Genetic deletion or pharmacological blockade of nociceptin/orphanin FQ receptors in the ventral tegmental area attenuates nicotine-motivated behaviour

Endogenous opiates and behavior: 2022

This paper is the forty-fifth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2022 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Abstinence-Induced Nicotine Seeking Relays on a Persistent Hypoglutamatergic State within the Amygdalo-Striatal Neurocircuitry

Nicotine robustly sustains smoking behavior by acting as a primary reinforcer and by enhancing the incentive salience of the nicotine-associated stimuli. The motivational effects produced by environmental cues associated with nicotine delivery can progressively manifest during abstinence resulting in reinstatement of nicotine seeking. However, how the activity in reward neuronal circuits is transformed during abstinence-induced nicotine seeking is not yet fully understood. In here we used a contingent nicotine and saline control self-administration model to disentangle the contribution of cue-elicited seeking responding for nicotine after drug abstinence in male Wistar rats. Using ex vivo electrophysiological recordings and a network analysis approach, we defined temporal and brain-region specific amygdalo-striatal glutamatergic alterations that occur during nicotine abstinence. The results from this study provide critical evidence indicating a persistent hypoglutamatergic state within the amygdalo-striatal neurocircuitry over protracted nicotine abstinence. During abstinence-induced nicotine seeking, electrophysiological recordings showed progressive neuroadaptations in dorsal and ventral striatum already at 14-d abstinence while neuroadaptations in subregions of the amygdala emerged only after 28-d abstinence. The observed neuroadaptations pointed to a brain network involving the amygdala and the dorsolateral striatum (DLS) to be implied in cue-induced reinstatement of nicotine seeking. Together these data suggest long-lasting neuroadaptations that might reflect neuroplastic changes responsible to abstinence-induced nicotine craving. Neurophysiological transformations were detected within a time window that allows therapeutic intervention advancing clinical development of preventive strategies in nicotine addiction.

Nicotine but not saline self-administering or yoked control conditions produces sustained neuroadaptations in the accumbens shell

Introduction

Using yoked animals as the control when monitoring operant drug-self-administration is considered the golden standard. However, instrumental learning per se recruits several neurocircuits that may produce distinct or overlapping neuroadaptations with drugs of abuse. The aim of this project was to assess if contingent responding for nicotine or saline in the presence of a light stimulus as a conditioned reinforcer is associated with sustained neurophysiological adaptations in the nucleus accumbens shell (nAcS), a brain region repeatedly associated with reward related behaviors.

Methods

To this end, nicotine-or saline-administrating rats and yoked-saline stimulus-unpaired training conditions were assessed in operant boxes over four consecutive weeks. After four additional weeks of home cage forced abstinence and subsequent cue reinforced responding under extinction conditions, ex vivo electrophysiology was performed in the nAcS medium spiny neurons (MSNs).

Results

Whole cell recordings conducted in voltage and current-clamp mode showed that excitatory synapses in the nAcS were altered after prolonged forced abstinence from nicotine self-administration. We observed an increase in sEPSC amplitude in animals with a history of contingent nicotine SA potentially indicating higher excitability of accumbal MSNs, which was further supported by current clamp recordings. Interestingly no sustained neuroadaptations were elicited in saline exposed rats from nicotine associated visual cues compared to the yoked controls.

Conclusion

The data presented here indicate that nicotine self-administration produces sustained neuroadaptations in the nAcS while operant responding driven by nicotine visual stimuli has no long-term effects on MSNs in nAcS.

Regulation of N-type calcium channels by nociceptin receptors and its possible role in neurological disorders

Activation of nociceptin opioid peptide receptors (NOP, a.k.a. opioid-like receptor-1, ORL-1) by the ligand nociceptin/orphanin FQ, leads to G protein-dependent regulation of Cav2.2 (N-type) voltage-gated calcium channels (VGCCs). This typically causes a reduction in calcium currents, triggering changes in presynaptic calcium levels and thus neurotransmission. Because of the widespread expression patterns of NOP and VGCCs across multiple brain regions, the dorsal horn of the spinal cord, and the dorsal root ganglia, this results in the alteration of numerous neurophysiological features. Here we review the regulation of N-type calcium channels by the NOP-nociceptin system in the context of neurological conditions such as anxiety, addiction, and pain.