No abstract

Altered motivated behaviour is a cardinal feature of several neuropsychiatric conditions including mood disorders. One well-characterized antecedent to the development of mood disorders is exposure to early life stress (ELS). A key brain substrate controlling motivated behaviour is the lateral hypothalamus (LH). Here, we examined the effect of ELS on LH activation and the motivation to self-administer sucrose. We tested whether chemogenetic activation of LH circuits could modify sucrose responding in ELS rats and examined the impact on LH cell populations. Male rat pups were maternally separated for 0 or 3 h on postnatal days 2-14. During adolescence, rats received bilateral injections of hM3D(Gq), the excitatory designer receptor exclusively activated by designer drugs, into LH. In adulthood, rats were trained to self-administer sucrose and tested under a progressive ratio schedule to determine their motivation for reward following injection with either vehicle or 5 mg/kg clozapine-N-oxide. Brains were processed for Fos-protein immunohistochemistry. ELS significantly suppressed lever responding for sucrose, indicating a long-lasting impact of ELS on motivation circuits. hM3D(Gq) activation of LH increased responding, normalizing deficits in ELS rats, and increased Fos-positive orexin and MCH cell numbers within LH. Our findings indicate that despite being susceptible to environmental stressors, LH circuits retain the capacity to overcome ELS-induced deficits in motivated behaviour.

No abstract

Hirschsprung disease occurs when children are born with no intrinsic nerve cells in varying lengths of the large intestine. In the most severe cases, neurons are also missing from the distal part of the small intestine. Nerve-mediated relaxation of the aganglionic bowel fails and fecal matter accumulates in the more proximal regions of the intestine. This is life threatening. Perforation of the bowel can ensue, causing sepsis and in some cases, death of the infant. Repopulation of the colon with neural stem cells is a potential therapy, but for this to be successful the patient or experimental animal needs to survive long enough for neural precursors to differentiate and make appropriate connections. We have developed a surgical procedure that can be applied to rats with Hirschsprung disease. A stoma was created to allow the normal bowel to empty and a second stoma leading to the aganglionic bowel was also created. This allowed homozygous mutants that would usually die at less than 3 weeks of age to survive into adulthood. During this time, the rats also required post-operative care of their stomas. The interventions we describe provide an animal model of Hirschsprung disease that is suited to assess the effectiveness of cell therapies in the treatment of this condition.

No abstract

Patients with Hirschsprung Disease lack enteric ganglia in the distal colon and propulsion of colorectal content is substantially impaired. Proposed stem cell therapies to replace neurons require surgical bypass of the aganglionic bowel during re-colonisation, but there is inadequate knowledge of the consequences of bypass. We performed bypass surgery in Ednrb-/- Hirschsprung rat pups. Surgically rescued rats failed to thrive, an outcome reversed by supplying electrolyte and glucose enriched drinking water. Histologically, the bypassed colon had normal structure, but grew substantially less in diameter than the functional region proximal to the bypass. Extrinsic sympathetic and spinal afferent neurons projected to their normal targets, including arteries and the circular muscle, in aganglionic regions. However, although axons of intrinsic excitatory and inhibitory neurons grew into the aganglionic region, their normally dense innervation of circular muscle was not restored. Large nerve trunks that contained TH, CGRP, nNOS, VIP and tachykinin immunoreactive axons occurred in the distal aganglionic region. We conclude that the rescued Ednrb-/- rat provides a good model for the development of cell therapies for the treatment of Hirschsprung disease.

Abbreviations: DMH: dorsomedial hypothalamus. PF: Perifornical hypothalamus. LHA; lateral hypothalamic/perifornical area. L-AP4; L-(+)-2-Amino-4-phosphonobutyric acid.mGluR; metabotropic glutamate receptor. AbstractThe perifornical/lateral hypothalamic area (LHA) orexin (hypocretin) system is involved in drug-seeking behavior elicited by drug-associated stimuli. Cocaine exposure is associated with presynaptic plasticity at LHA orexin cells such that excitatory input to orexin cells is enhanced, both acutely and into withdrawal. These changes may augment orexin cell reactivity to drug-related cues during abstinence and contribute to relapse-like behavior.Studies in hypothalamic slices from drug-naïve animals indicate that agonism of group III metabotropic glutamate receptors (mGluRs) reduces presynaptic glutamate release onto orexin cells. Therefore, we examined the group III mGluR system as a potential target to reduce orexin cell excitability in-vivo, and tested whether activating these receptors could normalize orexin cell activity following cocaine and reduce cocaine-seeking elicited by drugassociated stimuli during abstinence. First, we verified that group III mGluRs regulate orexin cell activity in vivo by showing that intra-LHA infusions of the selective agonist L-(+)-2-Amino-4-phosphonobutyric acid (L-AP4) reduces Fos expression in orexin cells following 24h food deprivation. Next, we extended these findings to show that intra-LHA L-AP4 infusions reduced discriminative stimulus-driven cocaine-seeking following withdrawal. L-AP4 had no effect on general motor activity of sucrose self-administration. Finally, using whole-cell patch clamp recordings from identified orexin cells in orexin-GFP transgenic mice, we show that enhanced presynaptic drive to orexin cells persists for up to 14d into withdrawal and that this plasticity is normalized by L-AP4. L-AP4 had no effect on measures of postsynaptic plasticity in cocaine-exposed animals. Together, these data indicate that agonism of LHA group III mGluRs reduces orexin cell activity in-vivo and is an effective strategy to suppress cocaine-seeking behavior following withdrawal. These effects are likely mediated, at least in part, by normalization of presynaptic plasticity at orexin cells that occurs as a result of cocaine exposure.