Evidence that sensory traps can evolve into honest signals

Conventional models explaining extreme sexual ornaments propose that these reflect male genetic quality or are arbitrary results of genetic linkage between female preference and the ornament. The chase-away model emphasizes sexual conflict: male signals attract females because they exploit receiver biases. As males gain control of mating decisions, females may experience fitness costs through suboptimal mating rates or post-copulatory exploitation. Elaboration of male signals is expected if females increase their response threshold to resist such exploitation. If ornaments target otherwise adaptive biases such as feeding responses, selection on females might eventually separate sexual and non-sexual responses to the signal. Here we show that the terminal yellow band (TYB) of several Goodeinae species evokes both feeding and sexual responses; sexual responsiveness phylogenetically pre-dates the expression of the TYB in males and is comparable across taxa, yet feeding responsiveness decreases in species with more elaborated TYBs. Displaying a TYB is costly, and thus provides an example where a trait arose as a sensory trap but has evolved into an honest signal.     

Chemical sympathectomy reveals pre- and postsynaptic effects of neuropeptide Y (NPY) in the cardiovascular system

Intravenous injection of neuropeptide Y (NPY) caused short-lasting dose-dependent pressor responses in anesthetized rats. NPY was equipotent with noradrenaline in producing proportional pressor effects. Chemical sympathectomy, following the administration of 100 mg/kg 6-hydroxydopamine (6-OHDA), significantly potentiated the systemic pressor effects elicited by NPY or noradrenaline. Pretreatment with 2 nmol NPY enhanced the noradrenaline-induced pressor response in control rats. NPY did not change the basal tension of isolated rat aortic strips but significantly potentiated the contractile activity induced by 16 nM noradrenaline. This effect of NPY was not observed in aortic strips from rats pretreated with 6-OHDA. The presence of pre- and postsynaptic sites of action for NPY in the cardiovascular system of the rat is discussed.     

Renal handling of bilirubin photoderivatives

The renal handling of unconjugated bilirubin in the dark and during light exposure was analyzed using an isolated rat kidney preparation. The parameters tested were pigment disappearance from the perfusion medium, pigment uptake by tissue, and its renal clearance. The results indicated that despite the fact that pigment disappearance from the medium was similar for both forms of pigment, the extraction ratio was higher for irradiated pigment than for pigment in the dark. When renal clearance of pigment was plotted vs pigment uptake of tissue, the results indicated that irradiated pigment may be more efficiently removed by the kidney. In addition, data on the rate of secretion of p-aminohippurate suggested that both pigment forms shared a common site for secretion.     

Metallothionein expression in the central nervous system of multiple sclerosis patients

Multiple sclerosis (MS) is a major chronic demyelinating and inflammatory disease of the central nervous system (CNS) in which oxidative stress likely plays a pathogenic role in the development of myelin and neuronal damage. Metallothioneins (MTs) are antioxidant proteins induced in the CNS by tissue injury, stress and some neurodegenerative diseases, which have been postulated to play a neuroprotective role. In fact, MT-I+II-deficient mice are more susceptible to developing experimental autoimmune encephalomyelitis (EAE), and treatment of Lewis rats with Zn-MT-II reduces EAE severity. We show here that, as in EAE, MT-I+II proteins were expressed in brain lesions of MS patients. Cells expressing MT-I+II were mainly astrocytes and activated monocytes/macrophages. Interestingly, the levels of MT-I+II were slightly increased in the inactive MS lesions in comparison with the active lesions, suggesting that MTs may be important in disease remission.     

Green tea epigallocatechin-3-gallate is an inhibitor of mammalian histidine decarboxylase

(–)-Epigallocatechin-3-gallate, an antiproliferative and antiangiogenic component of green tea, has been reported to inhibit dopa decarboxylase. In this report, we show that this compound also inhibits histidine decarboxylase, the enzymic activity responsible for histamine biosynthesis. This inhibition was proved by a double approach, activity measurements and UV-Vis spectra of enzyme-bound pyridoxal-5-phosphate. At 0.1mM (–)-epigallocatechin-3-gallate, histidine decarboxylase activity was inhibited by more than 60% and the typical spectrum of the internal aldimine form shifted to a stable major maximum at 345nm, suggesting that the compound causes a stable change in the structure of the holoenzyme. Since histamine release is one of the primary events in many inflammatory responses, a new potential application of (–)-epigallocatechin-3-gallate in prevention or treatment of inflammatory processes is suggested by these data.Received 8 April 2003; received after revision 20 May 2003; accepted 3 June 2003     

