Soma Area Research Articles

Morphological and distributional properties of SMI-32 immunoreactive ganglion cells in the rat retina.

SMI‐32 is widely used to identify entire populations of alpha retinal ganglion cells (RGCs), and several SMI‐32+ RGC subsets have been studied thoroughly in rodents. However, due to the thick cover of SMI‐32+ neurofilaments, the morphology of SMI‐32+ RGCs in the central retinal region is obscured and rarely described. Moreover, SMI‐32 labels more than one morphological RGC type and the full morphological characteristics and distribution of SMI‐32+ RGCs have yet to be discovered. Here, using intracellular neurobiotin injections combined with SMI‐32 antibody staining, we investigated morphological and distributional properties of the entire SMI‐32+ RGCs population in the rat retina. We found that SMI‐32+ RGCs were evenly distributed throughout the rat retina. We compared the morphological features of SMI‐32+ ON and OFF cells in the central, middle, and peripheral retinal regions. We found that SMI‐32+ RGCs in different regions have distinct characteristics, such as the soma area and the dendritic field area, and Sholl analysis of ON cells and OFF cells revealed significant differences between each region. We classified SMI‐32+ RGCs into five clusters based on morphological features and found that a majority of SMI‐32+ RGCs belong to alpha‐like cells; however, a small proportion of SMI‐32+ RGCs had small soma and small dendritic fields. Together, we present a full description of the morphology and distribution of SMI‐32 immunoreactive RGCs in the rat retina.

Proteomic Biomarker Analysis of Serum from Japanese Field Mice (Apodemus Speciosus) Collected within the Fukushima Difficult-to-return Zone.

The environmental impact of the Fukushima Daiichi nuclear power plant accident is a source of ongoing concern as there is uncertainty regarding the effects of chronic radiation exposure on local plant and animal life from Fukushima-derived radionuclides. In the current study, changes in proteomic biomarker expression due to chronic environmentally-derived radiation exposures was examined in wild field mice. Serum from 10 wild field mice (Apodemus speciosus) native to the Fukushima difficult-to-return zone and from eight wild field mice native to the Soma area (control) were collected. External dose estimations were completed using measurements of ambient radiation levels and calculating 137Cs concentrations in soil. Internal dose was estimated by counting whole mice using an HPGe detector. Age of the mice was estimated using molar wear. Serum was screened using the aptamer-based SOMAscan proteomic assay technology for changes in expression of 1,310 protein analytes. A subset panel of protein biomarkers that demonstrated significant changes in expression between control and exposed mice was determined and analyzed using Ingenuity Pathway Analysis (IPA). Control animals had a calculated lifetime dose range from 0.001 to 0.007 Gy, and exposed animals had a calculated lifetime dose range from 0.01 to 0.64 Gy. No discernable effect of dose rate was seen as relative dose rate correlated with dose for all samples. Detectable values were obtained for all 1,310 proteins included in the SOMAscan assay. Subset panels of proteins demonstrating significant (p < 0.05) changes in expression with either an upregulated or downregulated 1.5-fold change over control were identified for both the sample cohort inclusive of all exposed samples and the sample cohort restricted to samples from animals receiving "low" dose exposures. These panels of proteins from exposed animals were analyzed using IPA, which highlighted changes in key biological pathways related to injury, respiratory, renal, urological, and gastrointestinal disease, and cancer. Significant changes in expression of proteomic biomarkers were seen in the serum of wild field mice that received environmental exposure to Fukushima-derived radionuclides. Our findings demonstrate novel biomarkers of radiation exposure in wildlife within the Fukushima difficult-to-return zone.

Induced pluripotent stem cells for defining Parkinsonian patient subtypes: a further step toward precision medicine.

Induced pluripotent stem cells for defining Parkinsonian patient subtypes: a further step toward precision medicine.

Intrinsic Morphologic and Physiologic Development of Human Derived Retinal Ganglion Cells In Vitro.

