Cocaine potentiates excitatory drive in the perifornical/lateral hypothalamus
The Journal of Physiology, 2012•Wiley Online Library
Key points• Drugs of addiction are well‐established in their capacity to alter brain reward
pathways.• The perifornical/lateral hypothalamus has previously been shown to be drug
responsive, participate in relapse to drug taking, and project to key reward pathway
structures.• This study demonstrates that cocaine enhances excitatory drive to
perifornical/lateral hypothalamic neurones, and these changes involve altered presynaptic
function. Orexin‐positive neurones were among the populations that underwent these …
pathways.• The perifornical/lateral hypothalamus has previously been shown to be drug
responsive, participate in relapse to drug taking, and project to key reward pathway
structures.• This study demonstrates that cocaine enhances excitatory drive to
perifornical/lateral hypothalamic neurones, and these changes involve altered presynaptic
function. Orexin‐positive neurones were among the populations that underwent these …
Key points
- • Drugs of addiction are well‐established in their capacity to alter brain reward pathways.
- • The perifornical/lateral hypothalamus has previously been shown to be drug responsive, participate in relapse to drug taking, and project to key reward pathway structures.
- • This study demonstrates that cocaine enhances excitatory drive to perifornical/lateral hypothalamic neurones, and these changes involve altered presynaptic function. Orexin‐positive neurones were among the populations that underwent these presynaptic changes.
- • The results indicate that a greater understanding of the drug‐induced synaptic changes in perifornical/lateral hypothalamus may instruct future pharmacotherapies aimed at preventing drug relapse.
Abstract The hypothalamus is a critical controller of homeostatic responses and plays a fundamental role in reward‐seeking behaviour. Recently, hypothalamic neurones in the perifornical/lateral hypothalamic area (PF/LHA) have also been implicated in drug‐seeking behaviour through projections to extra‐hypothalamic sites such as the ventral tegmental area. For example, a population of neurones that expresses the peptide orexin has been strongly implicated in addiction‐relevant behaviours. To date, the effect of addictive drugs on synaptic properties in the hypothalamus remains largely unexplored. Previous studies focusing on the PF/LHA neurones, however, have shown that the orexin system exhibits significant plasticity in response to food or sleep restriction. This neuroadaptive ability suggests that PF/LHA neurones could be highly susceptible to modifications by drug exposure. Here, we sought to determine whether cocaine produces synaptic plasticity in PF/LHA neurones. Whole‐cell patch‐clamp techniques were used to examine the effects of experimenter‐administered (passive) or self‐administered (SA) cocaine on glutamatergic synaptic transmission in PF/LHA neurones. These experiments demonstrate that both passive and SA cocaine exposure increases miniature excitatory postsynaptic current (mEPSC) frequency in PF/LHA neurones. In addition, SA cocaine reduced the paired‐pulse ratio but the AMPA/NMDA ratio of evoked excitatory inputs was unchanged, indicative of a presynaptic locus for synaptic plasticity. Dual‐labelling for orexin and excitatory inputs using the vesicular glutamate transporter (VGLUT2), showed that passive cocaine exposure increased VGLUT2‐positive appositions onto orexin neurones. Further, a population of recorded neurones that were filled with neurobiotin and immunolabelled for orexin confirmed that increased excitatory drive occurs in this PF/LHA population. Given the importance of the PF/LHA and the orexin system in modulating drug addiction, we suggest that these cocaine‐induced excitatory synapse‐remodelling events within the hypothalamus may contribute to persistence in drug‐seeking behaviour and relapse.
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