Single-axon action potentials in the rat hippocampal cortex

Whether all action potentials propagate faithfully throughout axon arbors in the mammalian CNS has long been debated, and remains an important issue because many synapses occur far from the soma along extremely thin, unmyelinated, varicosity-laden branches of axon arbors. We detected unitary action potentials along individual axon branches of adult hippocampal CA3 pyramidal cells using extracellular electrodes, and analysed their conduction across long distances (mean, 2.1 mm) at 22 and 37 °C. Axons nearly always transmitted low-frequency impulses. At higher frequencies, most axons also transmitted impulses with striking fidelity. However, at paired-pulse frequencies in the hundreds of kilohertz range, axons exhibited variability: refractory periods ranged from 2.5 to 10 ms at 37 °C and from 5 to 40 ms at 22 °C. Although the basis for the refractory period variability could not be determined, these limits overlap with CA3 spike frequencies observed in vivo , raising the possibility that some axonal branches act as filters for the higher-order spikes in bursts, in contrast to the observed first-spike reliability. These results extend the observations of propagation reliability to a much longer distance and higher frequency domain than previously reported, and suggest a high safety factor for action potential propagation along thin, varicose axons.     

Conditioned effects of kindling three different sites in the hippocampal complex of the rat

Rats received kindling stimulations to the perirhinal cortex (PRh), ventral hippocampus (VH), or dorsal hippocampus (DH) in 1 environment and an equivalent number of sham stimulations in a 2nd environment. The PRh-kindled rats displayed rapid kindling and a swift emergence of conditioned interictal defensiveness. In contrast, the VH- and DH-kindled rats displayed much slower kindling and slow or no conditioning, respectively. No effects of conditioning on the convulsions, comparable with those associated with amygdala kindling, were observed. These results establish the generality of some of the previously reported kindling-related conditioned effects, confirm the site specificity of some of these effects, and suggest that the convulsions, rather than the stimulations, function as the unconditioned stimuli for the conditioning of interictal behavior.     

Isoflurane hyperpolarizes neurones in rat and human cerebral cortex

The effect of the anaesthetic gas isoflurane was studied by intracellular recordings in neurones from rat hippocampal cortex and neurones from human neocortex in vitro. Anaesthetic concentrations of isoflurane abolished spontaneous activity and reduced synaptically evoked activity without rendering individual cells inexcitable or preventing evoked synaptic activity to increased afferent input. Induced epileptiform activity was not observed. Isoflurane reversibly hyperpolarized the cell membrane in a dose-dependent manner, isoflurane 1.5, 3 and 5% causing 4 +/- 1, 6 +/- 2 and 8 +/- 2 mV (mean +/- SD) hyperpolarization, respectively. The hyperpolarization was accompanied by a reduction in the input resistance, 18 +/- 3% for 3% isoflurane. The effects remained unchanged after synaptic transmission was blocked. Five experiments with intracellular recordings from human cortical neurones in vitro showed identical results.     

Arginine-vasopressin binding sites in rat brain: a quantitative autoradiographic study

Specific binding sites for arginine-vasopressin (AVP) were detected in rat brain after incubation of tissue sections with [3H]AVP. AVP and two selective AVP antagonists are capable of displacing [3H]AVP with an IC50 in the 10(-8)-10(-7) molar range, while oxytocin and ACTH4-10 were much less effective. The neuroanatomical distribution of [3H]AVP-labeled sites was studied with autoradiography utilizing tritium-sensitive LKB film and computerized densitometry for quantitative analyses of the film images. The highest density of [3H]AVP binding sites was observed in hippocampal regions, the lateral septum, olfactory and amygdaloid nuclei, and the nucleus tractus solitarii (NTS) of the brainstem.     

异氟醚通过海马内源性大麻素调节条件恐惧大鼠恐惧记忆

目的:探讨异氟醚早期干预对条件恐惧大鼠恐惧记忆及海马内源性大麻素水平的影响。方法:以巴甫洛夫条件恐惧反射理论为基础,建立大鼠条件恐惧模型,模拟大鼠创伤后应激障碍(posttraumatic stress disorder,PTSD)恐惧记忆,高效液相色谱质谱分析和RT-PCR方法检测模型大鼠海马内源性大麻素2-AG(2-arachidonoylglycerol)、AEA(N-arachidonoylethanolamine)含量,行为学方法分析大鼠僵立时间,行为检测前给予异氟醚干预对海马内源性大麻素水平及大鼠僵立时间的影响,然后海马或者腹腔给予内源性大麻素受体1拮抗剂AM281,再次记录大鼠行为学表现。结果:条件恐惧模型大鼠的僵立时间与正常大鼠相比明显增加(P0.05)AEA水解酶FAAH(fatty acid amide hydrolase,FAAH)和2-AG合成酶DAGL(diacylglycerol lipase,DAGL)mRNA水平与正常大鼠比较无差别(P0.05),而2-AG水解酶MAGL(monoacylglycerol lipase,MAGL)mRNA水平明显升高(P0.05);异氟醚干预提高了模型大鼠海马2-AG水平(P0.05),减少了应激大鼠的僵立时间(P0.05)。海马内或者腹腔给予AM281均可抑制异氟醚对应激大鼠僵立时间的影响。结论:异氟醚通过海马内源性大麻素2-AG干预创伤后应激障碍模型大鼠的恐惧记忆的形成。     

