Designing a norepinephrine optical tracer for imaging individual noradrenergic synapses and their activity in vivo

Norepinephrine is a monoamine neurotransmitter with a wide repertoire of physiological roles in the peripheral and central nervous systems. There are, however, no experimental means to study functional properties of individual noradrenergic synapses in the brain. Development of new approaches for imaging synaptic neurotransmission is of fundamental importance to study specific synaptic changes that occur during learning, behavior, and pathological processes. Here, we introduce fluorescent false neurotransmitter 270 (FFN270), a fluorescent tracer of norepinephrine. As a fluorescent substrate of the norepinephrine and vesicular monoamine transporters, FFN270 labels noradrenergic neurons and their synaptic vesicles, and enables imaging synaptic vesicle content release from specific axonal sites in living rodents. Combining FFN270 imaging and optogenetic stimulation, we find heterogeneous release properties of noradrenergic synapses in the somatosensory cortex, including low and high releasing populations. Through systemic amphetamine administration, we observe rapid release of cortical noradrenergic vesicular content, providing insight into the drug’s effect

Prior alcohol use enhances vulnerability to compulsive cocaine self-administration by promoting degradation of HDAC4 and HDAC5

Addiction to cocaine is commonly preceded by experiences with legal or decriminalized drugs, such as alcohol, nicotine, and marijuana. The biological mechanisms by which these gateway drugs contribute to cocaine addiction are only beginning to be understood. We report that in the rat, prior alcohol consumption results in enhanced addiction-like behavior to cocaine, including continued cocaine use despite aversive consequences. Conversely, prior cocaine use has no effect on alcohol preference. Long-term, but not short-term, alcohol consumption promotes proteasome-mediated degradation of the nuclear histone deacetylases HDAC4 and HDAC5 in the nucleus accumbens, a brain region critical for reward-based memory. Decreased nuclear HDAC activity results in global H3 acetylation, creating a permissive environment for cocaine-induced gene expression. We also find that selective degradation of HDAC4 and HDAC5, facilitated by the class II–specific HDAC inhibitor MC1568, enhances compulsive cocaine self-administration. These results parallel our previously reported findings that the gateway drug nicotine enhances the behavioral effects of cocaine via HDAC inhibition. Together, our findings suggest a shared mechanism of action for the gateway drugs alcohol and nicotine, and reveal a novel mechanism by which environmental factors may alter the epigenetic landscape of the reward system to increase vulnerability to cocaine addiction

Excitatory transmission from the amygdala to nucleus accumbens facilitates reward seeking

Interactions between the basolateral amygdala (BLA) and nucleus accumbens (NAc) are involved in a number of reward-processing and addictive behaviours, but our understanding of the precise role of each of these brain areas has been limited by the inability to manipulate pathways selectively during behaviour. Stuber et al. use optogenetic technologies, in which light selectively activates or inhibits genetically-defined neuronal subpopulations, to reveal an unexpected role for the BLA a brain region usually associated with aversive behaviours. The BLA is shown to be important for processing both positive and negative effects, but glutamatergic pathways between the BLA and NAc are specifically associated with reward-seeking behaviours

Hypothalamic neurotensinergic projections promote reward by enhancing glutamate transmission in midbrain

The lateral hypothalamus (LH) is a brain region that provides one of the largest sources of glutamatergic and peptidergic input to the ventral tegmental area (VTA). Electrical stimulation in this area produces reward, however, the medial forebrain bundle courses through the LH. Therefore, understanding the role of the LH to VTA projection in mediating reward-related behavior and pathological states of reward-seeking such as drug abuse can be informed by separating the role of LH neurons from other descending forebrain inputs to the VTA. In the present study, we focus on the action of neurotensin (NT), one of the most abundant peptides in the LH to VTA projection, on excitatory synaptic transmission in the VTA and its relevance in goal-directed behavior. Whole-cell patch clamp techniques in midbrain slices of C57Bl/6 mice were used to demonstrate that NT potentiates NMDA-mediated excitatory postsynaptic currents (EPSCs) via the NT 1 receptor (Nts1). NT release at optogenetically-isolated LH-VTA terminals indicates synapse-specific effects ex vivo. Using in vivo optogenetic techniques, we demonstrate that animals display robust intracranial self-stimulation of lateral hypothalamic terminals in the VTA. This behavior is significantly attenuated by blockade of either Nts1 or NDMA receptors in the VTA. The striking behavioral and electrophysiological effects of lateral hypothalamic NT in the VTA highlight this pathway as an important component in mediating reward-related behavior