Bertha Prieto-Gómez

Melatonin modulates cholinergic transmission by blocking nicotinic channels in the guinea-pig submucous plexus

Melatonin, a hormone produced and released by the pineal gland is also synthesized by cells of the gastrointestinal wall, where it might be a local regulator of gut functions. In this study, we investigated the possible role of melatonin as a modulator of the enteric nervous system. Intracellular recordings were made in neurons of the submucosal plexus from the guinea-pig ileum to measure the melatonin effects on their electrophysiological properties. Melatonin did not alter the membrane potential, the membrane resistance and the noradrenergic inhibitory postsynaptic potentials. However, melatonin (30-3000 microM) reversibly decreased the amplitude of nicotinic excitatory postynaptic potentials (EPSPs) in a concentration-dependent manner (IC50 = 247 microM). These actions of melatonin were not modified by the presence of idazoxan and atropine indicating that they are not mediated by endogenous release of acetylcholine, noradrenaline, or by direct activation of alpha 2-adrenoceptors or muscarinic receptors. The superfusion of melatonin also blocked the nicotinic depolarizations induced by locally applied acetylcholine, indicating that at least part of its effects are postsynaptic. In voltage-clamp experiments, using the whole-cell configuration, melatonin also inhibited the nicotinic inward currents induced by acetylcholine (IACh) in a concentration-dependent manner (IC50 = 257 microM). Melatonin decreased the maximal IACh but did not affect the potency of acetylcholine to induce this current, indicating a noncompetitive antagonism. This effect was voltage-dependent. Our observations indicate that melatonin inhibits the fast EPSPs by directly and specifically blocking the nicotinic channels. The relative high concentrations of melatonin required to produce such an effect rules this out as one of its humoral actions. Such an effect, however, might be of physiological significance close to the cells that release melatonin in the gastrointestinal wall or in other organs.

Interferon modulates neuronal activity recorded from the hypothalamus, thalamus, hippocampus, amygdala and the somatosensory cortex

Neuromodulators interact with classically defined neurotransmitters to regulate a variety of biological processes. The aim of the present study was to study whether interferon-alpha (IFN) can be considered as a neuromodulator. Single cell recordings from five CNS structures were recorded before and following three different routes of IFN administration in Sprague-Dawley rats to substantiate that IFN is a neuromodulator. IFN modulated the majority of the hypothalamic (70%), amygdala (76%), hippocampus (75%) and cortical (82%) cells whether the route of administration was within the brain or given peripherally (i.v. or i.p.). The main difference among the three routes of IFN administration on the neuronal activity of these four CNS sites was the onset of the effect. However, the thalamic neurons responded differently. IFN injection within the brain modulated activity of 43% of thalamic neurons, but only 25% and 17% of the neurons when IFN was given i.v. or i.p., respectively. IFN, in general suppressed hypothalamic neuronal activity while accelerating neuronal activity in all the other studied CNS sites. In conclusion, IFN is an endogenous peptide synthesized and released both peripherally and centrally, with the same effects on neuronal activity whether it is given systemically or locally within the brain. This suggests that IFN can be considered as a neuromodulator.

Alpha and Gamma Interferons' Effects on Cortical and Hippocampal Neurons: Microiontophoretic Application and Single Cell Recording

Responses of 96 extracellular spontaneous active cortical and hippocampal neurons to microiontophoretically applied four types of alpha interferons (alpha-IFNs), one type of gamma interferon (gamma-IFN) as well as three fractions of gamma-IFNs were examined. All four types of alpha-IFN ejections increased the discharge of the majority of neuron tested. Significant differences of the number of cells excited and the intensity of the excitation among the 4 types of alpha-IFN were observed. The most significant effects were induced by Cantells human leukocyte alpha-IFN followed by the Hoffman-LaRoche recombinant alpha-IFN which exhibited a dose dependent effect (i.e., each higher dose of IFN affected more neurons and intensified the excitation) on the hippocampal and cortical cells respectively. Neither the IFN carrier (albumin), nor the gamma-IFNs and its fractions, as well as current ejection, altered the extracellular spontaneous active of these 96 cortical and hippocampal neurons respectively. These observations show that the immunomodulator alpha-IFNs, but not gamma-IFNs, exerts excitatory effects on neuronal activity recorded from these two brain structures and support the view that the brain is capable of communicating with the immune system.

Interferon modulates central nervous system function.

The interferons (IFNs) are an endogenous pleiotropic family of cytokines that perform fundamental physiological functions as well as protecting host organisms from disease and in maintaining homeostasis. This review covers the effects of endogenous IFN on the nervous system. It starts with the description of its receptors, followed how it modulate neuronal activity, mood, sleep, temperature, the endocrine system, the opioid system and how it regulate food consumption and the immune system. Similar to other multifunctional cytokines, an excessive or inappropriate activity of IFNs can cause toxicity and even death. Furthermore, IFNs are currently the major treatment modality for several malignant and non-malignant diseases such as chronic hepatitis C and B, multiple sclerosis, hematological malignancies, malignant melanoma, renal cell carcinoma, etc.

