Cat Thalamus Research Articles

Convergence of forepaw somatosensory and motor cortical projections in the striatum, claustrum, thalamus, and pontine nuclei of cats.

The basal ganglia and pontocerebellar systems regulate somesthetic-guided motor behaviors and receive prominent inputs from sensorimotor cortex. In addition, the claustrum and thalamus are forebrain subcortical structures that have connections with somatosensory and motor cortices. Our previous studies in rats have shown that primary and secondary somatosensory cortex (S1 and S2) send overlapping projections to the neostriatum and pontine nuclei, whereas, overlap of primary motor cortex (M1) and S1 was much weaker. In addition, we have shown that M1, but not S1, projects to the claustrum in rats. The goal of the current study was to compare these rodent projection patterns with connections in cats, a mammalian species that evolved in a separate phylogenetic superorder. Three different anterograde tracers were injected into the physiologically identified forepaw representations of M1, S1, and S2 in cats. Labeled fibers terminated throughout the ipsilateral striatum (caudate and putamen), claustrum, thalamus, and pontine nuclei. Digital reconstructions of tracer labeling allowed us to quantify both the normalized distribution of labeling in each subcortical area from each tracer injection, as well as the amount of tracer overlap. Surprisingly, in contrast to our previous findings in rodents, we observed M1 and S1 projections converging prominently in striatum and pons, whereas, S1 and S2 overlap was much weaker. Furthermore, whereas, rat S1 does not project to claustrum, we confirmed dense claustral inputs from S1 in cats. These findings suggest that the basal ganglia, claustrum, and pontocerebellar systems in rat and cat have evolved distinct patterns of sensorimotor cortical convergence.

Severity of neurological signs in feline hypertensive encephalopathy may be reflected through brain histopathological lesions

AbstractHypertensive encephalopathy (HE) was diagnosed in two aged cats with chronic kidney disease. The cause for admission was generalised epileptic seizures, with severe, interictal neurological dysfunction (dementia, locomotor dysfunction, cranial nerve deficits). Both cats had systolic hypertension (SH) (180‐220 mm Hg), bilateral retinal detachment, non‐regenerative anaemia and moderate renal azotaemia. Both cats died. Gross lesions were apparent in one cat consisting of white matter oedema in the parietal and temporal lobe and a focal area of malacia. Histopathological examination of brain tissue revealed bilateral severe oedema and astrocytic gliosis in the corona radiata, basal nuclei, thalamus and piriform lobe of both cats. Extensive hyaline and hyperplastic arteriolosclerosis, perivascular plasma exudation and haemorrhages were present throughout the meninges and neuroparenchyma. Histopathological findings reflected the severity of neurological deficits. This could indicate that the severity of the brain lesions is associated with the neurological manifestations of HE.

Therapeutic benefit after intracranial gene therapy delivered during the symptomatic stage in a feline model of Sandhoff disease.

Sandhoff disease (SD) is an autosomal recessive lysosomal storage disease caused by defects in the β-subunit of β-N-acetylhexosaminidase (Hex), the enzyme that catabolizes GM2 ganglioside (GM2). Hex deficiency causes neuronal storage of GM2 and related glycoconjugates, resulting in progressive neurodegeneration and death, typically in infancy. No effective treatment exists for human patients. Adeno-associated virus (AAV) gene therapy led to improved clinical outcome and survival of SD cats treated before the onset of disease symptoms. Most human patients are diagnosed after clinical disease onset, so it is imperative to test AAV gene therapy in symptomatic SD cats to provide a realistic indication of therapeutic benefits that can be expected in humans. In this study, AAVrh8 vectors injected into the thalamus and deep cerebellar nuclei of symptomatic SD cats resulted in widespread central nervous system enzyme distribution, although a substantial burden of storage material remained. Cats treated in the early symptomatic phase showed delayed disease progression and a significant survival increase versus untreated cats. Treatment was less effective when administered later in the disease course, although therapeutic benefit was still possible. Results are encouraging for the treatment of human patients and provide support for the development AAV gene therapy for human SD.

