The cytoarchitecture of the claustrum in the hedgehog (Erinaceus europaeus) brain, the morphology of its neurons, and the efferent connections with cortical and subcortical structures were studied with the Nissl and Klüver-Barrera, the Golgi, and the horseradish peroxidase methods. It was found that the claustrum is a well developed nucleus in the hedgehog telencephalon and, as in other mammals, is divided into dorsal and ventral parts. In Golgi-stained sections, spiny multipolar cells are the predominant neurons of both the dorsal and the ventral claustrum and are projection neurons. Aspiny multipolar neurons with fewer, often beaded, dendrites constitute a minority in both divisions and are interneurons. Injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in the prefrontal, motor, somatosensory, auditory and visual areas, and HRP or WGA-HRP injections in the thalamus showed that: (1) the claustroneocortical projections originate in the dorsal claustrum and are distributed to the entire neocortex; these projections are mainly ipsilateral but some also originate contralaterally; (2) the claustroneocortical projections show a rough topographic organization; there exists a substantial degree of overlap; and (3) the claustrothalamic projection, arising throughout the dorsal claustrum, is strictly ipsilateral. No evidence of a thalamoclaustral projection was found. The present results suggest that, although the hedgehog has been referred to as a "paleocortical mammal" owing to the great development of its rhinencephalic structures in comparison with its small neocortex, the dorsal claustrum is well developed and is connected with all neocortical areas as well as with the thalamus, establishing it as a key structure in the hedgehog forebrain.

Despite several studies showing that the rat supraoptic (SON) and paraventricular (PVN) nuclei are innervated by noradrenergic afferents, the respective contribution of these inputs to the oxytocinergic and vasopressinergic neuronal populations remains to be clearly defined. In the present study, we used the unbiased disector method to estimate the numerical density of noradrenergic varicosities on identified oxytocinergic and vasopressinergic somata in the rat SON and PVN. The analysis was carried out on semithin (1 micron) plastic sections cut from vibratome slices (50 microns) of the SON and PVN which had been double-labelled for noradrenaline (NA) and oxytocin- or vasopressin-related neurophysin. These preparations displayed many noradrenergic varicosities which electron microscopy showed to represent, in the main, synaptic boutons. Our quantitative analysis revealed that noradrenergic varicosities contacted oxytocinergic and vasopressinergic somata to a similar extent in male and female rats, under basal conditions of hormone secretion. The incidence of these axo-somatic contacts was similar in the SON and PVN. In contrast, in lactating rats, in which oxytocin secretion is enhanced, there was a significant increase in the density of noradrenergic varicosities apposed to oxytocinergic somata, in both nuclei. Our observations indicate that, in male and female rats under normal conditions, noradrenergic afferents innervate each type of neurosecretory somata, in both magnocellular nuclei, in a similar fashion. They reveal, moreover, that noradrenergic afferents participate in lactation-induced structural plasticity of synapses impinging on oxytocinergic somata.

Structural and functional dissociation between the septal and the temporal part of the dentate gyrus predispose for possible differentiations in the ongoing neurogenesis process of the adult hippocampus. In this study, BrdU-dated subpopulations of the rat septal and temporal dentate gyrus (coexpressing GFAP, DCX, NeuN, calretinin, calbindin, S100, caspase-3 or fractin) were quantified comparatively at 2, 5, 7, 14, 21, and 30 days after BrdU administration in order to examine the successive time-frames of the neurogenesis process, the glial or neuronal commitment of newborn cells and the occurring apoptotic cell death. Newborn neurons' migration from the neurogenic subgranular zone to the inner granular cell layer and expression of glutamate NMDA and AMPA receptors were also studied. BrdU immunocytochemistry revealed comparatively higher numbers of BrdU(+) cells in the septal part, but stereological analysis of newborn and total granule cells showed an identical ratio in the two parts, indicating an equivalent neurogenic ability, and a common topographical pattern along each part's longitudinal and transverse axis. Similarly, both parts exhibited extremely low levels of newborn glial and apoptotic cells. However, despite the initially equal division rate and pattern of the septal and temporal proliferating cells, their later proliferative profile diverged in the two parts. Dynamic differences in the differentiation, migration and maturation process of the two BrdU-incorporating subpopulations of newborn neurons were also detected, along with differences in their survival pattern. Therefore, we propose that various factors, including developmental date birth, local DG microenvironment and distinct functionality of the two parts may be the critical regulators of the ongoing neurogenesis process, leading the septal part to a continuous, rapid, and less-disciplined genesis rate, whereas the quiescent temporal microenvironment preserves a quite steady, less-demanding neurogenesis process.

The distribution pattern and the morphology of vasoactive intestinal polypeptide (VIP)- and cholecystokinin (CCK)-like-immunoreactive neurons were studied in the brain of the hedgehog and the sheep by means of the peroxidase-antiperoxidase immunocytochemical method. A total of 34 hedgehogs and 26 sheep of both sexes were used. Fourteen hedgehogs and 13 sheep received an intracerebroventricular injection of colchicine that enhanced the immunostaining and revealed "new" immunoreactive cell bodies. VIP-immunoreactive bipolar and multipolar neurons were observed in both species in the cerebral cortex, hippocampal formation, amygdaloid complex, hypothalamus, and central gray substance of the midbrain. CCK-immunoreactive bipolar, bitufted, and multipolar neurons displayed a broader distribution in both mammals than VIP neurons and were found in the cerebral cortex, the hippocampal formation, the amygdaloid complex, the hypothalamus, the mesencephalon, and the pons. In the cortex, in both the hedgehog and the sheep, VIP neurons were located in all layers but were concentrated in layers II and III, with the majority being typical bipolar. CCK neurons were more numerous in the superficial layers (I-III) but were found in the deep layers as well. They were bipolar, bitufted, or multipolar in morphology. From these neurons a small percentage, which were located almost exclusively in layers II and III of the visual cortex, exhibited also VIP immunoreactivity. Perikarya of such double-labeled cells were ovoid or round in shape with one or two main processes emanating from each pole of the cell body and oriented perpendicularly to the pia. The coexistence of the two peptides within individual neurons of the cortex has not been reported in other species and its physiological significance is discussed in relation to the GABAergic neurons of the cortex.

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