Evaluation of the anticonvulsant and neuroprotective effect of intracerebral administration of growth hormone in rats.

INTRODUCTION: The growth hormone (GH) has been reported as a crucial neuronal survival factor in the hippocampus against insults of diverse nature. Status epilepticus (SE) is a prolonged seizure that produces extensive neuronal cell death. The goal of this study was to evaluate the effect of intracerebroventricular administration of GH on seizure severity and SE-induced hippocampal neurodegeneration. METHODOLOGY: Adult male rats were implanted with a guide cannula in the left ventricle and different amounts of GH (70, 120 or 220ng/3µl) were microinjected for 5 days; artificial cerebrospinal fluid was used as the vehicle. Seizures were induced by the lithium-pilocarpine model (3mEq/kg LiCl and 30mg/kg pilocarpine hydrochloride) one day after the last GH administration. Neuronal injury was assessed by Fluoro-Jade B (F-JB) staining. RESULTS: Rats injected with 120ng of GH did not had SE after 30mg/kg pilocarpine, they required a higher number of pilocarpine injections to develop SE than the rats pretreated with the vehicle, 70ng or 220ng GH. Prefrontal and parietal cortex EEG recordings confirmed that latency to generalized seizures and SE was also significantly higher in the 120ng group when compared with all the experimental groups. FJ-B positive cells were detected in the hippocampus after SE in all rats, and no significant differences in the number of F-JB cells in the CA1 area and the hilus was observed between experimental groups. CONCLUSION: Our results indicate that, although GH has an anticonvulsive effect in the lithium-pilocarpine model of SE, it does not exert hippocampal neuroprotection after SE.

Evaluation of the anticonvulsant and neuroprotective effect of intracerebral administration of growth hormone in rats.

INTRODUCTION: The growth hormone (GH) has been reported as a crucial neuronal survival factor in the hippocampus against insults of diverse nature. Status epilepticus (SE) is a prolonged seizure that produces extensive neuronal cell death. The goal of this study was to evaluate the effect of intracerebroventricular administration of GH on seizure severity and SE-induced hippocampal neurodegeneration. METHODOLOGY: Adult male rats were implanted with a guide cannula in the left ventricle and different amounts of GH (70, 120 or 220ng/3µl) were microinjected for 5 days; artificial cerebrospinal fluid was used as the vehicle. Seizures were induced by the lithium-pilocarpine model (3mEq/kg LiCl and 30mg/kg pilocarpine hydrochloride) one day after the last GH administration. Neuronal injury was assessed by Fluoro-Jade B (F-JB) staining. RESULTS: Rats injected with 120ng of GH did not had SE after 30mg/kg pilocarpine, they required a higher number of pilocarpine injections to develop SE than the rats pretreated with the vehicle, 70ng or 220ng GH. Prefrontal and parietal cortex EEG recordings confirmed that latency to generalized seizures and SE was also significantly higher in the 120ng group when compared with all the experimental groups. FJ-B positive cells were detected in the hippocampus after SE in all rats, and no significant differences in the number of F-JB cells in the CA1 area and the hilus was observed between experimental groups. CONCLUSION: Our results indicate that, although GH has an anticonvulsive effect in the lithium-pilocarpine model of SE, it does not exert hippocampal neuroprotection after SE.

Pre-Bötzinger complex: Generation and modulation of respiratory rhythm. / El complejo pre-Bötzinger: generación y modulación del ritmo respiratorio.

INTRODUCTION: In mammals, the preBötzinger complex (preBötC) is a bilateral and symmetrical neural network located in the brainstem which is essential for the generation and modulation of respiratory rhythm. There are few human studies about the preBötC and, its relationship with neurological diseases has not been described. However, the importance of the preBötC in neural control of breathing and its potential participation in neurological diseases in humans, has been suggested based on pharmacological manipulation and lesion of the preBötC in animal models, both in vivo and in vitro. METHOD: In this review, we describe the effects of some drugs on the inspiratory activity in vitro in a transverse slice that contains the preBötC, as well as some in vivo experiments. Drugs were classified according to their effects on the main neurotransmitter systems and their importance as stimulators or inhibitors of preBötC activity and therefore for the generation of the respiratory rhythm. CONCLUSION: Clinical neurologists will find this information relevant to understanding how the central nervous system generates the respiratory rhythm and may also relate this information to the findings made in daily practice.

