V e h ic le M T -II

0

2

4

6

8

*

n = 6 n = 6

Enhanced electrical activity of supraoptic neurones

following systemic melanocortin administration

Luis Paiva, Nancy Sabatier, Gareth Leng, Mike Ludwig.

Centre for Integrative Physiology, University of Edinburgh, Edinburgh, UK.

Introduction

Melanocortins stimulate the central oxytocin systems which regulate social behaviours1. Alterations in central oxytocin has been linked to

neuropsychiatric disorders such as autism and anxiety, and melanocortins have been proposed for therapeutic treatment. Naturally occurring

melanocortins including alpha-melanocyte stimulating hormone (α-MSH) potently stimulate oxytocin release from the dendrites of oxytocin cells, but

inhibit their electrical activity2. α-MSH has a poor penetrance through the blood-brain barrier. Here we investigated whether Melanotan-II (MT-II), a

synthetic melanocortin agonist, affects the electrical activity of supraoptic (SON) oxytocin and vasopressin neurons when given intravenously.

Conclusions

Intravenous (i.v.) administration of MT-II induces neural activation in oxytocin and vasopressin cells of the SON. As oxytocin neurons are electrically

inhibited in response to direct application of melanocortin agonists, the actions of intravenous MT-II are likely to be mediated indirectly.

References

1. Modi et al. 2015. Melanocortin receptor agonists facilitate oxytocin-dependent partner preference formation in the prairie vole.

Neuropsychopharmacology 40: 1856-1865.

2. Sabatier et al. 2003. Alpha-melanocyte-stimulating hormone stimulates oxytocin release from the dendrites of hypothalamic

neurons while inhibiting oxytocin release from their terminals in the neurohypophysis. J Neurosci 23:10351-58.

Femoral

cannulation

MT-II

1mg/kg i.v.

Perfusion

120min 90min Processing for Fos and

oxytocin immunostaining

Adult male SD rat

Pentobarbital anaesthesia

6 rats per group

Methods

Fig. 1. The SON and paraventricular nucleus (PVN) are the main sites of synthesis of oxytocin and

vasopressin in the brain. (A) Coronal section showing immunostaining for Fos (black nuclear) and

oxytocin (brown cytoplasm) in the PVN and SON in a control rat. (B) I.v. injections of MT-II increase

Fos expression in the SON. (D) Fos expression in oxytocin cells of the SON increase following MT-II

administration. (C,E) Fos expression in the SON in vehicle (C) and MT-II (E) treated rats (no oxytocin

staining in these sections). Scale bar = 100µm. Means ± S.E.M.; *P<0.05, Mann-Whitney U test.

MT-II induces Fos expression in the SON

Fig. 2. (A) Typical example of the increase in firing rate in an oxytocin neuron in response to i.v.

administration of MT-II. (B) Mean change in firing rate of 8 oxytocin cells after MT-II i.v. in 30-s bins (±

S.E.M.; *P<0.05, Wilcoxon Signed Rank test).

MT-II enhances electrical activity in

oxytocin neurons when given i.v.

Fig. 3 (A) Typical example of the increase in firing rate in a vasopressin neuron in response to i.v.

administration of MT-II. (B) Mean change in 6 vasopressin cells in response to MT-II i.v. in 10-min bins

(± S.E.M; Wilcoxon Signed Rank test).

A

B

A

B

MT-II also enhances electrical activity

in vasopressin neurons

PVN

SON

D

C

A

25

20

15

10

5

0

Fir

ing

rate

(Sp

ikes/s

)

MT-II

min15 30 45 60 75

5 10 15 20 25 30 min

160

120

80

40

0

Fir

ing

rate

(Sp

ikes/3

0s)

MT-II

0

5

1 0

1 5

2 0

*

n = 6 n = 6

B

0 1 0 2 0 3 0 4 0 5 0

-1

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1

2

3

4

Mean

ch

an

ge i

n f

irin

g r

ate

(sp

ikes/s

)

Time since MT-II (min)

-5 0 5 1 0-0 .5

0 .0

0 .5

1 .0

1 .5

M T -II

*

Mean

ch

an

ge i

n f

irin

g r

ate

(sp

ikes/s

)

Time since MT-II (min)

E

Femoral

cannulation and

SON exposure

CCK 20 µg/kg i.v.

pharmacological

identification of either

vasopressin and

oxytocin cells

MT-II

1mg/kg i.v.

Adult male SD rat

Urethane anaesthesia

Data analysis

Immunohistochemistry

Electrophysiology

Supported by

Fo

s p

os

itiv

e c

ells

/1

04

µm

2F

os

po

sit

ive

ce

lls

/1

04

µm

2