COMPARATIVE AND REGIONAL DIFFERENCES IN SEROTONIN CONTENT OF REPTILIAN BRAINS

Cell Densities in the Mouse Brain: A Systematic Review

The mouse brain is the most extensively studied brain of all species. We performed an exhaustive review of the literature to establish our current state of knowledge on cell numbers in mouse brain regions, arguably the most fundamental property to measure when attempting to understand a brain. The synthesized information, collected in one place, can be used by both theorists and experimentalists. Although for commonly-studied regions cell densities could be obtained for principal cell types, overall we know very little about how many cells are present in most brain regions and even less about cell-type specific densities. There is also substantial variation in cell density values obtained from different sources. This suggests that we need a new approach to obtain cell density datasets for the mouse brain.

The projection of three extrathalamic cell groups to the cerebral cortex of the turtle Pseudemys

Three extrathalamic subcortical inputs to the part of the cerebral cortex that is known to receive thalamic fibers in the turtle were examined in the present study. Direct projections from the locus coeruleus, the superior medial raphe nucleus, and a wide area of the basal telencephalon that lies ventromedial to the globus pallidus were demonstrated with the horseradish peroxidase method. Fluorescence histochemistry confirmed the presence of catecholamine-containing fibers in the rostral half of dorsal cortex and also demonstrated a dense network of serotoninergic fibers. Biochemical analysis showed the concentration of both monoamines to be relatively high; the norepinephrine concentration was 709 ng/g and the serotonin concentration was 1,750 ng/g. No evidence was found to suggest the existence of either a dopamine fiber projection to cortex comparable to that of mammalian neocortex or the presence of an epinephrine pathway to turtle cortex equivalent to the epinephrine-containing fibers in the pallium of amphibians. The coexistence of the projections from the thalamus with noradrenergic projections from the locus coeruleus, serotoninergic projections from the superior medial raphe nucleus, and presumably cholinergic projections from the basal telencephalon provide at least four distinct subcortical inputs to the reptilian dorsal cortex. Neither thalamic nor similar extrathalamic inputs have been demonstrated in the dorsal pallium of amphibia. Mammalian neocortex, in contrast, has even more elaborately differentiated inputs of both types. These results support the idea that thalamic and extrathalamic inputs to cortex appear at the same time in vertebrate evolution, and that both types of inputs are required for the normal development and function of neocortex.

Parietal eye of the lizard: neuronal photoresponses and feedback from the pineal gland

The parietal eye of the lizard responds to illumination by sending afferent impulses to the pineal gland during daylight, the photophase. The pineal gland has efferently conducting neurons which are especially sensitive to norepinephrine and whose feedback to the parietal eye enhances its photo responsiveness. During the scotophase, at night, the eye generates afferent impulses to the cessation of light and the pineal efferents are most sensitive to serotonin. Thus, the photo-and chemoresponses of this system of interacting neurons are nearly reversed during the two phases of the daily photoperiod of the lizard.

[Pineal organ and parietal eye of Lacerta vivipara: a qualitative and quantitative microscopic study of the uptake of 3H-5-hydroxytryptophan during ontogenesis]

After comparison of results obtained by different modalities of 3h-5HTP injections (involving intraallantodic, intraventricular and intraperitoneal injections), the intraperitoneal one was retaineed to study experimental cytochemcal biosynthesis of indoleamines, in the epiphysis of Lacerta vivpara J., during ontogenesis. From stage 36 of embryogenesis, the selective radioautographic labelling, significant of atritiated indoleamines storage, was located in the distal part of the epiphysis. From stage 36 to 40 (just before hatching) and 3 days after hatching, microscopic and microphotometric studies point out, in the epiphysis epithelium, a highly significant increase in tritiated infoleamines rate. In contrast, the weak nonspecific reactions, in the neighbouring brain structures (dorsal telencephalon, tectum opticum and paraphysis), stay constant. The metabolism and storage sites of indoleamines belong to sensory line cells. During ontogenesis, these sites appear successively in distal, middle and proximal epiphysis and from the basal to the upper part of the sensory line cells. The embryonic parietal eye, in spite of structural analogies, does not take up the radioactive compound.