PurposeHuman retinal ganglion cells (hRGC) derived from human pluripotent stem cells are promising candidates to model, protect, and replace degenerating RGCs. Here, we examined intrinsic morphologic and physiologic development of hRGCs.MethodsWe used CRISPR-Cas9 to selectively express tdTomato under the RGC-specific promoter, BRN3B. Human pluripotent stem cells were chemically differentiated into hRGCs and cultured up to 7 weeks. We measured soma area, neurite complexity, synaptic protein, axon-related messenger RNA and protein, and voltage-dependent responses.ResultsSoma area, neurite complexity, and postsynaptic density protein 95 increased over time. Soma area and neurite complexity increased proportionally week to week, and this relationship was dynamic, strengthening between 2 and 3 weeks and diminishing by 4 weeks. Postsynaptic density 95 localization was dependent on culture duration. After 1 to 2 weeks, postsynaptic density 95 localized within somas but redistributed along neurites after 3 to 4 weeks. Axon initial segment scaffolding protein, Ankyrin G, expression also increased over time, and by 7 weeks, Ankyrin G often localized within putative axons. Voltage-gated inward currents progressively developed, but outward currents matured by 4 weeks. Current-induced spike generation increased over time but limited by depolarization block.ConclusionsHuman RGCs develop up to 7 weeks after culture. Thus, the state of hRGC maturation should be accounted for in designing models and treatments for optic neuropathies.Translational RelevanceWe characterized hRGC morphologic and physiologic development towards identifying key time points when hRGCs express mechanisms that may be harnessed to enhance the efficacy of neuroprotective and cell replacement therapies.

The Neuroprotective Effect of Carvedilol on Diabetic Neuropathy: An In Vitro Study.

Diabetic neuropathy serves as a major complication for diabetic patients across the world. The use of effective treatment is integral for reducing the health complications for diabetic patients. This study has evaluated the carvedilol potential neuroprotective effect on diabetic neuropathy. An in vitro model of diabetic neuropathy was used, including dorsal root ganglia (DRG) that were cultured from male adult mice C57BL. These were incubated for about twenty-four hours in high glucose (HG) media (45 mM). Some cells were incubated with carvedilol (10 μM). Neuronal viability, neuronal morphology, and activating transcription factor 3 (AFT3) were measured. The cell viability was decreased, along with neuronal length, soma area, and soma perimeter with HG media. Also, there was an overexpression of ATF3, which is a neuronal stress response marker. The pretreatment with carvedilol increased the viability of DRG as compared to HG-treated cells. Also, it significantly protected the DRG from HG-induced morphology changes. Though it shows a decrease in AFT3 expression, the statistical results were insignificant. The current study demonstrates the neuroprotective effect of carvedilol against HG-induced DN using an in vitro model. This could be through carvedilol antioxidant effects.

ОСОБЕННОСТИ ВОЗРАСТНОЙ ДИНАМИКИ НЕЙРОНОВ НАРУЖНОГО КОЛЕНЧАТОГО ТЕЛА КОШКИ ПРИ ИСПОЛЬЗОВАНИИ ФРОНТАЛЬНЫХ И САГИТТАЛЬНЫХ СРЕЗОВ

We carried out a comparative morphometric analysis of neurons in the cat dorsal lateral geniculate nucleus (dLGN) in frontal vs. sagittal slices. Using the SMI-32 antibody to non-phosphorylated domains of heavy-chain neurofilaments, the postnatal dynamic of soma parameters (area, roundness, orientation) of dLGN neurons was studied. Measurements were performed in kittens aged 0, 4, 10, 14, 21, 28, 34, 62, 123 days, and in adult cats. A comparison of data obtained in frontal vs. sagittal slices revealed the following significant differences: 1) the soma area of the immunopositive neurons was smaller in frontal vs. sagittal slices in all age groups, and this difference increased with age; 2) the soma orientation was also different in two cutting planes, and a significant age-related change in the soma orientation occurred only in the sagittal, but not frontal, plane. We assume that the difference in the soma area is due to the spatial arrangement of SMI-32-immunopositive neurons in the dLGN, because of which, in the sagittal plane, in contrast to the frontal, neuronal somas were cut parallel to their long axis. In turn, age-related changes in the soma orientation may reflect an internal rearrangement of the dLGN retinotopic organization with age.

