Somatostatin-expressing neurons in the Bed Nucleus of the Stria Terminalis

Research output: ThesisMaster's thesisTheses

Abstract

The bed nucleus of the stria terminalis (BNST) is currently widely studied due to its impact in the anxiety-, stress-, and fearrelated
behaviours, as well as in addiction. The BNST is highly heterogeneous brain area constituting of set of subnuclei and a
variety of neuron populations, properties of which have only partially been revealed by the earlier research. One of the neuron
populations, on which only a very little research has been conducted, is the somatostatin (Sst) expressing neurons, highly abundant
in the anterodorsal part of the BNST (adBNST), especially in oval and juxtacapsular nuclei of the BNST. This work aims to
elucidate the connectivity of this Sst-neuron population, and their role in the behaviours related to BNST activation, particularly
the anxiety-, reward-, and drug withdrawal-related behaviours.
To specifically study the somatostatin neuron population in the adBNST, I targeted the neurons using stereotaxic delivery of
AAV-vectors encoding a myristylated green fluorescent protein (GFP) for neuronal tracing to Sst-Cre-tdTomato reporter line
mice (n=2), and Cre-inducible hM3Dq-DREADDs to Sst-IRES-Cre mice (n=21), with Cre-inducible mCherry fluorescent protein
as a control (n=20). The mice were treated with activation-inducing 1.0 mg/kg i.p. clozapine-N-oxide (CNO) 30 min prior to the
behavioural tests. To assess acute anxiety-like behaviour, I used the elevated-plus maze paradigm and a modified open field test,
in which a novel object is introduced to the arena in the middle of the trial. To study the potential effect on reward-associated
behaviours, I used the biased conditioned place preference (CPP) test, and for the withdrawal-linked behaviours, we used a method
to precipitate the withdrawal symptoms with naltrexone in subchronically morphine-treated mice (n=9 hM3Dq, n=8 control).
The neuronal tracing revealed that the adBNST Sst-neurons project to areas known to partake in stress and fear reactions as well
as in autonomic and homeostatic control. Namely, projections were seen in medial and central amygdaloidal nuclei, lateral
hypothalamus, periaqueductal grey, ventral pallidum, and parabrachial nucleus. In the elevated-plus maze, the CNO-induced
activation of the Sst-neurons did not have any effect on the locomotor activity of the mice between the groups. At the same time,
Sst activation did not seem to have any significant effect on the time the mice spent in the open arms, nor in the exploratory
activities, like the frequency of the head dips or the stretch-attend postures. In line with these results, no effect on the movement
between the groups was observed in the open field test. Similarly, no differences in anxiety-related behaviours, like in the time
spent in the centre of the arena or in the number of contacts with the novel object during the last phase of the test, were observed.
The CPP test failed to show any meaningful rewarding or aversive properties of CNO-induced activation of the Sst-neurons, while
the movement rates of the groups during the conditioning trials were not different in statistically significant way. As for the
withdrawal symptoms, all the mice showed the predetermined symptoms, but the test failed to show any differences between the
study groups.
The neuronal tracing revealed connectivity for the adBNST Sst-neurons with brain regions involved in fear- and anxiety
behaviour, social encounters, and autonomic control. In spite of this, the CNO-induced chemogenetic activation of the adBNST
Sst-neurons failed to show any significant behavioural effects in the chosen paradigms for anxiety-, and reward-related behaviours,
and for withdrawal symptoms. Further research is needed to dissect the Sst-subcircuitry of adBNST, both in order to verify the
observed output regions, and to elucidate the role these neurons play in modification of behavioural phenotypes.
Original languageEnglish
Awarding Institution
  • Faculty of Pharmacy
Supervisors/Advisors
  • Korpi, Esa, Supervisor
  • de Miguel, Elena, Supervisor
Award date23 Jan 2018
Place of PublicationHelsinki
Publication statusPublished - 23 Jan 2018
MoE publication typeG2 Master's thesis, polytechnic Master's thesis

Fields of Science

  • 317 Pharmacy
  • somatostatin
  • BNST
  • anxiety
  • addiction
  • DREADD

Cite this