Anterior insula is more vulnerable than posterior insula to TDP-43 pathology in common dementias and ALS

Based on the anatomic proximity, connectivity, and functional similarities between the anterior insula and amygdala, we tested the hypothesis that the anterior insula is an important focus in the progression of TDP-43 pathology in LATE-NC. Blinded to clinical and neuropathologic data, phospho-TDP (pTDP) inclusion pathology was assessed in paired anterior and posterior insula samples in 105 autopsied patients with Alzheimer disease, Lewy body disease, LATE-NC and hippocampal sclerosis (HS), amyotrophic lateral sclerosis (ALS), and other conditions. Insular pTDP pathology was present in 34.3% of the study cohort, most commonly as neuronal inclusions and/or short neurites in lamina II, and less commonly as subpial processes resembling those described in the amygdala region. Among positive samples, pTDP pathology was limited to the anterior insula (41.7%), or occurred in both anterior and posterior insula (58.3%); inclusion density was greater in anterior insula across all diseases (p < .001). pTDP pathology occurred in 46.7% of ALS samples, typically without a widespread TDP-43 proteinopathy. In LATE-NC, it was seen in 30.4% of samples (mostly LATE-NC stages 2 and 3), often co-occurring with basal forebrain pathology and comorbid HS, suggesting this is an important step in the evolution of this pathology beyond the medial temporal lobe.

Disruption of orbitofrontal-hypothalamic projections in a murine ALS model and in human patients

Background

Increased catabolism has recently been recognized as a clinical manifestation of amyotrophic lateral sclerosis (ALS). The hypothalamic systems have been shown to be involved in the metabolic dysfunction in ALS, but the exact extent of hypothalamic circuit alterations in ALS is yet to be determined. Here we explored the integrity of large-scale cortico-hypothalamic circuits involved in energy homeostasis in murine models and in ALS patients.

Methods

The rAAV2-based large-scale projection mapping and image analysis pipeline based on Wholebrain and Ilastik software suites were used to identify and quantify projections from the forebrain to the lateral hypothalamus in the SOD1(G93A) ALS mouse model (hypermetabolic) and the Fus^ΔNLS ALS mouse model (normo-metabolic). 3 T diffusion tensor imaging (DTI)-magnetic resonance imaging (MRI) was performed on 83 ALS and 65 control cases to investigate cortical projections to the lateral hypothalamus (LHA) in ALS.

Results

Symptomatic SOD1(G93A) mice displayed an expansion of projections from agranular insula, ventrolateral orbitofrontal and secondary motor cortex to the LHA. These findings were reproduced in an independent cohort by using a different analytic approach. In contrast, in the Fus^ΔNLS ALS mouse model hypothalamic inputs from insula and orbitofrontal cortex were maintained while the projections from motor cortex were lost. The DTI-MRI data confirmed the disruption of the orbitofrontal-hypothalamic tract in ALS patients.

Conclusion

This study provides converging murine and human data demonstrating the selective structural disruption of hypothalamic inputs in ALS as a promising factor contributing to the origin of the hypermetabolic phenotype.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00241-6.

BNST-insula structural connectivity in humans

The bed nucleus of the stria terminalis (BNST) is emerging as a critical region in multiple psychiatric disorders including anxiety, PTSD, and alcohol and substance use disorders. In conjunction with growing knowledge of the BNST, an increasing number of studies examine connections of the BNST and how those connections impact BNST function. The importance of this BNST network is highlighted by rodent studies demonstrating that projections from other brain regions regulate BNST activity and influence BNST-related behavior. While many animal and human studies replicate the components of the BNST network, to date, structural connections between the BNST and insula have only been described in rodents and have yet to be shown in humans. In this study, we used probabilistic tractography to examine BNST-insula structural connectivity in humans. We used two methods of dividing the insula: 1) anterior and posterior insula, to be consistent with much of the existing insula literature; and 2) eight subregions that represent informative cytoarchitectural divisions. We found evidence of a BNST-insula structural connection in humans, with the strongest BNST connectivity localized to the anteroventral insula, a region of agranular cortex. BNST-insula connectivity differed by hemisphere and was moderated by sex. These results translate rodent findings to humans and lay an important foundation for future studies examining the role of BNST-insula pathways in psychiatric disorders.

The agranular and granular insula differentially contribute to gambling-like behavior on a rat slot machine task: effects of inactivation and local infusion of a dopamine D4 agonist on reward expectancy

RATIONALE

Rats, like humans, are susceptible to the reinforcing effects of reward-related stimuli presented within a compound stimulus array, putatively analogous to the so-called near-miss effect. We have previously demonstrated using a rodent slot machine task (rSMT) that the reward expectancy these stimuli elicit is critically mediated by the dopamine D4 receptor. D4 receptors are principally located in prefrontal regions activated during slot machine play in humans, such as the insular cortex. The insula has recently attracted considerable interest as it appears to play a crucial role in substance and behavioral addictions. However, the insula is a heterogeneous area, and the relative contributions of subregions to addictive behaviors are unclear.

METHODS

Male Long Evans rats were trained to perform the rSMT, and then bilateral cannula targeting either the granular or agranular insula were implanted. The effects of inactivation and local administration of a D4 agonist were investigated.

RESULTS

Temporary inactivation of the agranular, but not the granular insula impaired performance on the rSMT. In contrast, local infusion of the D4 agonist PD168077 into the agranular insula had no effect on task performance, but when administered into the granular insula, it improved animals' ability to differentiate winning from non-winning trials. The agranular insula may therefore modulate decision making when conflicting stimuli are present, potentially due to its role in generating a cohesive emotional percept based on both externally and internally generated signals, whereas the granular insular is not critical for this process. Nevertheless, D4 receptors within the granular insula may amplify the incentive salience of aversive environmental stimuli.

DISCUSSION

These data provide insight into the neurobiological mechanism underpinning maladaptive reward expectancy during gambling and provide further evidence that D4 receptors represent a potential target for developing pharmacotherapies for problem gambling.