Neural Stimulation In Vitro and In Vivo by Photoacoustic Nanotransducers

Summary Neuromodulation is an invaluable approach for the study of neural circuits and clinical treatment of neurological diseases. Here, we report semiconducting polymer nanoparticles based photoacoustic nanotransducers (PANs) for neural stimulation in vitro and in vivo. Our PANs strongly absorb the nanosecond pulsed laser in the near-infrared second window (NIR-II) and generate localized acoustic waves. PANs are shown to be surface modified and selectively bind onto neurons. PAN-mediated activation of primary neurons in vitro is achieved with ten 3-ns laser pulses at 1,030 nm over a 3-ms duration. In vivo neural modulation of mouse brain activities and motor activities is demonstrated by PANs directly injected into brain cortex. With submillimeter spatial resolution and negligible heat deposition, PAN stimulation is a new non-genetic method for precise control of neuronal activities, opening up potentials in non-invasive brain modulation.

ALS-CSF-induced structural changes in spinal motor neurons of rat pups cause deficits in motor behaviour.

Amyotrophic lateral sclerosis (ALS) is a late-onset, neurodegenerative disease associated with the loss of motor neurons in the spinal cord, brain stem and primary motor cortex. Deficit in the motor function is one of the clinical features of this disease. However, the association between adverse morphological alterations in the spinal motor neurons and motor deficit in sporadic ALS (SALS) is still debated. The present study has sought to investigate the effects of serial intrathecal injections of ALS-CSF into rat pups, at post-natal (P) days 3, 9 and 14, on the motor neuronal (MN) morphology at the cervical and lumbar levels of the spinal cord at P16 and P22. The present study used Cresyl violet and Golgi-Cox staining methods to determine the progressive changes in the morphology of spinal MNs in both cervical and lumbar extensions. The study found a loss of motor neurons in the spinal cord (36% for P16 in cervical and 41.7% in P16 lumbar and 49.57% for P22 cervical and 44.63% for P22 lumbar) and reduced choline acetyl transferase (ChAT) expression after repeated infusion of ALS-CSF. Significant increase in the soma area was also found in ALS-CSF rats (around 21% in P22 cervical and 26.4% in P22 lumbar). Soma hypertrophy was associated with increased dendritic arborization of MNs at both cervical and lumbar levels of the spinal cord. The data also showed a direct correlation between ALS-CSF induced changes in the MN number in the spinal cord and motor behavioral deficits. The loss of MNs, reduced ChAT, changes in soma and dendritic morphology with declined rotarod performance, thus, confirming the pathological phenotypes as seen in ALS patients.

Astrocyte remodeling in the beneficial effects of long-term voluntary exercise in Alzheimer\u2019s disease

BackgroundIncreased physical exercise improves cognitive function and reduces pathology associated with Alzheimer’s disease (AD). However, the mechanisms underlying the beneficial effects of exercise in AD on the level of specific brain cell types remain poorly investigated. The involvement of astrocytes in AD pathology is widely described, but their exact role in exercise-mediated neuroprotection warrant further investigation. Here, we investigated the effect of long-term voluntary physical exercise on the modulation of the astrocyte state.MethodsMale 5xFAD mice and their wild-type littermates had free access to a running wheel from 1.5 to 7 months of age. A battery of behavioral tests was used to assess the effects of voluntary exercise on cognition and learning. Neuronal loss, impairment in neurogenesis, beta-amyloid (Aβ) deposition, and inflammation were evaluated using a variety of histological and biochemical measurements. Sophisticated morphological analyses were performed to delineate the specific involvement of astrocytes in exercise-induced neuroprotection in the 5xFAD mice.ResultsLong-term voluntary physical exercise reversed cognitive impairment in 7-month-old 5xFAD mice without affecting neurogenesis, neuronal loss, Aβ plaque deposition, or microglia activation. Exercise increased glial fibrillary acid protein (GFAP) immunoreactivity and the number of GFAP-positive astrocytes in 5xFAD hippocampi. GFAP-positive astrocytes in hippocampi of the exercised 5xFAD mice displayed increases in the numbers of primary branches and in the soma area. In general, astrocytes distant from Aβ plaques were smaller in size and possessed simplified processes in comparison to plaque-associated GFAP-positive astrocytes. Morphological alterations of GFAP-positive astrocytes occurred concomitantly with increased astrocytic brain-derived neurotrophic factor (BDNF) and restoration of postsynaptic protein PSD-95.ConclusionsVoluntary physical exercise modulates the reactive astrocyte state, which could be linked via astrocytic BDNF and PSD-95 to improved cognition in 5xFAD hippocampi. The molecular pathways involved in this modulation could potentially be targeted for benefit against AD.

