Uptake 2 Transporter Blockade Can Ameliorate Sociability Deficits

Friday, May 15, 2015: 11:30 AM-1:30 PM
Imperial Ballroom (Grand America Hotel)
G. G. Gould1, C. M. Smolik1, W. Koek2, M. A. Javors3 and L. C. Daws1, (1)Physiology, The University of Texas Health Science Center at San Antonio, San Antonio, TX, (2)Psychiatry, The University of Texas Health Science Center at San Antonio, San Antonio, TX, (3)Psychiatry, The University of Texas Health Science Center, San Antonio, TX
Background:  Impaired social behavior is a persistent core symptom of autism that is generally treatment-resistant. Clinical findings and basic studies in rodents demonstrate that serotonin (5-HT) transmission is often disrupted in the socially-impaired brain. While selective 5-HT reuptake inhibitors (SSRIs) such as Prozac (fluoxetine) enhance sociability in limited subpopulations of patients, their efficacy is diminished when 5-HT transporter (SERT) function is compromised.  Aside from SERT, auxilliary transporters of 5-HT in the brain include organic cation transporters (OCTs) and the plasma membrane monoamine transporter (PMAT) among others collectively known as “uptake 2”.  Uptake 2 transporters typically have lower affinity for 5-HT, but remove it from extracellular fluid with greater capacity than SERT. Our hypothesis is that if uptake 2 is blocked, impaired social behavior may improve.

Objectives:  Our goal was to characterize the acute and sub-chronic effects of blocking uptake 2 transporters on the social behavior of two mouse lines with impaired sociability: BTBR T+Itpr3tf/J and SERT -/- mice, in three-chamber sociability tests. Only male mice were examined in these studies, since autism incidence is higher in males than females.

Methods:  We utilized the pseudoisocyanine decynium-22 (D-22) to block uptake 2 transporters, and administered it to mice via acute interperitoneal injection or sub-chronic (2 weeks) delivery of D-22 via surgically-implanted osmotic minipumps.  Subsequently behavioral performance in three chamber sociability tests was assessed.  In vitro uptake of [3H] 5-HT, [3H] citalopram binding and their competition with D-22 was performed in cortical and hippocampal synaptosomes or membranes to compare relative blockade capacity and affinity to the SSRI fluoxetine. Pharmacokinetics of D-22 in serum and brain were assessed by i.p. injection and HPLC.

Results:  Acute injections of D-22 (at 0.1 – 0.01 mg/kg) enhanced social interaction preference in both BTBR and SERT -/- mice, in terms of sniffing behavior and chamber dwelling time.  Inherent social novelty preference was not diminished by D-22 treatment in BTBR mice. Furthermore, sub-chronic administration of D-22 improved social interaction preference in both mouse lines, with no apparent adverse effects. D-22 blocks 5-HT uptake in mouse brain in vitro with Km = 90 ± 10 nM, and has little affinity for SERT (Ki > 3000 nM).  D-22 also appears to cross the blood-brain barrier. 

Conclusions:  Blockade of uptake 2 transporters appears to be an effective short or long-term treatment strategy for impaired social behavior in mice. However, clinical effects of uptake 2 blockade remain to examined, and a search for more selective uptake 2 blockers is warranted.