Inhibition of endoplasmic reticulum Ca²âº ATPase in preBötzinger complex of neonatal rat does not affect respiratory rhythm generation.

PreBötzinger complex (preBötC) neurons in the brainstem underlie respiratory rhythm generation in vitro. As a result of network interactions, preBötC neurons burst synchronously to produce rhythmic premotor inspiratory activity. Each inspiratory neuron has a characteristic 10-20 mV, 0.3-0.8 s synchronous depolarization known as the inspiratory drive potential or inspiratory envelope, topped by action potentials (APs). Mechanisms involving Ca(2+) fluxes have been proposed to underlie the initiation of the inspiratory drive potential. An important source of intracellular Ca(2+) is the endoplasmic reticulum (ER) in which active Ca(2+) sequestration is mediated by a class of transporters termed sarco/endoplasmic reticulum Ca(2+) ATPases (SERCAs). We aim to test the hypothesis that disruption of Ca(2+) sequestration into the ER affects respiratory rhythm generation. We examined the effect of inhibiting SERCA on respiratory rhythm generation in an in vitro slice preparation. Bath application of the potent SERCA inhibitors thapsigargin or cyclopiazonic acid (CPA) for up to 90 min did not significantly affect the period or amplitude of respiratory-related motor output or integral and duration of inspiratory drive in preBötC neurons. We promoted the depletion of intracellular Ca(2+) stores by a transient bath application of 30 mM K(+) (high K(+)) in the continuous presence of thapsigargin or CPA. After washing out the high K(+), respiratory rhythm period and amplitude returned to baseline values. These results show that after inhibition of SERCA and depletion of intracellular Ca(2+) stores, respiratory rhythm remains substantially the same, suggesting that this source of Ca(2+) does not significantly contribute to rhythm generation in the preBötC in vitro.

Oxidative stress and the deleterious consequences to the rat cochlea after prenatal chronic mild exposure to carbon monoxide in air.

Pregnant rats (starting on E5) were exposed chronically to carbon monoxide (CO) from gestational days 5-20. In the postnatal period, rat pups were grouped as follows: group A: prenatal exposure to CO only; group B: prenatal exposure to CO then exposed to CO from postnatal day (P) 5 to P20; group C, control (air without CO). Groups A and B showed similar deleterious effects after CO exposure. At P3, rat pup cochlea from group A showed a normal organization of the organ of Corti. There was no morphological deterioration, or loss of inner or outer hair cells. At P20, animals from group A and B showed vacuolization on the afferent terminals at the basal portion of the cochlea. We found synapsin-1 immunoreactivity (IR) to be decreased in efferent nerve terminals in CO-exposed pups at P3. From P12 to P20, synapsin-1-IR is low in efferent terminals. At P20, type I spiral ganglia neurons and afferent nerve fibers showed decreased neurofilament-IR in CO-exposed groups when compared with controls. Heme oxygenase-1 and superoxide dismutase-1-IR were elevated in the stria vascularis and blood vessels from CO-exposed rat pups at P12 and P20 in group B; in contrast group A showed a comparable expression to controls. Inducible nitric oxide synthase (iNOS) and nitrotyrosine-IR were increased in blood vessels of the cochlea in CO-exposed groups, from P3 to P20. iNOS up-regulation and the presence of nitrotyrosine in blood vessels of the cochlea indicated that CO exposure activates the production of nitric oxide via increased iNOS activity. Prenatal chronic CO exposure promotes oxidative stress in the cochlea blood vessels that in turn is reflected in damage to spiral ganglia neurons and inner hair cells, suggesting for the first time that prenatal exposure to CO at concentrations expected in poorly ventilated environments impairs the development of the inner ear.

GABA inhibition of immortalized gonadotropin-releasing hormone neuronal excitability involves GABA(A) receptors negatively coupled to cyclic adenosine monophosphate formation.