Changes in evoked potentials and amino acid content during fluorocitrate action studied in rat hippocampal cortex

Summary Fluorocitrate inhibits the glial tricarboxylic acid cycle and thereby the synthesis of glutamine, which is the main precursor for transmitter glutamate. We investigated the possibility that there is a functional correlate to fluorocitrate action by recording evoked field potentials in rat hippocampal slices. The excitatory postsynaptic potential (field-EPSP) was markedly depressed after 7–8 h of fluorocitrate action. The population spike was also reduced, but a major part of the reduction may be the result of weaker synaptic activation rather than reduced excitability of the postsynaptic cells. The activity of thin unmyelinated fibres was only slightly affected. Preceding the changes in the field-EPSP there was a decrease in the glutamine content in the fluorocitrate treated slices relative to controls. Only a small decrease in tissue glutamate was seen concomitantly with the synaptic failure, probably because the transmitter pool of glutamate in those fibres stimulated makes little contribution to the total tissue glutamate.     

Methicillin-resistant Staphylococcus aureus colonization at different body sites: a prospective, quantitative analysis

We quantified methicillin-resistant Staphylococcus aureus (MRSA) carriage. The greater the log(10) count in samples from the nares, the greater the likelihood that other body sites had been colonized. Log(10) counts among body sites were correlated. The greatest sensitivity value (98%) was determined for the combined results from 2 sites: the nares and the groin.     

Episodic long-term memory in the rat: effects of hippocampal stimulation

Rats with electrodes implanted in dorsal hippocampus were trained to perform a delayed spatial matching-to-sample task on a radial arm maze. Subseizure level electrical stimulation of the dorsal hippocampus applied during the study phase disrupted retention of a specific arm when tested at a 20-min delay but had no effects at 1- and 12-min delays. There were no state-dependent or proactive effects of stimulation. Subseizure level stimulation of the hippocampus immediately after the study phase resulted in normal retention. In contrast, seizure level stimulation of the hippocampus applied either during or immediately after the study phase disrupted retention at all three (1, 12, 20 min) retention delays. The data support the interpretation that the hippocampus is involved in the encoding of critical information (spatiotemporal attributes) in long-term working memory, but not short-term memory.     

The gamma-aminobutyric acid-mimetic action of omega-aminocaprylic acid in rat cortex

The 8-carbon chain analogue of gamma-aminobutyric acid (GABA), omega-aminocaprylic acid (omega-AC), was administered to single cortical neurones of rat by microiontophoresis and its effect on cell firing compared to the effect elicited by GABA. The spontaneous and glutamate-elicited firing rates of all cells examined were decreased by omega-AC, the molecule having an apparent potency approximately one-fifth that of GABA. Inhibitions induced by omega-AC were antagonized by bicuculline and enhanced by flurazepam. These data favour the view that extending chain length per se of the GABA molecule decreases the inhibitory potency of postsynaptic GABA receptor agonists. The results do not support the view that such structural changes alter the mode of action of GABA analogues, from inhibition to excitation, as has been suggested previously.     

Ontogeny of neurotensin receptor binding sites in the rat visual cortex

The ontogeny of neurotensin receptor binding sites in the rat visual cortex was examined by in situ receptor autoradiography. Binding sites were present in the embryonic cortex and showed extremely high densities at birth and in early postnatal life. Their densities began a gradual decline in the second postnatal week to reach very low levels in adult animals. These results suggest that neurotensin receptor binding sites may play a role in cortical development.     

