The striatum is the largest nucleus of the basal ganglia, and acts as a point of convergence for thalamic, cortical and midbrain inputs. It is involved in both motor and associative forms of learning, and is composed of spiny projection neurons (SPNs) whose output along the so-called "direct pathway" and "indirect pathway" is modified by the activity of diverse sets of interneurons. Four "classical" or major classes of striatal interneuron can be identified according to the selective expression of the molecular markers parvalbumin (PV), calretinin (CR), nitric oxide synthase (NOS) or choline acetyltransferase (ChAT). Although the interneurons within a class are generally considered to be homogeneous in form and function, there is emerging evidence that some classes encompass multiple types of neuron, and that the heterogeneity in striatal interneurons extends beyond these four classes. Defining the extent of interneuron heterogeneity is important for understanding how the striatum processes distinct, topographically-organized inputs from the cortex and thalamus in order to govern a wide range of behaviors. To address these issues, a combination of immunofluorescence microscopy and stereological cell counting approaches was used in striatal tissue from rat, mouse and non-human primate. This was supplemented by in vivo recording and juxtacellular labelling of single neurons in rat. A first set of experiments showed that secretagogin (Scgn), a calcium-binding protein, is expressed by a large number of interneurons in the dorsal striatum of rat and primate, but not in the mouse. In all species tested, secretagogin was expressed by a subset of PV+ interneurons and a subset of CR+ interneurons in the dorsal striatum, but also labelled a group of interneurons that did not express any of the classical markers of striatal interneurons. A second set of experiments in the rat demonstrated that the selective co-expression of Scgn by PV+ interneurons delineates two topographically-, physiologically- and morphologically-distinct cell populations. These topographical differences in distribution were largely conserved in the primate caudate/putamen. In rats, PV+/Scgn+ and PV+/Scgn- interneurons differed significantly in their firing rates, firing patterns and phase-locking to cortical oscillations. The axons of PV+/Scgn+ interneurons were more likely to form appositions with the somata of direct pathway SPNs than indirect pathway SPNs, whereas the opposite was true for the axons of PV+/Scgn- interneurons. These two populations of GABAergic interneurons provide a potential substrate through which either of the striatal output pathways can be rapidly and selectively inhibited, and in turn mediate the expression of behavioral routines. A third set of experiments showed that CR+ interneurons of the dorsal striatum can be separated into three populations based on their molecular, topographical and morphological properties. Small-sized ("Type 3") CR+ interneurons co-expressed Scgn and were restricted in their distribution towards the rostro-medial poles of the striatum in both rats and primates. In rats, these neurons also expressed the transcription factor SP8, suggesting that they may be newly generated throughout adulthood. Large-sized, ("Type 1") CR+ interneurons did not express Scgn, but could be further distinguished by their expression of the transcription factor Lhx7. Medium-sized ("Type 2") CR+ interneurons did not express Scgn or Lhx7, and had heterogeneous electrophysiological properties in vivo. The expression of Scgn, but not other classical interneuron markers, identified a group of interneurons that were restricted in their distribution towards the ventro-medial aspects of the dorsal striatum. A fourth set of experiments showed that these neurons are also present in the core and the shell of the nucleus accumbens. Unlike the case of dorsal striatum, however, PV+ interneurons and CR+ interneurons of the nucleus accumbens did not co-express Scgn. Moreover, many of the interneuron populations studied had greater densities in the ventral striatum compared to the dorsal striatum, and had quantifiably strong biases in their distribution towards a variety of axes within both the core and the shell of the nucleus accumbens. These data thus highlight some major differences in the constituent elements of the microcircuits of dorsal striatum and nucleus accumbens. In conclusion, these studies have revealed a great deal of molecular, topographical, electrophysiological and structural heterogeneity within the interneuron populations of the striatum. As several of these interneuron populations were not evenly distributed throughout the striatum, this ultimately suggests that the microcircuit of the striatum is specialized according to regions that differ in their cortical, thalamic and dopaminergic inputs.

