The developing prefrontal cortex receives a dense serotonergic innervation, yet little is known about the actions of serotonin

Classic hallucinogens such as lysergic acid diethylamide are thought to elicit their psychotropic actions via serotonin receptors of the 5-hydroxytryptamine 2A subtype (5-HT 2AR). One likely site for these effects is the prefrontal cortex (PFC). Previous studies have shown that activation of 5-HT2ARs in this region results in a robust increase in spontaneous glutamatergic synaptic activity, and these results have led to the widely held idea that hallucinogens elicit their effect by modulating synaptic transmission within the PFC. Here, we combine cellular and molecular biological approaches, including single-cell 5-HT 2ARs inactivation and 5-HT2AR rescue over a 5-HT 2AR knockout genetic background, to distinguish between competing hypotheses accounting for these effects. The results from these experiments do not support the idea that 5-HT 2ARs elicit the release of an excitatory retrograde messenger nor that they activate thalamocortical afferents, the two dominant hypotheses. Rather, they suggest that 5-HT 2ARs facilitate intrinsic networks within the PFC. Consistent with this idea, we locate a discrete subpopulation of pyramidal cells that is strongly excited by 5-HT 2AR activation.gene gun ͉ in vitro electrophysiology ͉ organotypic slices ͉ serotonin ͉ hallucinogen T he idea that classic hallucinogens such as lysergic acid diethylamide and psylocibin act by interfering with serotonergic neurotransmission can be traced to the middle of the 20th century (1). It was, however, not until the 1980s that serotonin receptors of the 5-hydroxytryptamine 2A subtype (5-HT 2A R) were identified as the molecular target for these agents (refs. 2, 3; reviewed in refs. 4, 5). Subsequent brain imaging studies in human subjects have extended these findings to identify the prefrontal cortex (PFC), which is highly enriched in these receptors, as a key brain region in mediating the effects of hallucinogens (6, 7). These findings have led to the now widely accepted view that activation of 5-HT 2A R in the prefrontal is a key biological step leading to the psychological effects of hallucinogens (5, 8).Our understanding of the mechanisms by which 5-HT 2A R activation elicits the sensory and behavioral manifestation of hallucinogens would be enriched by a precise understanding of how these receptors modulate cellular and network excitability in the PFC. To that effect, a number of studies have addressed the electrophysiological effects signaled by 5-HT 2A Rs in this region. There is general concordance that the most robust cellular effect observed in pyramidal cell of the PFC on stimulation of 5-HT 2A Rs involves an increase in both the frequency and amplitude of glutamatergic spontaneous excitatory postsynaptic potentials/spontaneous excitatory postsynaptic currents (sEPSCs) (9)(10)(11)(12)(13)(14). This observation thus points to 5-HT 2A Rs as powerful modulators of the excitability of PFC networks and reconciles evidence implicating both glutamatergic and serotonergic systems in the actions of hallucinogens (15).Although multiple ...

Summary Fat and muscle lipolysis involves functional interactions of adipose triglyceride lipase (ATGL), α-β hydrolase domain-containing protein 5 (ABHD5), and tissue-specific perilipins 1 and 5 (PLIN1 and PLIN5). ABHD5 potently activates ATGL, but this lipase-promoting activity is suppressed when ABHD5 is bound to PLIN proteins on lipid droplets. In adipocytes, protein kinase A (PKA) phosphorylation of PLIN1 rapidly releases ABHD5 to activate ATGL, but mechanisms for rapid regulation of PLIN5-ABHD5 interaction in muscle are unknown. Here we identify synthetic ligands that release ABHD5 from PLIN1 or PLIN5 absent PKA activation and rapidly activate adipocyte and muscle lipolysis. Molecular imaging and affinity probe labeling demonstrated ABHD5 is directly targeted by these synthetic ligands and additionally revealed that ABHD5-PLIN interactions are regulated by endogenous ligands including long-chain acyl-CoA. Our results reveal a new locus of lipolysis control and suggest ABHD5 ligands might be developed into novel therapeutics that directly promote fat catabolism.

Alpha-beta hydrolase domain-containing 5 (ABHD5), the defective gene in human Chanarin-Dorfman syndrome, is a highly conserved regulator of adipose triglyceride lipase (ATGL)-mediated lipolysis that plays important roles in metabolism, tumor progression, viral replication, and skin barrier formation. The structural determinants of ABHD5 lipolysis activation, however, are unknown. We performed comparative evolutionary analysis and structural modeling of ABHD5 and ABHD4, a functionally distinct paralog that diverged from ABHD5 ~500 million years ago, to identify determinants of ABHD5 lipolysis activation. Two highly conserved ABHD5 amino acids (R299 and G328) enabled ABHD4 (ABHD4 N303R/S332G) to activate ATGL in Cos7 cells, brown adipocytes, and artificial lipid droplets. The corresponding ABHD5 mutations (ABHD5 R299N and ABHD5 G328S) selectively disrupted lipolysis without affecting ATGL lipid droplet translocation or ABHD5 interactions with perilipin proteins and ABHD5 ligands, demonstrating that ABHD5 lipase activation could be dissociated from its other functions. Structural modeling placed ABHD5 R299/G328 and R303/G332 from gain-of-function ABHD4 in close proximity on the ABHD protein surface, indicating they form part of a novel functional surface required for lipase activation. These data demonstrate distinct ABHD5 functional properties and provide new insights into the functional evolution of ABHD family members and the structural basis of lipase regulation.

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