Inherent resilience, major marine environmental change and revitalisation of coastal communities in Soma, Fukushima Prefecture, Japan

The Fukushima Dai'ichi nuclear accident presents challenging circumstances for disaster recovery in coastal communities, as ongoing uncertainties around the nuclear plant's decommissioning may create new risks in the future. Within disaster risk studies, inherent resilience – informal practices of resilience sustained through social memory and everyday actions – is seen as important for longer-term recovery. Yet whilst inherent resilience has been studied for acute disasters like earthquakes and hurricanes, less is known about inherent resilience under major and long-term environmental change of the kind seen in Fukushima. Through interview-based research in the Soma area of Fukushima Prefecture, Japan, this paper thus evaluates the potential for inherent resilience practices to support recovery when communities may have to respond multiple times as new setbacks emerge. We show that despite the challenging situation in Soma, inherent resilience practices have helped recovery on the coast by re-establishing a sense of identity and purpose for fishing communities in particular. Equally, however, we also find that ongoing uncertainty about the nuclear plant and emerging pressures linked to climate change make the full re-establishment of some cultural practices associated with inherent resilience difficult. Our findings contribute to existing research by showing that although inherent resilience may well help communities maintain core functions in a way formal institutional support cannot, changes to the physical environment of the kind seen in Fukushima may affect daily living and social relations to the extent it becomes difficult to undertake practices necessary to sustain social memory and community relations.

Neuromorphometric changes associated with photostimulated migratory phenotype in the Palaearctic-Indian male redheaded bunting.

Neural substrates, including brain areas, differential gene expression and neuroendocrine basis, of migration are known. However, very little is known about structural changes in the brain that underlie the development and cessation of migration in long-distance avian migrants. Towards this, we investigated neuromorphological changes in the higher-order associative areas in male redheaded bunting (Emberiza bruniceps), which is a Palaearctic-Indian night migrant with wintering grounds in India. Photosensitive birds (8L:16D; SD) were exposed to stimulatory long days (16L:8D; LD), with controls retained on non-stimulatory short days. LD birds depicted shifts to, and sustained night-time activity as recorded by actograms. LD birds demonstrated increased body mass, fat deposition and testicular volume in keeping with the migratory phenotype. When LD birds had exhibited 10.0 ± 2.4 cycles of Zugunruhe (intense nighttime activity in captives, akin to night migratory flight in the wild), bird brains were fixed by transcardial perfusion, and changes in the neuronal morphometry of pallial, sub-pallial and hypothalamic brain regions studied using rapid Golgi technique with modifications, as used and validated in our laboratory. There were significant differences in both area and perimeter of soma in the visual hyperpallium apicale implicated in migratory orientation and the neuroendocrine control region for timing of migration, the mediobasal hypothalamus. We attribute these neuromorphometric changes in the soma area and perimeter to the photostimulated changes associated with the development of migration and reproductive phenotypes in redheaded buntings. It is suggested that changes in the neuronal plasticity in brain control regions parallel photoperiod-induced physiological responses.

Hydrogen Sulfide Reverses LPS-Induced Behavioral Deficits by Suppressing Microglial Activation and Promoting M2 Polarization.

Activation of microglia is ahallmark ofneuroinflammationand has been implicated in thedevelopment of manypsychiatric disorders. Hydrogen sulfide (H2S); a gasotransmitter has recently emerged as a potent antioxidant and anti-inflammatory molecule. However, the protective potential of H2Sandits underpin molecularmechanisms in neuroinflammation associated behavioral deficits arestill unknown. The present study has been designed to investigate the effect of sodium hydrogen sulfide (NaHS; a source of H2S) on microglial activation and associated behavior phenotype in response to lipopolysaccharide (LPS)-induced neuroinflammation. LPS treatment decreased H2S levels with a concomitant increase in reactive oxygen species (ROS) in the cortex and hippocampus. However, NaHS administration restored the endogenous H2S levels to thenormal and decreased ROS levels. NaHS supplementation reduced the number of active microglia in the cortex and hippocampus of LPS treated animals. Morphological analysis of microglia showed significant increase in microglial density, span ratio and soma area in the cortex and hippocampus of LPS treated animals which was decreased byNaHS supplementation. Moreover, NaHS administration reduced the expression of microglialM1 phenotype markers (IL-1β, TNF-α and nitrite) and concomitantlyincreased the expression of M2 phenotype markers (IL-4 and TGF-β) in the brain regions of LPS treated animals. Furthermore, LPS-induced anxiety-like behavior assessed by open fieldtest and elevated plus maze was reversed by NaHS supplementation. Taken together, these findings suggest that H2S supplementation ameliorates LPS-induced behavioral deficits by suppressing pro-inflammatory and promoting anti-inflammatory microglial response. Therefore, H2S releasing drugs may be potential therapeutics to treat neuroinflammation associated psychiatric disorders. Graphical abstract.

