Nina Patzke

Navigation‐induced ZENK expression in the olfactory system of pigeons (Columba livia)

A large body of evidence indicates that pigeons use olfactory cues to navigate over unfamiliar areas with a differential contribution of the left and right hemispheres. In particular, the right nostril/olfactory bulb (OB) and left piriform cortex (Cpi) have been demonstrated to be crucially involved in navigation. In this study we analysed behaviour‐induced activation of the olfactory system, indicated by the expression of the immediate early gene ZENK, under different homing conditions. One experimental group was released from an unfamiliar site, the second group was transported to the unfamiliar site and back to the loft, and the third group was released in front of the loft. To evaluate the differential contribution of the left and/or right olfactory input, the nostrils of the pigeons were either occluded unilaterally or not. Released pigeons revealed the highest ZENK cell density in the OB and Cpi, indicating that the olfactory system is activated during navigation from an unfamiliar site. The groups with no plug showed the highest ZENK cell density, supporting the activation of the olfactory system probably being due to sensory input. Moreover, both Cpis seem to contribute differently to the navigation process. Only occlusion of the right OB resulted in a decreased ZENK cell expression in the Cpi, whereas occlusion of the left nostril had no effect. This is the first study to reveal neuronal activation patterns in the olfactory system during homing. Our data show that lateralized processing of olfactory cues is indeed involved in navigation over unfamiliar areas.

ORGANIZATION OF TELENCEPHALOTECTAL PROJECTIONS IN PIGEONS: IMPACT FOR LATERALIZED TOP-DOWN CONTROL

Birds display hemispheric specific modes of visual processing with a dominance of the right eye/left hemisphere for detailed visual object analysis. In pigeons, this behavioral lateralization is accompanied by morphological left-right differences in the ascending tectofugal pathway. This system is also asymmetrically modulated by descending telencephalotectal input whereby the left forebrain displays a much more pronounced physiological control over ipsilateral left and contralateral right visual thalamic processes. In the present study we aimed to answer the question if this top-down asymmetry that up to now had been demonstrated in single cell recording studies is due to anatomical asymmetries in the size of the fiber systems descending from the telencephalon to the tectum. We approached this question by means of a quantitative retrograde tracing study. Cholera toxin subunit B (CtB) was injected unilaterally into either the left or right optic tectum of adult pigeons. After immunohistochemical detection of CtB-positive cells, the number of ipsi- and contralaterally projecting neurons was estimated. Retrogradely labeled cells were located within the arcopallium, the hyperpallium apicale (HA) and the temporo-parieto-occipital area (TPO). Descending projections from HA, arcopallium, and TPO were mainly or exclusively ipsilateral with the contralateral projection being extremely small. Moreover, there was no difference between left and right hemispheric projections. These anatomical data sharply contrast with behavioral and electrophysiological ones which reveal an asymmetric and bilateral top down control. Therefore, contralateral and lateralized forebrain influences onto tectofugal processing are possibly not the direct result of asymmetrical descending axon numbers. Those influences emerge by a lateralized intra- and/or interhemispheric integration of ascending and descending input onto the rotundus.

Telencephalic organization of the olfactory system in homing pigeons (Columba livia)

Pigeons use olfactory cues to navigate over unfamiliar areas, and any impairment of the olfactory system generates remarkable reduction of homing performance. Lesion and deprivation studies suggest a critical involvement of the right nostril and thus, the right olfactory bulb (OB) and the left piriform cortex (CPi) for initial orientation. This functional pattern suggests that OB and CPi are asymmetrically connected with a stronger projection from the right OB to the left CPi. However, the structural organization of the olfactory system is not unequivocally clarified yet. Thus, we re-analyzed the system by antero- and retrograde tract tracing with biotinylated dextran amine and choleratoxin subunit B, and we especially evaluated quantitative differences in the number of cells in the OB innervating the left and right CPi. Our anterograde tracing data verified a strong bilateral input to the CPi, and the prepiriform cortex (CPP), as well as small projections to the ipsilateral medial septum and the dorsolateral corticoid area and the nucleus taeniae of the amygdala in both hemispheres. Apart from the bilateral bulbar afferents, CPi in turn receives unequivocal input from the ipsilateral CPP, hyperpallium densocellulare, dorsal arcopallium, and from a cluster of cells located within the frontolateral nidopallium. Thus, an indirect connection between OB and CPi is only mediated by the CPP. For quantitative analysis of bulbar input to the CPi, we counted the number of ipsi- and contralaterally projecting neurons located in the OB after injections into the left or right CPi. Retrogradely labeled cells were found bilaterally in the OB with a higher number of ipsilaterally located cells. The bilaterality index did not differ after left- or right-sided CPi injections indicating that the functional lateralization of the olfactory system is not simply based on differences in the number of projecting axons of the major processing stream.

Architectural organization of the african elephant diencephalon and brainstem.

