Flexible cue anchoring strategies enable stable head direction coding in both sighted and blind animals

Vision plays a crucial role in instructing the brain's spatial navigation systems. However, little is known about how vision loss affects the neuronal encoding of spatial information. Here, recording from head direction (HD) cells in the anterior dorsal nucleus of the thalamus in mice, we find stable and robust HD tuning in blind animals. In contrast, placing sighted animals in darkness significantly impairs HD cell tuning. We find that blind mice use olfactory cues to maintain stable HD tuning and that prior visual experience leads to refined HD cell tuning in blind adult mice compared to congenitally blind animals. Finally, in the absence of both visual and olfactory cues, the HD attractor network remains intact but the preferred firing direction of HD cells continuously drifts over time. We thus demonstrate remarkable flexibility in how the brain uses diverse sensory information to generate a stable directional representation of space.

An Integrated Perspective of Evolution and Development: From Genes to Function to Ear, Lateral Line and Electroreception

Four sensory systems (vestibular, lateral line, electroreception, auditory) are unique and project exclusively to the brainstem of vertebrates. All sensory neurons depend on a common set of genes (Eya1, Sox2, Neurog1, Neurod1) that project to a dorsal nucleus and an intermediate nucleus, which differentiate into the vestibular ear, lateral line and electroreception in vertebrates. In tetrapods, a loss of two sensory systems (lateral line, electroreception) leads to the development of a unique ear and auditory system in amniotes. Lmx1a/b, Gdf7, Wnt1/3a, BMP4/7 and Atoh1 define the lateral line, electroreception and auditory nuclei. In contrast, vestibular nuclei depend on Neurog1/2, Ascl1, Ptf1a and Olig3, among others, to develop an independent origin of the vestibular nuclei. A common origin of hair cells depends on Eya1, Sox2 and Atoh1, which generate the mechanosensory cells. Several proteins define the polarity of hair cells in the ear and lateral line. A unique connection of stereocilia requires CDH23 and PCDH15 for connections and TMC1/2 proteins to perceive mechanosensory input. Electroreception has no polarity, and a different system is used to drive electroreceptors. All hair cells function by excitation via ribbons to activate neurons that innervate the distinct target areas. An integrated perspective is presented to understand the gain and loss of different sensory systems.

Dopamine in Auditory Nuclei and Lemniscal Projections is Poised to Influence Acoustic Integration in the Inferior Colliculus

Dopamine (DA) modulates the activity of nuclei within the ascending and descending auditory pathway. Previous studies have identified neurons and fibers in the inferior colliculus (IC) which are positively labeled for tyrosine hydroxylase (TH), a key enzyme in the synthesis of dopamine. However, the origins of the tyrosine hydroxylase positive projections to the inferior colliculus have not been fully explored. The lateral lemniscus (LL) provides a robust inhibitory projection to the inferior colliculus and plays a role in the temporal processing of sound. In the present study, immunoreactivity for tyrosine hydroxylase was examined in animals with and without 6-hydroxydopamine (6-OHDA) lesions. Lesioning, with 6-OHDA placed in the inferior colliculus, led to a significant reduction in tyrosine hydroxylase immuno-positive labeling in the lateral lemniscus and inferior colliculus. Immunolabeling for dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT), enzymes responsible for the synthesis of norepinephrine (NE) and epinephrine (E), respectively, were evaluated. Very little immunoreactivity for DBH and no immunoreactivity for PNMT was found within the cell bodies of the dorsal, intermediate, or ventral nucleus of the lateral lemniscus. The results indicate that catecholaminergic neurons of the lateral lemniscus are likely dopaminergic and not noradrenergic or adrenergic. Next, high-pressure liquid chromatography (HPLC) analysis was used to confirm that dopamine is present in the inferior colliculus and nuclei that send projections to the inferior colliculus, including the cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus, and auditory cortex (AC). Finally, fluorogold, a retrograde tracer, was injected into the inferior colliculus of adult rats. Each subdivision of the lateral lemniscus contained fluorogold within the somata, with the dorsal nucleus of the lateral lemniscus showing the most robust projections to the inferior colliculus. Fluorogold-tyrosine hydroxylase colocalization within the lateral lemniscus was assessed. The dorsal and intermediate nuclei neurons exhibiting similar degrees of colocalization, while neurons of the ventral nucleus had significantly fewer colocalized fluorogold-tyrosine hydroxylase labeled neurons. These results suggest that several auditory nuclei that project to the inferior colliculus contain dopamine, dopaminergic neurons in the lateral lemniscus project to the inferior colliculus and that dopaminergic neurotransmission is poised to play a pivotal role in the function of the inferior colliculus.