Plasticity of thoracic interneurones rostral to a lateral spinal cord lesion

The morphology and projections of ventral horn interneurones in the segment above an ipsilateral thoracic lateral spinal cord lesion were studied in the cat by intracellular injections of Neurobiotin at 6 to 18 weeks post-lesion and compared with previously published control data from uninjured spinal cords. The cell axons ascended, descended or both, mostly contralaterally and mostly spared by the lesion. Unusual morphological dendritic features were seen in the lesion group, mostly growth-related, including complex dendritic appendages, twisted or multiple-branched terminal dendrites, commissural dendrites, apparently swollen proximal dendrites and rostrocaudal asymmetries. Significant quantitative differences included more dendritic spines in the lesion group (3.4×) and smaller soma areas in the lesion group (with similar numbers of primary dendrites and rostrocaudal dendritic spans). Immunoreactivity to microtubule associated protein 2a/b was detected in the proximal, but not distal, dendrites of cells in the lesion group, corresponding to an overall decrease in immunoreactivity in the ventral horns on the lesion side compared to the other. For axon collaterals, significant increases for the lesion group were seen in the number of collaterals in the first 4 mm of axon and in the area of ventral/intermediate horn occupied by terminals, including increased innervation of some regions, among which were the intermediolateral columns. This dendritic and axonal plasticity makes the interneuones candidates for a role in detour circuits but also for a maladaptive role in autonomic hyperreflexia.

Specialist counselling in the social work with a person and a family after a traumatic experience

Times we live in make us question what is going to happen with the world after the pandemic. The struggle against COVID-19 and changes produced will have impact on the mind of many people. Some lose their relatives, who they cannot bury. Others live in a constant state of fear about their health and future living. The world will never be the same. People will never be as they were before this traumatic event. The invisible enemy – coronavirus – will leave a lasting mark on their memory. Many will need support which can be provided by specialist counselling. Many will struggle with a trauma, which will make the return to “normality” impossible for a long time. A traumatic experience is a psychological trauma suffered by a person and caused by a strong, sudden stimulus. This stimulus is intensive enough to cause changes in the areas of soma, psyche and polis, and it also directly threatens health or life of a person. People after a traumatic experience require a complex assistance to return to their normal functioning. Currently, this stimulus is a deadly virus. The article presents the role of the specialist counselling in the area of social work with a person and their family after a traumatic experience.

MiR-29a Promotes the Neurite Outgrowth of Rat Neural Stem Cells by Targeting Extracellular Matrix to Repair Brain Injury.

Neural stem cells (NSCs) can generate new neurons to repair brain injury and central nervous system disease by promoting neural regeneration. MicroRNAs (miRNAs) involve in neural development, brain damage, and neurological diseases repair. Recent reports show that several miRNAs express in NSCs and are important to neurogenesis. Neurites play a key role in NSC-related neurogenesis. However, the mechanism of NSC neurite generation is rarely studied. We surprisingly noticed that the neurites increased after bone morphogenetic protein (BMP) treatment in rat NSCs. This process was accompanied by the dynamic change of miRNA-29. Then we discovered that miR-29a regulated neural neurites in rat hippocampus NSCs. Overexpression of miR-29a reduced the cell soma area and promoted the neurite outgrowth of NSCs. Cell soma area became small, whereas the number of neurite increased. Moreover, neurite complexity increased dramatically, with more primary and secondary branches after miR-29a overexpression. In addition, miR-29a overexpression still maintained the stemness of NSCs. Besides, we identified that miR-29a can promote the neurite outgrowth by targeting extracellular matrix-related genes like Fibrillin 1 (Fbn1), Follistatin-like 1 (Fstl1), and laminin subunit gamma 2 (Lamc2). These findings may provide a novel role of miR-29a to regulate neurite outgrowth and development of NSCs. We also offered a possible theoretical basis to the migration mechanism of NSCs in brain development and damage repair.

