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PubMed1999

Electrical stimulation of the horizontal limb of the diagonal band of broca modulates population EPSPs in piriform cortex.

Electrical stimulation of the horizontal limb of the diagonal band of Broca (HDB) was coupled with recording of evoked potentials in the piriform cortex. Stimulation of the HDB caused an enhancement of the late, disynaptic component of the evoked potential elicited by stimulation of the lateral olfactory tract but caused a suppression of the synaptic potential elicited by stimulation of the posterior piriform cortex. The muscarinic antagonist scopolamine blocked both effects of HDB stimulation. The enhancement of disynaptic potentials could be due to cholinergic depolarization of pyramidal cells, whereas the suppression of potentials evoked by posterior piriform stimulation could be due to presynaptic inhibition of intrinsic fiber synaptic transmission by acetylcholine.

Animals↗
PubMed1997

Protein synthesis inhibitors delay transneuronal death in the piriform cortex of young adult rats.

It has been demonstrated that apoptotic cell death is an active process that is dependent on RNA and protein synthesis. The question remains as to whether neuronal death in adult, mammalian brains can also be demonstrated in vivo to be dependent on protein synthesis. To address this question we have analysed transneuronal death in the piriform (olfactory) cortex. Following unilateral olfactory bulb ablation in young adult rats, layer IIa of the piriform cortex undergoes rapid degeneration, that commences 12 h after ablation and that is almost complete at 48 h. In order to block protein synthesis, three to six subcutaneous injections of the short acting protein synthesis inhibitor anisomycin, were given at 2 h intervals beginning just before the ablation of the olfactory bulb. In other cases a single injection of the long acting protein synthesis inhibitor emetine were made intracerebrally just before or after olfactory bulb ablation. The number of dying cells was then counted in sections through the rostrocaudal extent of the piriform cortex. Both anisomycin and emetine injections markedly reduced the number of pyknotic cells in layer IIa of the piriform cortex after olfactory bulb ablation. The effect of anisomycin was dose-dependent, near lethal doses leading to an almost complete absence of cell death (six injections of 100 mg/kg). As the doses of anisomycin were reduced, more dying cells were observed. Emetine was only effective at near lethal doses (10 mg/kg) and showed a greater capacity to reduce the levels of cell death when injected into structures near the piriform cortex (e.g., accumbens nucleus) than when injected into more distant structures. To further confirm that the cell death observed was due to apoptosis, we analysed sections by tunel staining to demonstrate DNA fragmentation. We found that tunel-positive cells were also always pyknotic, one of the landmarks of apoptosis. The appearance of pyknotic cells labelled by the tunel method demonstrated that the dying cells in the piriform cortex did indeed undergo apoptosis.

Animals↗
PubMed1992

Benzodiazepines block long-term potentiation in slices of hippocampus and piriform cortex.

The effects of two benzodiazepines, diazepam and triazolam, on long-term potentiation were tested in slices of hippocampus and piriform cortex. The drugs had little influence on baseline synaptic responses but both were very effective in blocking LTP elicited by theta pattern stimulation. The effects were fully reversible upon washout. Diazepam reduced the increase in burst responses that occurs during theta stimulation and thus appears to interfere with the initial triggering events for long-term potentiation. This may reflect the enhancing action of the drug on GABA-mediated inhibitory potentials. Triazolam did not detectably change the burst responses elicited by theta pattern stimulation. Experiments with slices of piriform cortex indicated that triazolam also failed to disrupt the development of long-term potentiation but instead caused the potentiation to decay back to baseline in 15-30 min. Triazolam thus seems to act on the mechanisms that stabilize long-term potentiation. These results provide a possible explanation for the amnestic effects of benzodiazepines in humans and animals and support the hypothesis that long-term potentiation contributes to memory encoding.

Analysis of Variance↗
PubMed1984

Intranuclear inclusions in rat piriform cortex: increase with age and preferential location within superficial layer II.

