Distribution of acetylcholinesterase in the hippocampal region of the mouse: II. Subiculum and hippocampus.

The distribution of acetylcholinesterase (AChE) was examined in the subiculum and hippocampus of the adult mouse (Mus musculus domesticus). A distinctly stratified AChE pattern was observed in both areas and was compared in detail with cytoarchitectural fields and layers. In the subiculum, the lateral plexiform layer was lightly stained superficially and moderately stained at depth, where it abutted the lateral, moderately stained cell layer. Medially, a moderately stained deep plexiform layer separated the darkly stained superficial plexiform layer from the equally AChE-intense cell layer. At depth, the subicular cell layer was delimited by a band of very high AChE activity. In regio superior of the hippocampus, AChE-intense bands delimited the moderately stained strata moleculare, radiatum, and oriens toward the subjacent layers. In the stratum pyramidale, precipitate insinuated between the cell bodies gave a dark appearance to the deep part of the layer. The homologous strata of regio inferior appeared darker, but the relative staining intensities corresponded largely to those in regio superior. AChE activity in the layer of mossy fibers was almost absent septally but increased gradually to very high levels temporally. The AChE staining pattern, in conjunction with cytochemical and morphological evidence, strongly suggests a division of the pyramidal cell layer of the mouse and rat into superficial and deep substrata and discourages the definition of a prosubiculum in rodents. A comparative analysis of the AChE pattern reveals that: 1) in the subiculum, differences between species are observed within a generalized pattern of medial darkly staining and lateral lightly staining portions; 2) in the hippocampus, a conservation of the AChE pattern is seen in strata associated with intrinsic hippocampal connection; while 3) numerous interspecific differences are found in the stratum moleculare.     

Distribution of acetylcholinesterase in the hippocampal region of the mouse. III. The area dentata

The distribution of acetylcholinesterase (AChE) was examined in the area dentata of the adult mouse (Mus musculus domesticus). A distinctly stratified distribution of the enzyme was observed and was compared in detail with cytoarchitectural fields and layers. In the stratum moleculare, bands of relatively high AChE activity were seen immediately beneath the pia, at the borders between the outer, middle, and deep portions of the stratum moleculare, and superficial to the granule cell layer. AChE activity was low in the intervening parts of the stratum moleculare. In contrast to the rat, three sublaminae could be discerned in the hilus of the mouse at most septotemporal levels: a limiting subzone, a hilar plexiform layer, and a deep hilar cell mass. Deep to the granule cell layer, AChE activity was high in the limiting subzone and, septally, in the hilar plexiform layer. The deep hilar cell mass stained lightly towards the septal pole of the region but darker at more temporal levels. Numerous AChE-stained cells were seen in the hilus, with the exception of the most temporal levels. A comparative analysis of the AChE pattern of the area dentata reveals that (1) AChE-intense supra- and infragranular bands are found in all mammals, whereas (2) considerable differences between various strains of mice and between species are seen in the stratum moleculare. The functional significance of the AChE pattern is discussed in relation to species differences and connectivity and also with respect to possible activities of the enzyme other than hydrolysis of ACh, which may be involved in growth-related functions and in the plastic and degenerative processes observed in Alzheimer's disease. © 1993 Wiley-Liss, Inc.     

Distribution of acetylcholinesterase in the hippocampal region of the rabbit: I. Entorhinal area, parasubiculum, and presubiculum

