Download cannabinoids augment the release of neuropeptide y from the rat

CANNABINOIDS AUGMENT THE RELEASE OF NEUROPEPTIDE Y FROM THE
RAT HYPOTHALAMUS
Kevin M. Gamber, Heather Macarthur, and Thomas C. Westfall
Department of Pharmacological and Physiological Science, Saint Louis University, USA
The orexigenic properties of Neuropeptide Y (NPY) have been well established within
the hypothalamus. This activity is located specifically to pathways emerging from the
arcuate nucleus (ARC) and projecting to the paraventricular nucleus (PVN), lateral
hypothalamus (LH), dorsomedial hypothalamus (DMH), and ventromedial hypothalamus
(VMH). The orexigenic effect of cannabinoids has also been well established. Both
exogenous (as the psychoactive constituents found in marijuana) and endogenous (as the
arachidonic acid derivative anandamide) forms of cannabinoids have been shown to
produce appetite-stimulating effects. Furthermore, cannabinoid CB1 receptors have been
found throughout the hypothalamus, including the ARC, PVN, LH, and VMH.
Cannabinoids have been shown to affect the release of a variety of neurotransmitters via
action at presynaptic receptors, and, depending on the transmitter, may inhibit or augment
release. The regulatory effect of cannabinoids on NPY has been previously unknown.
However, the release of NPY is regulated by a variety of other factors with orexigenic
and anorectic activity. Typically, anorectic factors such as leptin and alpha melanocyte
stimulating hormone (-MSH) inhibit NPY release, whereas orexigenic factors such as
agouti related peptide (AgRP) and orexin stimulate its release. The functional similarities
of cannabinoids and NPY as well as the localization in the same brain structures strongly
suggest the existence of an interaction between them.
Therefore, we have investigated the effect of cannabinoids on the release of NPY within
the hypothalamus of the rat. The hypothalamus of the rat brain was removed and placed
in a wire mesh basket and immersed into a Krebs’-MOPS buffer. The hypothalamic
slices were then incubated for a 30-minute equilibration period followed by a 60-minute
exposure to cannabinoid agonist and/or antagonist, and a final 15-minute exposure to 50
mM KCl. The resulting superfusates were first examined for cAMP content as a positive
control, as cannabinoids are known to modulate adenylate cyclase activity. In addition,
these studies established the necessity of a full 60-minute exposure time. In subsequent
experiments, the superfusates were analyzed by enzyme immunoassay for NPY content.
The cannabinoid CP 55,940 was found to dose-dependently enhance the KCl-induced
release of NPY, with a maximal effect at 100 nM. Furthermore, the cannabinoid
antagonist AM 251 was found to block this effect.
(Supported by USPHS Grant NHLBI-60260 and NIGMS GM08306)