Elisia Rodríguez-Veiga

Double bouquet cell in the human cerebral cortex and a comparison with other mammals.

Double bouquet cells (DBCs) are neocortical γ‐aminobutyric acid (GABA)ergic interneurons characterized by the vertical bundling of its axon, which are generally termed “bundles” or “horse‐tails.” Using immunocytochemistry for the calcium binding protein calbindin, we have analyzed the morphology, density, and distribution of DBC horse‐tails in different cortical areas of the human cortex (Brodmanns areas 10, 4, 3b, 22, 18, and 17). Although DBC horse‐tails were very numerous and regularly distributed in all cortical areas, variations were observed both in terms of morphology and density. We distinguished two major classes of DBC horse‐tails: the thicker complex type (type I) that had more axon collaterals; and the simple type (type II). The density of DBC horse‐tails was significantly higher in areas 17, 18, 22, and 4 than in areas 3b and 10. Moreover, the proportion of type I and type II DBC horse‐tails varied in the cortical areas studied. We also examined the distribution of DBC horse‐tails in frontal, parietal, and occipital areas of different mammalian species. We found DBCs to be present in carnivores but not in rodents, lagomorphs, or artiodactyls. In carnivores, relatively few DBC horse‐tails can be identified and they were generally found in the occipital cortex. Therefore, there is significant variability in the morphology and distribution of DBC horse‐tails in different species and cortical areas. We conclude that, although these interneurons may be an important element in the organization of cortical microcolumns in primates, this is not the case in other mammalian species. J. Comp. Neurol. 486:344–360, 2005.

GABAergic and non-GABAergic thalamic, hypothalamic and basal forebrain projections to the ventral oral pontine reticular nucleus : Their implication in REM sleep modulation

The ventral part of the oral pontine reticular nucleus (vRPO) is a demonstrated site of brainstem REM-sleep generation and maintenance. The vRPO has reciprocal connections with structures that control other states of the sleep-wakefulness cycle, many situated in the basal forebrain and the diencephalon. Some of these connections utilize the inhibitory neurotransmitter GABA. The aim of the present work is to map the local origin of the basal forebrain and diencephalon projections to the vRPO whether GABAergic or non-GABAergic. A double-labelling technique combining vRPO injections of the neuronal tracer, cholera-toxin (CTB), with GAD-immunohistochemistry, was used for this purpose in adult cats. All of the numerous CTB-positive neurons in the reticular thalamic and dorsocaudal hypothalamic nuclei were double-labelled (CTB/GAD-positive) neurons. Approximately 15%, 14% and 16% of the CTB-positive neurons in the zona incerta and the dorsal and lateral hypothalamic areas are, respectively, CTB/GAD-positive neurons. However, only some double-labelled neurons were found in other hypothalamic nuclei with abundant CTB-positive neurons, such as the paraventricular nucleus, perifornical area and H1 Forel field. In addition, CTB-positive neurons were abundant in the central amygdaline nucleus, terminal stria bed nuclei, median preoptic nucleus, medial and lateral preoptic areas, dorsomedial and ventromedial hypothalamic nuclei, posterior hypothalamic area and periventricular thalamic nucleus. The GABAergic and non-GABAergic connections described here may be the morphological pillar through which these prosencephalic structures modulate, either by inhibiting or by exciting, the vRPO REM-sleep inducing neurons during the different sleep-wakefulness cycle states.

Serotonergic connections to the ventral oral pontine reticular nucleus: Implication in paradoxical sleep modulation

Cholinergic microstimulation of the ventral part of the oral pontine reticular nucleus (vRPO) in cats generates and maintains paradoxical sleep. The implication of rostral raphe nuclei in modulating the sleep‐wakefulness cycle has been based on their serotonergic projections to the pontine structures responsible for the induction of paradoxical sleep. However, serotonergic neurons have also been described in brainstem structures other than the raphe nuclei. The aim of the present work is to trace the origin of the serotonergic afferents to the vRPO and to the locus coeruleus α and perilocus coeruleu α nuclei, closely related with different paradoxical sleep events. Anterograde and retrograde horseradish peroxidase conjugated with wheat germ agglutinin tracer injections in these nuclei in cats were combined with serotonin antiserum immunohistochemistry. Our results demonstrate that reciprocal connections linking the rostral raphe nuclei to those oral pontine nuclei are scarce. The percentage of double‐labeled neurons after injections in the vRPO averaged 18% in rostral raphe nuclei, while a level of 82% was estimated in mesopontine tegmentum structures other than the raphe nuclei. These results showed that the main source of serotonin to the vRPO, implicated in generation and maintenance of paradoxical sleep, arises from these mesopontine tegmentum structures. This indicates that the serotonin modulation of paradoxical sleep could be the result of activation in non‐raphe mesopontine tegmentum structures. The existence of a complicated network in the vRPO, which maintains a balance between different neurotransmitters responsible for the generation and alternance of paradoxical sleep episodes, is discussed. J. Comp. Neurol. 418:93–105, 2000.

