Banting memorial lecture 2013. A life in balance: wandering the pathways of control

The historical progression of positron emission tomography research in neuroendocrinology

The rapid and continual development of a number of radiopharmaceuticals targeting different receptor, enzyme and small molecule systems has fostered Positron Emission Tomography (PET) imaging of endocrine system actions in vivo in the human brain for several decades. PET radioligands have been developed to measure changes that are regulated by hormone action (e.g., glucose metabolism, cerebral blood flow, dopamine receptors) and actions within endocrine organs or glands such as steroids (e.g., glucocorticoids receptors), hormones (e.g., estrogen, insulin), and enzymes (e.g., aromatase). This systematic review is targeted to the neuroendocrinology community that may be interested in learning about positron emission tomography (PET) imaging for use in their research. Covering neuroendocrine PET research over the past half century, researchers and clinicians will be able to answer the question of where future research may benefit from the strengths of PET imaging.

Restoration of Hypoglycemia Awareness Alters Brain Activity in Type 1 Diabetes

OBJECTIVE

Impaired awareness of hypoglycemia (IAH) in type 1 diabetes (T1D) is a major risk factor for severe hypoglycemia (SH) and is associated with atypical responses to hypoglycemia in brain regions involved in arousal, decision making, and memory. Whether restoration of hypoglycemia awareness alters these responses is unknown. We sought to investigate the impact of awareness restoration on brain responses to hypoglycemia.

RESEARCH DESIGN AND METHODS

Twelve adults with T1D and IAH underwent pseudocontinuous arterial spin labeling functional MRI during a hypoglycemic clamp (5-2.6 mmol/L) before and after a hypoglycemia avoidance program of structured education (Dose Adjustment for Normal Eating), specialist support, and sensor-augmented pump therapy (Medtronic MiniMed 640G). Hypoglycemic cerebral blood flow (CBF) responses were compared pre- and postintervention using predefined region-of-interest analysis of the thalamus, anterior cingulate cortex (ACC), orbitofrontal cortex (OFC), and hippocampus.

RESULTS

Postintervention, Gold and Clarke scores fell (6.0 ± 1.0 to 4.0 ± 1.6, P = 0.0002, and 5.7 ± 1.7 to 3.4 ± 1.8, P = 0.0008, respectively), SH rates reduced (1.5 ± 2 to 0.3 ± 0.5 episodes per year, P = 0.03), hypoglycemic symptom scores increased (18.8 ± 6.3 to 27.3 ± 12.7, P = 0.02), and epinephrine responses did not change (P = 0.2). Postintervention, hypoglycemia induced greater increases in ACC CBF (P = 0.01, peak voxel coordinates [6, 40, -2]), while thalamic and OFC activity did not change.

CONCLUSIONS

Increased blood flow is seen within brain pathways involved in internal self-awareness and decision making (ACC) after restoration of hypoglycemia awareness, suggesting partial recovery of brain responses lost in IAH. Resistance of frontothalamic networks, involved in arousal and emotion processing, may explain why not all individuals with IAH achieve awareness restoration with education and technology alone.