Respiratory activity during seizures induced by pentylenetetrazole

This study investigated the respiratory activity in adult Wistar rats across different behavioral seizure severity induced by pentylenetetrazole (PTZ). Animals underwent surgery for electrodes implantation, allowing simultaneous EEG and diaphragm EMG (DIAEMG) recordings and the respiratory frequency and DIAEMG amplitude were measured. Seizures were acutely induced through PTZ injection and classified based on a pre-established score, with absence-like seizures (spike wave discharge (SWD) events on EEG) representing the lowest score. The respiratory activity was grouped into the different seizure severities. During absence-like and myoclonic jerk seizures, the breathing frequency decreased significantly (∼50% decrease) compared to pre- and post-ictal periods. Pronounced changes occurred with more severe seizures (clonic and tonic) with periods of apnea, especially during tonic seizures. Apnea duration was significantly higher in tonic compared to clonic seizures. Notably, during PTZ-induced tonic seizures the apnea events were marked by tonic DIAEMG contraction (tonic-phase apnea). In the majority of animals (5 out of 7) this was a fatal event in which the seizure-induced respiratory arrest preceded the asystole. In conclusion, we provide an assessment of the respiratory activity in the PTZ-induced acute seizures and showed that breathing dysfunction is more pronounced in seizures with higher severity.

Parasitological assessment of wild ring-tailed coatis (Nasua nasua) from the Brazilian Atlantic rainforest

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Anisomycin administered in the olfactory bulb and dorsal hippocampus impaired social recognition memory consolidation in different time-points

To identify an individual as familiar, rodents form a specific type of memory named social recognition memory. The olfactory bulb (OB) is an important structure for social recognition memory, while the hippocampus recruitment is still controversial. The present study was designed to elucidate the OB and the dorsal hippocampus contribution to the consolidation of social memory. For that purpose, we tested the effect of anisomycin (ANI), which one of the effects is the inhibition of protein synthesis, on the consolidation of social recognition memory. Swiss adult mice with cannulae implanted into the CA1 region of the dorsal hippocampus or into the OB were exposed to a juvenile during 5 min (training session; TR), and once again 1.5 h or 24 h later to test social short-term memory (S-STM) or social long-term memory (S-LTM), respectively. To study S-LTM consolidation, mice received intra-OB or intra-CA1 infusion of saline or ANI immediately, 3, 6 or 18 h after TR. ANI impaired S-LTM consolidation in the OB, when administered immediately or 6h after TR. In the dorsal hippocampus, ANI was amnesic only if administered 3 h after TR. Furthermore, the infusion of ANI in either OB or CA1, immediately after training, did not affect S-STM. Moreover, ANI administered into the OB did not alter the animal's performance in the buried food-finding task. Altogether, our results suggest the consolidation of S-LTM requires both OB and hippocampus participation, although in different time points. This study may help shedding light on the specific roles of the OB and dorsal hippocampus in social recognition memory.

Sleep pattern and learning in knockdown mice with reduced cholinergic neurotransmission

Impaired cholinergic neurotransmission can affect memory formation and influence sleep-wake cycles (SWC). In the present study, we describe the SWC in mice with a deficient vesicular acetylcholine transporter (VAChT) system, previously characterized as presenting reduced acetylcholine release and cognitive and behavioral dysfunctions. Continuous, chronic ECoG and EMG recordings were used to evaluate the SWC pattern during light and dark phases in VAChT knockdown heterozygous (VAChT-KDHET, n=7) and wild-type (WT, n=7) mice. SWC were evaluated for sleep efficiency, total amount and mean duration of slow-wave, intermediate and paradoxical sleep, as well as the number of awakenings from sleep. After recording SWC, contextual fear-conditioning tests were used as an acetylcholine-dependent learning paradigm. The results showed that sleep efficiency in VAChT-KDHET animals was similar to that of WT mice, but that the SWC was more fragmented. Fragmentation was characterized by an increase in the number of awakenings, mainly during intermediate sleep. VAChT-KDHET animals performed poorly in the contextual fear-conditioning paradigm (mean freezing time: 34.4±3.1 and 44.5±3.3 s for WT and VAChT-KDHET animals, respectively), which was followed by a 45% reduction in the number of paradoxical sleep episodes after the training session. Taken together, the results show that reduced cholinergic transmission led to sleep fragmentation and learning impairment. We discuss the results on the basis of cholinergic plasticity and its relevance to sleep homeostasis. We suggest that VAChT-KDHET mice could be a useful model to test cholinergic drugs used to treat sleep dysfunction in neurodegenerative disorders.

