Habituation of the eyeblink response in humans with stimuli presented in a sequence of incremental intensity

In an experiment we examined whether the repeated presentation of tones of gradually increasing intensities produces greater decrement in the eyeblink reflex response in humans than the repetition of tones of constant intensities. Two groups of participants matched for their initial level of response were exposed to 110 tones of 100-ms duration. For the participants in the incremental group, the tones increased from 60- to 90- dB in 3-dB steps, whereas participants in the constant group received the tones at a fixed 90-dB intensity. The results indicated that the level of response in the last block of 10 trials, in which both groups received 90-dB tones, was significantly lower in the incremental group than in the constant group. These findings support the data presented by Davis and Wagner (7) with the acoustic response in rats, but differ from several reports with autonomic responses in humans, where the advantage of the incremental condition has not been observed unambiguously. The discussion analyzes theoretical approaches to this phenomenon and the possible involvement of separate neural circuits.

Neonatal hyperekplexia: the Stiff-Baby syndrome.

Neonatal hyperekplexia is a rare autosomal dominant startle disorder. Presenting soon after birth, it is often mistakenly diagnosed as spastic quadriparesis, epilepsy etc. While the long-term prognosis is relatively benign, sudden death due to severe spasms have been seen in sporadic cases. We report a case of hyperekplexia with some typical and some unusual findings.

Routine post-weaning handling of rats prevents isolation rearing-induced deficit in prepulse inhibition

Rats reared under isolation conditions from weaning present a number of behavioral changes compared to animals reared under social conditions (group housing). These changes include deficits in prepulse inhibition (PPI) of the startle reflex to a loud sound. PPI refers to the reduction of the magnitude of the startle reflex when a relatively weak stimulus (the prepulse) precedes by an appropriate time interval the intense startle-elicing stimulus (the pulse). PPI is useful for studying sensorimotor integration. The present study evaluated the effect of handling on the impairment of PPI induced by isolation-rearing. Male Wistar rats (N = 11-15/group) were housed in groups (5 per cage and handled three times a week) or isolated (housed individually) since weaning (21 days) for 10 weeks when they reach approximately 150 g. The isolated rats were divided into "minimally handled" animals (handled once a week for cleaning purposes only) or "handled" animals (handled three times a week). This handling consisted of grasping the rat by the tail and moving it to a clean cage (approximately 5 s). A statistically significant reduction (52 percent) in the PPI test was found only in the isolated group with minimal handling while no difference was seen between grouped animals and isolated handled animals. These results indicate that isolation rearing causes disruption in the PPI at adult age, which serves as an index of attention deficit. This change in the sensory processing of information induced by post-weaning isolation can be prevented by handling during the development of the animal.

Organizaçäo neural de diferentes tipos de medo e suas implicaçöes na ansiedade / Neural organization of different types of fear: implications for the understanding of anxiety

A natureza das respostas de medo em animais expostos a situaçöes ameaçadoras depende da intensidade e da distância do estímulo aversivo. Esses estímulos podem ser potencialmente perigosos, distais ou proximais ao animal. Esforços têm sido feitos no sentido de identificar os circuitos neurais recrutados na organizaçäo das reaçöes defensivas a estas condiçöes aversivas. Neste artigo, sumarizamos evidências que associam os sistemas cerebrais de defesa ao conceito de medo-stress-ansiedade. Respostas de orientaçäo ao estímulo de perigo, à esquiva e à preparaçäo para o enfrentamento do perigo parecem estar associados à ansiedade. O giro do cíngulo e o córtex pré-frontal de um lado; o núcleo mediano da rafe, septo e o hipocampo de outro fazem parte dos circuitos cerebrais que integram essas respostas emocionais. No outro extremo, estímulos de medo que induzem formas ativas de defesa, mas pouco elaboradas, determinam estados emocionais de natureza diferente e parecem associadas a manifestaçöes elementares de medo. A substância cinzenta periaquedutal dorsal constitui o principal substrato neural para a integraçäo desses estados aversivos no cérebro. Comportamentos defensivos desse tipo säo produzidos pela estimulaçäo elétrica e química desta estrutura. A medida que os estímulos ameaçadores, potenciais e distais däo lugar a estímulos de perigo muito intensos ou säo substituídos por estímulos proximais de medo, ocorre uma comutaçäo (switch) dos circuitos neurais usualmente responsáveis pela produçäo de respostas condicionadas de medo para reaçöes defensivas com baixo nível de regulaçäo e organizaçäo que se assemelham aos ataques de pânico. Portanto, dependendo da natureza do evento estressor ou do estímulo incondicionado, o padräo de respostas defensivas orientadas e organizadas cede lugar a respostas motoras incoordenadas e incompletas. A amígdala e o hipotálamo medial podem funcionar como uma espécie de interface comutando os estímulos para os substratos neurais apropriados para elaboraçäo das respostas defensivas condicionadas ou incondicionadas

Behavioral correlates of the activity of serotonergic and non-serotonergic neurons in caudal raphe nuclei