Intranuclear inclusions have been observed in layer II neurons of rat piriform cortex. These inclusions have the form of a filamentous lattice and resemble those described by others previously. The frequency of lattice-containing nuclei shows a significant fourfold increase over a period of 3-33 months of age, with the largest increase occurring after 18 months. The incidence of these inclusions is highest in the superficial third of layer II and is significantly greater than what would be expected from the distribution of all neuronal nuclei in layer II. The presence of intranuclear lattices may be related to the high level of electrical activity in piriform cortex, and their increase with age may reflect a long-term cumulative effect of this activity.

Aging↗
PubMed1993

The effects of lesions of the posterior piriform cortex on amygdala kindling in the rat.

The piriform cortex (PC) is thought to be critically involved in the genesis of forebrain (limbic type) seizures, including limbic kindled seizures. More recent studies have shown that the posterior PC is particularly sensitive to kindling stimulation, suggesting that the posterior PC contains specific generating sites which may be important for the stepwise progression of kindling. In the present experiments, we used microinjections of ibotenate to study the effect of selective lesions of the posterior PC on amygdala kindling in rats. Large unilateral lesions of the posterior PC and adjacent endopiriform nucleus markedly decreased the susceptibility of the ipsilateral basolateral amygdala to electrical stimulation, thus indicating that the posterior PC may normally contribute to regulation of physiologic excitability in amygdala. During kindling, rats with large lesions of the PC stayed longer in the initial phase of kindling (stage 1) than sham-lesioned controls, consistent with involvement of the posterior PC in the early stages of seizure propagation during kindling acquisition. However, the PC lesions were not capable of blocking or even severely retarding kindling. Following kindling development, rats with large lesions of the posterior PC had significantly higher focal seizure thresholds than kindled rats without lesion or rats with only small PC lesions, which suggests that the posterior PC is involved in the mechanisms which are responsible for the marked increase in seizure susceptibility induced by kindling. Taken together, the data substantiate that PC structures play a facilitatory role in kindling.

Amygdala↗
PubMed1988

Metabolic mapping of 2-deoxyglucose uptake in the rat piriform cortex using computerized image processing.

Using a computerized image processing method, the metabolic activity of the unfolded molecular and pyramidal layers of the piriform cortex was studied in rats during odorous stimulation. Animals were either intact or had sustained a bilateral transection of the lateral olfactory tract. 2-DG labelling was observed in corresponding areas across these two layers. No spatial pattern of 2-DG uptake could be seen in correlation with the odorant quality. These results are discussed with respect to the known anatomical and functional properties of the piriform cortex.

Animals↗
PubMed1993

Cholecystokinin (CCK)-8-immunoreactivity in the piriform cortex of the rat with special reference to its fine structures.

Characteristic features of cholecystokinin-8 (CCK-8) containing neuronal structures in the rat piriform cortex were examined by the immunocytochemistry at the light and electron microscopic levels. CCK-immunoreactive (CCKI) neurons were divided into at least four distinct morphological classes; bipolar, bitufted, multipolar and semilunar types. Each type of CCKI cells as well as CCKI axon terminals were studied by the electron microscopy in the layer II and III where most of them were located. Bipolar and bitufted types of CCKI cells made synaptic contacts with both non-CCKI and CCKI axon terminals with the former predominance. A total of 200 synaptic contacts formed by CCKI axon terminals were examined by random section analysis. Over 98% of CCKI axon terminals formed symmetrical synapses. In several cases, non-immunoreactive postsynaptic targets were identified; the pyramidal cells and small/medium sized multipolar cells in the layer II and III, and semilunar cells in the layer II. Additionally, the axonal initial segments of non-immunoreactive pyramidal cells were occasionally made symmetrical contacts with CCKI axon terminals. These findings suggest that CCK afferents exert monosynaptic influences on both projecting neurons and interneurons in the piriform cortex, and are thereby involved in the control of cortical neuronal activities.

