Correspondence between L7-lacZ-expressing Purkinje cells and labeled olivocerebellar fibers during late embryogenesis in the mouse.

It has been suggested that Purkinje cells (PC) play a role in organizing topographic relationships of several cerebellar afferent systems, including olivocerebellar fibers. This hypothesis is based on the observation that PC in the rat express biochemical heterogeneities during the presumptive period of olivocerebellar fiber ingrowth to the cerebellum. Previous studies designed to investigate the organization of murine olivocerebellar fibers during embryogenesis have suggested that interactions with PC may play a role in segregating olivocerebellar fibers after they enter the cerebellum. To determine whether PC heterogeneities are related to olivocerebellar fiber organization, transgenic mice carrying a beta-galactosidase (beta-gal) reporter gene linked to the promoter from the PC-specific gene L7/pcp-2 were used in neuroanatomical tracing experiments. Expression of the transgene mirrors endogenous L7/pcp-2 expression, which is upregulated earliest in parasagittal strips of the vermal cortex. Studies were conducted in vitro by using brainstem-cerebellar explants from embryonic day 17/18 (E17/18) and 18/19 mice. Applications of neuroanatomical tracer (horseradish peroxidase or neurobiotin) were made in either the caudal medial accessory olive (cMAO) or the rostral olive. These studies indicate that groups of olivocerebellar fibers and clusters of L7/lacZ+ and L7/lacZ-Purkinje cells respect common distribution boundaries during late embryogenesis. The strong correspondence between the distribution patterns generated by these two markers suggests that expression of L7/pcp-2 and the topographic organization of olivocerebellar (OC) fibers are not interdependent, but may be regulated by a common event or interaction, of a presently unknown nature, which occurs earlier during cerebellar development.

Developmental analysis of GFAP immunoreactivity in the cerebellum of the meander tail mutant mouse.

It is thought that Bergmann glial fibers assist in the inward migration of granule cells. Model systems in which there is a perturbation of either the migrating cells or the glial cell population have been useful in understanding the migratory process. In the meander tail mutant mouse, the anterior cerebellar region is agranular, whereas the posterior cerebellum is relatively unaffected by the mutation. This study presents a qualitative analysis of the development of cerebellar radial glia in mea/mea and +/mea mice aged from postnatal day 0 to adult, using an antibody against the glia specific antigen, glial fibrillary acidic protein. The results indicate a slight delay in the onset of immunoreactivity in the mea/mea cerebellum and abnormal glial formation in the anterior and posterior regions by postnatal day 5. At postnatal day 11, the full complement of labeled fibers appears to be present and although they appear abnormal in formation, they eventually reach the surface and terminate in oddly shaped and irregularly spaced endfeet. In adult mea/mea and +/mea mice, as compared to the early postnatal stages, there is a significant reduction in GFAP immunoreactive fibers. Cresyl violet stained adult mea/mea sections revealed the presence of ectopic granule cells in radial columns and small clumps at the surface of and within the molecular layer of the caudal cerebellum. Quantitative analyses revealed a 4- to 5-fold increase in the number of ectopic granule cells in lobule VIII of the mea/mea when compared with the +/mea cerebellum. These results suggest that the radial glia in the mea/mea cerebellum exhibit some uncharacteristic morphologies, but that these abnormalities are most likely the consequence of environmental alterations produced by the mutant gene.

Development of the spinocerebellar projection in the prenatal mouse.

An abundance of information is available concerning the spinocerebellar projection in adult mammals. However, only a few studies have attempted a developmental analysis of this important projection system in early postnatal and/or prenatal animals. The present study provides an analysis of the development of the projection from the spinal cord to the cerebellum in fetal mice using anterograde tracing techniques in an in vitro preparation. After applications of biocytin to the caudal cervical spinal cord, anterogradely labelled fibers were present in the brainstem of embryonic day 12 (E12/13) mice, however, there was no indication of label in the cerebellum. At E13/14, labelled fibers were evident in the rostrolateral portions of the cerebellum/isthmus region. By E15/16, labelled spinocerebellar fibers had progressed farther into the cerebellum and were seen crossing the midline in a very superficial position. At older ages, the number of crossing fibers increased, and they became more ventrally positioned within the cerebellum. At E17/18 and E18/19, labelled spinocerebellar fibers were observed to branch and invade deeper portions of the cerebellum including the cerebellar nuclei. However, at E18/19, there was no indication of the parasagittal organization characteristic of this projection in the adult animal. The results of this study indicate that spinocerebellar fibers are present within the cerebellum significantly earlier than the development and differentiation of their primary targets, the granule cells. Furthermore, these data suggest that spinocerebellar fibers may form associations with cerebellar nuclear cells during fetal development.

