Melatonin reverts CGRP expression induced by capsaicin

Introduction: CGRP, a neuropeptide synthetized and released in the central nervous system and potent vasodilator, has been implicated in migraine physiopathology. Because of that, there are CGRP targeted therapies that decrease CGRP levels. Melatonin, a pineal gland secretion, has already proved its analgesic effect. We aimed to study CGRP expression in an animal model comparing capsaicin, CGRP and melatonin. Methods: We used in our study male animal rats and separated them into groups based in the kind of received solution (control group, capsaicin only and melatonin plus capsaicin). It was prepared brain stem slices and measured the CGRP levels in the trigemino nucleus caudalis (TNC). Results: Capsaicin group (N = 5) presented low intensity of GCRP expression and animals that received capsaicin plus melatonin (N = 5) showed high intensity of CGRP expression compared to capsaicin group. Conclusion: Melatonin decreases CGRP in an experimental model in rats induced by capsaicin, reducing its inflammatory action in cerebral vessels.

Muscarinic acetylcholine receptors enhance neonatal mouse hypoglossal motoneuron excitability in vitro

In brain stem slices from neonatal ( postnatal days 0–4) CD-1 mice, muscarinic ACh receptors (MAChRs) increased rhythmic inspiratory-related and tonic hypoglossal nerve discharge and depolarized single hypoglossal motoneurons (HMs) via an inward current without changing input resistance. These responses were blocked by the MAChR antagonist 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP; 100 nM). MAChRs shifted voltage-dependent activation of the hyperpolarization-activated cation current to more positive levels. MAChRs increased the HM repetitive firing rate and decreased rheobase, with both effects being blocked by 4-DAMP. Muscarinic agonists reduced the afterhyperpolarization of single action potentials (APs), suggesting that small-conductance Ca2+-dependent K+ current inhibition increased the HM firing rate. Muscarinic agonists also reduced the AP amplitude and slowed its time course, suggesting that MAChRs inhibited voltage-gated Na+ channels. To compare muscarinic excitation of single HMs to muscarinic excitatory effects on motor output in thicker brain stem slices requiring higher extracellular K+ for rhythmic activity, we tested the effects of muscarinic agonists on single HM excitability in high-K+ artificial cerebrospinal fluid (aCSF). In high-K+ aCSF, muscarinic agonists still depolarized HMs and altered AP size and shape, as in standard aCSF, but did not increase the steady-state firing rate, decrease afterhyperpolarization, or alter threshold potential. These results indicate that the basic cellular response of HMs to muscarinic receptors is excitatory, via a number of distinct mechanisms, and that this excitatory response will be largely preserved in rhythmically active brain stem slices.

Graded Reductions in Oxygenation Evoke Graded Reconfiguration of the Isolated Respiratory Network

Neurons depend on aerobic metabolism, yet are very sensitive to oxidative stress and, as a consequence, typically operate in a low O2 environment. The balance between blood flow and metabolic activity, both of which can vary spatially and dynamically, suggests that local O2 availability markedly influences network output. Yet the understanding of the underlying O2-sensing mechanisms is limited. Are network responses regulated by discrete O2-sensing mechanisms or, rather, are they the consequence of inherent O2 sensitivities of mechanisms that generate the network activity? We hypothesized that a broad range of O2 tensions progressively modulates network activity of the pre-Bötzinger complex (preBötC), a neuronal network critical to the central control of breathing. Rhythmogenesis was measured from the preBötC in transverse neonatal mouse brain stem slices that were exposed to graded reductions in O2 between 0 and 95% O2, producing tissue oxygenation values ranging from 20 ± 18 (mean ± SE) to 440 ± 56 Torr at the slice surface, respectively. The response of the preBötC to graded changes in O2 is progressive for some metrics and abrupt for others, suggesting that different aspects of the respiratory network have different sensitivities to O2.