The distribution of acetylcholinesterase (AChE) was examined in three areas of the hippocampal region of adult rabbit, viz., the entorhinal area, the parasubiculum, and the presubiculum. AChE was demonstrated histochemically according to a modification of the Koelle copper thiocholine method. In each of the examined areas the pattern of AChE was distinctly stratified and corresponded extensively to fields and layers defined on the basis of cyto- and fibro-architectonics. The enzyme activity was mainly present in the neuropil, but in addition, moderately to weakly stained nerve cell bodies were seen scattered in the entorhinal area and the presubiculum. Only a very small minority of the total number of neuronal somata showed an intense staining reaction for AChE. Two subfields were discernible in the entorhinal area, these being termed pars medialis and pars lateralis. Pars medialis showed a distinctly stratified enzyme distribution, whereas stratification was less conspicuous in pars lateralis, especially at basal levels. The deep cortical layers (IV-VI) showed a similar distribution of AChE in all three areas--a medium-stained layer IV, a weakly stained layer V, and a weakly to moderately stained layer VI. However, at more dorsal horizontal levels of pars medialis, heavily stained patches occurred in layer IV. In the entorhinal area, the superficial cortical layers (I-III) contained most enzyme activity in the superficial two-thirds of layer I, the interstices between the stellate cell bodies in layer II, and the superficial part of layer III. In the parasubiculum, layers I-III formed a wedge-shaped field with a very high content of AChE. The presubiculum was well stained in layers I and III, whereas the densely packed cell bodies of layer II were unstained. The distribution of AChE in the rabbit was compared with that in the rat and guinea pig, previously described. The staining pattern is fundamentally similar in all three species, but certain clear differences exist. Possible structural correlates to the AChE observed in the three areas are considered in detail, especially the relation to the distribution of afferent systems known from experimental studies in other animal species. Although a substantial amount of the enzyme is probably associated with the septohippocampal projection, at present it cannot be excluded that other fiber systems may account for some of the observed AChE.     

Distribution of acetylcholinesterase in the hippocampal region of the rabbit: III. The dentate area

The distribution of acetylcholinesterase (AChE) in the dentate area, a part of the hippocampal region, of the adult rabbit was described. A modification of the Koelle copper thiocholine method was used for the histochemical demonstration of AChE. The dentate area contained high amounts of this enzyme, distributed in a well-defined stratified pattern. Thus, in the molecular layer seven distinct and differently stained layers were observed at most septotemporal levels. The granular cell bodies were entirely devoid of AChE, but stained precipitate occurred between the cell bodies, in particular in the superficial half of the granular cell layer. In the hilus, five layers of alternating stronger and weaker activity were recognizable. In the molecular layer and the granular cell layer, almost all activity was restricted to the neuropil, whereas a great number of intensely stained cell bodies were observed in the hilus. Criteria for the delimitation of the dentate area, as defined by Blackstad, are discussed in view of the concepts of Cajal and Lorente de Nó and in relation to more recent hodological and histochemical data. The results obtained in the present report compare well with the concept of a layered rabbit hilus, the cytoarchitecture of this being representative of one group of animals including the guinea pig, monkey, and humans and differing from the nonlayered hilus found in, for example, the rat and mouse. The distribution of AChE in the rabbit was compared with that in the rat and guinea pig, described previously. Very striking differences in the staining pattern of the molecular layer were observed, whereas the granular cell layer had a virtually identical appearance. The stratified pattern observed in the rabbit hilus corresponds to the distribution profile of the enzyme in the guinea pig, but contrasts with the rather diffuse distribution in the rat. This variation in the staining pattern of the hilus, however, mainly reflects the differences in cytomorphology between the rabbit and guinea pig on the one hand and the rat on the other, rather than being representative of a true species difference. The possible correlation of the AChE observed in the rabbit dentate area with cyto- and fibroarchitecture, in particular the terminal fields of fiber systems known from experimental investigations, is discussed in detail. The possibility that some of the AChE observed in the hippocampal region could be involved in the hydrolysis of a number of neuropeptides, in particular substance P and enkephalin, is considered.     

Distribution of acetylcholinesterase in the hippocampal region of the rabbit: II. Subiculum and hippocampus

