Hypothalamic proopiomelanocortin (POMC) neurons and their peptide products mediate important aspects of energy balance, analgesia, and reward. In addition to peptide products, there is evidence that POMC neurons can also express the amino acid transmitters GABA and glutamate, suggesting these neurons may acutely inhibit or activate downstream neurons. However, the release of amino acid transmitters from POMC neurons has not been thoroughly investigated in an intact system. In the present study, the light-activated cation channel channelrhodopsin-2 (ChR2) was used to selectively evoke transmitter release from POMC neurons. Whole-cell electrophysiologic recordings were made in brain slices taken from POMC-Cre transgenic mice that had been injected with a viral vector containing a floxed ChR2 sequence. Brief pulses of blue light depolarized POMC-ChR2 neurons and induced the release of GABA and glutamate onto unidentified neurons within the arcuate nucleus, as well as onto other POMC neurons. To determine if the release of GABA and glutamate from POMC terminals can be readily modulated, opioid and GABAB receptor agonists were applied. Agonists for mu and kappa, but not delta, opioid receptors inhibited transmitter release from POMC neurons, as did the GABAB receptor agonist baclofen. This regulation indicates that opioids and GABA released from POMC neurons may act at presynaptic receptors on POMC terminals in an autoregulatory manner to limit continued transmission. The results show that in addition to the relatively slow and long-lasting actions of peptides, POMC neurons can rapidly affect the activity of downstream neurons via GABA and glutamate release.
Intrinsically photosensitive retinal ganglion cells (ipRGCs) encode light intensity and trigger reflexive responses to changes in environmental illumination. In addition to functioning as photoreceptors, ipRGCs are post-synaptic neurons in the inner retina, and there is increasing evidence that their output can be influenced by retinal neuromodulators. Here we show that opioids can modulate light-evoked ipRGC signaling, and we demonstrate that the M1, M2 and M3 types of ipRGCs are immunoreactive for μ-opioid receptors (MORs) in both mouse and rat. In the rat retina, application of the MOR-selective agonist DAMGO attenuated light-evoked firing ipRGCs in a dose-dependent manner (IC 50 < 40 nM), and this effect was reversed or prevented by co-application of the MOR-selective antagonists CTOP or CTAP. Recordings from solitary ipRGCs, enzymatically dissociated from retinas obtained from melanopsin-driven fluorescent reporter mice, confirmed that DAMGO exerts its effect directly through MORs expressed by ipRGCs. Reduced ipRGC excitability occurred via modulation of voltage-gated potassium and calcium currents. These findings suggest a potential new role for endogenous opioids in the
Coding a wide range of light intensities in natural scenes poses a challenge for the retina: adaptation to bright light should not compromise sensitivity to dim light. Here we report a novel form of activity-dependent synaptic plasticity, specifically, a "weighted potentiation" that selectively increases output of Mb-type bipolar cells in the goldfish retina in response to weak inputs but leaves the input-output ratio for strong stimuli unaffected. In retinal slice preparation, strong depolarization of bipolar terminals significantly lowered the threshold for calcium spike initiation, which originated from a shift in activation of voltage-gated calcium currents (I Ca ) to more negative potentials. The process depended upon glutamate-evoked retrograde nitric oxide (NO) signaling as it was eliminated by pretreatment with an NO synthase blocker, TRIM. The NO-dependent I Ca modulation was cGMP independent but could be blocked by N-ethylmaleimide (
Nitric oxide (NO) synthesis in the retina is triggered by light stimulation. NO has been shown to modulate visual signal processing at multiple sites in the vertebrate retina, via activation of the most sensitive target of NO signaling, soluble guanylate cyclase. NO can also alter protein structure and function and exert biological effects directly by binding to free thiol groups of cysteine residues in a chemical reaction called S-nitrosylation. However, in the central nervous system, including the retina, this reaction has not been considered to be significant under physiological conditions. Here we provide immunohistochemical evidence for extensive S-nitrosylation that takes place in the goldfish and mouse retinas under physiologically relevant light intensities, in an intensity-dependent manner, with a strikingly similar pattern in both species. Pre-treatment with NEM, which occludes S-nitrosylation, or with TRIM, an inhibitor of neuronal NO synthase, eliminated the light-evoked increase in S-nitrosylated protein immunofluorescence (SNI) in the retinas of both species. Similarly, light did not increase SNI, above basal levels, in retinas of transgenic mice lacking neuronal NO synthase. Qualitative analysis of the light-adapted mouse retina with mass spectrometry revealed more than 300 proteins that were S-nitrosylated upon illumination, many of which are known to participate directly in retinal signal processing. Our data strongly suggest that in the retina, light-evoked NO production leads to extensive S-nitrosylation and that this process is a significant post-translational modification affecting a wide range of proteins under physiological conditions.
TPS608 Background: In US clinical practice, GnRH agonists are widely used to suppress ovarian function in pre/perimenopausal patients with breast cancer that is moderate-to high-risk for recurrence. Despite extensive use of leuprolide acetate (LA) for ovarian suppression, regulatory approval for this indication has not been established in the US. Additionally, existing three month formulations may not reliably provide ovarian suppression, as demonstrated by escapes in estradiol (E2). An extended-release LA product with a 3-month dosing period specifically developed for ovarian suppression in patients with breast cancer could fill this unmet need. TOL2506 is a 3-month, extended-release formulation of 30 mg of LA. This combination of active drug and in situ polymeric extended release technology is expected to deliver higher exposure to drug than the currently available 3-month (22.5 mg) formulations of LA marketed for advanced prostate cancer and potentially reduce escapes in E2 over the dosing period. Methods: TOL2506A (OVELIA) is a phase 3, single arm, open-label study evaluating the effectiveness of TOL2506 to suppress ovarian function in premenopausal women with HR+, HER2-negative breast cancer. Approximately 250 subjects will be enrolled, with 30% aged 40 years or younger. Subjects must be premenopausal women, age 18-49, with a diagnosis of Stage I, II, or III HR+, HER2-negative breast cancer (ER > 1% and/or, PR > 1%, HER2-negative per ASCO CAP guidelines), who are candidates for ovarian suppression with endocrine therapy. For subjects receiving chemotherapy, premenopausal status will be determined, and confirmed by central lab hormone testing, prior to initiating chemotherapy. Male subjects with HR+, HER2-negative breast cancer may also be eligible, but will be evaluated for safety analyses only. Eligible subjects will enter the 48 week treatment period in 2 groups: those receiving tamoxifen concurrently with TOL2506 or those who initiate therapy with an aromatase inhibitor (AI; letrozole, anastrozole, or exemestane) beginning 6 weeks after the first administration of TOL2506, if E2 < 20 pg/mL has been achieved. After Week 12, subjects will be allowed to switch from receiving an AI to receiving tamoxifen or from tamoxifen to AI at the Investigator’s discretion. Subjects will receive 4 doses of TOL2506 every 12 weeks over the 48 week study duration. Achievement of ovarian suppression will be defined as ≥ 90% of subjects with luteinizing hormone (LH) levels < 4 IU/L at Week 6. Secondary endpoints include suppression of LH, E2 (< 20 pg/mL for tamoxifen cohort and < 2.72 pg/mL for AI cohort) and absence of menses at weeks 6, 12, 24, 36, and 48. Clinical trial information: NCT04906395.
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