A Low Protein Diet Causes an Increase in the Basal Levels and Variability of Mean Arterial Pressure and Heart Rate in Fisher Rats

The correlation between nutrition and cardiovascular related disorders is a well-established fact. Previous work from our Laboratory has suggested a significant compromise of cardiovascular reflexes in conscious rats submitted to a low-protein (LP) diet. Our working hypothesis is that the basal level of mean arterial pressure (MAP), variability of the mean arterial pressure (VMAP), heart rate (HR) and variability of heart rate (VHR) are altered in rats submitted to a protein restricted diet. Two experimental groups were used: control group (normal protein 15%, NP) and malnourished group (low-protein 6%, LP). In order to verify the efficiency of the dietary restriction we measured body weight, total blood protein, plasma albumin, urea and glucose. Our experiments demonstrated that the malnourished rats presented augment levels of basal MAP (LP 122+/-2 mmHg vs. NP 113+/-1 mmHg) and of VMAP (LP 12.8+/-1.5mmHg vs. NP 9+/-1mmHg) when compared to the control group. We observed similar increased levels, in the malnourished group, for both HR (LP 429+/-8 bpm vs. NP 381+/-7bpm) and VHR (LP 67.6+/-8.3bpm vs. NP 44.4+/-4.9bpm). Our results suggest a correlation between the LP diet in Fisher rats and the increased basal levels of mean arterial pressure, HR and their respective variability.

Computerized invasive measurement of time-dependent intraocular pressure

Several methods have been described to measure intraocular pressure (IOP) in clinical and research situations. However, the measurement of time varying IOP with high accuracy, mainly in situations that alter corneal properties, has not been reported until now. The present report describes a computerized system capable of recording the transitory variability of IOP, which is sufficiently sensitive to reliably measure ocular pulse peak-to-peak values. We also describe its characteristics and discuss its applicability to research and clinical studies. The device consists of a pressure transducer, a signal conditioning unit and an analog-to-digital converter coupled to a video acquisition board. A modified Cairns trabeculectomy was performed in 9 Oryctolagus cuniculus rabbits to obtain changes in IOP decay parameters and to evaluate the utility and sensitivity of the recording system. The device was effective for the study of kinetic parameters of IOP, such as decay pattern and ocular pulse waves due to cardiac and respiratory cycle rhythm. In addition, there was a significant increase of IOP versus time curve derivative when pre- and post-trabeculectomy recordings were compared. The present procedure excludes corneal thickness and error related to individual operator ability. Clinical complications due to saline infusion and pressure overload were not observed during biomicroscopic evaluation. Among the disadvantages of the procedure are the requirement of anesthesia and the use in acute recordings rather than chronic protocols. Finally, the method described may provide a reliable alternative for the study of ocular pressure dynamic alterations in man and may facilitate the investigation of the pathogenesis of glaucoma.

An electrographic analysis of the synchronous discharge patterns of GEPR-9s generalized seizures

