Pressor effects elicited by stimulation within the medullary raphe nuclei of the golden hamster (Mesocricetus auratus)

The medullary raphe nuclei are involved in central autonomic regulation. In all species investigated, electrical stimulation of the raphe nuclei causes cardiovascular responses, although these changes vary between species. The present study was designed to investigate the participation of these nuclei in cardiovascular regulation in the hamster. We studied the effect on arterial blood pressure (BP) and heart rate (HR) of electrical stimulation (isolated cathodal square wave pulses for 10 sec at 100 Hz, 40-100 muA and 1-msec pulse duration) within the medullary raphe nuclei in urethane-anesthetized (1.2 g/kg, iv, after ether induction) golden hamsters (Mesocricetus auratus, 130 to 150 g, either sex). Electrical stimulation of the same sites was performed on a group of paralysed (Flaxedi1(, 1 mg/kg, iv) and artificially ventilated animals. Stimulation sites were histologically defined and maps of the stimuli were obtained for the effect of electrical stimulation on arterial blood pressure. In another series of experiments L-glutamate (0.18 M) was microinjected (75 to 150 nl) into the nucleus raphe obseurus. Electrical stimulation of the raphe nuclei produced predominantly pressor responses (delta =+ 12 to + 100 mmHg; 49.3 per cent of the stimulated sites). Hypotension (delta =-5 to -20 mmHg; 14.6 per cent of the stimulated sites) and no change in BP (35.3 per cent) were evoked from fewer stimulation sites. Pressor responses were also predominant in paralysed animals (delta =+ 15 to + 95 mmHg; 62.5 per cent of the stimulated sites), and after microinjection of L-glutamate into the raphe obscurus (delta = +35 to + 135 mmHg). The present results demonstrate that in the hamster the stimulation of these nuclei evokes mainly pressor responses. These responses are similar to those obtained in the rat and guinea pig but opposite to those observed in the cat and rabbit.

Pacemaker interactions in the mammalian circadian system

Circadian rhythms in mammals are generated by pacemaker cells located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. The identity of these cells, however, is not known, and little information exists regarding the mechanisms by which they communicate with each other and with the organism. Nonetheless, pacemaker interactions must occur to produce single, coherent rhythms of behavior and physiology. Recently it has become possible to observe the result of these interactions using circadian chimeras, animals with two clocks with distinct periods, that have been produced by SCN transplantation. Using the tau mutation in golden hamsters, chimeras expressing two circadian rhythms of behavior simultaneously were created. The two rhythms exhibited complex interactions including cases of relative coordination. This basic result indicates that pacemaker interactions are rhythmic and phase dependent. Further analysis should help to elucidate the nature of the coupling signal and the identity of the pacemaker cells.

Retinotopic organization of striate and extrastriate visual cortex in the golden hamster (Mesocricetus auratus)

The visual topography within striate and lateral extrastriate visual cortices was studied in adult hamsters. The cortical areas 17 and 18a in the left hemisphere were electrophysiologically mapped upon stimulation of the right eye, correlating receptive field positions in the visual field with cortical recording sites. Reference lesions were placed at selected cortical sites. Like in rats and other mammals, the lateral extrastriate cortex contained multiple representations of the visual field. Rostral area 18a contained the rostrolateral maps, with medial and lateral divisions. More caudally and sharing a common border with V1, maps in lateromedial, posterolateral and posterior areas were found. More laterally and forming a ®third tier® of visual maps, anterolateral, laterolateral-anterior, laterolateral and laterolateral-posterior areas were found. There was also an indication of a possible pararhinal map. The plan so defined is virtually identical to that of rats. The results may be useful to understand a basic mammalian plan in the organization of the visual cortex

Effects of centchroman, a synthetic estrogen antagonist on the fertility of female hamsters.

Centchroman (3, 4-trans-2, 2-dimethyl-3-phenyl-4-p-beta-pyrrolidinoethoxy-phenyl-7-methoxy-chroman) , a non-steroidal, estrogen antagonist, injected subcutaneously (2 mg/kg body wt) on days 1, 2 and 3 post-coitum in hamsters, prevented implantation in 70% of the animals. A significant decrease in the circulating levels of estradiol and progesterone was observed on day 4 post-coitum as compared to control animals following the treatment of centchroman. The activities of various lysosomal enzymes were also found diminished in the treated animals. This study shows that centchroman may act as an anti-implantation agent in hamsters indicating that estrogen plays a key role during the process of ovum implantation in this species.