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El Perú es el principal productor de camélidos sudamericanos en el mundo, con más del 85% de alpacas, a pesar de ello, se conoce muy poco de la neuroanatomía de los camélidos sudamericanos, por consiguiente, es poco el conocimiento que se tiene acerca de los núcleos de los hemisferios cerebrales. El presente estudio se realizó utilizando 10 cabezas de alpacas adultas (5 machos y 5 hembras), provenientes del Camal Municipal de Nuñoa, provincia de Melgar, Puno, luego de la extracción, los cerebros fueron conservados en Formol al 10% por 1 semana, posteriormente, se realizaron cortes transversales en 7 de los cerebros y cortes longitudinales en 3 de los cerebros restantes, estos cortes se conservaron con Formol al 10% y posteriormente fueron procesados mediante la Técnica de Mulligan, se realizó la tinción con Cloruro férrico y Ferrocianuro de Potasio para la observación macroscópica de las estructuras anatómicas. Los resultados fueron descritos según la Nómina Anatómica Veterinaria (2012) y demostraron la presencia de los núcleos basales de los hemisferios cerebrales en los cortes transversales realizados. A nivel del lóbulo parietal y tercer ventrículo, se apreció la cabeza del núcleo caudado, el Globus pallidus y el putamen lateral, el siguiente corte realizado a nivel también del lóbulo parietal y tercer ventrículo, evidenció la presencia de la cápsula interna y externa; y, en la última porción del lóbulo parietal y tercer ventrículo, se apreció la cola del núcleo caudado. No se observaron las estructuras en los cortes longitudinales. Se comprobó la similar disposición anatómica de los núcleos basales de la alpaca con otras especies doméstica como el equino y bovino. Palabras claves: Alpaca, núcleos basales, anatomía / --- Perú is the main producer of camelids in the world, with over 85% of alpacas, nevertheless, very little of the neuroanatomy of South American camelids is known, therefore, there is little knowledge we have about nuclei of the cerebral hemispheres. The present study was conducted using 10 heads of adult alpacas (5 males and 5 females) from the Municipal Slaughterhouse Nuñoa province of Melgar, Puno, after extraction, the brains were preserved in 10% formalin for 1 week, subsequently transverse sections were performed in 7 of the brains and longitudinal sections in 3 of the remaining brains, these cuts were preserved with 10% formalin and were subsequently processed using the technique Mulligan, staining was performed with ferric chloride and ferrocyanide potassium for macroscopic observation of anatomical structures. The results were described as the anatomical Payroll Veterinary Science (2012) and showed the presence of the basal nuclei of the cerebral hemispheres in the transverse cuts made. At the level of the parietal lobe and the third ventricle, the head of the caudate nucleus was observed, and the Globus pallidus lateral putamen, the next cut made at the level of the parietal lobe and also third ventricle, showed the presence of internal and external capsule, and, the last portion of the parietal lobe and third ventricle, the tail of the caudate nucleus was observed. No structures in the longitudinal sections were observed. Similar anatomical arrangement of the basal nuclei of the alpaca with other domestic species such as horses and cattle was found. Keywords: Alpaca, basal ganglia, anatomy

The basal ganglia are a collection of interconnected subcortical nuclei which have been implicated inmotor, cognitive and limbic functions. The subthalamic nucleus is the sole excitatory structure within the basal ganglia. Given its central position influencingmany basal ganglia nuclei, it is likely to play an important role in the processing that is performed by the basal ganglia. In this thesis a theoretical analysis of the subthalamic nucleus is presented. In order to explore the multiple facets of processing that may be occurring, models that are designed to capture aspects of the subthalamic nucleus at different levels are developed. These include anatomical, network processing and single neuron multi–compartmental models. Through the integration of the results obtained from these models a new and coherent view of the processing of the subthalamic nucleus is presented. It is predicted that the subthalamic nucleus be considered as a massively connected excitatory network. Two distinct modes of asymptotic behaviour exist in such a network: a low resting state and a high self–sustained state. The single neuron multi– compartmental model demonstrates that the calcium T–type channel is the primary determinant of characteristic neuron behaviour. Such behaviour includes a slowaction potential, initial spike clustering, and a post-response quiescence. The network and single neuron results taken togetherprovide an intrinsicmechanismfor termination of uniform high activity generated by the excitatory network. It is therefore predicted that large regions of the subthalamic nucleus respond uniformly to stimuli, in the form of a pulse of activity with a sharp rise and fall. In addition, the single neuron model indicates that pulses will occur in pairs. It is proposedthat the subthalamic nucleus acts as a “braking mechanism”. It can induce, via intermediate structures, awide-spread pulse of inhibition on basal ganglia target nuclei. Furthermore, the sequence of two pulses can generate a window of disinhibition over the basal ganglia targets. The width of this time window may be under direct striatal control. Variable interpulse duration implies a role for the subthalamic nucleus in temporal processing.

The Basal Unit of West Woodbourne Field in Barbados is a 250 m thick succession of finely-interbedded sandstones and mudstones deposited by Paleogene, fine-grained, deep-water systems off the northern South American margin and deformed as sediments were translated to the subduction zone of the Caribbean and Atlantic plates. Closely spaced gamma ray, neutron, density, spontaneous potential, formation microimager and dip meter logs, limited core, and published reports of local outcrops, were used to define three scales of vertical stratigraphic variation within this 1.5 km2 field: (1) decimeters to meters thick log facies; (2) meters to tens of meters thick log successions; and (3) tens to hundred meter thick intervals that are continuous laterally across the field. These variations record changes in sediment supply and depositional energy during progradation and abandonment events varying in scale from local shifts in distributary channels to regional changes in sediment transport along the basin. Well log correlations suggest the Basal Unit comprises a turbidite fan system (250 m thick) trending north to northeast, composed of six, vertically-stacked, distributary channel complexes. Three architectural elements are identified within each distributary channel complex: (1) Major amalgamated channels (30-40 m thick, 150-200 m wide and at least 900 m long) pass down depositional dip into proximal second-order channels that bifurcate basinward (15-20 m thick, symmetric successions); (2) Lobe deposits (20-50 m thick, 400 m wide, and at least 400 m long) are composed of upward-coarsening successions that contain distal second-order channels (1-10 m thick); and (3) Laterally extensive overbank deposits (5-10 m thick), which vertically separate distributary channel-lobe complexes. Reservoir heterogeneities within the Basal Unit are defined by the lateral extent and facies variations across a hierarchy of strata within channel-lobe complexes. Although laterally extensive muddy overbank deposits generally inhibit vertical communication between stacked channel-lobe complexes, in places where high-energy first-order channel sandstones incise underlying muddy overbank deposits, sandstones in subsequent intervals are partially connected. The Basal Unit is bounded on the southwest by a northwest-southeast trending fault that rises 30 degrees towards the northwest to define a structural trap on the northeast side of the field.

