GABA neurons provide a rich input to microvessels but not nitric oxide neurons in the rat cerebral cortex: a means for direct regulation of local cerebral blood flow.

Basal forebrain neurons project to microvessels and the somata of nitric oxide (NO) synthase-containing neurons in the cerebral cortex, and their stimulation results in increases in cortical perfusion. gamma-Aminobutyric acid (GABA) is the second major neurotransmitter synthesized by these neurons and it has also been reported to modify cerebromicrovascular tone. We thus investigated by light and electron microscopy the association of GABA neurons (labeled for glutamic acid decarboxylase [GAD]) with cortical microvessels and/or NO neurons (identified by nicotinamide adenine dinucleotide [NADPH-D] histochemistry) within the frontoparietal and perirhinal cerebral cortex in the rat. On thick and semithin sections, a high density of GAD puncta was observed, several surrounded intracortical blood vessels and neuronal perikarya. In contrast, NADPH-D cell somata and proximal dendrites were only occasionally contacted by GAD nerve terminals. Perivascular and perisomatic GAD appositions were identified at the ultrastructural level as large (0.44-0.50 microm(2)) neuronal varicosities located in the immediate vicinity of, or being directly apposed to, vessels or unstained neuronal cell bodies. In both cortical areas, perivascular GAD terminals were located at about 1 microm from the vessels and were seen to frequently establish junctional contacts (synaptic frequency of 25-40% in single thin sections) with adjacent neuronal but not vascular elements. Ibotenic or quisqualic acid lesion of the substantia innominata did not significantly affect the density of cortical and perivascular GAD terminals, suggesting that they mostly originated locally in the cortex. These results suggest that GABA terminals can interact directly with the microvascular bed and that the somata and proximal dendrites of NO neurons are not a major target for cortical GABA neurotransmission. However, based on the colocalization of GABA and NADPH-D in a subset of cortical neurons, we suggest that these interneurons could be implicated in the cortical vascular response elicited by stimulation of basal forebrain neurons.

Pollination, wounding and jasmonate treatments induce the expression of a developmentally regulated pistil dioxygenase at a distance, in the ovary, in the wild potato Solanum chacoense Bitt.

Pollination and fertilization trigger unique developmental programs leading to embryogenesis, ovary maturation and seed set. Pistil tissues are actively involved in pollen tube growth and respond to the presence of the growing pollen tubes by modulating the expression of specific genes. Using subtractive hybridization to isolate genes involved in pollen-pistil interactions and fertilization, we have isolated a pollination- and fertilization-induced dioxygenase which is predominantly expressed in the pistil. In situ hybridization analyses revealed that the SPP2 dioxygenase (Solanum pollinated pistil) from the self-incompatible wild potato Solanum chacoense Bitt. is also developmentally regulated, with mRNA levels gradually regressing from the tip of the style towards the ovary during pistil development. At maturity, the upper limit of SPP2 transcript distribution coincided with the abscission zone of the style and SPP2 dioxygenase expression in ovaries coincided with the fertilization receptivity period of the flower. Pollination, as well as wounding of the style, induced an increase in SPP2 mRNA steady-state levels at a distance, in the ovary. Treatments with stress hormones including methyl jasmonate, jasmonic acid and salicylic acid mimicked the wound response and also induced SPP2 transcripts in the ovary. The SPP2 dioxygenase could be involved in the biosynthesis of deterrent alkaloids in reproductive tissues or in generating chemical signals involved in pollen tube guidance.

Fertilization and wounding of the style induce the expression of a highly conserved plant gene homologous to a Plasmodium falciparum surface antigen in the wild potato Solanum chacoense Bitt.

Pistil tissues are actively involved in pollen tube growth and respond to the presence of the growing pollen tubes by modulating the expression of specific genes. Once fertilization has occurred, complex developmental programs lead to embryogenesis, ovary maturation, and seed set. In order to understand the early events that follow pollination and fertilization we have used a subtractive hybridization approach to characterize genes which are related to pollination and fertilization events. One cDNA clone isolated and named SPP30 (Solanum pollinated pistil) was found to share significant sequence identities with a Plasmodium falciparum (malaria parasite) surface antigen and a yeast gene of unknown function. Searches in recent EST databases also revealed that SPP30 homologues are found in both monocot and dicot species. The presence of this conserved gene in evolutionarily distant organisms such as yeast, Plasmodium, and plants suggests that it codes for an essential cellular function. This is also strengthened by its extremely high sequence conservation in both monocots and dicots where virtually all substitutions tolerated are conservative.