La diversitat de l'activitat econòmica a la Catalunya Moderna: més enllà de la renda feudal

Escollir com a concepte organitzador d'una ponència la idea de la diversitat i plantejar-lo com a innovador fa pensar que anteriorment els historiadors pensaven en clau d'una Catalunya homogènia, sense diversitat. Segurament tampoc no era ben bé així, però alguns tòpics portaven a pensar-ho: a) L'agricultura, basada en el conreu del cereal, la vinya i l'olivera, era fonamentalment de subsistència, amb baixos rendiments i molt poca comercialització de productes (els masos produïen per consumir, no per vendre).1 No hi havia, per tant, mercat, ni altres models. b) El feudalisme -i el complex entramat de jurisdiccions i drets senyorials- era la pesada llosa que requeia sobre l'agricultura i l'endarreria, desviant part de la producció pagesa i dificultant la transició al capitalisme. És cert que, sobre aquest tema, hi ha hagut un ampli debat sobre el pes del feudalisme a Catalunya: per a uns, la Sentència Arbitral..

Neurotransmitters and Neuropeptides of Invertebrates

This chapter introduces working definitions of neuropeptides and neurotransmitters from the perspective of invertebrate physiological processes. Neuropeptides and neurotransmitters are intercellular chemical signaling agents used by all animals. Chemical signaling augments or substitutes for electrical communication in the nervous system. When these agents act as neurotransmitters, they convert electrical signals to chemical signals across the synapse. As hormones, they circulate from a site of release to act at a more distant site in the body of the organism. Neuropeptides and neurotransmitters are classified into these groups mostly on the basis of their molecular size. This article describes several neuropeptide superfamilies and their wide scope of actions in model invertebrates. The article also describes the main neurotransmitters used by invertebrates

Voltage-Gated ion currents of schwann cells in cell culture models of human neurofibromatosis

K(+) (K) channels play a role in the proliferation of many cell types in normal cells and certain disease states. Several laboratories have studied K currents in cultured Schwann cells from models of the human diseases, neurofibromatosis type 1 (NF1) and neurofibromatosis type 2 (NF2). These diseases are characterized by the growth of Schwann cell tumors. In all cell culture NF models the K current properties differ in tumor-derived and normal Schwann cells. Depending on the model however, the type of K channel abnormality differs. K channels appear to play a role in the proliferation of Schwann cell cultures of these disease models, because a link has been established between K current blockade and the inhibition of Schwann cell proliferation in NF1 and NF2. Differences in the proliferation response of normal Schwann cells to K channel blockers suggest that in vitro regulation of proliferation in neoplastic and normal Schwann cells is complex

The development of excitatory capability in Aplysia californica bag cells observed in cohorts

The bag cells of Aplysia release egg laying hormone in sexually mature animals. Bag cells cannot sustain the long-lasting excitatory afterdischarge (AD) required for hormone release prior to sexual maturity (T.A. Nick, L.K. Kaczmarek, T.J. Carew, Ionic currents underlying developmental regulation of repetitive firing in Aplysia bag cell neurons, J. Neurosci. 1996;16:7583–7598; L.A. Fieber, Characterization of Na + and Ca 2+ currents in bag cells of sexually immature Aplysia californica, J. Exp. Biol. 1998;201:745–754). To investigate the development of bag cell excitability, whole-cell voltage-clamp experiments were executed in dissociated bag cells from four cohorts (batches) of hatchery-reared A. californica maintained at 13–15°C. K + current densities, representing the sum of at least four different outward K + currents (Nick et al., 1996), declined significantly as a function of age, beginning at least 2–3 months before sexual maturity. The K + current decreases coincided with the first appearance of Na + and Ca 2+ currents in bag cells, which occurred at ages 6–7 months. Whole cell K + currents were not decreased significantly by a cAMP analog earlier than 1 month prior to the onset of reproductive activity. The frequency of observing Na + currents in whole cell recordings was low for developmental times earlier than sexual maturity. In one winter batch, both control and PMA-treated Na + currents increased significantly with age, and PMA-treated current densities were significantly greater than controls, but the other two batches studied had significant differences in Na + current frequency only at sexual maturity. Ca 2+ currents were reliably measured in more cells than were Na + currents. The Ca 2+ current frequency increased significantly with maturity in one winter batch. Ca 2+ currents were significantly increased by phorbol ester treatment beginning 6–8 weeks before reproductive activity in the two winter batches. These observations support the hypothesis that bag cell excitability is not fully developed until shortly before sexual maturity