Distribution and Morphology of Cortical Terminals in the Cat Thalamus from the Anterior Ectosylvian Sulcus

Two main types of cortical terminals have been identified in the cat thalamus. Large (type II) have been proposed to drive the response properties of thalamic cells while smaller (type I) are believed to modulate those properties. Among the cat’s visual cortical areas, the anterior ectosylvian visual area (AEV) is considered as one of the highest areas in the hierarchical organization of the visual system. Whereas the connections from the AEV to the thalamus have been recognized, their nature (type I or II) is presently not known. In this study, we assessed and compared the relative contribution of type I and type II inputs to thalamic nuclei originating from the AEV. The anterograde tracer BDA was injected in the AEV of five animals. Results show that (1) both type I and II terminals from AEV are present in the Lateral Posterior- Pulvinar complex, the lateral median suprageniculate complex and the medial and dorsal geniculate nuclei (2) type I terminals significantly outnumber the type II terminals in almost all nuclei studied. Our results indicate that neurons in the AEV are more likely to modulate response properties in the thalamus rather than to determine basic organization of receptive fields of thalamic cells.

Intracranial infarcts in two cats with suspected thoracic limb and pulmonary neoplasia

Cerebrovascular accidents (CVAs) or strokes are now widely accepted to occur in cats and dogs and may occur following either intracranial blood vessel rupture (haemorrhagic) or occlusion (ischaemic). Neoplasia is...

Characteristics of the Distribution of Acetylcholinesterase in the Posterolateral Nucleus of the Thalamus in Cats

Studies using histochemical detection of the enzyme acetylcholinesterase (AChE) showed that two-weekold cats (n = 4) had loci with higher enzyme activity in the lateral nucleus of the posterolateral complex of the thalamus and that these were not present in 14-week-old cats (n = 4). These loci were distributed opposite to similar loci in the medial nucleus of the posterolateral complex. A possible relationship between these AChE loci and the organization of thalamocortical and corticothalamic projections is discussed.

Corticothalamic Feedback Controls Sleep Spindle Duration In Vivo

Spindle oscillations are commonly observed during stage 2 of non-rapid eye movement sleep. During sleep spindles, the cerebral cortex and thalamus interact through feedback connections. Both initiation and termination of spindle oscillations are thought to originate in the thalamus based on thalamic recordings and computational models, although some in vivo results suggest otherwise. Here, we have used computer modeling and in vivo multisite recordings from the cortex and the thalamus in cats to examine the involvement of the cortex in spindle oscillations. We found that although the propagation of spindles depended on synaptic interaction within the thalamus, the initiation and termination of spindle sequences critically involved corticothalamic influences.

Neurometabolic Coupling in the Lateral Geniculate Nucleus Changes With Extended Age

Attempts have been made in various studies to identify and trace changes in function in the aging visual system. Some results are conflicting and we report here a unique approach in an attempt to resolve selected issues. We have estimated neurometabolic coupling in the central visual pathway in young and old cats. Our technique provides high resolution simultaneous measurements of neuronal activity and changes in concentration of tissue oxygen in the thalamus of young and old cats. Following visual stimulation, we find shorter latency and time to peak in tissue oxygen responses in old compared with young animals. Estimates of local activity induced initial negative oxygen response show substantial reductions in older animals. Measurements of neural activity in the form of multiple unit activity are similar in the two age groups. To investigate the mechanisms underlying the changes in tissue oxygen response in older animals, we measured vascular capillary density and found it to be substantially lower in old than that in young animals. Together, these findings suggest that the changes in metabolic responses with age may be largely accounted for by alterations in the cerebral microvasculature rather than by changes in neural activity.

Coherent gamma oscillations couple the amygdala and striatum during learning

The basolateral amygdala (BLA) mediates the facilitating effects of emotions on memory. The BLA's enhancing influence extends to various types of memories, including striatal-dependent habit formation. To shed light on the underlying mechanisms, we carried out unit and local field potential (LFP) recordings in BLA, striatum, auditory cortex and intralaminar thalamus in cats trained on a stimulus-response task in which the presentation of one of two tones predicted reward delivery. The coherence of BLA, but not of cortical or thalamic, LFPs was highest with striatal gamma activity, and intra-BLA muscimol infusions selectively reduced striatal gamma power. Moreover, coupling of BLA-striatal unit activity increased when LFP gamma power was augmented. Early in training, the rewarded and unrewarded tones elicited a modest increase in coherent BLA-striatal gamma. As learning progressed, this gamma coupling selectively increased in relation to the rewarded tone. Thus, coherent gamma oscillations coordinate amygdalostriatal interactions during learning and might facilitate synaptic plasticity.

