Regulation of adult hippocampal neurogenesis exerted by sexual, cognitive and physical activity: An update.

In 1962, Joseph Altman described that the brain generates neurons after the postnatal period, and this continues throughout your life (Altman, 1962). This was a breakthrough in the neuroscience field because before this the accepted paradigm was that the brain only generated neurons during the embryonal development. This discovery has been controversial ever since, especially since one of the areas of the brain with neurogenic properties is the hippocampus, which is the area involved in memory storage and neurodegenerative processes. The adult hippocampal neurogenesis modulates in response to different environmental factors. In this article, we review how exercise and cognitive and sexual activity can regulate the generation of new neurons in the hippocampal in an adult brain and the impact of these new neurons in the brain circuitry.

[A brief history of marijuana in the western world]. / Breve historia sobre la marihuana en Occidente.

Marijuana is a substance with a long and controversial history. At different times in its history, which goes back over 5,000 years, this plant has been used for different purposes, ranging from recreational and leisure to its use in the treatment of several diseases or to offer relief in processes that entail a certain type of malaise, and including its consideration as a means of relaxation and meditation. Although it was supposed that the roots of marijuana lay in Central America, it is now known that this is but an urban legend with little credibility and that its origins can be found recorded in Chinese medical references dating back to the year 2737 BC. Although this plant was not originally from Central America, it has aroused interest around the world, and above all in Mexico. It is in this country where the use of cannabis has gone from applications in textiles and medicine to its free sale, the bans on its use due to political and social pressures, its tolerance and, recently, its decriminalisation for recreational and medicinal use. Unfortunately there are few references on the history of this plant in Mexico, and thus we have considered it interesting to present some data about the generalities of marijuana, a brief history in the world, the development of decriminalisation in North America, its medicinal uses and its course through Mexico to the present day.

TITLE: Breve historia sobre la marihuana en Occidente.La marihuana es una sustancia con una extensa y controvertida historia. A lo largo del tiempo, esta planta, y desde hace mas de 5.000 años, ha sido utilizada para diferentes fines, que van desde el uso ludico y recreativo, pasando por un medio de relajacion y meditacion, hasta su uso en el tratamiento de varias enfermedades o el alivio de procesos vinculados a cierto tipo de malestares. Aunque se supuso que la marihuana tenia su origen en Mesoamerica, ahora se sabe que es solo una leyenda urbana de poca credibilidad y que sus origenes los podemos registrar en referencias medicas chinas datadas alrededor del año 2737 a. de C. Si bien esta planta no tiene un origen mesoamericano, si ha generado interes en el mundo, y sobre todo en Mexico. Es en este pais donde el uso del cannabis ha ido desde intereses textiles y medicinales hasta el consumo ludico, pasando por su venta libre, la prohibicion por presiones politicas y sociales, su tolerancia y, recientemente, su despenalizacion para uso ludico y medicinal. Desgraciadamente existen pocas referencias de la historia de esta planta en Mexico, por lo que ha sido de nuestro interes presentar algunos datos sobre las generalidades de la marihuana, una breve historia en el mundo, el desarrollo de la despenalizacion en Norteamerica, sus usos medicinales y su paso por Mexico hasta nuestros dias.

Substance P excites GABAergic neurons in the mouse central amygdala through neurokinin 1 receptor activation.

Substance P (SP) is implicated in stress regulation and affective and anxiety-related behavior. Particularly high expression has been found in the main output region of the amygdala complex, the central amygdala (CE). Here we investigated the cellular mechanisms of SP in CE in vitro, taking advantage of glutamic acid decarboxylase-green fluorescent protein (GAD67-GFP) knockin mice that yield a reliable labeling of GABAergic neurons, which comprise 95% of the neuronal population in the lateral section of CE (CEl). In GFP-positive neurons within CEl, SP caused a membrane depolarization and increase in input resistance, associated with an increase in action potential firing frequency. Under voltage-clamp conditions, the SP-specific membrane current reversed at -101.5 ± 2.8 mV and displayed inwardly rectifying properties indicative of a membrane K(+) conductance. Moreover, SP responses were blocked by the neurokinin type 1 receptor (NK1R) antagonist L-822429 and mimicked by the NK1R agonist [Sar(9),Met(O2)(11)]-SP. Immunofluorescence staining confirmed localization of NK1R in GFP-positive neurons in CEl, predominantly in PKCδ-negative neurons (80%) and in few PKCδ-positive neurons (17%). Differences in SP responses were not observed between the major types of CEl neurons (late firing, regular spiking, low-threshold bursting). In addition, SP increased the frequency and amplitude of GABAergic synaptic events in CEl neurons depending on upstream spike activity. These data indicate a NK1R-mediated increase in excitability and GABAergic activity in CEl neurons, which seems to mostly involve the PKCδ-negative subpopulation. This influence can be assumed to increase reciprocal interactions between CElon and CEloff pathways, thereby boosting the medial CE (CEm) output pathway and contributing to the anxiogenic-like action of SP in the amygdala.