Effects of a solid lipid curcumin particle formulation on chronic activation of microglia and astroglia in the GFAP-IL6 mouse model

Chronic glial activation is characterized by increased numbers of activated glial cells, secreting free radicals and cytotoxic cytokines, subsequently causing neuronal damage. In order to investigate the anti-inflammatory activity of Longvida® Optimised Curcumin (LC), we fed 500 ppm of LC to 2-month-old wild type and GFAP-IL6 mice for 6 months. LC feeding led to a significant reduction in the number of Iba-1+ microglia by 26% in the hippocampus and by 48% in the cerebellum, GFAP+ astrocytes by 30%, and TSPO+ cells by 24% in the hippocampus and by 31% in the cerebellum of the GFAP-IL6 mice. The morphology of the cells was assessed and LC significantly decreased the dendritic length of microglia and the convex area, convex perimeter, dendritic length, nodes and number of processes of astrocytes in the hippocampus while decreasing the soma area and perimeter in the cerebellum, in LC-fed GFAP-IL6 mice. In addition, LC feeding increased pre- and postsynaptic protein levels and improved balance measured by Rotarod. Together, these data suggest that LC is able to attenuate the inflammatory pathology and ameliorate neurodegeneration and motor deficits in GFAP-IL6 mice. For patients with neuro-inflammatory disorders, LC might potentially reverse the detrimental effects of chronic glial activation.

Rapamycin blocks the neuroprotective effects of sex steroids in the adult birdsong system

In adult songbirds, the telencephalic song nucleus HVC and its efferent target RA undergo pronounced seasonal changes in morphology. In breeding birds, there are increases in HVC volume and total neuron number, and RA neuronal soma area compared to nonbreeding birds. At the end of breeding, HVC neurons die through caspase-dependent apoptosis and thus, RA neuron size decreases. Changes in HVC and RA are driven by seasonal changes in circulating testosterone (T) levels. Infusing T, or its metabolites 5α-dihydrotestosterone (DHT) and 17 β-estradiol (E2), intracerebrally into HVC (but not RA) protects HVC neurons from death, and RA neuron size, in nonbreeding birds. The phosphoinositide 3-kinase (PI3K)-Akt (a serine/threonine kinase)-mechanistic target of rapamycin (mTOR) signaling pathway is a point of convergence for neuroprotective effects of sex steroids and other trophic factors. We asked if mTOR activation is necessary for the protective effect of hormones in HVC and RA of adult male Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii). We transferred sparrows from breeding to nonbreeding hormonal and photoperiod conditions to induce regression of HVC neurons by cell death and decrease of RA neuron size. We infused either DHT+E2, DHT+E2 plus the mTOR inhibitor rapamycin, or vehicle alone in HVC. Infusion of DHT+E2 protected both HVC and RA neurons. Coinfusion of rapamycin with DHT+E2, however, blocked the protective effect of hormones on HVC volume and neuron number, and RA neuron size. These results suggest that activation of mTOR is an essential downstream step in the neuroprotective cascade initiated by sex steroid hormones in the forebrain.

Rapid testosterone-induced growth of the medial preoptic nucleus in male canaries

Testosterone activates singing within days in castrated male songbirds but full song quality only develops after a few weeks. Lesions of the medial preoptic nucleus (POM) inhibit while stereotaxic testosterone implants into this nucleus increase singing rate suggesting that this site plays a key role in the regulation of singing motivation. Testosterone action in the song control system works in parallel to control song quality. Accordingly, systemic testosterone increases POM volume within 1–2 days in female canaries, while the increase in volume of song control nuclei takes at least 2 weeks. The current study tested whether testosterone action is associated with similar differences in latencies in males. Photosensitive castrated male canaries were implanted with testosterone-filled Silastic™ implants and control castrates received empty implants, while simultaneously the photoperiod was switched from short- to long-days. Brains were collected from all subjects two days later. Plasma testosterone was elevated in testosterone-treated but not in controls. HVC volumes were not affected, but testosterone significantly increased the POM volume as identified by the dense group of aromatase-immunoreactive neurons, the number and somal area of these neurons and the fractional area they cover in POM. Testosterone-treated females from a previous experiment had a smaller POM volume in similar conditions suggesting the existence of a stable sex difference potentially affecting singing behavior. Thus testosterone induces male POM growth and aromatase expression in this nucleus within two days without affecting HVC size, further supporting the notion that testosterone increases singing motivation via its action in POM.