Involvement of the lemniscal and paralemniscal pathways in the perception of direction and neuronal activity in the barrel cortex in rodent single-whisker stimulation

We recorded the neuronal activities from, stimulated, and produced lesions in, various regions in the brainstem of thalamic cats. Neuronal activities were recorded during stepping on a motor-driven treadmill, and were averaged by using the flexor EMG as the trigger. In wide regions of the brainstem, an averaged response was obtained with similar latency as the ipsilateral flexor EMG; however, in the paralemniscal pontine reticular formation (PLRF) the averaged response preceded the flexor EMG. When repetitive electrical stimulation was applied to the PLRF on one side, coordinated movements of bilateral forelimbs were elicited. The ipsilateral forelimb was flexed and the contralateral forelimb extended. EMG recordings revealed that on the side ipsilateral to the stimulation, flexor EMGs appeared and increased gradually in amplitude, and the extensor EMG was suppressed, while the extensor EMG was increased and no flexor EMG was obtained on the side contralateral to the stimulation. When pulse train stimulation was alternatingly applied to the PLRF on bilateral sides, alternating forelimb movement, as in stepping, was evoked, depending on each stimulation. A small, unilateral lesion in the PLRF reduced forelimb stepping on a motor-driven treadmill, particularly the flexor muscle contraction in the forelimb ipsilateral to the lesion. Bilateral PLRF lesions abolished forelimb stepping on both sides. Unilateral transection of the ventral quadrant at the cervical cord abolished PLRF-elicited flexor EMGs and associated suppression of extensor EMG ipsilateral to the transection; however, the side contralateral to the transection remained intact. These results suggest that the PLRF exerts a patterned control of the bilateral forelimb muscles and plays a role in initiating and maintaining forelimb stepping.

Task-Dependent Modulation of Medial Geniculate Body Is Behaviorally Relevant for Speech Recognition

SummaryRecent work has shown that responses in first-order sensory thalamic nuclei are modulated by cortical areas [1–5]. However, the functional role of such corticothalamic modulation and its relevance for human perception is still unclear. Here, we show in two functional magnetic resonance imaging (fMRI) studies that the neuronal response in the first-order auditory thalamus, the medial geniculate body (MGB), is increased when rapidly varying spectrotemporal features of speech sounds are processed, as compared to processing slowly varying spectrotemporal features of the same sounds. The strength of this task-dependent modulation is positively correlated with the speech recognition scores of individual subjects. These results show that task-dependent modulation of the MGB serves the processing of specific features of speech sounds and is behaviorally relevant for speech recognition. Our findings suggest that the first-order auditory thalamus is not simply a nonspecific gatekeeper controlled by attention [6]. Together with studies in nonhuman mammals [4, 5], our findings imply a mechanism in which the first-order auditory thalamus, possibly by corticothalamic modulation, reacts adaptively to features of sensory input.

Co-localization of Glutamic Acid Decarboxylase and Phosphate-activated Glutaminase in Neurons of Lateral Reticular Nucleus in Feline Thalamus

Immunohistochemical methods were used to label singly and/or in combination glutamic acid decarboxylase (GAD, the sole synthesizing enzyme for the inhibitory neurotransmitter gamma-aminobutyric acid) and phosphate-activated glutaminase (GLN, a synthesizing enzyme for glutamate) in neurons of lateral reticular nucleus (LRN) of thalamus of adult cats. (1) GAD- and GLN-immunoreactivity (IR) exhibited matching regional patterns of organization within LRN. (2) GAD- and GLN-IR co-localized within most if not all LRN neuronal cell bodies as shown by light microscopy. (3) GAD- and GLN-IR had distinct subcellular localizations in LRN neurons as shown by correlative light/electron microscopy. LRN neurons are important conceptual models where strongly inhibitory cells receive predominant excitatory glutamatergic afferents (from neocortex). Consistent with known actions of intermediary astrocytes, LRN neurons demonstrate GLN enrichment synergistically coupled with glutamatergic innervation to supplement the glutamate pool for GABA synthesis (via GAD) and for metabolic utilization (via the GABA shunt/tricarboxylic acid cycle) but not, apparently, for excitatory neurotransmission.