Previous results from our Laboratory have shown a synchronous discharge pattern (less than 1 ms apart) in monopolar recordings from electrodes placed in the cortex, inferior colliculus, and medulla of seizing GEPR-9s. However, the wave morphology of the ictal EEG is quite different for electrodes placed in different anatomical structures. These results lead us to hypothesize that wave morphology was indicative of neural circuitry involved in the GEPR9 seizure and that volume conduction was accounting for synchronous epileptiform EEG pattern. We decided to approach the problem by using a set of two experiments. Experiment 1: Perform a complete precollicular transection in GEPR-9s before inducing seizure in order to observe changes in EEG morphology after forebrain circuitry removal. Experiment 2: A novel methodological approach using a three-dimensional bipolar array enabled the reconstruction of a vector indicative of to which direction is voltage increasing. Such time-varying vector is indicative of the source direction of the high-amplitude epileptiform EEG signal. By placing such an array of electrodes, used to record the 3 bipolar EEGs, in the forebrain, midbrain, and hindbrain, we were able to use a simple intersection method to infer source localization. Our results suggest that the slow wave component of the GEPR9 epileptiform ictal EEG pattern is associated with a midbrain-forebrain circuit while the spike component is associated with a midbrain-hindbrain substrate. These results are supported by experiment 1 in which only the spike component of EEG remained after the precollicular transection.

Vasopressinergic hypothalamic neurons are recruited during the audiogenic seizure of WARs

The Wistar Audiogenic Rat (WAR) is a genetic model of reflex epilepsy with seizures induced by high-intensity sound stimulation (120 dB SPL). In spite of the known neural substrates involved in WAR seizure phenotype, neuroendocrine hypothalamic neurons were never investigated. In this work, AVP immunohistochemistry in the hypothalamus and radioimmunoassay (RIA) in plasma and in hypothalamic and hypophysial tissues were performed on both controls and WARs in order to evaluate the dynamics of AVP release due to seizure induction. Susceptible animals (WARs) displayed at least tonic-clonic convulsions followed by clonic spasms, while resistant Wistar rats (R) had no convulsive behavior. Animals were sacrificed at 3 instances: basal condition (without stimulus) and at 3 and 10 min after sound stimulation. For the immunohistochemistry AVP study, brains were harvested and processed by the avidin-biotin-peroxidase detection method. Optic densitometry was used for quantifying AVP labeling in supraoptic (SON) and paraventricular (PVN) hypothalamic nuclei. SON presented higher densitometry levels (%D--relative to background) for both WARs and R when compared to PVN. Nevertheless, both nuclei presented a marked decrease, referenced to basal levels, in %D for WARs at 3 min (approximately 35%) against a discrete change for R (approximately 90%). RIA results were significantly higher in the hypophysis of WARs when compared to R rats, at 3 min. Also, at 3 min, plasma AVP in WARs (89.32 +/- 24.81 pg/mL) were higher than in R (12.01 +/- 2.39 pg/mL). We conclude, based on the AVP releasing profiles, that vasopressinergic hypothalamic neurons are recruited during the audiogenic seizure of WARs.

Baroreflex function in conscious rats submitted to iron overload

Our hypothesis is that iron accumulated in tissue, rather than in serum, may compromise cardiovascular control. Male Fischer 344 rats weighing 180 to 220 g were divided into 2 groups. In the serum iron overload group (SIO, N = 12), 20 mg elemental iron was injected ip daily for 7 days. In the tissue iron overload group (TIO, N = 19), a smaller amount of elemental iron was injected (10 mg, daily) for 5 days followed by a resting period of 7 days. Reflex heart rate responses were elicited by iv injections of either phenylephrine (0.5 to 5.0 microg/kg) or sodium nitroprusside (1.0 to 10.0 microg/kg). Baroreflex curves were determined and fitted to sigmoidal equations and the baroreflex gain coefficient was evaluated. To evaluate the role of other than a direct effect of iron on tissue, acute treatment with the iron chelator deferoxamine (20 mg/kg, iv) was performed on the TIO group and the baroreflex was re-evaluated. At the end of the experiments, evaluation of iron levels in serum confirmed a pronounced overload for the SIO group (30-fold), in contrast to the TIO group (2-fold). Tissue levels of iron, however, were higher in the TIO group. The SIO protocol did not produce significant alterations in the baroreflex curve response, while the TIO protocol produced a nearly 2-fold increase in baroreflex gain (-4.34 +/- 0.74 and -7.93 +/- 1.08 bpm/mmHg, respectively). The TIO protocol animals treated with deferoxamine returned to sham levels of baroreflex gain (-3.7 +/- 0.3 sham vs -3.6 +/- 0.2 bpm/mmHg) 30 min after the injection. Our results indicate an effect of tissue iron overload on the enhancement of baroreflex sensitivity.