Neuroarchitectonics of the medulla oblongata of cattle

The article presents data from the study of neuroarchitectonics of the medulla oblongata of cattle. The main attention was paid to the peculiarities of neuronal morphology, determination of their type and prevalence of a certain population of cells in the tissue. The study was performed on 23 brain samples taken from animals aged 2–11 years. To reveal the architectonics of neurons, methods of fabric impregnation with silver were used according to Golgi, Ramon-Kahal and Bolshovsky. The main criteria for determining the type of cells were such features as: cell body size, its shape, number and distribution of processes, their thickness, tortuosity and branching. According to the results, we can identify four main populations of neurons, which are represented by such morphofunctional cell types as: reticular, large polygonal (motor), small round (sensory) and spindle-shaped. The largest population consists of reticular neurons, the second most common are sensory, then motor and the least represented spindle-shaped. It was found that the population of sensory-type neurons includes such structures as the Gracilis and Cutaneus nucleus, the complex of olive inferior nuclei and the nucleus of the solitary tract. Motor are represented respectively in the dorsal, ventral and lateral motor nuclei, the hipoglossy nucleus, the ventral nucleus of the vagus nerve and the ventral subunit of the dorsal nucleus of the vagus nerve. Spindle-shaped neurons are represented only in the dorsal subunit of the dorsal nucleus of the vagus nerve, and reticular form the largest population represented by the reticular formation and the lateral nucleus. A certain pattern of distribution of cell types in the tissue is traced. Thus, the most archaic and architectural – reticular neurons form the center of cell mass, while specialized forms of cells – motor and sensory distributed on the periphery. In a separate type, spindle-shaped neurons of the dorsal nucleus of the vagus nerve are isolated, as cells of the transition link from reticular to motor.

Description of Longidorus barsii Radivojević & De Luca sp. n. (Nematoda: Longidoridae) from Serbia and observations on some taxonomic characters

Summary Longidorus barsii sp. n., from Mt Tara in the Balkan Peninsula, is described and characterised by using a polyphasic approach. The species has numerous males. The female body is 5-7 mm long, rather stout and resembles a large Xiphinema. The lip region is wide, with rounded sides continuous with the neck, frontally flattened and depressed around the oral aperture, amphids are pouch-like and distinctly bi-lobed and the odontostyle is moderately long. The nuclei of the pharyngeal glands are in the normal position, the dorsal nucleus located somewhat posterior to anterior third of bulb. The uteri are long, the distal inner epithelium densely covered with papilla-like outgrowths. The tail is rounded, bluntly conoid and very short. Alpha-numerical identification codes: A4/5, B45, C3, D3, E2, F3, G 1(2), H1, I2, J1, K67. The morphologically most similar species are L. kheirii, L. polyae and L. profundorum. Additional observations are provided on the anterior body region and genital organs in L. barsii sp. n., L. piceicola, L. silvae, and L. uroshis. Selected features are discussed from the taxonomic and functional points of view. The D2-D3 expansion domains of the 28S rRNA gene and the ITS region of L. barsii sp. n. were amplified and sequenced. Phylogenetic analysis using the D2-D3 expansion domains of the 28S rRNA gene revealed close evolutionary relationships with L. polyae, L. athesinus and three unidentified Longidorus spp.