Postnatal development of the corticothalamic projections from the visual association cortex to the lateralis posterior complex in the cat

The postnatal development of the corticothalamic projection from the lateral suprasylvian cortex (LS) to the lateral medialis-suprageniculate nucleus (LM-Sg) of the cat thalamus was assessed by means of the anterograde tracer biocytin. In the adult, two types of corticothalamic fibers were found: type I established a network of fine fibers present throughout the LM-Sg, it was characterized by a linear sequence of small (less than 0.5 microm in diameter), single terminal boutons making contact mainly with thin dendrites and/or dendritic spines. Type II, found less frequently, gave off short, side branches near axon terminals and formed clusters of 5-10 large terminal boutons (0.5-1.5 microm in diameter), making contact predominately with medium-sized dendrites and/or vesicle-containing profiles, forming a synaptic glomerulus. At birth (P0), anterogradely-labeled fibers were found in the LM-Sg as in adults. In the early postnatal period (until P6) as well as around the time of eye-opening (P7-P10) to P21, neonatal fibers were largely unbranched many of them having axons tipped with growth cones. Axon terminals containing synaptic vesicles were rarely observed but when present these exhibited considerable variation in their morphological appearance of synapses. Thus, it was not possible to categorize them into the two types of axons which characterize the adult. After P25, terminal swellings bearing a close resemblance to those of type II fibers begin to appear. In this way, the main two corticothalamic fiber types could be identified. These findings demonstrate that significant postnatal changes occur in the synaptology of corticothalamic fibers in the LM-Sg, particularly with the maturation of type II fibers.

Serendipity and the Siamese Cat: The Discovery That Genes for Coat and Eye Pigment Affect the Brain

One day in the late 1960s, Ray Guillery was examining brain sections through the visual thalamus of cats, and he recognized that the arrangement of layers in the lateral geniculate nucleus (LGN) of one cat was strangely abnormal. The cat was identified as a Siamese cat, one of a breed selected for its unusual coat color, with reduced pigment over much of the body and eyes. This chance observation and the recognition of its significance led to a broad-ranging series of investigations. These experiments showed that the lack of normal levels of pigment in the retina in Siamese cats (and other hypopigmented mammals) was the critical factor in the misdirection of many of the projections of the retina to the brain, the nature of the projection error, and the developmental consequences of the relay of the misdirected retinal inputs to visual cortex. As a result, we have a better understanding of how the brain forms proper connections and of the neural basis of visual problems in albino humans.

Thalamocortical cells in the cat pulvinar nucleus transiently express nitric oxide synthase during development

We examined the postnatal expression of the neuronal form of nitric oxide synthase (nNOS) within the pulvinar and lateral posterior (LP) nuclei of the cat thalamus using immunocytochemical techniques. During the first postnatal month, nNOS was expressed in many cells within the pulvinar nucleus and medial subdivision of the LP nucleus; fewer neurons in the lateral LP nucleus were stained by the nNOS antibody. We examined the pulvinar nucleus to determine what cell types express nNOS. A comparison of the soma sizes of nNOS-stained cells to the overall population of Nissl-stained cells and interneurons (stained with an antibody against glutamic acid decarboxylase) suggests that within the pulvinar nucleus, thalamocortical cells express nNOS during development. In addition, the nNOS antibody stained axon bundles that traverse the pulvinar nucleus to enter the optic radiations, suggesting that thalamocortical cell axons also contain nNOS during development. However, this staining pattern was dramatically reduced by postnatal day 42 and later ages; the size of the remaining nNOS-stained cells was closer to that of interneurons, a subset of which contain nNOS in the adult pulvinar nucleus. This contrasts with our previous findings that nNOS is specifically expressed within interneurons in the developing dorsal lateral geniculate nucleus (LGN) and serves as further confirmation that the pulvinar nucleus and LGN represent distinct categories of thalamic nuclei.

