Evaluating old truths: Final adult size in holometabolous insects is set by the end of larval development.

For centuries, it has been understood that the final size of adult holometabolous insects is determined by the end of the larval stage, and that once they transform to adults, holometabolous insects do not grow. Despite this, no previous study has directly tested these "old truths" across holometabolous insects. Here, we demonstrate that final adult size is set at the end of the last larval stage in species representing each of the four orders of holometabolous insects: the fruit fly Drosophila melanogaster (Diptera), the tobacco hornworm Manduca sexta (Lepidoptera), the dung beetle Onthophagus taurus (Coleoptera), and the Florida carpenter ant Camponotus floridanus (Hymenoptera). Furthermore, in both D. melanogaster and C. floridanus, we show that the size of adult individuals fluctuates but does not significantly change. Therefore, our study finally confirms these two basic assumptions in the biology of insects, which have for centuries served as the foundation for studies of insect growth, size, and allometry.

Serotonin is a common thread linking different classes of antidepressants.

Depression pathology remains elusive. The monoamine hypothesis has placed much focus on serotonin, but due to the variable clinical efficacy of monoamine reuptake inhibitors, the community is looking for alternative therapies such as ketamine (neurogenesis theory of antidepressant action). There is evidence that different classes of antidepressants may affect serotonin levels; a notion we test here. We measure hippocampal serotonin in mice with voltammetry and study the effects of acute challenges of escitalopram, fluoxetine, reboxetine, and ketamine. We find that pseudo-equivalent doses of these drugs similarly raise ambient serotonin levels, despite their differing pharmacodynamics because of differences in Uptake 1 and 2, rapid SERT trafficking, and modulation of serotonin by histamine. These antidepressants have different pharmacodynamics but have strikingly similar effects on extracellular serotonin. Our findings suggest that serotonin is a common thread that links clinically effective antidepressants, synergizing different theories of depression (synaptic plasticity, neurogenesis, and the monoamine hypothesis).

Serotonin is a Common Thread Linking Different Classes of Antidepressants.

Depression pathology remains elusive. The monoamine hypothesis has placed much focus on serotonin, but due to the variable clinical efficacy of monoamine reuptake inhibitors, the community is looking for alternative therapies such as ketamine (synaptic plasticity and neurogenesis theory of antidepressant action). There is evidence that different classes of antidepressants may affect serotonin levels; a notion we test here. We measure hippocampal serotonin in mice with voltammetry and study the effects of acute challenges of antidepressants. We find that pseudo-equivalent doses of these drugs similarly raise ambient serotonin levels, despite their differing pharmacodynamics because of differences in Uptake 1 and 2, rapid SERT trafficking and modulation of serotonin by histamine. These antidepressants have different pharmacodynamics but have strikingly similar effects on extracellular serotonin. Our findings suggest that serotonin is a common thread that links clinically effective antidepressants, synergizing different theories of depression (synaptic plasticity, neurogenesis and the monoamine hypothesis).