The distribution of acetylcholinesterase (AChE) has been examined in two areas of the hippocampal region of the adult rabbit, viz., the subiculum and the hippocampus. AChE was demonstrated histochemically by using a modification of the Koelle copper thiocholine method. Moderate amounts of AChE were observed in the subiculum, whereas the hippocampus had a high content of this enzyme. In each area, the AChE staining displayed a distinctly stratified pattern which has been compared in detail with the fields and layers defined on the basis of cyto- and fibro-architectonics. Most of the enzyme activity was confined to the neuropil, but a considerable number of nerve cell bodies were moderately or intensely stained in both the subiculum and the hippocampus. In the subiculum, the plexiform layer showed a complex distribution of AChE, displaying four horizontal, differently stained subzones. In the cell layer, the staining was most intense in two narrow bands, one being immediately beneath the plexiform layer and the other bordering directly on the white matter. The remaining major part of the subicular cell layer generally had a low AChE content. In regio superior of the hippocampus, intense staining was observed in the deep part of the molecular layer, in a narrow suprapyramidal zone of the stratum radiatum, and in the stratum oriens. In regio inferior, very high AChE activity was present in the molecular layer, in two narrow bands bordering the mossy fiber layer superficially and at depth, and in the stratum oriens. The pyramidal cell bodies and the mossy fibers were unstained. The distribution of AChE in the rabbit was compared with that in the rat and guinea pig; the latter two have been reported. The staining patterns of all three species share many conspicuous histochemical features, though notable species-specific traits do exist. Detailed consideration is given to possible structural correlates of the AChE observed in the two areas, in particular the relation to fiber systems known from either normal material or experimental investigations. A considerable portion of the enzyme is probably contained in afferents of septal origin, but it seems very likely that some of the AChE is associated with other fiber systems, the identity of which are unknown at present. A possible role of some of the AChE observed in the hippocampal region in the hydrolysis of substance P and enkephalin is discussed briefly.     

Neuron numbers in the presubiculum,parasubiculum, and entorhinal area of the rat

Estimates of neuron numbers have been useful in studies of neurodegenerative disorders, and in their animal models, and in the computational modeling of hippocampal function. Although the retrohippocampal region (presubiculum, parasubiculum, and entorhinal area) is an integral part of the hippocampal circuitry and is affected selectively in a number of disorders, estimates of neuron numbers in the rat retrohippocampal region have yet to be published. Such data are necessary ingredients for computational models of the function of this region and will also facilitate a comparison of this region in rats and primates, which will help to determine how well we may expect rat models to predict function and dysfunction in primate brains. In the present study, we used the optical fractionator to estimate the number of neurons in the rat retrohippocampal region. The following estimates were obtained: 3.3 × 10⁵ in presubicular layers II and III, 1.5 × 10⁵ in parasubicular layers II and III, 2.2 × 10⁵ in the combined pre- and parasubicular layers V and VI, 6.6 × 10⁴ in medial entorhinal area (MEA) layer II, 1.3 × 10⁵ in MEA layer III, 1.9 × 10⁵ in MEA layers V and VI, 4.6 × 10⁴ in lateral entorhinal area (LEA) layer II, 1.2 × 10⁵ in LEA layer III, and 1.4 × 10⁵ in LEA layers V and VI. A surprising finding was the large numbers of neurons in the pre- and parasubiculum, which indicate an important role of these areas in the control of the entorhino-hippocampal projection. A comparison of the numbers of neurons in the hippocampus and entorhinal areas in rats with similar estimates in humans revealed that gross input-output relations are largely conserved. Differences between rats and humans may be accounted for by more prominent entorhino-neocortical projections in primates and consequent increases in the number of neurons in the hippocampus and retrohippocampal region, which are dedicated to these projections. J. Comp. Neurol. 385:83–94, 1997. © 1997 Wiley-Liss, Inc.     

Histochemical demonstration of zinc in the hippocampal region of the domestic pig: III. The dentate area

The distribution of zinc was described in the dentate area, a part of the hippocampal region, of the domestic pig. A modification of Timm's sulphide silver procedure, the Neo-Timm method, was used for the histochemical demonstration of zinc. The staining of the dentate area exhibited a well-defined stratified pattern, the predominant part of the staining being restricted to the neuropil, although weakly stained nerve cell bodies were observed in the hilus fasciae dentatae. In the molecular layer, three distinct sublaminae were seen at most septotemporal levels. The outer and inner sublaminae displayed medium staining intensity, whereas the intermediate sublamina appeared extremely pale. The granular cell layer was well stained in its superficial two thirds, because of dense masses of staining occupying the interstices between the unstained granular cells. In the hilus fasciae dentatae, extreme differences in staining intensity were seen between the layers, ranging from very intense staining of the outer hilar cell layer to generally weak staining of the inner plexiform layer. The distribution of zinc in the pig was compared with that in the guinea pig and rat, described previously. The staining pattern of the molecular layer showed striking species differences, whereas the granular cell layer appeared very near identical. The stratified staining pattern seen in the hilus of the pig is very similar to the distribution observed in the guinea pig, but differs from the essentially homogeneous staining of the rat hilus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histochemical demonstration of zinc in the hippocampal region of the domestic pig: II. Subiculum and hippocampus.