Microstructural integrity of the major nuclei of the thalamus in Parkinson’s disease

BackgroundPrevious research has shown an association between thalamus and cognition in Parkinson’s disease (PD).ObjectivesTo investigate the microstructural integrity of the nuclei of the thalamus and relationship with cognition.MethodsLevel II Movement Disorder Society Task Force Criteria characterised patients with Parkinson’s disease as cognitively normal (PDN, n=51); with mild cognitive impairment (PD-MCI, n=16) or with dementia (PDD, n=15). Twenty-three healthy control subjects were included for comparison. A k-means clustering approach segmented the thalamus into regions representing nine major nuclei. Volume, fractional anisotropy and mean diffusivity of nuclei were compared between cognitive groups and the relationship with cognitive domain z-scores investigated using hierarchical Bayesian regression models.ResultsThere was an overall progressive increase in mean diffusivity as cognition deteriorated (PDN: 1.4 µm2/s (95% uncertainty interval [0.2, 2.7]), PDMCI: 2.4 µm2/s [0.8,4.0], PDD: 4.5 µm2/s [2.8, 6.3]). The largest increase was in the lateral dorsal nucleus (PDN: 0.3 µm2/s [-6.7, 7.2], PDMCI: 5.4 µm2/s [-4.7, 16.1], PDD: 14.8 µm2/s [5.0, 25.0]). Fractional anisotropy showed minimal change between cognitive groups (PDN: 0.001 [-0.005, 0,007], PDMCI: −0.005 [-0.013, 0.003], PDD: −0.005 [-0.014, 0.003]). Increase in mean diffusivity of the thalamus is associated with a global decline in cognition, the magnitude of the effect was greatest in lateral dorsal nucleus. Fractional anisotropy only showed evidence of a relationship with cognitive domain scores in the lateral dorsal nucleus.ConclusionsThe relationship between lateral dorsal nucleus integrity and cognitive changes is likely due to its primary connectivity with frontal and temporal regions.

Ultrasonography of the Vagus Nerve in the Diagnosis of Parkinson’s Disease

Background. It is currently impossible to diagnose Parkinson’s disease (PD) in the premotor phase even though at the time of motor symptom onset the number of already degenerated dopaminergic substantia nigra neurons is considerable. Degeneration of the dorsal nucleus of the vagus nerve (VN) has been reported early in the disease course, and it could lead to impaired function of the VN, resulting in certain nonmotor symptoms of PD. Therefore, we raised a hypothesis that the loss of VN neurons could result in a smaller diameter of the VN among PD patients. Methods. 20 PD patients and 20 age- and gender-matched individuals without any neurodegenerative disease were enrolled in a pilot study. The diameters of the right and left VNs were measured using ultrasonography, their average was calculated, and the narrower VN diameter was noted separately. Results. No difference was found between the PD and control groups neither in the average VN diameter (mean 1.17; 95% confidence interval (CI) 1.10–1.24 vs. 1.13; 1.07–1.18, mm; p=0.353) nor in the narrower VN diameter (mean 1.11; 95% confidence interval (CI) 1.02–1.20 vs. 1.07; 1.02–1.13, mm; p=0.421). The narrower VN diameter and the average VN diameter were not able to distinguish between PD patients and controls (area under curve (AUC) = 0.588, 95% CI = 0.408–0.767, and p=0.344; and AUC = 0.578, 95% CI = 0.396–0.759, and p=0.402). Conclusions. To conclude, no differences were found in VN diameter between the PD and control groups. Therefore, our data do not support the hypothesis that PD could be associated with a smaller diameter of the VN.

Distributed interactive brain circuits for object-in-place memory: A place for time?

Rodents will spontaneously learn the location of an individual object, an ability captured by the object-in-place test. This review considers the network of structures supporting this behavioural test, as well as some potential confounds that may affect interpretation. A hierarchical approach is adopted, as we first consider those brain regions necessary for two simpler, ‘precursor’ tests (object recognition and object location). It is evident that performing the object-in-place test requires an array of areas additional to those required for object recognition or object location. These additional areas include the rodent medial prefrontal cortex and two thalamic nuclei (nucleus reuniens and the medial dorsal nucleus), both densely interconnected with prefrontal areas. Consequently, despite the need for object and location information to be integrated for the object-in-place test, for example, via the hippocampus, other contributions are necessary. These contributions stem from how object-in-place is a test of associative recognition, as none of the individual elements in the test phase are novel. Parallels between the structures required for object-in-place and for recency discriminations, along with a re-examination of the demands of the object-in-place test, signal the integration of temporal information within what is usually regarded as a spatial-object test.