Ionic currents mediated by activation of nicotinic and purinergic receptor-channels in cultured neurons dissociated from rat parasympathetic cardiac ganglia

The cholinergic innervation of the rat parasympathetic cardiac ganglion was verified by anatomical and histochemical techniques. A tissue culture method designed for electrophysiological studies on principal cells of the cardiac ganglia is described. The passive and active membrane properties of cultured cardiac neurons were studied under whole cell current and voltage clamp conditions. The cultured neurons have an input resistance of 1 G$\Omega$ and action potentials are generated in response to injected currents up to a stimulus frequency of 20 Hz. A detailed description of the pharmacological and ion selectivity properties of receptor-mediated ionic currents in cardiac neurons is presented. Whole-cell responses of cardiac neurons to the agonists, acetylcholine (ACh) and adenosine triphosphate (ATP) are similar in that both evoke excitatory responses of similar magnitude and time course but are pharmacologically distinct. The pharmacological profile of the purinergic (ATP) receptor-channel obtained from the relative potencies for activation was ATP = 2-methylthioATP $\u3e$ \beta\sb{\gamma}methyleneATP $\u3e$ \beta\sb{\gamma}methylene ATP and inhibition by the receptor antagonist, reactive blue 2, indicate that ATP-induced currents are mediated by the activation of P\sb{\rm 2y} receptors. Single ATP-evoked channels studied in cell-attached and excised membrane patches had a conductance of 80 and 50 pS, respectively. ACh-induced currents were inhibited by ganglionic nicotinic receptor antagonists but not by atropine suggesting that they are mediated by nicotinic receptor activation. ACh-induced channel currents were obtained in excised membrane patches and had conductances of 25 and 66 pS. Ion substitution experiments demonstrated the cation selectivity of nicotinic and purinergic receptor operated channels, and in particular, that both agonist-activated channels have a high permeability to Ca\sp{2+}

Life history and aging of captive-reared California sea hares (Aplysia californica)

Although the California sea hare, Aplysia californica, is well known from neurobiological studies and is raised in the laboratory for this purpose, various aspects of its life history in the laboratory, such as aging dynamics, are unknown. Therefore we collected life history data on 4 cohorts of eggs from hatchery-reared animals and performed an actuarial analysis of mortality data. Temperature was controlled at 13 to 15 degrees C, the photoperiod was a 14:10-h light:dark cycle, and the seawater O2 concentration, pH, and salinity were held at optimized levels. The feeding protocol for 3 cohorts was unrestricted access to the red macroalga Gracilaria ferox, whereas the remaining cohort was fed standard hatchery rations of G. ferox 4 times per week. Growth was sigmoidal in each cohort and resulted in linear growth rates of 1.25 to 3.62 g/d during the exponential phase; these rates were not influenced by feeding level. Sexual maturity occurred at approximately 160 g, at ages ranging from 144 to 241 d. Egg production was highly variable in the different cohorts. Mean lifespan of cohorts fed ad libitum was approximately 228 d. In contrast, the cohort fed standard rations lived an average of 375 d and showed a lower initial mortality rate, suggesting that calorie restriction on a single-species diet prolongs lifespan in California sea hares

Aging in Sensory and Motor Neurons Results in Learning Failure in Aplysia californica

The physiological and molecular mechanisms of age-related memory loss are complicated by the complexity of vertebrate nervous systems. This study takes advantage of a simple neural model to investigate nervous system aging, focusing on changes in learning and memory in the form of behavioral sensitization in vivo and synaptic facilitation in vitro. The effect of aging on the tail withdrawal reflex (TWR) was studied in Aplysia californica at maturity and late in the annual lifecycle. We found that short-term sensitization in TWR was absent in aged Aplysia. This implied that the neuronal machinery governing nonassociative learning was compromised during aging. Synaptic plasticity in the form of short-term facilitation between tail sensory and motor neurons decreased during aging whether the sensitizing stimulus was tail shock or the heterosynaptic modulator serotonin (5-HT). Together, these results suggest that the cellular mechanisms governing behavioral sensitization are compromised during aging, thereby nearly eliminating sensitization in aged Aplysia