Anticonflict action of chlordiazepoxide in rats with combined lesions.

Lesions of brain areas thought to promote anxiety do not diminish the anticonflict effects of benzodiazepines (BZDs). After initial training in the lick-suppression conflict test, eight rats received electrolytic lesions of the amygdala, dorsal raphe, locus coeruleus, and mammillary bodies. Ten others received sham lesions. Postoperative testing revealed a significant increase in punished licking at two stages after surgery in lesioned animals when compared with their own preoperative baseline levels and with the punished licking of control animals. Systemic administration of chlordiazepoxide (CDP, 2.5-10.0 mg/kg) resulted in a comparable dose-dependent increase in punished licking in both groups. These results suggest that the several structures lesioned need not be intact for CDP to have an antianxiety effect. It appears that sites of anxiolytic action are much more widely spread than currently believed and that other brain areas should be considered.

The role of the lateral septum in anxiolysis.

Behavior of rats in the water-lick conflict test was examined during stimulation, and after lesions of the lateral septal nucleus. Continuous low-current stimulation resulted in an anxiolytic effect, an increase in the number of licks, and hence in the number of shocks, during a signaled, punished period. This effect is similar to the one seen with peripheral administration of benzodiazepine and other anxiolytic agents. Rewarding medial forebrain stimulation did not have this effect. Conversely, septal lesions resulted in an anxiogenic effect, a significant decrease in the number of licks during the punished period. Lesions had this effect when the conflict behavior was already well established. Septal lesions performed before acquisition of the conflict behavior resulted in initial retardation of acquisition. The results suggest an important role for the lateral septum in the inhibition of anxiety and in the acquisition of behaviors reinforced by alleviation of anxiety.

Anxiolytic effects of benzodiazepines in amygdala-lesioned rats.

The role of the amygdala in the anxiolytic action of benzodiazepines was examined. Performance on a water-licking conflict paradigm was tested in rats with localized damage to the central nucleus of the amygdala (ACE) or with general damage to the entire amygdaloid complex. The effects of the benzodiazepine chlordiazepoxide (2.5-20.0 mg/kg) on conflict behavior in these animals was also examined. Electrolytic lesions of either ACE or of the entire amygdaloid complex resulted in a pronounced increase of punished responding, an effect that persisted for at least 12 sessions postoperatively. After shock levels were adjusted in the lesioned groups to match their baseline punished behavior to that of the controls, various doses of chlordiazepoxide were administered. Not only did the lesioned animals show an increase in punished behavior in response to the drug, they were more sensitive than controls to the lower drug doses. A complete model of anxiolytic action may have to include both mechanisms that block anxiogenic regions and those that activate anxiolytic regions.

Placenta ingestion enhances opiate analgesia in rats.

Analgesia, produced by either a morphine injection or footshock, was monitored (using a tail-flick test) in nonpregnant female rats. Analgesia was induced within minutes of having the rats eat one of several substances. When the substance eaten was rat placenta, both the morphine- and shock-induced types of analgesia were significantly greater than in controls that ingested other substances (or nothing). When footshock (hind-paw) was administered in conjunction with the opiate antagonist naltrexone, the analgesia produced was attenuated but detectable; in this case, placenta ingestion did not enhance the analgesia, suggesting that the effect of placenta is specific to opiate-mediated analgesia. Placenta ingestion, in the absence of an analgesia-producing manipulation, did not elevate pain threshold. It is possible that this enhancement of analgesia is one of the principal benefits to mammalian mothers of ingesting the placenta and birth fluids (placentophagia) at delivery.