Calbindin D28k and parvalbumin immunoreactivity in the rabbit superior colliculus: An anatomical study

The expression pattern of two calcium binding proteins (CaBP), calbindin D28k (CB) and parvalbumin (PV), in the superior colliculus (SC) of the adult rabbit, as well as the morphology of the immunoreactive cells were examined. The study was performed on 12 rabbits. Coronal sections from postmortem SC were analyzed by light microscopy, and drawings of CaBP‐labeled cells were obtained using a drawing tube. No previous information is available on either the CB/PV expression or the morphology of CB/PV positive cells in the SC of the adult rabbit. Therefore, in this study we show that CB neurons and neuropil form three main tiers: the first located within the stratum zonale (SZ) and the upper part of the stratum griseum superficiale (SGS), the second located within the stratum griseum intermedium (SGI), and the third, located within the medial and central areas of the stratum griseum profundum (SGP). In contrast to this layer labeling, almost no CB‐positivity is found within the other collicular layers. On the other hand, the densest concentration of PV labeled cells and terminals is found within a single dense tier that spanned the ventral part of the startum griseum superficiale (SGS) and the dorsal part of the stratum opticum (SO). Anti‐PV neurons are also scattered through the deeper layers below the dense tier. In contrast, almost no anti‐PV labeled neurons or neuropil are found within the stratum zonale (SZ) and upper SGS. This distribution represents a new pattern of sublamination in the SC of this species. All the previously described cell types in other mammals are observed in the rabbit SC: marginal cells, horizontal cells, pyriform cells, narrow‐field vertical cells, wide‐field vertical cells, and stellate/multipolar cells. Detailed drawings of all these cellular types are represented to show their complete morphology. The results of this study indicate that both CB and PV are present in a variety of neurons, which present a number of homologies between mammals, but have a different location and/or distribution, according to the different species. These findings are thus relevant to better understand the organisation of the SC in mammals. Anat Rec 259:334–346, 2000.

A quantitative study of the brainstem cholinergic projections to the ventral part of the oral pontine reticular nucleus (REM sleep induction site) in the cat

The ventral part of the cat oral pontine reticular nucleus (vRPO) is the site in which microinjections of small dose and volume of cholinergic agonists produce long-lasting rapid eye movement sleep with short latency. The present study determined the precise location and proportions of the cholinergic brainstem neuronal population that projects to the vRPO using a double-labeling method that combines the neuronal tracer horseradish peroxidase–wheat germ agglutinin with choline acetyltransferase immunocytochemistry in cats. Our results show that 88.9% of the double-labeled neurons in the brainstem were located, noticeably bilaterally, in the cholinergic structures of the pontine tegmentum. These neurons occupied not only the pedunculopontine and laterodorsal tegmental nuclei, which have been described to project to other pontine tegmentum structures, but also the locus ceruleus complex principally the locus ceruleus α and peri-α, and the parabrachial nuclei. Most double-labeled neurons were found in the pedunculopontine tegmental nucleus and locus ceruleus complex and, much less abundantly, in the laterodorsal tegmental nucleus and the parabrachial nuclei. The proportions of these neurons among all choline acetyltransferase positive neurons within each structure were highest in the locus ceruleus complex, followed in descending order by the pedunculopontine and laterodorsal tegmental nuclei and then, the parabrachial nuclei. The remaining 11.1% of double-labeled neurons were found bilaterally in other cholinergic brainstem structures: around the oculomotor, facial and masticatory nuclei, the caudal pontine tegmentum and the praepositus hypoglossi nucleus. The disperse origins of the cholinergic neurons projecting to the vRPO, in addition to the abundant noncholinergic afferents to this nucleus may indicate that cholinergic stimulation is not the only or even the most decisive event in the generation of REM sleep.

A Quantitative Study of Ganglion Cells in the Goat Retina

As in a number of mammals, the most prominent feature of the ganglion‐cell layer in the retina of the murciano‐granadina goat is an increase in the density of ganglion cells in the central area, as well as a concentration along a ridge extending horizontally across the retina, below the optic disc, and in the upper temporal retina. Thus, there is an area of maximum density and two streaks that are known as the ‘horizontal’ and ‘vertical’ streak. The isodensity lines of ganglion‐cell distribution is roughly concentric, with their values varying from 304 cells/mm2 in the periphery to 3592 cells/mm2 in the central area, with the cells densely packed. There were some individual differences amongst the animal studied, although all of them were purebred animals.

