Molecular mapping of the C locus for presence of pungency in Capsicum.

Pungency owing to the presence of capsaicinoids is a unique character of pepper (Capsicum spp.). Capsaicinoids are produced in the placenta and it has long been known that a single dominant gene, C, is required for pungent genotypes to produce capsaicinoids. We mapped C to pepper chromosome 2 in a cross between a pungent Capsicum frutescens wild accession and a non-pungent Capsicum annuum bell pepper. This position confirmed results from earlier studies. The RFLP marker TG 205 cosegregated with C and two additional RFLP markers were also located within 1 cM. The recessive allele at the C locus is used in breeding programs around the world focused on very diverse germplasm, hence any of these tightly linked markers may be of value as potential sources of useful markers for marker-assisted selection. To demonstrate this point, we developed a PCR-based CAPS (cleaved amplified polymorphic sequence) marker linked to C using the sequence of the Capsicum fibrillin gene located 0.4 cM from C. The use of molecular markers for high-throughput screening for the c allele in pepper breeding programs is discussed.     

Temporal integration of pungency

Four experiments explored possible temporal summation in olfactionand the common chemical sense. In one experiment, participantsjudged the perceived magnitude of various concentrations anddurations (1.25–3.75 s) of the pungent odorant ammoniaand the nonpungent odorant isoamyl butyrate. The perceived magnitudeof ammonia increased during an inhalation whereas the magnitudeof isoamyl butyrate did not. Time-intensity trading relationsfor ammonia indicated nearly perfect temporal summation. Inanother experiment, modulation of the concentration of ammoniaduring an inhalation led to assessments of perceived magnitudethat confirmed the high degree of temporal summation seen inthe first experiment. That is, approximately equal time-integratedmass of inhaled ammonia led to approximately equal perceivedintensity. A third experiment indicated that temporal summationfor ammonia arose from its pungency rather than from its odor,a fourth that trigeminally-mediated reflex apnea in responseto ammonia also exhibits temporal summation. The degree of temporalsummation measured with the reflex came very close to that assessedpsychophysically. When stimulated with ammonia, the common chemicalsense behaves more like a totalmass detector than a concentrationdetector. The investigation raises the possibility that theshortterm sensory reaction to most pungent stimuli may followthis simple rule.     

Participation of the rostral portion of the spinal nucleus of the trigeminal sensory complex in nociception

Single unit responses elicited through noxious mechanical stimulation of orofacial receptive fields were recorded, with glass micro-electrodes, within the rat ventrobasal complex of the thalamus. The evoked activities were compared before and after de-afferentation of the caudal sub-nucleus by trigeminal tractotomy at the level of the obex. Only units responding to noxious stimulation of oral receptive fields were unaffected by tractotomy. These results provide evidence that the rostral part of the spinal nucleus is involved in trigeminal painful sensation.     

Effect of capsaicin upon afferent and efferent mechanisms of nociception and temperature regulation in birds

(1) Acute capsaicin effects on nociception in the conscious chicken were tested by close arterial injection. The threshold dose to elicit nocifensive and autonomic responses was 50 micrograms, i.e., two to three orders of magnitude higher than in mammals but four times lower than in pigeons. (2) Foot withdrawal from hot water remained unchanged after capsaicin was injected either intravenously in the chicken at a cumulative dose of 600 mg/kg or perineurally at a dose of 100 micrograms into the sciatic nerve of pigeons. (3) Temperature regulation and body temperature in the chicken were not affected by subcutaneous injection of capsaicin, but intravenous infusion at rates of 2-5 or 10-13 mg X min-1 X kg-1 transiently lowered body temperature by 1.5 degrees C and stimulated panting and sometimes vasodilatation of the comb. Repeated capsaicin infusion produced temporary tachyphylaxia but no permanent desensitization. (4) A cumulative dose of 1 g/kg body weight capsaicin reduced the relationship between breathing frequency and respiratory evaporative heat loss in the duck. This deficit was compensated by more pronounced panting and, thus, did not indicate any impairment of temperature regulation. (5) Injection of capsaicin into the sciatic nerve depleted substance P in the dorsal horn of rats. Similar treatment in pigeons caused an increase of substance P immunoreactivity in the dorsal horn. (6) The effects of high capsaicin doses in birds indicate only low susceptibility of afferent neural mechanisms. Some of the effects may be due to a capsaicin action upon efferent neural mechanisms.     