The Basal Unit of West Woodbourne Field in Barbados is a 250 m thick succession of finely-interbedded sandstones and mudstones deposited by Paleogene, fine-grained, deep-water systems off the northern South American margin and deformed as sediments were translated to the subduction zone of the Caribbean and Atlantic plates. Closely spaced gamma ray, neutron, density, spontaneous potential, formation microimager and dip meter logs, limited core, and published reports of local outcrops, were used to define three scales of vertical stratigraphic variation within this 1.5 km2 field: (1) decimeters to meters thick log facies; (2) meters to tens of meters thick log successions; and (3) tens to hundred meter thick intervals that are continuous laterally across the field. These variations record changes in sediment supply and depositional energy during progradation and abandonment events varying in scale from local shifts in distributary channels to regional changes in sediment transport along the basin. Well log correlations suggest the Basal Unit comprises a turbidite fan system (250 m thick) trending north to northeast, composed of six, vertically-stacked, distributary channel complexes. Three architectural elements are identified within each distributary channel complex: (1) Major amalgamated channels (30-40 m thick, 150-200 m wide and at least 900 m long) pass down depositional dip into proximal second-order channels that bifurcate basinward (15-20 m thick, symmetric successions); (2) Lobe deposits (20-50 m thick, 400 m wide, and at least 400 m long) are composed of upward-coarsening successions that contain distal second-order channels (1-10 m thick); and (3) Laterally extensive overbank deposits (5-10 m thick), which vertically separate distributary channel-lobe complexes. Reservoir heterogeneities within the Basal Unit are defined by the lateral extent and facies variations across a hierarchy of strata within channel-lobe complexes. Although laterally extensive muddy overbank deposits generally inhibit vertical communication between stacked channel-lobe complexes, in places where high-energy first-order channel sandstones incise underlying muddy overbank deposits, sandstones in subsequent intervals are partially connected. The Basal Unit is bounded on the southwest by a northwest-southeast trending fault that rises 30 degrees towards the northwest to define a structural trap on the northeast side of the field.

An important function of the brain is to inhibit irrelevant behaviors. This thesis examines the role of the basal ganglia in response suppression using saccadic eye movements as a model of behavior. We measured the activity of single saccade-related neurons in primate Substantia Nigra pars reticulata (SNr), a main output structure of the basal ganglia, while the context surrounding the initiation and suppression of saccades was manipulated. Inserting a temporal gap of no stimuli between the disappearance of a central visual fixation point and the appearance of a peripheral visual target leads to a reduction in saccadic reaction times (SRT); the ‘gap’ effect. SNr pause neurons decreased their activity during the gap and this decrease correlated with SRT. This finding suggests the SNr may contribute directly to producing the gap effect and that signals related to the effect are propagating through a frontal-basal ganglia circuitry to impact pre-saccade processing. Interleaving pro-saccade (look towards a visual stimulus) and anti-saccade (look away from visual stimulus) trials allowed us to investigate how neural processes change when preparing to suppress a saccade instead of making one automatically. We show that SNr neurons exhibit activity consistent with both suppression of automatic responses and facilitation of voluntary responses, during anti-saccades. These data provide direct neurophysiological evidence for a dual role of inhibitory and disinhibitory basal ganglia outputs in the flexible shaping of behavior. Parkinson’s disease (PD) is a neurodegenerative disorder that impairs motor function due to depletion of dopamine in the striatum. Using an oculomotor countermanding paradigm, we found that PD patients were unable to suppress saccades to a peripheral target, providing evidence that the SNr performs a gating function that mediates the initiation and suppression of saccades. When pathology to the circuitry occurs, inhibitory control over saccades is affected. In Conclusion, using a variety of behavioral contexts, this thesis has demonstrated that the basal ganglia, specifically the SNr, mediates the suppression and voluntary initiation of saccades, possibly via an inhibitory gating mechanism, and that this role is important for successful interaction with a dynamic environment. / Thesis (Ph.D, Physiology) -- Queen's University, 2008-07-16 12:06:19.188