Thalamocortical cells in the cat pulvinar nucleus transiently express nitric oxide synthase during development

We examined the postnatal expression of the neuronal form of nitric oxide synthase (nNOS) within the pulvinar and lateral posterior (LP) nuclei of the cat thalamus using immunocytochemical techniques. During the first postnatal month, nNOS was expressed in many cells within the pulvinar nucleus and medial subdivision of the LP nucleus; fewer neurons in the lateral LP nucleus were stained by the nNOS antibody. We examined the pulvinar nucleus to determine what cell types express nNOS. A comparison of the soma sizes of nNOS-stained cells to the overall population of Nissl-stained cells and interneurons (stained with an antibody against glutamic acid decarboxylase) suggests that within the pulvinar nucleus, thalamocortical cells express nNOS during development. In addition, the nNOS antibody stained axon bundles that traverse the pulvinar nucleus to enter the optic radiations, suggesting that thalamocortical cell axons also contain nNOS during development. However, this staining pattern was dramatically reduced by postnatal day 42 and later ages; the size of the remaining nNOS-stained cells was closer to that of interneurons, a subset of which contain nNOS in the adult pulvinar nucleus. This contrasts with our previous findings that nNOS is specifically expressed within interneurons in the developing dorsal lateral geniculate nucleus (LGN) and serves as further confirmation that the pulvinar nucleus and LGN represent distinct categories of thalamic nuclei.

Electrical properties affecting discharge of units of the mid and posterolateral thalamus of conscious cats

Discharge properties in response to intracellularly applied, rectangular currents were measured in units of the mid (lateralis dorsalis and centrolateral nuclei) and posterolateral (lateralis posterior and pulvinar nuclei) thalamus of conscious cats. A separate aim was to determine if neuronal excitability changed in association with changes in stimulus-evoked activity after the animals were trained to discriminate between two acoustic stimuli when performing a conditioned motor response. Low threshold spike (l.t.s.) discharges were observed in three of 272 cells given 1 nA intracellular, hyperpolarizing current pulses of 40 ms duration. This finding supports the view that thalamic neurons of conscious animals operate mainly in the relay as opposed to the oscillatory mode. Application of larger and longer hyperpolarizing currents in the cells produced rebound l.t.s. discharges, supporting the expectation that most thalamic neurons are capable of producing this type of discharge. Decrements of spike afterhyperpolarizations (AHP) and broadening of spike bases upon repeated discharge also were observed in each area of the thalamus studied. After conditioning, changes were found in the posterolateral thalamus (but not in the mid-thalamus) in the proportions of cells with spontaneous, rapid (≥50 Hz), repetitive, discharges (RRD) and rapid, sustained discharges at rates ≥100 Hz during application of depolarizing current (RSD). In the posterolateral thalamus the percentage of units responding to 1 nA depolarization with RSD fell from 71% before conditioning to 45% after conditioning. The percentage of cells with RRD decreased from 69% to 46%. The changes were accompanied by a 3 mV hyperpolarization of the membrane potentials of the cells and a decrease in baseline activity. After conditioning, increases in excitability were found in cells of the mid thalamus that responded selectively to the click conditioned stimulus (CS) that elicited the conditioned response, and decreases in excitability were found in cells of the posterolateral thalamus that responded to the discriminative acoustic stimulus (DS) to which the animals were trained not to respond. An earlier study showed a potentiation of discharge in response to the CS in units of the midthalamus after similar conditioning and a reduction of the proportion of DS responsive units and peak discharge to the DS in units of the posterolateral thalamus. We conclude that the discharge properties of units of the mid and posterolateral thalamus can change to support discrimination between acoustic stimuli of different functional significance after conditioning.

Thalamic terminal morphology and distribution of single corticothalamic axons originating from layers 5 and 6 of the cat motor cortex.