Retinal Topography in Two Species of Baleen Whale (Cetacea: Mysticeti)

Little is known about the visual systems of large baleen whales (Mysticeti: Cetacea). In this study, we investigate eye morphology and the topographic distribution of retinal ganglion cells (RGCs) in two species of mysticete, Bryde’s whale (Balaenoptera edeni) and the humpback whale (Megaptera novaeanglia). Both species have large eyes characterised by a thickened cornea, a heavily thickened sclera, a highly vascularised fibro-adipose bundle surrounding the optic nerve at the back of the eye, and a reflective blue-green tapetum fibrosum. Using stereology and retinal whole mounts, we estimate a total of 274,268 and 161,371 RGCs in the Bryde’s whale and humpback whale retinas, respectively. Both species have a similar retinal topography, consisting of nasal and temporal areas of high RGC density, suggesting that having higher visual acuity in the anterior and latero-caudal visual fields is particularly important in these animals. The temporal area is larger in both species and contains the peak RGC densities (160 cells mm^–2 in the humpback whale and 200 cells mm^–2 in Bryde’s whale). In the Bryde’s whale retina, the two high-density areas are connected by a weak centro-ventral visual streak, but such a specialisation is not evident in the humpback whale. Measurements of RGC soma area reveal that although the RGCs in both species vary substantially in size, RGC soma area is inversely proportional to RGC density, with cells in the nasal and temporal high-density areas being relatively more homogeneous in size compared to the RGCs in the central retina and the dorsal and ventral retinal periphery. Some of the RGCs were very large, with soma areas of over 2,000 µm². Using peak RGC density and eye axial diameter (Bryde’s whale: 63.5 mm; humpback whale: 48.5 mm), we estimated the peak anatomical spatial resolving power in water to be 4.8 cycles/degree and 3.3 cycles/degree in the Bryde’s whale and the humpback whale, respectively. Overall, our findings for these two species are very similar to those reported for other species of cetaceans. This indicates that, irrespective of the significant differences in body size and shape, behavioural ecology and feeding strategy between mysticetes and odontocetes (toothed whales), cetacean eyes are adapted to vision in dim light and adhere to a common “bauplan” that evolved prior to the divergence of the two cetacean parvorders (Odontoceti and Mysticeti) over 30 million years ago.

Respiratory motoneuron properties during the transition from gill to lung breathing in the American bullfrog.

Amphibian respiratory development involves a dramatic metamorphic transition from gill to lung breathing and coordination of distinct motor outputs. To determine whether the emergence of adult respiratory motor patterns was associated with similarly dramatic changes in motoneuron (MN) properties, we characterized the intrinsic electrical properties of American bullfrog trigeminal MNs innervating respiratory muscles comprising the buccal pump. In premetamorphic tadpoles (TK stages IX-XVIII) and adult frogs, morphometric analyses and whole cell recordings were performed in trigeminal MNs identified by fluorescent retrograde labeling. Based on the amplitude of the depolarizing sag induced by hyperpolarizing voltage steps, two MN subtypes (I and II) were identified in tadpoles and adults. Compared with type II MNs, type I MNs had larger sag amplitudes (suggesting a larger hyperpolarization-activated inward current), greater input resistance, lower rheobase, hyperpolarized action potential threshold, steeper frequency-current relationships, and fast firing rates and received fewer excitatory postsynaptic currents. Postmetamorphosis, type I MNs exhibited similar sag, enhanced postinhibitory rebound, and increased action potential amplitude with a smaller-magnitude fast afterhyperpolarization. Compared with tadpoles, type II MNs from frogs received higher-frequency, larger-amplitude excitatory postsynaptic currents. Input resistance decreased and rheobase increased postmetamorphosis in all MNs, concurrent with increased soma area and hyperpolarized action potential threshold. We suggest that type I MNs are likely recruited in response to smaller, buccal-related synaptic inputs as well as larger lung-related inputs, whereas type II MNs are likely recruited in response to stronger synaptic inputs associated with larger buccal breaths, lung breaths, or nonrespiratory behaviors involving powerful muscle contractions.