Estudo biométrico, peso corpóreo e peso de órgäos em animais de experimentaçäo biomédica - III. Hamster (Mesocricetus auratus) / Biological correlation of lenght, weight of body and organs in experimental animals. III.Hamster

Com base nos dados obtidos em 60 hamsters (30 machos, 30 fêmeas), fornecidos pelo Biotério Central da UNESP (Botucatu) e divididos em 3 grupos etários (25, 60, 90 dias) foram estudadas correlaçöes biométricas referentes a peso e comprimento do animal e peso de órgäos (cérebro, coraçäo, pulmäo, fígado, baço, rim, gônadas); encontrou-se regressäo linear significante. Estudou-se correlaçäo entre peso fresco e peso seco dos órgäos. Foram também analisados o peso de órgäos em relaçäo ao peso corpóreo e peso dos órgäos em relaçäo ao peso do cérebro para cada grupo

Características citoquímicas e ultraestruturais do epitélio de revestimento na parte distal do epidídimo do hamster (Mesocricetus auratus) / Cytochemical and ultraestructural characteristics of the lining epithelium in the terminal segment of the hamster (Mesocricetus auratus) epididymidis

Na parte distal do epidídimo (Cauda epididymidis) do hamster champanha notou-se alguma evidência de secreçäo protêica merócrina ao nível das células principais e evidências de secreçäo granular presumivelmente de glicoproteínas, nas células colunares claras, no epitélio de revestimento ductular. As reatividades celulares ao PAS e para a detecçäo de proteínas totais (Reaçäo de Millon), em ambos os tipos celulares, mas com especial ênfase nas células claras, säo sugestivas da presença de síntese e secreçäo de complexos de glicosaminoglicanas e proteínas, que do epitélio passa ao lumén do ducto o seu conteúdo. Um complexo microvacuolar-vesicular, aparentemente formado à partir do complexo de Golgi, é observado nas células principais. Foi sugerido que este complexo poderia representar pequenos vacúolos e vesículas de secreçäo merócrina, nestas células. Gränulos elétro-densos säo observados em todo o citoplasma das células claras, com correspondência a grânulos semelhantes e PAS-positivos observados nestas células, â microscopia de luz. Estes grânulos säo efetivamente secretados para o lúmen do ducto, pelo citoplasma apical das células claras nas observaçöes ta resoluçäo de microscopia de pinocitose bem como pela presença de corpos multivesiculares, de morfologia subcelular típica, ou pela observaçäo de grandes vacúolos supranucleares, com membranas limitantes, presumivelmente um outro tipo de corpos multivesiculares de conteúdo grandemente hidratado

Relationship between sperm concentration and the rate of fertilization in vitro of golden hamster eggs

El éxito de la fecundación depende de una interacción gamética adecuada. La evidencia disponible sugiere que el espermatozoide atravesará la zona pelúcida sólo cuando se asocia con ella en foram oblicua a través de sus bordes dorsal/ventral y anterior. Esta asociación es mediada por receptores espermáticos presentes en el borde externo de la zona pelúcida. La eficiencia de la penetración espermática podría estar asociada con la posibilidad que el espermatozoide pueda establecer ese tipo de asociación. Esta hipótese de trabajo se ensayó con un estudio realizado in vitro en el cual ovocitos de hamster con zona pelúcida se inseminaron con espermatozoides capacitados a concentraciones de 1.000, 24.111 y 48.000 espermatozoides/µl. Los resultados mostraron que al aumentar la concentración espermática, la tasa de fecundación bajó de un 97.7%, con la concentración espermática más baja, a un 63% con la concentración más alta. De la misma manera se observó que el promedio de 2,77 cuando se usó la concentració más alta. En ambos casos las diferencias fueron estadísticamente significativas (P < 0.001). Las observaciones con el microscopio electrónico de barrido mostraron que al usar concentraciones bajas de espermatozoides, éstos se asociaban con la zona pelúcida por sus bordes dorsa/ventral y anterior. Al usar concentraciones altas de espermatozoides, éstos se asociaban a través de su borde anterior. En el primer caso la asociación resultaba en una penetración exitosa, en cambio en el segundo caso, muchos espermatozoides eran incapaces de cruzar la zona