We investigated the axonal morphology of single corticothalamic (CT) neurons of the motor cortex (Mx) in the cat thalamus, using a neuronal tracer, biotinylated dextran amine (BDA). After localized injection of BDA into the Mx, labeled CT axons were found ipsilaterally in the thalamic reticular nucleus (TRN), the ventroanterior-ventrolateral complex (VA-VL), the central lateral nucleus (CL), the central medial nucleus, and the centromedian nucleus, but with the primary focus in the VA-VL. The terminals in the VA-VL formed a large laminar cluster, which extended approximately in parallel with the internal medullary lamina. The laminar organization mirrored morphologic features of single CT axons. We reconstructed the trajectories of 25 single CT axons that arose from layer V (16 axons) or layer VI (9 axons) and terminated in the VA-VL. Terminals of single CT axons that originated from both layer V and layer VI were confined within a laminar structure about 700 microm thick, suggesting the existence of laminar input organization in the VA-VL. Otherwise, the two groups of the CT axons showed contrasting features. All of the CT axons derived from layer VI gave rise to a few short collaterals to the TRN and then formed extensive arborization with numerous small, drumstick-like terminals in the VA-VL. On the other hand, the CT axons arising from layer V gave rise to collaterals whose main axons descended into the cerebral peduncle. Each collateral projected to the VA-VL or CL without projection to the TRN and formed a few small clusters of giant terminals. The two groups of CT neurons in the same cortical column had convergent rather than segregated termination in the VA-VL. However, the terminals of layer VI CT neurons were distributed diffusely and widely in the VA-VL, whereas the terminals of layer V CT neurons were much more focused and surrounded by the terminals of the former group. These contrasting features of the two types of CT projections appear to represent their different functional roles in the generation of motor commands and control of movements in the Mx.

2 視床における咬筋痛覚ニューロンの分布と機能特性とについて(第473回 大阪歯科学会例会)

2 視床における咬筋痛覚ニューロンの分布と機能特性とについて(第473回 大阪歯科学会例会)

Distribution of terminals from pedunculopontine tegmental nucleus and synaptic organization in lateralis medialis-suprageniculate nucleus of cat's thalamus: anterograde tracing, immunohistochemical studies, and quantitative analysis.

The cat's lateralis medialis-suprageniculate nuclear complex (LM-Sg) in the thalamus receives input from various brain regions such as the superior colliculus, brain stem, and spinal cord, as well as from visual association cortex. In a previous study, we demonstrated that LM-Sg receives cholinergic fibers from the pedunculopontine tegmental nucleus (PPT) and that cholinergic terminals make synaptic contacts with the dendrites of glutamatergic projection neurons and of GABAergic interneurons (Hoshino et al., 1997). In this study, we investigate the distribution and the organization of PPT terminals by means of a combined anterograde tracer (biotinylated dextran amine, BDA) and immunohistochemical methods. When stained by acetylcholinesterase (AChE), the LM-Sg is not uniformly immunoreactive, but rather is patchily labeled and shows a streaming type of reactivity. The tissue content appears high in enzyme activity in AChE-positive zones and is much lighter in activity in AChE-negative zones. We compared the synaptic organization between AChE-positive and AChE-negative portions of the LM-Sg in separate groups of electron-microscopic material: four types of vesicle containing profiles (RS, RL, F1, and PSD) as well as synaptic glomeruli were observed in this nucleus. Among these, the PSD profiles were observed more frequently in AChE-positive portions than in AChE-negative zones. Furthermore, the number of glomeruli was significantly higher in AChE-positive than in AChE-negative zones. Following the injection of BDA into PPT, labeled terminals within LM-Sg were rather more concentrated in the AChE-positive portion. Although the majority of PPT terminals made synaptic contacts with dendrites in the neuropil, a few terminals were involved in the synaptic glomeruli. The present results show that the synaptic organization is distinctly different between the AChE-positive and AChE-negative portions of LM-Sg. These results suggest that the AChE-positive portions of LM-Sg are relatively more involved in integrating information arising from a diverse set of inputs and processing that information within glomeruli in a complex manner than occurs in the AChE-negative portion of LM-Sg.