Elucidation of the neurobiology of depression: insights from a novel genetic animal model

Topiramate is currently used in the treatment of epilepsy, but this anticonvulsant drug has also been reported to exert mood-stabilizing effects and induce weight loss in patients. Neuropeptide Y (NPY) is abundantly and widely distributed in the mammalian central nervous system and centrally administered NPY markedly reduces pharmacologically induced seizures and induces antidepressant-like activity as well as feeding behavior. Two other peptides, galanin and corticotropin-releasing hormone (CRH), have also been proposed to play a modulatory role in mood, appetite, and seizure regulation. Consequently, we investigated the effects of single and repeated topiramate (10 days, once daily: 40 mg/kg i.p.) or vehicle treatment in 'depressed' flinders sensitive line (FSL) and control Flinders resistant line (FRL) rats on brain regional peptide concentrations of NPY, galanin, and CRH. The handling associated with repeated injections reduced hippocampal levels of NPY-and galanin-like immunoreactivities (LI) while NPY-and CRH-LI levels were increased in the hypothalamus, regardless of strain or treatment. In the hippocampus, concentrations of NPY-LI, galanin-LI, and CRH-LI were lower in FSL than FRL animals. Repeated topiramate treatment selectively normalized NPY-LI in this region in the FSL animals. In the hypothalamus, galanin-LI was reduced in FSL compared to FRL animals. Topiramate elevated the hypothalamic concentrations of NPY-LI, CRH-LI, and galanin-LI in both strains. Furthermore, topiramate elevated serum leptin but not corticosterone levels. The present findings show that topiramate has distinct effects on abnormal hippocampal levels of NPY, with possible implications for its anticonvulsant and mood-stabilizing effects. Furthermore, stimulating hypothalamic NPY-LI, CRH-LI and galanin-LI as well as serum leptin levels may be associated with the weight loss-inducing effects of topiramate.

Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 99%

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Topiramate Normalizes Hippocampal NPY-LI in Flinders Sensitive Line ‘Depressed’ Rats and Upregulates NPY, Galanin, and CRH-LI in the Hypothalamus: Implications for Mood-Stabilizing and Weight Loss-Inducing Effects

Husum

Kammen

Termeer

et al. 2003

“…However, there was no evidence for anhedonia or cognitive disturbances (Overstreet et al, 2005) in FSL rats. Furthermore, FSL rats display severe immobility on the forced swim task (Kulkarni and Dhir, 2009;Overstreet et al, 1994) that is reversed with chronic treatment of antidepressants (Yadid et al, 2000). For a complete review of the studies conducted in this rat model, the reader is referred to Overstreet et al, 2005. As alterations in glutamatergic neurotransmission may be an underlying cause in the pathology of depression, we decided to study resting glutamate levels in the FSL rats compared with the control FRL rats.…”

Section: Introductionmentioning

confidence: 99%

Resting Glutamate Levels and Rapid Glutamate Transients in the Prefrontal Cortex of the Flinders Sensitive Line Rat: A Genetic Rodent Model of Depression

Hascup

Stephens

et al. 2011

Despite the numerous drugs targeting biogenic amines for major depressive disorder (depression), the search for novel therapeutics continues because of their poor response rates (B30%) and slow onset of action (2-4 weeks). To better understand role of glutamate in depression, we used an enzyme-based microelectrode array (MEA) that was selective for glutamate measures with fast temporal (2 Hz) and high spatial (15 Â 333 mm) resolution. These MEAs were chronically implanted into the prefrontal cortex of 3-to 6-month-old and 12-to 15-month-old Flinders Sensitive Line (FSL) and control Flinders Resistant Line (FRL) rats, a validated genetic rodent model of depression. Although no changes in glutamate dynamics were observed between 3 and 6 months FRL and FSL rats, a significant increase in resting glutamate levels was observed in the 12-to 15-month-old FSL rats compared with the 3-to 6-month-old FSL and age-matched FRL rats on days 3-5 post-implantation. Our MEA also recorded, for the first time, a unique phenomenon in all the four rat groups of fluctuations in resting glutamate, which we have termed glutamate transients. Although these events lasted only for seconds, they did occur throughout the testing paradigm. The average concentration of these glutamate-burst events was significantly increased in the 12-to 15-month-old FSL rats compared with 3-to 6-month-old FSL and age-matched FRL rats. These studies lay the foundation for future studies of both tonic and phasic glutamate signaling in rat models of depression to better understand the potential role of glutamate signaling in depression.

“…These rats exhibit behavioral features characteristic of depression in association with changes in the mesolimbic dopaminergic and serotonergic systems. Chronic, but not acute, treatment of the FSL rats with various antidepressants abrogates their behavioral manifestations of depression (for review, see (Overstreet et al, 2005;Yadid et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

DHEA Lessens Depressive-Like Behavior via GABA-ergic Modulation of the Mesolimbic System

Genud

Merenlender

Gispan-Herman

et al. 2008

Self Cite

Alterations in the levels of dehydroepiandrosterone (DHEA) in the brain can allosterically modulate g-aminobutyric-acid-type-A (GABA A R), N-methyl-D-aspartate (NMDAR), and Sigma-1 (s1R) receptors. In humans, DHEA has antidepressive effects; however, the mechanism is unknown. We examined whether alterations in DHEA also occur in an animal model of depression, the Flinders-sensitiveline (FSL) rats, with the intention of determining the brain site of DHEA action and its antidepressant mechanism. We discovered that DHEA levels were lower in some brain regions involved with depression of FSL rats compared to Sprague-Dawley (SD) controls. Moreover, DHEA (1 mg/kg IP for 14 days)-treated FSL rats were more mobile in the forced swim test than FSL controls. In the NAc and VTA, significant changes were observed in the levels of the d-subunit of GABA A , but not of s1R mRNA, in FSL rats compared to SD rats. The d-subunit controls the sensitivity of the GABA A R to the neurosteroid. Indeed, treatment (14 days) of FSL rats with the GABA A agonist muscimol (0.5 mg/kg), together with DHEA (a negative modulator of GABA A ), reversed the effect of DHEA on immobility in the swim test. Perfusion of DHEA sulfate (DHEAS) (3 nM and 30 nM for 14 days) into the VTA and NAc of FSL rats improved their performance in the swim test for at least 3 weeks post-treatment. Our results imply that alterations in DHEA are involved in the pathophysiology of depression and that the antidepressant action of DHEA is mediated via GABA A Rs in the NAc and VTA.