cAMP Modulates Intracellular Ca2+ Sensitivity of Fast-Releasing Synaptic Vesicles at the Calyx of Held Synapse

cAMP potentiates neurotransmitter release from the presynaptic terminal in many CNS synapses, but the underlying mechanisms remain unclear. Here we addressed this issue quantitatively by performing double patch-clamp recordings from the pre- and postsynaptic compartments of the calyx of Held synapse in rat brain stem slices in combination with Ca2+ uncaging. We found that elevation of cAMP increased intracellular Ca2+ sensitivity for transmitter release especially at lower Ca2+ concentrations. The change in Ca2+ sensitivity was limited to the fast-releasing synaptic vesicles, which could be released rapidly on action potentials. cAMP did not affect the slowly releasing vesicles. Fit of the data using a simplified allosteric model indicated that cAMP increased the fusion “willingness,” thereby facilitating transmitter release. We suggest that synaptic vesicles have to be positionally primed to the release sites close to the Ca2+ channel cluster for cAMP to modulate intracellular Ca2+ sensitivity of transmitter release.

Dopamine effects on identified rat vagal motoneurons

Catecholaminergic neurons of the A2 area play a prominent role in brain stem vagal circuits. It is not clear, however, whether these neurons are noradrenergic or adrenergic, i.e., display tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DβH) immunoreactivity (-IR) or dopaminergic (i.e., TH- but not DβH-IR). Our aims were to investigate whether a subpopulation of neurons in the A2 area was dopaminergic and, if so, to investigate the effects of dopamine (DA) on the membrane of gastric-projecting vagal motoneurons. We observed that although the majority of A2 neurons were both TH- and DβH-IR, a small percentage of nucleus tractus solitarius neurons were TH-IR only, suggesting that DA itself may play role in these circuits. Whole cell recordings from thin brain stem slices showed that 71% of identified gastric-projecting motoneurons responded to DA (1–300 μM) with either an excitation (28%) or an inhibition (43%) of the membrane; the remaining 29% of the neurons were unresponsive. The DA-induced depolarization was mimicked by SK 38393 and prevented by pretreatment with SCH 23390. Conversely, the DA-induced inhibition was mimicked by bromoergocryptine and prevented by pretreatment with L741626. When tested on the same neuron, the effects of DA and NE were not always similar. In fact, in neurons in which DA induced a membrane depolarization, 77% were inhibited by NE, whereas 75% of neurons unresponsive to DA were inhibited by NE. Our data suggest that DA modulates the membrane properties of gastric-projecting motoneurons via D1- and D2-like receptors, and DA may play different roles than norepinephrine in brain stem vagal circuits.

Urethane inhibits the GABAergic neurotransmission in the nucleus of the solitary tract of rat brain stem slices

Because urethane is a widely used anesthetic in animal experimentation, in the present study, we evaluated its effects on neurons of the nucleus of the solitary tract (NTS) in brain stem slices from young rats (25–30 days old). Using the whole cell configuration of the patch-clamp technique, spontaneous postsynaptic currents (sPSCs) and evoked excitatory postsynaptic currents (eEPSCs) were recorded. Urethane (20 mM) decreased by ∼60% the frequency of GABAergic sPSCs (1.0 ± 0.2 vs. 0.4 ± 0.1 Hz) but did not change the frequency, amplitude, or half-width of glutamatergic events or TTX-resistant inhibitory sPSCs [miniature inhibitory postsynaptic currents (IPSCs)]. Miniature IPSCs were measured in the presence of urethane plus 1 mM diazepam (1 mM), and no changes were seen in their amplitude. This suggests that the GABA concentration in the NTS synapses is set at saturating level. We also evaluated the effect of urethane on eEPSCs, and no significant change was observed in the amplitude of N-methyl-d-aspartate [NMDA; 44.2 ± 11.5 vs. 37.6 ± 10.6 pA (holding potential = 40 mV)] and non-NMDA currents [204.4 ± 35.5 vs. 196.6 ± 31.2 pA (holding potential = −70 mV)]. Current-clamp experiments showed that urethane did not alter the action potential characteristics and passive membrane properties. These data suggest that urethane has an inhibitory effect on GABAergic neurons in the NTS but does not change the spontaneous or evoked excitatory responses.