The distribution of zinc has been described in two areas of the hippocampal region of the domestic pig, viz., the subiculum and the hippocampus. Zinc was demonstrated histochemically according to the Neo-Timm method, a modification of the sulphide-silver procedure. In each of the examined areas the staining displayed a distinctly stratified pattern which has been compared in detail to fields and layers defined on the basis of cyto- and fibroarchitecture, resulting in a combined chemo- and cytoarchitectonic map. Most of the staining was confined to the neuropil, but a considerable number of stained nerve cell bodies were seen in both the subiculum and the hippocampus. In the subiculum, the plexiform layer was divided into a superficial, weakly stained subzone and a deep, better stained subzone. The cell layer was generally well stained, but displayed a complex staining pattern with differences in staining intensity of both the cell bodies and neuropil. In regio superior of the hippocampus, the stratum moleculare appeared weakly stained, with the exception of a tapering process of more darkly stained tissue projecting from the plexiform layer of the subiculum into the deepest part of the layer. Stratum radiatum and the superficial subzone of stratum oriens showed a weak staining intensity, contrasting to the relatively darkly stained pyramidal cell layer and the intensely stained deep subzone of stratum oriens. In regio inferior, the stratum moleculare was divided into a moderately stained superficial part and an unstained deep part. Stratum radiatum and stratum oriens both appeared weakly stained. The layer of mossy fibers was very intensely stained and appeared almost homogeneously black in its main suprapyramidal part, whereas the infrapyramidal part was looser in character. The pyramidal cell layer was darker than in regio superior. The distribution of zinc in the pig was compared with that in the guinea pig and rat, described previously. The staining pattern is fundamentally similar in all three species, though notable species-specific traits do exist.     

Postnatal development of zinc-containing cells and neuropil in the hippocampal region of the mouse

The present study describes the postnatal development of zinc-containing boutons and their neurons of origin in the hippocampal region of the mouse. Ages investigated for the development of zinc-containing neuropil were postnatal days 0 (P0), P3, P7, P11, P15, P21, and P28. For zinc-containing cell bodies P7, P15, P21, and P28 were studied. In the area dentata, zinc-containing neuropil appeared first by P3 adjacent to the suprapyramidal limb of the granule cell layer and extended later toward the infrapyramidal limb. By P15, inter- and intralaminar gradients corresponded to those seen in adult animals. The appearance of labeled granule cells followed closely, although temporally delayed, the pattern of granule cell neurogenesis. All granule cells were labeled by P28. In the hippocampus proper, zinc-containing neuropil was seen by P0, but staining of the incipient mossy fiber zone was first visible by P3. Staining pattern and intensity developed gradually until they reached their mature appearance by P15. The distribution of labeled cells was identical to that seen in mature animals by P7 in CA3, but first by P21 in CA1. In the subiculum, neuropil staining first appeared proximally by P7, included all of this area by P11, and appeared mature by P21. A few labeled cells were seen in the proximal subiculum at all ages at which labeled cells were present in CA1. Labeled cells which extended further distally became first visible by P21. Their number and labeling intensity reached mature levels by P28. In the presubiculum, retrosplenial area 29e, and parasubiculum, neuropil staining first appeared by P3. The retrosplenial area 29e could be distinguished by P11. This area and the presubiculum reached their adult appearance by P21. This occurred first by P28 in the parasubiculum due to the late maturation of the parasubiculum a. Labeled cells were first seen by P7 in layer III of the presubiculum and by P15 in the retrosplenial area 29e and the parasubiculum. Cell labeling appeared mature by the same times as the neuropil staining. In the entorhinal areas a very light neuropil stain was apparent in the deeper layers by P0. A distinct rise in staining intensity was first observed by P7 in layers I–III. Thereafter, mature characteristics developed gradually and were attained by P21. Cell labeling was not seen in the medial entorhinal area. A few labeled cells were apparent by P7 in the lateral entorhinal area. After a slight increase by P15, numerous labeled cells were found in layer II and layer VI by P21. Their distribution and labeling intensity appeared mature by P28. Zinc-containing cells appear to represent cells formed late in the course of neurogenesis in all areas aside from the lateral entorhinal area. As far as intrinsic connections are concerned, it is the development of projections from this subset of neurons which is monitored in this study. We suggest that the appearance of zinc may contribute via its different effects on N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors to the end of a developmental phase that is permissive to changes in synaptic efficacy. Species differences and alternative functions of zinc are considered. Hippocampus 7:321–340, 1997. © 1997 Wiley-Liss, Inc.     

