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The development of the efferent cells of the main olfactory bulb and the development of the bulbar part of the anterior commissure were studied in the rat from E16 to P7. DiI was used in fixed tissues as a neuronal tracer. From E16 onwards cells located in the olfactory bulb anlage were stained in a Golgi-like appearance. The morphological changes of these cells were: from E16 to P4, re-orientation from a tangential position to a radial position, elongation of the principal dendrite and spreading out of the secondary dendrites. From P4 onwards, there was a lack of migrating mitral cells in the inner part of the bulb. At E16 some fibers of the anterior commissure reached the midline, the number of fibers increased slowly until P0/P1. At P2 there was an explosive increase in the number of fibers crossing the midline and reaching the contralateral bulb. The development in two stages is hypothesized.

Carbocyanine DiI is described as a suitable fluorescent tracer to investigate the connectivity of cortical transplants. DiI was applied in 2 ways: in tissue previously fixed with aldehydes, and in vivo for labelling the donor tissue prior to transplantation. When applied in fixed tissue DiI travelled anterogradely, allowing the study of efferent connections from the transplant to the host. When DiI was applied in vivo, it travelled retrogradely showing the afferents to the transplant from the host.

Previous reports suggest that the specificity of connectivity between cortical areas and their related thalamic nuclei is established during development. We have used heterotopic E15, E17 and E19 transplants to determine at which embryonic age the cortex is mature enough to establish such specific connections. Carbocyanine DiI or Fluoro-Gold were used for labelling transplants. Efferent cortico-cortical, callosal and collicular connections were observed when DiI was applied in fixed tissue. Thalamic nuclei were labelled when DiI was used 'in vivo' or the transplants were labelled with Fluoro-Gold. The connections of the transplants were those corresponding to the area in which the transplants were placed. This suggests that up to E19 the embryonic cortex is too immature to define the specific thalamo-cortical connections.

The McCarthy Scales and the Children's Embedded Figures Test, as a measure of field dependence-independence, were administered to 32 girls and 18 boys, aged 7 yr. and in their second year of primary education. No significant correlations between the number of correct embedded figures and the total raw scores on the McCarthy Scales were observed, but the embedded figures scores were significantly related to scores on the Perceptual-Performance and Quantitative subscales. Boys and girls show different score patterns. The Verbal, Memory and Motor scales were independent of scores on field dependence-independence for these 7-yr.-olds.

Autoradiographic and Golgi techniques are used to study the origin, developmental characteristics, and adult morphology of the cells of sublayer VIb in the somatosensory cortex of the rat. In the adult rat, this sublayer forms a stratum of two to three rows of cells located immediately above the white matter. It is clearly separated from the remaining cortical layers by a light plexus of fibers. The cortical plate begins to appear in the lateral wall of the brain hemisphere at embryonic day 15 (E15). By using tritiated thymidine autoradiography, we can see that cells generated between E12 and E14 become located in layers I, V, and VI in the adult. After injections on E12, heavily labeled cells were found almost exclusively in layer I and in sublayer VIb, indicating that these are the earliest generated cells in the neocortex of the rat. No labeled cells were found in sublayer VIb after injection on E15. We describe the morphology of cells of layer VI from E15 to the adult using the Golgi technique. Our observations show the existence of different types of cells, among which we found horizontal bipolar cells very early during development. They transform into horizontal and inverted pyramidal cells, which are the predominant morphological types found in the adult. Horizontal cells lie at the lower part of sublayer VIb. Inverted pyramidal cells have descending apical dendrites penetrating the white matter. Their axons form ascending loops turning into projection fibers. A correlation with previous studies and some functional implications indicating the unique role of sublayer VIb in the rat during development and in the adult are discussed.

Effect of septal lesions has been studied in rats to find if they alter aspects of its SSDR. Results may be summarized as follows: 1. Animals with the septal syndrome tried to attack only when about to be caught, while they showed exaggerate freezing and submissive responses once caught. 2. A shock associated situation caused an increase in the freezing behavior and a decrease in the number of boluses excreted. 3. The septal animals never left walls of the open field, and did not explored its internal areas, showed in increase in thigmotaxis. 4. They showed an increase in the emergence time. The results are interpreted as due to an enhancement of the species-specific defence reactions.

The effect of anteroventral and anterodorsal thalamic nuclei lesions on emotional reactivity has been studied. The behavior of 18 rats (half of them bearing thalamic lesions) was studied by means of the open field and the acquisition of a conditioned emotional response (Estes and Skinner technique). Results show that no differences between control and experimental animals were found in exploratory behavior in the open field, where the number of defecations in each group was similar. They also show great impairment in the acquisition of a conditioned emotional response in experimental animals. These results suggest that the structures under study might be involved in the regulation of emotional reactivity.

The effects of the lesion of the postcommissural part of the septum on behavior of the rat has been studied. Results may be summarized as follows. An increase in the exploratory behavior in the open field which decreases rapidly; a decrease in the number of defecations in this test and a decrease in time leaving a dark environment for exploration. In the shuttle box test, no facilitation of the acquisition, but a permanent and quite significant increase in the intertrial activity has been found. We conclude that the lesions tend to decrease the emotivity of the subjects. An interpretation on the basis of the species -- specific defensive reactions explains the transitory and permanent effects of the lesions on the spontaneous activity.