Molecular mechanisms of apoptosis

Apoptosis (Programmed Cell Death) is a genetically regulated, morphologically distinct form of cell death that can be initiated by many different physiological and pathological stimuli. Such strategic intracellular programming is initiated in many instances during normal life cycle and development in order to maintain the homeostasis of a multicellular organism, to eliminate unwanted cells. However, apoptosis is also involved in a wide range of pathologic conditions, including neurodegenerative and cardiovascular diseases, cancer and autoimmune diseases. Therefore, the ability to understand and manipulate the cell death machinery is an obvious goal of medical research. Here we review the basic components of the death machinery, discuss their interaction in regulation of apoptosis, and describe the main pathways that are used to activate apoptosis.     

Molecular mechanisms of macroevolution

The present paper is devoted to the evolutionary role of genetic modules shuffing. The mechanisms capable to produce new molecular functions and significant complications of ontogenesis are reviewed. Two-step model of macroevolution is proposed. This model comprises: (1) Arising of a new combination of genetic modules. This step does not result in formation of a new taxon but makes necessary ground for that process. (2) Precise structure completing of the new combination of modules and corresponding genome optimization by use of various mechanisms including point mutations. This step concerns many genes and finally leads to formation of a new taxon. It is shown that arising of new combinations of genetic modules might work out as molecular basis for progressive evolution, while alternative structural completing of the same combination might result in adaptive radiation.     

Molecular mechanisms of photosensitization

The first part of this article is devoted to basic concepts of photosensitization and to the primary photophysical and photochemistry processes involved in the reaction. The electronic configuration of molecular oxygen in its ground or activated states, which intervene in numerous photosensitized reactions, is reviewed. Finally, the main photosensitized reactions are reviewed and classified into three different groups: reactions due to radicals (type I), reactions due to singlet oxygen (type II) and those which do not involve oxygen (type III).     

Molecular mechanisms of stress

Data on molecular mechanisms of stress are presented (appearance of stress-proteins in the blood, as well as products of peroxidation products of lipids, and changes of the cell ion balance in stress). Particular accent was made on appearance of endogenous inhibiting agents in the blood: Na+,K+-ATPase, in response to extremal factor actions inducing stress.     

Molecular mechanisms of O-GlcNAcylation

Protein glycosylation with O-linked N-acetylglucosamine (O-GlcNAc) is a reversible post-translational modification of serines/threonines on metazoan proteins and occurring with similar time scales, dynamics and stoichiometry as protein phosphorylation. Levels of this modification are regulated by two enzymes-O-GlcNAc transferase (OGT) and O-GlcNAc hydrolase (OGA). Although the biochemistry of these enzymes and functional implications of O-GlcNAc have been studied extensively, until recently the structures and molecular mechanisms of OGT/OGA were not understood. This review covers a body of recent work that has led to an understanding of the structure of OGA, its catalytic mechanism and the development of a plethora of different inhibitors that are finding their use in cell biological studies towards the functional implications of O-GlcNAc. Furthermore, the very recent structure determination of a bacterial OGT orthologue has given the first insights into the contribution of the tetratricopeptide repeats (TPRs) to the active site and the role of some residues in catalysis and substrate binding.     

Molecular mechanisms of learning and memory

Memory is the process by which organisms are able to record their experiences, and use this information to adapt their responses to the environment. As such, it is vital for survival. In recent years, the development of spatially and temporally selective techniques for the regulation of gene expression has allowed the molecular details of this process to emerge. Here we review the molecular mechanisms thought to underlie memory acquisition and storage, as well as discuss recent evidence regarding the mechanisms of subsequent memory consolidation.