Connection matrix of the hippocampal formation: I. The dentate gyrus

The hippocampal formation presents a special opportunity for realistic neural modeling since its structure, connectivity, and physiology are better understood than that of other cortical components. A review of the quantitative neuroanatomy of the rodent dentate gyrus (DG) is presented in the context of the development of a computational model of its connectivity. The DG is a three-layered folded sheet of neural tissue. This sheet is represented as a rectangle, having a surface area of 37 mm² and a septotemporal length of 12 mm. Points, representing cell somata, are distributed in the model rectangle in a roughly uniform fashion. Synaptic connectivity is generated by assigning each presynaptic cell a spatial zone representing its axonal arbor. For each postsynaptic cell, a list of potential presynaptic cells is compiled, based on which arbor zones the given postsynaptic cell falls within. An appropriate number of presynaptic inputs are then selected at random. The principal cells of the DG, the granule cells, are represented in the model, as are non-principal cells, including basket cells, chandelier cells, mossy cells, and GABAergic peptidergic polymorphic (GPP) cells. The neurons of layer II of the entorhinal cortex are included also. The DG receives its main extrinsic input from these cells via the perforant path. The basket cells, chandelier cells, and GPP cells receive perforant path and granule cell input and exert both feedforward and feedback inhibition onto the granule cells. Mossy cells receive converging input from granule cells and send their output back primarily to distant septotemporal levels, where they contact both granule cells and non-principal cells. To permit numerical simulations, the model must be scaled down while preserving its anatomical structure. A variety of methods for doing this exist. Hippocampal allometry provides valuable clues in this regard. © 1995 Wiley-Liss, Inc.     

Architectonic identification of the core region in auditory cortex of macaques, chimpanzees, and humans.

The goal of the present study was to determine whether the architectonic criteria used to identify the core region in macaque monkeys (Macaca mulatta, M. nemestrina) could be used to identify a homologous region in chimpanzees (Pan troglodytes) and humans (Homo sapiens). Current models of auditory cortical organization in primates describe a centrally located core region containing two or three subdivisions including the primary auditory area (AI), a surrounding belt of cortex with perhaps seven divisions, and a lateral parabelt region comprised of at least two fields. In monkeys the core region can be identified on the basis of specific anatomical and physiological features. In this study, the core was identified from serial sets of adjacent sections processed for cytoarchitecture, myeloarchitecture, acetylcholinesterase, and cytochrome oxidase. Qualitative and quantitative criteria were used to identify the borders of the core region in individual sections. Serial reconstructions of each brain were made showing the location of the core with respect to gross anatomical landmarks. The position of the core with respect to major sulci and gyri in the superior temporal region varied most in the chimpanzee and human specimens. Although the architectonic appearance of the core areas did vary in certain respects across taxonomic groups, the numerous similarities made it possible to identify unambiguously a homologous cortical region in macaques, chimpanzees, and humans.     

Neural correlates of flight loss in a Mexican grasshopper, Barytettix psolus. I. Motor and sensory cells