Distribution and kinetics of GABAB binding sites in rat central nervous system: a quantitative autoradiographic study

[3H]GABA quantitative autoradiography was used to examine the binding kinetics and regional distribution of GABAB receptors in rat brain. The regional distribution was compared to that of GABAA receptors. At 4 degrees C, [3H]GABA binding to GABAB receptors reached equilibrium within 45 min. The association and dissociation rate constants for GABAB binding to outer neocortical layers were 2.87 +/- 0.17 X 10(5) min-1 M-1 and 0.0966 +/- 0.0118 min-1, respectively, indicating a dissociation constant of 336 +/- 40 nM. Saturation binding studies in the same region yielded a dissociation constant for GABAB receptors of 341 +/- 41 nM while that of GABAA receptors was 92 +/- 10 nM. While the affinities of each type of GABA receptor were uniform across brain regions, the maximal number of binding sites for both types of GABA receptor varied across regions. The distributions of the two receptors in rat brain were different in the olfactory bulb, cerebellum, thalamus, neocortex, medial habenula and interpeduncular nucleus. Areas high in GABAB binding included the medial and lateral geniculates, the superior colliculus and certain amygdaloid nuclei. Binding to white matter tracts and ventricles was negligible. The distribution of GABAB receptors was in agreement with previously postulated sites of action of baclofen.     

Morphological alterations of hippocampal pyramidal neurons heterotopically transplanted into the somatosensory cortex of adult rats: a quantitative Golgi study

A characteristic feature of hippocampal organization is the laminated termination of extrinsic and intrinsic afferents. At present, it is not known to what extent these layer-specific fiber projections modulate the development and final shape of the dendritic arbor of hippocampal target neurons. In the present study, pieces of late embryonic (E18) rat hippocampus were transplanted heterotopically into a cavity in the somatosensory cortex of 6–8 week-old recipient rats. Here, the transplanted neurons differentiated and survived up to several months in the absence of their specific extrinsic afferents. Moreover, tracing of transplant connections with the carbocyanine dye DiI revealed only a limited projection between the transplant and the host neocortex. Golgi-impregnated transplants were used to analyze the postsynaptic structures (dendrites and spines) of hippocampal pyramidal cells quantitatively. Compared with controls, the transplanted pyramidal neurons showed a significant reduction of apical primary dendrites and basal dendritic branches, i.e. of peripheral dendritic portions that originate farther from the soma. In contrast, the number of basal primary dendrites originating directly from the perikaryon was enhanced. Spine density on the main apical dendritic shaft was significantly lower in all peripheral dendritic segments in transplanted neurons. We conclude from our results that the absence of layerspecific extrinsic afferents that normally terminate on peripheral parts of the dendritic arbor of hippocampal pyramidal neurons caused a reduction of these peripheral dendrites and spines. In contrast, the increase of dendrites and spines near the cell body might be induced by intrinsic fibers that normally terminate on these proximal dendritic portions and are known to sprout under transplant conditions.     

Calcium discriminates two [3H]kainate binding sites with different molecular target sizes in rat cortex

Binding of [3H]kainate to the kainate subtype of excitatory amino acid receptors revealed two binding sites. The high-affinity site (Kd = 3.5 nM) was sensitive to calcium ions and has a molecular target size as determined by high-energy radiation inactivation analysis of 76,600 daltons. The low-affinity site (Kd = 65 nM) was insensitive to calcium ions and has a molecular target size similar to the quisqualate-subtype of excitatory amino acid receptors. The change in binding parameters of the two sites with radiation dose strongly suggests that low affinity, calcium-insensitive [3H]kainate binding sites are equivalent to quisqualate sites.     

Excitatory amino acid binding sites in the basal ganglia of the rat: a quantitative autoradiographic study.

Quantitative receptor autoradiography was used to determine the distribution of excitatory amino acid binding sites in the basal ganglia of rat brain. alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid, N-methyl-D-aspartate, kainate, quisqualate-sensitive metabotropic and non-N-methyl-D-aspartate, non-kainate, non-quisqualate glutamate binding sites had their highest density in striatum, nucleus accumbens, and olfactory tubercle. Kainate binding was higher in the lateral striatum but there was no medial-lateral striatal gradient for other binding sites. N-Methyl-D-aspartate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding sites were most dense in the nucleus accumbens and olfactory tubercle. There was no dorsal-ventral gradient within the striatal complex for the other binding sites. Other regions of the basal ganglia had lower densities of ligand binding. To compare binding site density within non-striatal regions, binding for each ligand was normalized to the striatal binding density. When compared to the striatal complex, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and metabotropic binding sites had higher relative density in the globus pallidus, ventral pallidum, and subthalamic nucleus than other binding sites. Metabotropic binding also had a high relative density in the substantia nigra. Non-N-methyl-D-aspartate, non-kainate, non-quisqualate glutamate binding sites had a high relative density in globus pallidus, ventral pallidum, and substantia nigra. N-Methyl-D-aspartate binding sites had a low relative density in pallidum, subthalamic nucleus, substantia nigra and ventral tegmental area. Our data indicate heterogeneous distribution of excitatory amino acid binding sites within rat basal ganglia and suggest that the character of excitatory amino acid-mediated neurotransmission within the basal ganglia is also heterogeneous.     