NADPH-diaphorase distribution in the rabbit superior colliculus and co-localization with calcium-binding proteins

Nitric oxide (NO) and calcium‐binding proteins (CaBP) are important neuromodulators implicated in brain plasticity and brain disease. In addition, the mammalian superior colliculus (SC) has one of the highest concentrations of NO within the brain. The present study was designed to determine the distribution of nitric oxide‐synthesizing neurons in the SC of the rabbit by enzyme histochemistry for reduced nicotinamide adenine dinucleotide phosphate‐diaphorase (NADPH‐d), and its degree of co‐localization with CaBP, parvalbumin (PV) and calbindin (CB). NADPH‐d‐labelled fibres formed dense patches of terminal buttons within the intermediate grey layer and streams of fibres within the deepest layers of SC. Cells expressing NOS constitute a subpopulation of neurons in which practically all cell types are represented. Combined PV/NADPH‐d experiments showed a complete lack of co‐localization within individual neurons and fibres. On the contrary, double‐labelled neurons appeared in CB/NADPH‐d‐stained sections, only in the superficial layers, and mostly in the SGS and SO. These cells, which were intermingled with other neurons containing either NADPH‐d or CB, appear to be a subtype of narrow‐field and wide‐field vertical cells, and display an anterior–posterior gradient of density. Owing to the involvement of the superficial layers of the SC in the organization and integration of the visual information, it is suggested that these neurons may play a concrete role within the visual circuits. Our data indicate a clear selectivity in the expression of NADPH‐d, PV and CB in the SC, and that NO and CB probably serve as co‐modulators and/or co‐transmitters in the connectivity of the superficial layers of this midbrain structure.

A Quantitative Study of Ganglion Cells in the German Shepherd Dog Retina

As in the number of mammals, the most prominent feature of the ganglion‐cell layer in the retina of the German shepherd dog is the sharp increase in the density of ganglion cells in the central area. There is an area of maximum density and also a ‘cat‐like’ visual streak, located dorsal to the optic disc. The isodensity lines of ganglion‐cell distribution is roughly concentric. Their values vary from 5300‐13 000 cells/mm2 in the central area, with the cells densely packed, to 1000 cells/mm2 or less in the periphery, where the cells are sparsely distributed. There were some individual differences amongst the animals studied, although all of them were pure‐bred dogs. This suggests that the configuration of the retina in the canine species is not only dependent on the breed itself but also on some other parameters such as phylogenetic heritage, environment, aptitude, lifestyle, or even training.

The thalamic reticular and perireticular nuclei in developing rabbits: patterns of parvalbumin expression.

Due to its strategic position, the thalamic reticular nucleus (TRN) plays an important role within the thalamo-cortical circuits. The perireticular thalamic nucleus (PRN) is a smaller group of cells, which is associated with the TRN and lies among the fibres of the internal capsule (IC). Studies of nuclei in rodents and carnivores have been conducted employing a number of different tools. The use of calcium-binding proteins is one example. It needs to be noted that rabbits have been regarded as intermediate between rodents and carnivores in relation to local GABAergic circuits. In the present study, sections from rabbits at different ages (prenatal, postnatal and adult) were examined to determine the parvalbumin (PV) expression in the developing TRN and PRN. In the TRN, there is one wave of PV expression during development, from caudal parts of the nucleus towards the rostral pole. At E22 there is already an incipient PV expression. In the adult stage, the TRN is completely positive to PV. The present study clearly indicates the presence of the PRN in the developing rabbit. The first PV positive cells were visible at E24, meanwhile the immunoreactivity was at its maximum at early postnatal stages (P0-P8). Two different types of perireticular cells in the IC were identified and the changes concerning neuronal morphology and orientation were described. The comparison between these results and previous data obtained in rats, ferrets or cats suggest that rabbits could represent an intermediate stage in the evolution of thalamic circuits and could be considered as useful neurobiological model.

Neurochemical heterogeneity of the thalamic reticular and perireticular nuclei in developing rabbits: patterns of calbindin expression

The thalamic reticular nucleus (TRN) forms an essential part of the circuits that link the thalamus to the cortex, whereas the perireticular thalamic nucleus (PRN) consists of scattered neurons that are located in the internal capsule, in close relation to the TRN. A common feature of these nuclei in different species is the immunoreactivity for some calcium binding proteins with a developmental pattern of expression. In the present study, sections from rabbits at different ages were examined to determine the calbindin (CB) expression in the developing TRN and PRN at the first stages of development. These CB-expressing cells constitute an important subpopulation of neurons in the caudal half of the developing TRN. In the adult, there are still positive CB somata in the middle and caudal halves of the nucleus. In the PRN, where the developmental pattern of CB expression has not been described before, the number of CB perireticular cells decreases progressively. Our results, together with previous data in the rabbit suggest the existence of remarkable neurochemical heterogeneity in the TRN and PRN of the rabbit.