RESUMEN
Many new neurons are added to the adult avian brain. Most of them die 3-5 weeks after they are born (Nature (Lond.) 335 (1988) 353; J. Comp. Neurol 411 (1999) 487). Those that survive replace, numerically, older ones that have died (Neuron 25 (2000) 481). It has been suggested that the new neurons enhance the brain's ability to acquire new long-term memories (review in Sci. Am. 260 (1989) 74). If so, perhaps an increase in social complexity affects the survival of new neurons in a social species. To test this hypothesis, we treated adult zebra finches (Taeniopygia guttata) with [3H]-thymidine immediately before introducing them into one of three different social environments that differed in complexity and killed them 40 days later. There was a significant difference between experimental groups in the number of [3H]-labeled neurons in neostriatum caudale (NC), high vocal center (HVC) and Area X, three forebrain regions that are involved in vocal communication. In these regions, birds placed in a large heterosexual group had more new neurons than birds kept singly or as male-female pairs. Regulation of new neuron survival by extent of circuit use may be a general mechanism for ensuring that neuronal replacement is closely attuned to environmental change.
Asunto(s)
Neuronas/fisiología , Prosencéfalo/citología , Prosencéfalo/fisiología , Medio Social , Pájaros Cantores/fisiología , Animales , Benzoxazinas , Peso Corporal/fisiología , Mapeo Encefálico , Recuento de Células , Núcleo Celular/ultraestructura , Tamaño de la Célula/fisiología , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/fisiología , Colorantes , Femenino , Inmunohistoquímica , Masculino , Neostriado/anatomía & histología , Neostriado/citología , Neostriado/fisiología , Neuronas/efectos de los fármacos , Oxazinas , Prosencéfalo/efectos de los fármacos , Reclutamiento Neurofisiológico/fisiología , Tinción con Nitrato de Plata , Aislamiento Social , Timidina/farmacología , Vocalización Animal/fisiologíaRESUMEN
Inactivation, dissociation, and unfolding of tetrameric alcohol dehydrogenase I from Kluyveromyces lactis (KlADH I) were investigated using guanidinium chloride (GdmCl) as denaturant. Protein transitions were monitored by enzyme activity, intrinsic fluorescence and gel filtration chromatography. At low denaturant concentrations (less than 0.3 M), reversible transformation of enzyme into tetrameric inactive form occurs. At denaturant concentrations between 0.3 and 0.5 M, the enzyme progressively dissociates into structured monomers through an irreversible reaction. At higher denaturant concentrations, the monomers unfold completely. Refolding studies indicate that a total reactivation occurs only with the enzyme denatured between 0 and 0.3 M GdmCl concentrations. The enzyme denatured at GdmCl concentrations higher than 0.3 M refolds only partially. All together, our results indicate that unfolding of the KlADH I is a multistep process, i.e., inactivation of the structured tetramer, dissociation into partially structured monomers, followed by complete unfolding.
Asunto(s)
Alcohol Deshidrogenasa/efectos de los fármacos , Proteínas Fúngicas/efectos de los fármacos , Guanidina/farmacología , Kluyveromyces/enzimología , Alcohol Deshidrogenasa/química , Sitios de Unión , Cromatografía en Gel , Proteínas Fúngicas/química , Modelos Químicos , Concentración Osmolar , Conformación Proteica/efectos de los fármacos , Desnaturalización Proteica , Espectrometría de FluorescenciaRESUMEN
Based on morphological and behavioral findings we suggest that the seismic vibratory signals that blind mole-rats (Spalax ehrenbergi) use for intraspecific communication are picked up from the substrate by bone conduction and processed by the auditory system. An alternative hypothesis, raised by others, suggest that these signals are processed by the somatosensory system. We show here that brain stem and middle latency responses evoked by vibrations are similar to those evoked by high-intensity airborne clicks but are larger in their amplitudes, especially when the lower jaw is in close contact with the vibrating substrate. Bilateral deafening of the mole-rat or high-intensity masking noise almost completely eliminated these responses. Deafening also gradually reduced head-drumming behavior until its complete elimination about 4-6 weeks after surgery. Successive vibrations, at a rate of 0.5 vibrations/s, elicited prominent responses. At rates higher than 2 vibrations/s the amplitude of the brain stem response did not change, yet the middle latency response disappeared almost completely. It is concluded that the seismic signals that mole rate use for long distance communication are indeed processed primarily by the auditory system.
Asunto(s)
Comunicación Animal , Conducta Animal/fisiología , Audición/fisiología , Ratas Topo/fisiología , Estimulación Acústica , Animales , Sordera/fisiopatología , Electrofisiología , Femenino , Masculino , Estimulación Física , VibraciónRESUMEN
The mole rat Spalax ehrenbergi is a fossorial rodent. Although its peripheral visual system--eye and optic nerve--is highly degenerated, it shows some sensitivity to light. However, in the usual sense, it is essentially blind. An auditory take-over of the visual lateral geniculate nucleus and at least part of the visual cortices was recently demonstrated. In order to visualize the retinal projections during ontogeny, we used an anterograde tracing technique, with monocular injection of wheat germ agglutinin-labeled horseradish peroxidase (WGA-HRP). In the newborn mole rat the retina projects to most of its normal targets as compared with seeing rodents, with bilateral projections to the suprachiasmatic nuclei, the dorsal and ventral lateral geniculate nuclei, the lateroposterior nuclei, the optic tract nuclei and the superior colliculi. During the course of ontogeny, the retinohypothalamic connection is stabilized but the main optic tract undergoes progressive degeneration. In adults, only a few retinal fibers enter the contralateral ventral lateral geniculate nucleus, the lateroposterior nucleus, the optic tract nucleus and the superior colliculus. No retinal fibers could be detected in the dorsal lateral geniculate nucleus. Thus, the retinofugal projections in the adult mole rat could explain its reduced sensitivity to light, whereas the complete degeneration of the retino-dorsal lateral geniculate nucleus projection could underlie the invasion of auditory input into this normally visual center.
Asunto(s)
Degeneración Nerviosa , Retina/fisiología , Roedores/fisiología , Animales , Animales Recién Nacidos , Peroxidasa de Rábano Silvestre , Retina/citología , Roedores/anatomía & histología , Vías Visuales/anatomía & histología , Vías Visuales/crecimiento & desarrollo , Vías Visuales/fisiología , Aglutininas del Germen de TrigoRESUMEN
The anatomy of the middle ear of the blind mole rat, a subterranean rodent that uses seismic signals for long distance communication, is described qualitatively and quantitatively. The ossicular chain is of the parallel type with a lever arms ratio of 0.55 and an effective areal ratio of stapedial footplate to eardrum of 0.09. Assuming an ideal mechanical transform, the calculated fraction of acoustical energy theoretically transmitted to the cochlea, indicate low efficiency for airborne sounds. This is in accordance with the relatively high electrophysiological and behavioral threshold, shown previously. We suggest that a unique morphology of the middle ear and of the articulation between the lower jaw and the skull, as well as a peculiar 'jaw listening behavior' enable seismic vibrations to be transmitted to the inner ear mainly by bone conduction, thereby compensating for the limitation in receiving airborne signals.