Isoflurane and ketamine anesthesia have different effects on ventilatory pattern variability in rats

We hypothesize that isoflurane and ketamine impact ventilatory pattern variability (VPV) differently. Adult Sprague-Dawley rats were recorded in a whole-body plethysmograph before, during and after deep anesthesia. VPV was quantified from 60-s epochs using a complementary set of analytic techniques that included constructing surrogate data sets that preserved the linear structure but disrupted nonlinear deterministic properties of the original data. Even though isoflurane decreased and ketamine increased respiratory rate, VPV as quantified by the coefficient of variation decreased for both anesthetics. Further, mutual information increased and sample entropy decreased and the nonlinear complexity index (NLCI) increased during anesthesia despite qualitative differences in the shape and period of the waveform. Surprisingly mutual information and sample entropy did not change in the surrogate sets constructed from isoflurane data, but in those constructed from ketamine data, mutual information increased and sample entropy decreased significantly in the surrogate segments constructed from anesthetized relative to unanesthetized epochs. These data suggest that separate mechanisms modulate linear and nonlinear variability of breathing.     

The cholinergic innervation develops early and rapidly in the rat cerebral cortex: a quantitative immunocytochemical study.

A recently developed method for determining the length of cholinergic axons and number of cholinergic axon varicosities (terminals) in brain sections immunostained for choline acetyltransferase was used to estimate the areal and laminar densities of the cholinergic innervation in rat frontal (motor), parietal (somatosensory) and occipital (visual) cortex at different postnatal ages. This cortical innervation showed an early beginning, a few immunostained fibers being already present in the cortical subplate at birth. In the first two postnatal weeks, it developed rapidly along three parameters: a progressive increase in the number of varicosities per unit length of axon, and a lengthening and branching of the axons. Between postnatal days 4 and 16, the number of varicosities increased steadily from two to four per 10 microm of cholinergic axon. The mean densities of cholinergic axons increased from 1.4 to 9.6, 1.7 to 9.3 and 0.7 to 7.2 m/mm(3), and the corresponding densities of varicosities from 0.4 to 3.9, 0.4 to 3.5, and 0.2 to 2.6x10(6)/mm(3) in the frontal, parietal and occipital areas, respectively. The rate of growth was maximal during these first two weeks, after which the laminar pattern characteristic of each area appeared to be established. Adult values were almost reached by postnatal day 16 in the parietal cortex, but maturation proceeded further in the frontal and particularly in the occipital cortex.These quantitative data on the ingrowth and maturation of the cholinergic innervation in postnatal rat cerebral cortex substantiate a role for acetylcholine in the development of this brain region and emphasize the striking growth capacity of individual cholinergic neurons.     

Working memory impairment and reduced hippocampal and prefrontal cortex c-Fos expression in a rat model of cirrhosis

Hepatic encephalopathy (HE) is a frequent neurological complication observed in patients with liver malfunction. Previous studies have shown memory impairment in these patients. In order to investigate brain substrates of spatial working memory impairment in chronic HE, neuronal expression of c-Fos protein was studied in an experimental model of cirrhosis. Control and cirrhotic rats were trained on a spatial working memory task in the Morris water maze (MWM). Differences between groups were found in the working memory task. Cirrhotic rats were unable to locate the platform in the retention trial. Neuronal activation, measured by c-Fos protein, was compared between groups. No differences were found in c-Fos expression of control and cirrhotic rats that were not tested in the MWM. Working memory task produced increase in c-Fos positive cells in dorsal hippocampus, CA1 and CA3, and prefrontal cortex in control group compared to thioacetamide group or naïve, which only swam in the maze during a similar time. These findings suggest that cirrhotic rats show spatial working memory impairment that could be linked to dysfunction in neuronal activity in prefrontal cortex and hippocampus.     

Somatically recorded Ca-currents in guinea-pig hippocampal and olfactory cortex neurones are resistant to adenosine action

Inward membrane currents were recorded in tetrodotoxin-treated neurones of hippocampus and olfactory cortex in vitro after impalement with CsCl-containing microelectrodes to suppress potassium conductances. They were blocked by the Ca²⁺-channel blocker Cd²⁺ but were unaffected by adenosine alone (up to 1 mM), adenosine (20 μM) in the presence of the uptake blocker dipyridamole (1 μM) or the stable analogue cyclohexyladenosine (100 μM). This ineffectiveness of adenosine on Ca-currents was in contrast to its known potent suppression of synaptic transmission in these preparations, and its inhibition of Ca-dependent action potentials.