Alpha-interferon suppresses food intake and neuronal activity of the lateral hypothalamus

Alpha-interferon (alpha-IFN) treatment in humans induces anorexic effects. However, the mechanisms and sites of action are unknown. Rats implanted with an intracerebroventricular (i.c.v.) cannula for local injection, and semi-microelectrodes in the lateral hypothalamic (LH) area for neuronal recording were used. The animals were kept in metabolic cages, and food and water intake was measured daily at 7:00 and 19:00 hr for 35 days, including: 5 days before the experiment; 10 days during daily alpha-IFN application (either i.p. 1500 I.U./gbw, or i.c.v. 1500 and 150 I.U./animal) and/or a vehicle control group; and 20 days post drug treatment. The unitary activity recording from the LH area was made before (30 min), during (10 min) and after (200 min) the alpha-IFN applications. alpha-IFN elicited a reversible dose-related decrease of both food intake and body weight. This decrease in food intake following alpha-IFN injections was correlated with a depression of LH neuronal electrical activity. Since direct brain application (i.c.v.) and systemic (i.p.) alpha-IFN treatment elicited identical responses, it is possible to assume that alpha-IFN suppresses food intake by a direct action on CNS sites including the LH neurons.

Melatonin attenuates the decrement of dendritic protein MAP-2 immuno-staining in the hippocampal CA1 and CA3 fields of the aging male rat.

Neuronal death during brain aging results, at least in part, from the disruption of synaptic connectivity caused by oxidative stress. Synaptic elimination might be caused by increased instability of the neuronal processes. In vitro evidence shows that melatonin increases MAP-2 expression, a protein that improves the stability of the dendritic cytoskeleton, opening the possibility that melatonin could prevent synaptic elimination by increasing dendritic stability. One way to begin exploring this issue in vivo is to evaluate whether long-term melatonin treatment changes the intensity of MAP-2 immuno-staining in areas commonly afflicted by aging that are rich in dendritic processes. Accordingly, we evaluated the effects of administering melatonin for 6 or 12 months on the intensity of MAP-2 immuno-staining in the strata oriens and lucidum of the hippocampal CA1 and CA3 fields of aging male rats, through semi-quantitative densitometry. Melatonin treated rats showed a relative increment in the intensity of MAP-2 immuno-staining in both regions after 6 or 12 months of treatment, as compared with age matched control rats. Although melatonin untreated and treated rats showed a decrease of MAP-2 immuno-staining in the hippocampus with increasing age, such decrement was less pronounced following melatonin treatment. These findings were confirmed by qualitative Western blot analyses. The melatonin effect seems specific because MAP-2 staining in the primary somatosensory cortex was not affected by the treatment. Thus, chronic melatonin administration increases MAP-2 immuno-staining and attenuates its decay in the adult aging hippocampus. These results are compatible with the idea that melatonin could improve dendritic stability and thus diminish synaptic elimination in the aging brain.

Novel effects of interferon on the brain: Microiontophoretic application and single cell recording in the rat ☆

Interferon (IF), one of the most controversial drugs in cancer therapy, induces a variety of CNS side effects. Therefore, IF was tested on single neuronal activity and compared with other drugs. Recombinant leukocyte A IF, morphine sulfate and L-glutamate were applied microiontophoretically to 18 cortical and 29 thalamic neurons. The majority of the cortical cells were excitated by IF while most of the thalamic cells did not respond to IF; however, morphine and glutamate elicited on these neurons the expected effects. IF produced a long-lasting increase in firing discharges and exhibited dose-response characteristics.

Morphine administration and abrupt cessation alter the behavioral diurnal activity pattern

In mammals, there is an underlying mechanism that dictates the organisms biological functions and daily activity schedule, known as circadian rhythms, which play a major role in maintaining steady metabolism, homeostasis, and immunity. Limited research has been done investigating the effects of continuous opiate administration on the circadian rhythm activity pattern. A change in circadian activity pattern is suggested as an experimental model to demonstrate long-term effect of the drug. The objective of this study was to investigate the effects of morphine treatment on the long term activity (24 h) of the animal as well as the activity after abrupt removal, since prescribed medication containing morphine is widely used and abused and its long term effects are not known. Male Sprague-Dawley rats were contained in stable conditions with a standard light/dark cycle recordings taken before, during and after morphine pellet implantation. Cosinor analysis was used to fit a 24-hour curve to the activity pattern. Results indicate that morphine pellet administration alters the mesor, amplitude, the day-time and night-time activity levels, and demonstrates a remarkable change in the maximal circadian rhythm timing during the withdrawal period. The question whether morphine changes the circadian rhythm or a change in circadian rhythm results in tolerance and withdrawal is discussed.

Noxious and non-noxious responses in the medial thalamus of the rat.

Single-cell experiments were undertaken to localize and characterize the medial thalamic (MT) neurons which respond to noxious and non-noxious input in the rat. The observations demonstrated that: (1) 61 and 42% of MT neurons respond to noxious (Nox) and non-noxious (NN) stimulation, respectively; (2) MT neurons exhibit 4 cell types according to their pattern of response; Type A units were excited exclusively by Nox stimulation; Type B units were excited exclusively by NN stimulation; Type C units were excited by both (Nox and NN) stimulation, and Type D units exhibited decreases in firing rate following both stimulation modalities; (3) neurons of the parafascicularis nucleus exhibit more noxious responses (Type A units) than other medial thalamic areas.

Microiontophoretic application of morphine and naloxone to neurons in hypothalamus of rat

The present experiments used urethane-anesthetized rats and single cell recording to study the electrophysiological properties of ventromedial hypothalamic (VMH) cells following different doses of morphine and naloxone, applied microiontophoretically. More than 45% of ventromedial hypothalamic units reacted in a dose-response fashion to local application of morphine. In the majority of the ventromedial hypothalamic neurons, naloxone failed to reverse the effects of morphine. Naloxone alone had effects on 37% of the ventromedial hypothalamic units. The ventromedial hypothalamic units exhibited different response patterns from those observed from other CNS sites in response to the microiontophoretic application of morphine and naloxone; this difference is discussed. The present neurophysiological findings support the existence of opiate target sites with multiple opiate receptors within the ventromedial hypothalamus.