Mutations in CLCN2 encoding a voltage-gated chloride channel are associated with idiopathic generalized epilepsies

Idiopathic generalized epilepsy (IGE) is an inherited neurological disorder affecting about 0.4% of the world's population. Mutations in ten genes causing distinct forms of idiopathic epilepsy have been identified so far, but the genetic basis of many IGE subtypes is still unknown. Here we report a gene associated with the four most common IGE subtypes: childhood and juvenile absence epilepsy (CAE and JAE), juvenile myoclonic epilepsy (JME), and epilepsy with grand mal seizures on awakening (EGMA; ref. 8). We identified three different heterozygous mutations in the chloride-channel gene CLCN2 in three unrelated families with IGE. These mutations result in (i) a premature stop codon (M200fsX231), (ii) an atypical splicing (del74-117) and (iii) a single amino-acid substitution (G715E). All mutations produce functional alterations that provide distinct explanations for their pathogenic phenotypes. M200fsX231 and del74-117 cause a loss of function of ClC-2 channels and are expected to lower the transmembrane chloride gradient essential for GABAergic inhibition. G715E alters voltage-dependent gating, which may cause membrane depolarization and hyperexcitability.     

Cyclin-dependent kinase 2 is essential for meiosis but not for mitotic cell division in mice

We targeted the locus encoding the cyclin-dependent kinase 2 (CDK2) by homologous recombination in mouse embryonic stem (ES) cells. Embryonic fibroblasts lacking CDK2 proliferate normally and become immortal after continuous passage in culture. Elimination of a conditional Cdk2 allele in immortal cells does not have a significant effect on proliferation. Cdk2-/- mice are viable and survive for up to two years, indicating that CDK2 is also dispensable for proliferation and survival of most cell types. But CDK2 is essential for completion of prophase I during meiotic cell division in male and female germ cells, an unforeseen role for this cell cycle kinase.     

A very energetic supernova associated with the gamma-ray burst of 29 March 2003

Over the past five years evidence has mounted that long-duration (>2 s) gamma-ray bursts (GRBs)-the most luminous of all astronomical explosions-signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model.     

Craniometric evidence for Palaeoamerican survival in Baja California

A current issue on the settlement of the Americas refers to the lack of morphological affinities between early Holocene human remains (Palaeoamericans) and modern Amerindian groups, as well as the degree of contribution of the former to the gene pool of the latter. A different origin for Palaeoamericans and Amerindians is invoked to explain such a phenomenon. Under this hypothesis, the origin of Palaeoamericans must be traced back to a common ancestor for Palaeoamericans and Australians, which departed from somewhere in southern Asia and arrived in the Australian continent and the Americas around 40,000 and 12,000 years before present, respectively. Most modern Amerindians are believed to be part of a second, morphologically differentiated migration. Here we present evidence of a modern Amerindian group from the Baja California Peninsula in Mexico, showing clearer affinities with Palaeoamerican remains than with modern Amerindians. Climatic changes during the Middle Holocene probably generated the conditions for isolation from the continent, restricting the gene flow of the original group with northern populations, which resulted in the temporal continuity of the Palaeoamerican morphological pattern to the present.     

Trans-synaptic shift in anion gradient in spinal lamina I neurons as a mechanism of neuropathic pain

Modern pain-control theory predicts that a loss of inhibition (disinhibition) in the dorsal horn of the spinal cord is a crucial substrate for chronic pain syndromes. However, the nature of the mechanisms that underlie such disinhibition has remained controversial. Here we present evidence for a novel mechanism of disinhibition following peripheral nerve injury. It involves a trans-synaptic reduction in the expression of the potassium-chloride exporter KCC2, and the consequent disruption of anion homeostasis in neurons of lamina I of the superficial dorsal horn, one of the main spinal nociceptive output pathways. In our experiments, the resulting shift in the transmembrane anion gradient caused normally inhibitory anionic synaptic currents to be excitatory, substantially driving up the net excitability of lamina I neurons. Local blockade or knock-down of the spinal KCC2 exporter in intact rats markedly reduced the nociceptive threshold, confirming that the reported disruption of anion homeostasis in lamina I neurons was sufficient to cause neuropathic pain.