The current study examined the organization of the diencephalon and brainstem of the African elephant (Loxodonta africana) - a region of the elephant brain that has not been examined for at least 50 years. The current description, employing material amenable for use with modern neuroanatomical methods, shows that, for the most part, the elephant diencephalon and brainstem are what could be considered typically mammalian, with subtle differences in proportions and topology. The variations from these previous descriptions, where they occurred, were related to four specific aspects of neural information processing: (1) the motor systems, (2) the auditory and vocalization systems, (3) the orexinergic satiety/wakefulness centre of the hypothalamus and the locus coeruleus, and (4) the potential neurogenic lining of the brainstem. For the motor systems, three specific structures exhibited interesting differences in organization - the pars compacta of the substantia nigra, the facial motor nerve nucleus, and the inferior olivary nuclear complex, all related to the timing and learning of movements and likely related to the control of the trunk. The dopaminergic neurons of the substantia nigra appear to form distinct islands separated from each other by large fibre pathways, an appearance unique to the elephant. Each island may send topologically organized projections to the striatum forming a dopaminergic innervation mosaic that may relate to trunk movements. At least five regions of the combined vocalization production and auditory/seismic reception system were specialized, including the large and distinct nucleus ellipticus of the periaqueductal grey matter, the enlarged lateral superior olivary nucleus, the novel transverse infrageniculate nucleus of the dorsal thalamus, the enlarged dorsal column nuclei and the ventral posterior inferior nucleus of the dorsal thalamus. These specializations, related to production and reception of infrasound, allow the proposal of a novel concept regarding the reception and localization of infrasonic sources. The orexinergic system of the hypothalamus displayed a medial hypothalamic parvocellular cluster of neurons in addition to the magnocellular clusters typical of mammals located in the lateral hypothalamus, and a novel medial division of the locus coeruleus was observed in the pons. These systems are related to appetitive drive and promotion of wakefulness, two aspects of elephant behaviour that appear to be inextricably linked. Lastly, we observed an extensive potential neurogenic lining of the ventricles throughout the brainstem that is present in even quite old elephants, although the function of these cells remains elusive. These observations combined demonstrate that, while much of the elephant brainstem is typically mammalian, certain aspects of the anatomy related to specialized behaviour of elephants are present and instructive in understanding elephant behaviour.

Organization and number of orexinergic neurons in the hypothalamus of two species of Cetartiodactyla: a comparison of giraffe (Giraffa camelopardalis) and harbour porpoise (Phocoena phocoena).

The present study describes the organization of the orexinergic (hypocretinergic) neurons in the hypothalamus of the giraffe and harbour porpoise--two members of the mammalian Order Cetartiodactyla which is comprised of the even-toed ungulates and the cetaceans as they share a monophyletic ancestry. Diencephalons from two sub-adult male giraffes and two adult male harbour porpoises were coronally sectioned and immunohistochemically stained for orexin-A. The staining revealed that the orexinergic neurons could be readily divided into two distinct neuronal types based on somal volume, area and length, these being the parvocellular and magnocellular orexin-A immunopositive (OxA+) groups. The magnocellular group could be further subdivided, on topological grounds, into three distinct clusters--a main cluster in the perifornical and lateral hypothalamus, a cluster associated with the zona incerta and a cluster associated with the optic tract. The parvocellular neurons were found in the medial hypothalamus, but could not be subdivided, rather they form a topologically amorphous cluster. The parvocellular cluster appears to be unique to the Cetartiodactyla as these neurons have not been described in other mammals to date, while the magnocellular nuclei appear to be homologous to similar nuclei described in other mammals. The overall size of both the parvocellular and magnocellular neurons (based on somal volume, area and length) were larger in the giraffe than the harbour porpoise, but the harbour porpoise had a higher number of both parvocellular and magnocellular orexinergic neurons than the giraffe despite both having a similar brain mass. The higher number of both parvocellular and magnocellular orexinergic neurons in the harbour porpoise may relate to the unusual sleep mechanisms in the cetaceans.

Consequences of different housing conditions on brain morphology in laying hens

The aim of this study was to analyze the impact of physical and social stress on the avian forebrain morphology. Therefore, we used laying hens kept in different housing systems from puberty (approximately 16 weeks old) until the age of 48 weeks: battery cages, small littered ground pen, and free range system. Cell body sizes and catecholaminergic and serotonergic innervation patterns were investigated in brain areas expected to be sensitive to differences in environmental stimulation: hippocampal substructures and the nidopallium caudolaterale (NCL), a functional analogue of the prefrontal cortex. Our analysis shows both structures differing in the affected morphological parameters. Compared to battery cage hens, hens in the free range system developed larger cells in the dorsomedial hippocampus. Only these animals exhibited an asymmetry in the tyrosine hydroxylase density with more fibres in the left dorsomedial hippocampus. We assume that the higher spatial complexity of the free range system is the driving force of these changes. In contrast, in the NCL the housing systems affected only the serotonergic innervation pattern with highest fibre densities in free range hens. Moreover hens of the free range system displayed the worst plumage condition, which most likely is caused by feather pecking causing an altered serotonergic innervation pattern. Considering the remarkable differences between the three housing conditions, their effects on hippocampal structures and the NCL were surprisingly mild. This observation suggests that the adult brain of laying hens displays limited sensitivity to differences in social and physical environment induced post-puberty, which warrants further studies.

