells, which project to a single somatosensory structure, also send axon collaterals to other relay sites along the same ascending somatosensory pathway. Taken together, these results suggest that the LC-noradrenergic system maintains a more selective relationship with functionally related efferent targets than has been previously appreciated.

Exogenous hormone applications at pollination for in vitro and in vivo production of cotton interspecific hybrids.

Interspecific hybridization of cotton (Gossypium) has been assisted by ovule and embryo culture. These culture methods were compared to exogenous hormone applications for efficient plant production from crosses between Upland cotton, G. hirsutum L., as the maternal parent, and various diploid and tetraploid wild species as the pollen donor. The best exogenous hormone treatment resulted in an average production of five seeds per boll and 4% boll abscission. Generally, exogenous hormones used with standard hybridization techniques were superior to in vitro methods, but for some crosses, embryo culture following hormone applications was warranted.

Inhibition of elicitor-induced phytoalexin formation in cotton and soybean cells by citrate.

Addition of an elicitor preparation from Verticillium dahliae to soybean or cotton cell suspension cultures induces the formation of the phytoalexins, glycelollin or sesquiterpene aldehydes, respectively. Recent work (PS Low, PF Heinstein 1986 Arch Biochem Biophys 249: 472-479) has shown that the induction of phytoalexin biosynthesis in these cells is preceded by rapid changes in the plant cell membrane which can be conveniently monitored by membrane associated fluorescent probes. Using this elicitation assay, we have found that citrate, a common metabolite of higher plants, acts as a potent inhibitor of elicitation when added prior to treatment with elicitor. The citrate concentration required to obtain a 50% inhibition of the elicitor-induced fluorescence transition in cultured cotton cells was found to be about 2 millimolar, while the concentration of citrate observed to inhibit elicitor-induced sesquiterpene aldehyde formation in the same cell suspensions was also 2 millimolar. Curiously, in the presence of elicitor, citrate at less than ID(50) concentrations increased cell mass accumulation significantly above control incubations without elicitor. A similar inhibition of glyceollin formation with an increase in cell mass accumulation was also observed upon addition of 1 to 5 millimolar citrate to soybean cell suspension cultures. The physiological significance of the inhibition by citrate of phytoalexin formation in plant cell suspensions was supported by the observation that a similar inhibition of sesquiterpene aldehyde formation occurs in cotton plantlets elicited by cold shock or V. dahliae stress. The specificity of citrate as an inhibitor of phytoalexin formation was demonstrated by data showing that other di- and tricarboxylic-hydroxy acids did not inhibit, with the exception of malate which inhibited phytoalexin formation in soybean cells with roughly half the potency of citrate. These experiments not only demonstrate that citrate can act as a specific inhibitor of elicitation, but they further confirm the validity of monitoring elicitation and its modulation with fluorescent probes.