The nervous systems of locusts (Schistocerca gregaria) and flightless grasshoppers (Barytet tix psolus) are compared to evaluate modifications to neurons which are associated with flight loss. Locusts are well known for their powerful flight capability. Barytettix never fly. They lack hindwings, have immobile vestiges of forewings, and are devoid of skeletal specializations for wing movement. Their pterothoracic musculature is similar to that of locusts, except for the absence of those muscles that, in locusts, have the primary function of moving the wings. Individually identified leg motorneurons, the extensors of the tibia, were compared between locusts and Barytettix and were found to have very similar morphologies. Nerve roots which correspond to those supplying wing muscles of locusts were stained by cobalt backfilling in Barytettix to test for presence of counterparts to wing muscle motorneurons. Cobalt backfills of metathoracic nerve 1 reveal the presence in Barytet tix of neurons corresponding to locust dorsal longitudinal motorneurons--neurons which persist in adult Barytettix in the complete absence of peripheral targets. These cells occupy characteristic positions within the CNS but their soma sizes are greatly reduced by comparison to their locust counterparts. Locust metathoracic ganglia bear large flight motorneurons on their ventral anterolateral margin. Viewed in toluidine blue-stained wholemounts, Barytettix ganglia show considerably smaller neuron somata in the corresponding region. In locusts, comparisons of the fast extensor tibiae (FETi) motorneuron soma profile areas with those of the largest anterior cell showed no significant difference between the two, while in Barytettix, the largest anterior cell is 51% smaller than the FETi. A counterpart to the locust wing hinge stretch receptor (SR) was revealed by backfilling metathoracic nerve 1 in Barytettix. Despite its lack of function as a wing movement detector, the central projection of Barytettix SR differs from its locust counterpart only in reduced spread of specific central branches.     

Distribution of immunoreactive somatostatin (ISRIF) in the nervous system of the squid, Loligo pealei

Somatostatin (SRIF) is a neuropeptide with a widespread distribution in the mammalian CNS. In the present study we have examined the distribution of immunoreactive-like SRIF (ISRIF)-containing elements in the nervous system of the cephalopod mollusk Loligo pealei, or the Woods Hole squid. ISRIF was localized by light immunocytochemistry in sections of the squid-optic lobe, circumesophageal ganglia-and in stellate ganglion. In the optic lobe, ISRIF neurons were found in the internal granule cell layer and medulla and immunoreactive fibers were seen throughout the lobe and in the optic tract but were absent from the optic nerve, i.e., the projection between the retina and optic lobe. In the supraesophageal complex, ISRIF neurons were found in all lobes, but primarily in the vertical, subvertical, and frontal. In the subesophageal ganglion, ISRIF neurons were seen mainly following unilateral pallial nerve lesions; these neurons were primarily small-to-medium sized. ISRIF fibers were seen in many of the nerves exiting from the brain and in nerves extending between the sub- and supra-esophageal ganglia. In the stellate ganglion, ISRIF was present in many neurons as well as in a plexus of fibers within the ganglion; the peptide was absent from the second-order fibers and the giant axon. The data suggest that a molecule immunologically similar to vertebrate SRIF may be a major transmitter/modulator in this invertebrate. These results provide a foundation for further studies to evaluate the role of this molecule.     

Immunocytochemical distribution of catecholamine-synthesizing neurons in the hypothalamus and pituitary gland of pigs: Tyrosine hydroxylase and dopamine-β-hydroxylase

This study describes the distribution of catecholaminergic neurons in the hypothalamus and the pituitary gland of the domestic pig, Sus scrofa, an animal that is widely used as an experimental model of human physiology in addition to its worldwide agricultural importance. Hypothalamic catecholamine neurons were identified by immunocytochemical staining for the presence of the catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine-β-hydroxylase. Tyrosine hydroxylase-immunoreactive perikarya were observed in the periventricular region throughout the extent of the third ventricle, the anterior and retrochiasmatic divisions of the supraoptic nucleus, the suprachiasmatic nucleus, the ventral and dorsolateral regions of the paraventricular nucleus and adjacent dorsal hypothalamus, the ventrolateral arcuate nucleus, and the posterior hypothalamus. Perikarya ranged from parvicellular (10–15 μm) to magnocellular (25–50 μm) and were of multiple shapes (rounded, fusiform, triangular, or multipolar) and generally had two to five processes with branched arborization. No dopamine-β-hydroxylase immunoreactive perikarya were observed within the hypothalamus or in the adjacent basal forebrain structures. Both tyrosine hydroxylase- and dopamine-β-hydroxylase-immunoreactive fibers and punctate varicosities were observed throughout areas containing tyrosine hydroxylase perikarya, but dopamine-β-hydroxylase immunoreactivity was very sparse within the median eminence. Within the pituitary gland, only tyrosine hydroxylase fibers, and not dopamine-β-hydroxylase immunoreactive fibers, were located throughout the neurohypophyseal tract and within the posterior pituitary in both pars intermedia and pars nervosa regions. Generally, the location and patterns of both catecholamine-synthesizing enzymes were similar to those reported for other mammalian species except for the absence of the A15 dorsal group and the very sparse dopamine-β-hydroxylase immunoreactive fibers and varicosities in the median eminence in the pig. These findings provide an initial framework for elucidating behavioral and neuroendocrine species differences with regard to catecholamine neurotransmitters. © 1996 Wiley-Liss, Inc.     