Nuclear organisation of some immunohistochemically identifiable neural systems in three Afrotherian species—Potomogale velox, Amblysomus hottentotus and Petrodromus tetradactylus

The present study describes the organisation of the cholinergic, catecholaminergic, and serotonergic neurons in the brains of the giant otter shrew, the Hottentot golden mole and the four-toed sengi, and the orexinergic (hypocretinergic) system in the giant otter shrew and four-toed sengi. The aim of the present study was to investigate the possible differences in the nuclear complement of these neural systems in comparison to previous studies on other Afrotherian species and mammalian species in general. Brains of the golden mole, sengi and giant otter shrew were coronally sectioned and immunohistochemically stained with antibodies against cholineacetyl-transferase, tyrosine hydroxylase, serotonin and orexin-A. The majority of nuclei revealed in the current study were similar among the species investigated, to other Afrotherian species, and to mammals generally, but certain differences in the nuclear complement highlighted phylogenetic interrelationships. The golden mole was observed to have cholinergic interneurons in the cerebral cortex, hippocampus, olfactory bulb and amygdala. The four-toed sengi had cholinergic neurons in both colliculi and in the cochlear nucleus, but lacked the catecholaminergic A15d group in the hypothalamus. In both the golden mole and the four-toed sengi, the locus coeruleus (A6d group) was made up of few neurons. The golden mole also exhibited an unusual foreshortening of the brain, such that a major (mesencephalic?) flexure in the brainstem was evident.

The Evolutions of Large Brain Size in Mammals: The ‘Over-700-Gram Club Quartet'

The current paper details our developing understanding of the evolution of large brains in mammals. In order to do this, we first define brains that we consider to be large - those that have passed the apparent 700-gram ceiling on brain mass evolution in the class Mammalia. The over-700-gram club includes certain species within the genus Homo, order Cetacea, order Proboscidea, and suborder Pinnipedia. Our analysis suggests that selection for body size appears to be the most important factor in the evolution of large brain size, but there also appear to be internal morphophysiological constraints on large brain size evolution that need to be overcome in order for brains to break the 700-gram barrier. These two aspects appear to be common themes in the evolution of large brains. This significantly diminishes the explanatory value of selection for greater cognitive capacities as a principal factor in the evolution of enlarged brain sizes above the 700-gram threshold.

Organisation and chemical neuroanatomy of the African elephant (Loxodonta africana) olfactory bulb.

The olfactory system of mammals can be divided into a main and accessory olfactory system with initial processing for each system occurring in the olfactory bulb. The main and accessory olfactory bulbs have similar structural features, even though they appear to be functionally independent. In mammals the main olfactory bulb (MOB) is also one of two established sites of lifelong generation of new cells. The present study describes the histological and immunohistochemical neuroanatomy of the olfactory bulb of the African elephant (Loxodonta africana). The morphology of MOB of the elephant does not differ significantly from that described in other mammals; however, it lacks the internal plexiform layer. In addition, the glomeruli of the glomerular layer are organised in 2–4 “honey-combed” layers, a feature not commonly observed. The cell types and structures revealed with immunohistochemical stains (parvalbumin, calbindin, calretinin, tyrosine hydroxylase, orexin-A, glial fibrillary acidic protein) were similar to other mammals. Neurogenesis was examined using the neurogenic marker doublecortin. Migration of newly generated cells was observed in most layers of the MOB. No accessory olfactory bulb (AOB) was observed. Based on the general anatomy and the immunohistochemical observations, it is evident that the morphology of the African elephant MOB is, for the most part, similar to that of all mammals, although very large in absolute size.

Nuclear organization of cholinergic, putative catecholaminergic, serotonergic and orexinergic systems in the brain of the African pygmy mouse (Mus minutoides): Organizational complexity is preserved in small brains

This study investigated the nuclear organization of four immunohistochemically identifiable neural systems (cholinergic, catecholaminergic, serotonergic and orexinergic) within the brain of the African pygmy mouse (Mus minutoides). The African pygmy mice studied had a brain mass of around 275 mg, making these the smallest rodent brains to date in which these neural systems have been investigated. In contrast to the assumption that in this small brain there would be fewer subdivisions of these neural systems, we found that all nuclei generally observed for these systems in other rodent brains were also present in the brain of the African pygmy mouse. As with other rodents previously studied in the subfamily Murinae, we observed the presence of cortical cholinergic neurons and a compactly organized locus coeruleus. These two features of these systems have not been observed in the non-Murinae rodents studied to date. Thus, the African pygmy mouse displays what might be considered a typical Murinae brain organization, and despite its small size, the brain does not appear to be any less complexly organized than other rodent brains, even those that are over 100 times larger such as the Cape porcupine brain. The results are consistent with the notion that changes in brain size do not affect the evolution of nuclear organization of complex neural systems. Thus, species belonging to the same order generally have the same number and complement of the subdivisions, or nuclei, of specific neural systems despite differences in brain size, phenotype or time since evolutionary divergence.