We investigated the behavioral correlates of the activity of serotonergic and non-serotonergic neurons in the nucleus raphe pallidus (NRP) and nucleus raphe obscurus (NRO) of unanesthetized and unrestrained cats. The animals were implanted with electrodes for recording single unit activity, parietal oscillographic activity, and splenius, digastric and masseter electromyographic activities. They were tested along the waking-sleep cycle, during sensory stimulation and during drinking behavior. The discharge of the serotonergic neurons decreased progressively from quiet waking to slow wave sleep and to fast wave sleep. Ten different patterns of relative discharge across the three states were observed for the non-serotonergic neurons. Several non-serotonergic neurons showed cyclic discharge fluctuations related to respiration during one, two or all three states. While serotonergic neurons were usually unresponsive to the sensory stimuli used, many non-serotonergic neurons responded to these stimuli. Several non-serotonergic neurons showed a phasic relationship with splenius muscle activity during auditory stimulation. One serotonergic neuron showed a tonic relationship with digastric muscle activity during drinking behavior. A few non-serotonergic neurons exhibited a tonic relationship with digastric and/or masseter muscle activity during this behavior. Many non-serotonergic neurons exhibited a phasic relationship with these muscle activities, also during this behavior. These results suggest that the serotonergic neurons in the NRP and NRO constitute a relatively homogeneous population from a functional point of view, while the non-serotonergic neurons form groups with considerable functional specificity. The data support the idea that the NRP and NRO are implicated in the control of somatic motor output

Alarm pheromones and the influence of pupal odor on the aggressiveness of Polybia paulista (Ihering) (Hymenoptera: Vespidae)

Field bioassays were used to demonstrate that aggressive behavior of Polybia paulista (Ihering) workers is elicited by alarm pheromones present in the venom reservoirs of nest defenders and that the brood care pheromone (pupal odor) produced by the young inside the nest also plays an important defensive role. Pupal odor was extracted from the surface of pupa bodies with methanol. When bioassayed alone, the pupal odor elicited onlyu attractiveness of workers towards the odor source, but no stinging attacks were observed. However, in the presence of alarm pheromones, the brood care pheromone potentiated the effect caused by the pupal odors, increasing the number of stinging attacks during an action of colony defense. Thus, the presence of pupae within the nest not only releases brood care but also enhances the aggressiveness of workers in P. paulista colonies.

Evaluacion de la reaccion de alarma inducida por la determinacion de la presion arterial / Evaluation of the alarm reaction induced by blood pressure determination

El objetivo de este trabajo fue evaluar las características de la reacción de alarma que induce un aumento de la PA sobre la "basal" al enfrentarse el paciente con el observador que realizará el procedimiento. Este aumento "suplementario" que se suma a la PA "basal" fue analizado mediante la caída de los niveles de PAZ que se presenta luego de diez tomas consecutivas separadas por intervalos de 3 minutos en 85 individuos con cifras de PA en un amplio rango. 91 por ciento de los pacientes presentaron una disminución en tomas sucesivas y sólo 9 por ciente presentaron ascensos o ningún cambio significativo en los niveles de PAS. El descenso mostró buena correlación con la función exponencial (r = 0,99). La asíntola fue para la PAS de -8,7 + or - ,81 mmHG (P<0,01) con una constante de timpo T (Tau) de 4,7 + or - 1,3 minutos. No hubo correlación entre la magnitud del descenso y los niveles de PA, lo cual no apoya la idea de que esta reacción esté aumentada en hipertensos. El descenso en la PAD fue menor (3,87 + or - 59 mmHG, P<0,01) pero con características similares. Si consideramos las características de la caída exponencial y el hecho de que luego de 4 ó 5 tomas, llegamos a valores cercanos a la asíntola, la PA basal podría determinarse simplesmente por el promedio de 2 ó 3 determinaciones con intervalos de 3 minutos, tomadas luego de desechar las dos o tres primeras tomadas en las mismas condiciones. Esta presión "basal" parece ser de importancia en determinar la repercusión de las cifras tensionales sobre los órganos "blanco" y aunque no lo hallamos comprobado, sus valores serían similares a los obtenidos en el hogar o por monitoreo ambulatorio. Las características exponenciales de la caída de la PA en tomas consecutivas, permite calcular la PA "basal" mediante el cálculo de la asíntota de la ecuación respectiva

Maternal perception of sound-provoked fetal movement as a test of antepartum fetal wellbeing.

Maternal perception of sound-provoked fetal movement test was studied on 506 occasions in 443 women with obstetric or medical antenatal risk factors after 26 weeks gestation. The response was compared with a nonstress test (NST) performed immediately after a three-second vibroacoustic stimulation with an electronic artificial larynx. A positive response to sound stimulation, recorded as a fetal movement by the mother, occurred on 497 occasions (97.3%) and was accompanied by a reactive NST on 484 occasions; giving a specificity of 99.6 per cent and a negative predictive value of 97.4 per cent. An inconclusive or negative response to sound (2.7%) had a sensitivity of 35.0 per cent and a positive predictive value for a nonreactive NST of 77.8 per cent. Results of sound-provoked fetal movement test and NST, performed within a week of delivery, in 434 women were compared with fetal outcome. The maternal perception of sound-provoked fetal movement test had better specificity (99.1% vs 96.9%), positive predictive value (55.6% vs 35.0%) for poor fetal outcome than the NST, although its sensitivity (50.0% vs 70.0%) and negative predictive value (98.8% vs 99.3%) were lower. Maternal perception of sound-provoked fetal movement test may suffice as an inexpensive and simple method of evaluating antepartum fetal well-being in risk situations. When the mother does not feel any sound provoked fetal movement, NST is then performed. This clinical application can be helpful in a primary health care setting where rapid assessment of fetal health at risk is required.

Comportamiento de triatominos / Behavior of triatominae

Se hace una revisión bibliográfica sobre el comportamiento de triatominos, enfatizándose en la reacción estímulo-reacción y su base fisiológica. Se describen las manifestaciones de comportamiento más características: estado de repouso (akinesis); estado de alerta y de activación locomotors; estímulos claves relacionados con la búsqueda de alimento; mecanismos de orientación; intensidad motivacional; comunicación química entre los insectos; localización de la fuente de alimentos; reducción de riesgos, programación endógena de umbrales de sensibilidad; y comunicación intraespecífica