Gamma-aminobutyric acid (GABA) has been implicated in the regulation of reproduction, particularly in the developmental modulation of gonadotropin-releasing hormone (GnRH) secretion. GnRH neurons are innervated by GABA-containing processes, and the administration of GABA stimulates and inhibits GnRH secretion in vivo and in vitro. We have previously shown that GABA can exert both of these actions in sequence, by acting directly on immortalized GnRH neurons. While the stimulation is the result of a GABA(A) receptor-mediated depolarization of the plasma membrane, the mechanism involved in the delayed inhibition is the subject of the present investigation. GABA (1 nM-10 microM) decreased the intracellular concentration of cyclic adenosine monophosphate (cAMP) in a dose- and time-dependent fashion. This effect was blocked by bicuculline and mimicked by muscimol but not by baclofen. To analyze the effect of GABA on cellular excitability, we used fura-2 loaded GT1-7 cells. Activation of voltage-sensitive calcium channels by high K+-induced depolarization (35 mM) increased [Ca2+]i. GABA (10 microM) and muscimol (10 microM) reduced the amplitude of K+-induced [Ca2+]i transients. This inhibition was blocked by forskolin (20 microM) or 8-Br-cAMP (1 mM). Altogether, these results show that GABA(A) receptors mediate a sustained inhibitory effect of GABA on GnRH neurons, and suggest the involvement of the cAMP pathway decreasing cellular excitability.

Manipulations during forced wakefulness have differential impact on sleep architecture, EEG power spectrum, and Fos induction.

We propose a hypothesis suggesting that the most prominent experiences occurring during wakefulness activate specific clusters of neurons related to such experiences. These neurons could possibly then evoke the release of various types of sleep-inducing molecules, thereby causing different patterns of sleep architecture. In this study, we therefore sought to determine whether manipulations of behavior during wakefulness, such as forced wakefulness induced by gentle handling, forced wakefulness associated with a stressful condition such as immobilization, or forced wakefulness associated with excess intake of palatable food, could result in a variation of Fos immunoreactivity in selective brain structures and could also result in different sleep and EEG power density patterns. The results showed that the sleep-wake cycle of rats after all the experimental manipulations was different not only with respect to the control group but also among themselves. Additionally, power spectrum analysis showed an increase of 0.25-4.0 Hz in all experimental manipulations, whereas the 4.25-8.0 Hz increase occurred only in the situation of forced wakefulness plus stress. The Fos induction showed activation of cell clusters in cortical areas and telencephalic centers, in several hypothalamic nuclei, in monoaminergic cell groups, and in brain stem nuclei. The density of Fos-immunoreactive neurons varied in relation to the different paradigms of forced wakefulness. These results suggest that activation of cell clusters in the brain are related to the type of manipulation imposed on the rat during wakefulness and that such variation in cell activation prior to sleep may be associated with sleep architecture and EEG power.

Delay in manifestations of aging by grafting NGF cultured chromaffin cells in adulthood.

Dopamine agonists or grafts compensate impaired motor functions in aged rats. However, there is no evidence showing whether grafting in adulthood retard aging manifestations. Motor performance of 13-month-old rats was tested on 2 meter-long wooden beams which had a 15 degree inclination and whose thickness varied from 3, 6, 12, 18, to 24 mm. Rats at 14 months were randomly assigned to 3 groups: sham graft (Group 1); intrastriatal graft of chromaffin cells cultured with NGF (Group 2); intrastriatal graft of chromaffin cells (Group 3). Motor performance was tested at monthly intervals up until rats were 26 months old. Two more groups were included: 26-month-old naive rats (Group 4); and 3- to 5-month-old naive rats (Group 5) both evaluated only once. At 26 months, the basal activity of ventral mesencephalic dopaminergic neurons was recorded. Results showed in Group 2 delay of motor detriments seen in aged rats, maintenance of basal firing rates of nigral cells compared to those of younger rats, and greater survival of substantia nigra cells. It is suggested that NGF cultured chromaffin cells produce a delay of motor detriments in aged rats, as a result of inducing survival and firing rates of nigral cells comparable to those seen in young rats.