Neurosteroids increase tonic GABAergic inhibition in the lateral section of the central amygdala in mice.

Neurosteroids are formed de novo in the brain and can modulate both inhibitory and excitatory neurotransmission. Recent evidence suggests that the anxiolytic effects of neurosteroids are mediated by the amygdala, a key structure for emotional and cognitive behaviors. Tonic inhibitory signaling via extrasynaptic type A γ-aminobutyric acid receptors (GABA(A)Rs) is known to be crucially involved in regulating network activity in various brain regions including subdivisions of the amygdala. Here we provide evidence for the existence of tonic GABAergic inhibition generated by the activation of δ-subunit-containing GABA(A)Rs in neurons of the lateral section of the mouse central amygdala (CeAl). Furthermore, we show that neurosteroids play an important role in the modulation of tonic GABAergic inhibition in the CeAl. Taken together, these findings provide new mechanistic insights into the effects of pharmacologically relevant neurosteroids in the amygdala and might be extrapolated to the regulation of anxiety.

Regular firing of a single output neuron reduces its own inhibition through endocannabinoids in substantia nigra pars reticulata of juvenile mice.

Depolarization-induced suppression of inhibition in substantia nigra pars reticulata suggests that burst-like activity but not regular firing suffices to activate presynaptic endocannabinoid CB1 receptors. To more closely determine the type of activity required, we applied gramicidin perforated patch recording under visual control to substantia nigra slices of juvenile mice. We found that evoked inhibitory postsynaptic currents (eIPSCs) were reduced in amplitude by the spontaneous firing of a neuron under study, whereas silencing this neuron enhanced inhibitory responses. Autonomous firing reduced eIPSCs to 78%+/-2% in a time- but not frequency-dependent manner. The phenomenon which we termed firing-induced suppression of inhibition was cannabinoid receptor subtype 1-dependent, whereas adenosine A1 receptors played only a minor role. Depletion of intracellular Ca(2+) stores abolished the firing-induced suppression of inhibition suggesting that Ca(2+) release from internal stores is necessary for the production of endocannabinoids during autonomous firing. We suggest that the Ca(2+) influx during autonomous activity of pars reticulata neurons suffices to selectively dampen incoming inhibition from striatal neurons because it is amplified by ryanodine receptor-mediated Ca(2+) release from intracellular stores.

Orphanin-FQ/nociceptin inhibits kindling epileptogenesis and enhances hippocampal feed-forward inhibition.

The role of Orphanin-FQ/nociceptin in synaptic plasticity was assessed by its potency in modulating kindling epileptogenesis in vivo, and feed-forward inhibition in hippocampal recordings in vitro. In addition, a specific rabbit antiserum against this peptide was obtained and the immunohistochemical distribution of nociceptin was determined in rat brain slices. After the establishment of kindling epilepsy, by daily electrical stimulation of the piriform cortex, the i.c.v. injection of nociceptin, 20 min before the kindling stimulation, was not able to block the generation of the generalized seizures, nor to alter their duration. However, the i.c.v. injection of nociceptin, 20 min before each stimulation along the kindling process, depressed its development in a dose-dependent manner. This effect was specific since the nociceptin antagonist [Phe1psi(CH2-NH)Gly2]NC(1-13)NH2, but not the broad-spectrum opiate antagonist, naloxone, was able to completely block nociceptin actions. The inhibitory role of nociceptin was assessed by in vitro recordings from entorhinal cortex-hippocampal slices. By single pulses applied over the Schaffer collaterals, we found that synaptic transmission was facilitated onto CA1, but using a paired-pulse protocol, we found that nociceptin potentiated feed-forward inhibition. The immunohistochemical data show that nociceptin is expressed in limbic cortical regions, including the piriform cortex and the hippocampus. Our results demonstrate that nociceptin exerts a modulatory role in limbic excitability and suggest that it provides an inhibitory control in the development of epilepsy by possibly inhibiting the spread of excitation through the system, by favoring feed-forward inhibition.