A comprehensive electrographic and behavioral analysis of generalized tonic-clonic seizures of GEPR-9s

This study records noise-free intracerebral EEG of the genetically epilepsy prone rat (GEPR-9), along with behavioral correlates, during a seizure on unanesthetized freely behaving unrestrained animals. The GEPR-9 exhibits acoustically triggered generalized tonic-clonic seizures, and often times the EEG, recorded with conventional techniques, has resulted in data with imbedded movement artifact. For noise-free video-EEG recordings, we used a previously developed system that consists of a head connector with a FET preamplifier and battery, signal conditioning device (5000x gain, 1 Hz-100 Hz filters), A/D converter and video/PC-PC/video computer boards for recording image data. Each animal was implanted with three monopolar/referential electrodes chosen among the following areas: cortex, inferior colliculus, reticular formation and caudal medulla. The video-EEG data were quite similar for all recorded animals: (1) basal desynchronized EEG before sound stimulus; (2) increase in EEG frequency after stimulus and before seizure onset; (3) high-amplitude polyspikes during massive myoclonic thrusts with or without a very fast running episode; (4) an electrodecremental response during tonic extension; (5) wave and spike complex during forelimb and hindlimb tonic rigidity and posttonic clonus; (6) low-amplitude EEG during postictal depression. Time sequenced spectral analysis also highlights the epileptiform EEG pattern during seizure with high reproducibility between animals. While testing seizure naive GEPR-9s, there was a clear evolution from modest epileptiform EEG activity on the first acoustic stimulation to progressively higher amplitude, duration and frequency epileptiform EEG activity throughout seizure repetition.

Assessment of the seizure susceptibility of Wistar Audiogenic rat to electroshock, pentyleneterazole and pilocarpine

This work evaluates the seizure susceptibility of nai;ve female Wistar Audiogenic rats (WARs), a genetic model of reflex epilepsy in which seizures are induced by high-intensity sound stimulation (120 dB SPL), to other pro-convulsive stimuli: transauricular electroshock (ES), pentylenetetrazole (PTZ) and pilocarpine (PILO). Normal Wistar rats from the main breeding stock of the Institute of Biological Sciences, UFMG were taken as controls. Electroshock seizures were induced through a pair of ear-clip electrodes (10 mA, at a frequency of 60 Hz, applied for 1 s). In order to test WAR susceptibility to chemically induced seizures, animals were treated either with PTZ (37.5 mg/kg i.p.) or PILO (200, 270 and 300 mg/kg i.p.). Seizure severity was evaluated by appropriate behavioral severity index scales (SI) specific to each epilepsy model and tested for statistical significance using the non-parametric Mann-Whitney Rank Sum test. Results show a significantly greater susceptibility of WARs for ES (SI(WAR)=3+/-3/3, SI(Wistar)=1+/-1/1; median+/-interquartile range 25%/75%, P<0.01) and PTZ (SI(WAR)=4+/-4/4, SI(Wistar)=1+/-1/4; median+/-interquartile range 25%/75%, P<0.02), as indicated by significantly higher SI scores and shorter latencies for seizure onset (T(WAR)=71+/-7 s, T(Wistar)=94+/-8 s; P<0.05 Student t-test, mean+/-S.E.M.). Although PILO also caused higher SI scores in WARs (WAR(200 mg)=1+/-1/1, Wistar(200 mg)=1+/-1/1; WAR(270 mg)=1.5+/-1/2, Wistar(270 mg)=1+/-1/1.25; WAR(300 mg)=9+/-1/9, Wistar(300 mg)=4+/-1.5/7.5; median+/-interquartile range 25%/75%), statistically significant differences were not observed. In conclusion, our results show that WARs have an inherited broader predisposition for seizures.