The connections of the hippocampal region. New observations on efferent connections in the guinea pig, and their functional implications

This article deals with the efferent connections of the hippocampal region, and considers the functional implications of these projections. The hippocampus receives indirect sensory information from many structures in the brain. Most of these afferents terminate in the superficial layers (I-III) of the entorhinal area. From cells in layers II and III of entorhinal area projections arise which terminate in hippocampus and fascia dentata, the perforant paths. Internal hippocampal projections constitute a unidirectional system of connections which project back to the deep layers (IV-VI) of the entorhinal area. The efferents from these layers may be divided into cortically terminating efferents, which originate from layer IV, and subcortically terminating efferents, which originate from layers V and VI. The cortically terminating projections end in regions of association cortex, and in limbic cortex. The subcortical projections terminate in the caudate, the putamen, and the accumbens nucleus. A hippocampal influence on these subcortical structures may seem surprising, but is logical when one takes into consideration reports on the functional associations between the striatum and the hippocampus. The findings suggest that the role of the hippocampus may be to gather input from all sensory modalities, to assign priorities continuously between these inputs, and as a result, to modify behavior via its influence on subcortical motor centres.     

Distribution of choline acetyltransferase immunoreactivity in the pigeon brain

We have investigated the distribution of cholinergic perikarya and fibers in the brain of the pigeon (Columba livia). With this aim, pigeon brain sections were processed immunohistochemi-cally by using an antiserum specific for chicken choline acetyltransferase. Our results show cholinergic neurons in the pigeon basal telencephalon, the hypothalamus, the habenula, the pretectum, the midbrain tectum, the dorsal isthmus, the isthmic tegmentum, and the cranial nerve motor nuclei. Cholinergic fibers were prominent in the dorsal telencephalon, the striatum, the thalamus, the tectum, and the interpeduncular nucleus. Comparison of our results with previous studies in birds suggests some major cholinergic pathways in the avian brain and clarifies the possible origin of the cholinergic innervation of some parts of the avian brain. In addition, comparison of our results in birds with those in other vertebrate species shows that the organization of the cholinergic systems in many regions of the avian brain (such as the basal forebrain, the epithalamus, the isthmus, and the hindbrain) is much like that in reptiles and mammals. In contrast, however, birds appear largely to lack intrinsic cholinergic neurons in the dorsal (“neocortex-like”) parts of the telencephalon. © 1994 Wiley-Liss, Inc.     

Neural correlates of flight loss in a Mexican grasshopper, Barytettix psolus. II. DCMD and TCG interneurons

Comparison of the nervous systems of a flightless grasshopper (Barytettix psolus), and locusts (Schistocerca) is extended to include two large interneurons, the descending contralateral movement detector (DCMD) and the tritocerebral commissure giant (TCG). These interneurons are thought to play a role in locust flight. Both were visualized in Barytettix with cobalt staining techniques. Most features of the two neurons are similar in both locusts and Barytettix. Yet, several differences were noted. In locusts, the dorsal DCMD branch in its metathoracic projection terminates in dorsolateral neuropile and synapses with flight motorneurons (Pearson and Goodman, '79). In Barytettix, no branch terminates in the corresponding region. Of the animals examined, 52% lacked branches corresponding to locust dorsal branches. When present, they all had abnormal projections by comparison to their counterparts in locusts. The maintenance of the TCG in Barytettix with so similar a form to that of locusts suggests that the role of the cell in behavior other than flight should be examined. The differences in DCMD projection suggest that a discrete set of output connections may have been modified in Barytettix by the alteration of a single first-order axonal branch.