Animals↗
PubMed1983

Structure of the piriform cortex of the opossum. III. Ultrastructural characterization of synaptic terminals of association and olfactory bulb afferent fibers.

Terminals of olfactory bulb afferent (OB) and association (ASSN) fibers within the piriform cortex were characterized ultrastructurally. Identification was by electron microscopic (EM) autoradiography following injections of tritiated amino acids into the olfactory bulb and anterior piriform cortex. The results show that terminals of both fiber systems contain round vesicles and make asymmetrical synaptic contacts predominantly onto dendritic spines. Profiles with pleomorphic vesicles do not appear to be labeled from either site. Since there is strong evidence that both fiber systems generate excitatory postsynaptic potentials (EPSPs) in pyramidal cells, these results provide additional examples in the mammalian CNS of terminals with round vesicles and asymmetrical contacts that mediate an excitatory effect. Percentage density analysis and quantitative study of a large number of heavily labeled terminals revealed that while OB and ASSN terminals are similar in terms of vesicle shape and contact type, they differ in many morphological details including pre- and postsynaptic profile size, the packing density and distribution of synaptic vesicles, synaptic contact shape, and the presence of overlying neuroglial lamellae. However, large variations in appearance of different terminals of the same type are also present so that a small percentage of OB and ASSN terminals are indistinguishable morphologically in the absence of label. An important finding of the quantitative analysis is that spines contacted by lateral olfactory tract (LOT) terminals appear to be of two types based on a bimodal distribution in size and differences in morphology, while spines contacted by ASSN terminals appear to be of a single type. Comparison of these data with results from Golgi analysis indicates that ASSN terminals predominantly contact pyramidal cell spines while OB terminals contact both pyramidal and semilunar cell spines. Quantitative analysis of synaptic vesicles revealed that histograms of vesicle size for OB and ASSN terminals are virtually identical in shape, but peaks are slightly displaced (ASSN vesicles are 5% larger; significant with P less than .002). An analysis of the laminar distribution of OB and ASSN synaptic terminals revealed that while most OB terminals are segregated in layer Ia and most ASSN terminals in layer Ib, occasional OB terminals are observed up to approximately 50 micro deep to the Ia-Ib boundary and occasional ASSN terminals up to approximately 50 micro superficial to this boundary.

Afferent Pathways↗
PubMed1984

The development of physiological responses of the piriform cortex in rats to stimulation of the lateral olfactory tract.

Extracellular recording techniques in rats were used to follow the postnatal development of the evoked response of the piriform cortex to electrical stimulation of the lateral olfactory tract (LOT) from birth to adulthood. As in other species, LOT shock in adult rats produces short-latency activation of units in piriform cortex and an extracellular field potential consisting of three components: a surface-negative component, the A1 wave (corresponding to the cortical monosynaptic EPSP evoked by the LOT fibers); a second surface-negative component, the B1 wave (corresponding to reactivation of layer I dendrites by intracortical fibers); and a late surface-positive component, the period 2 wave. A conditioning shock 20-150 msec before the test shock profoundly inhibits both evoked unit activity and the B1 wave, while it facilitates the A1. At birth, units can be orthodromically activated by LOT stimulation in association with the A1 wave. There is also a surface-positive spikelike wave, the S wave, which represents the summation of cortical unit activity. The B1 wave is apparent early in the first postnatal week. However, in contrast to the prominent inhibition in the adults, for the first few days after birth, single-unit responses, multiple-unit activity, and the S wave are all facilitated by a preceding conditioning shock with intervals of 200 msec or less, in association with the facilitation of the A1 wave. A shift to inhibition is apparent with longer intershock intervals of 300-700 msec, which exceed the period during which paired shocks facilitate the A1 wave. During the remainder of the first two postnatal weeks,, partial suppression of evoked activity with intervals of less than 200 msec appears and progressively increases in strength, but inhibition at very long intershock intervals remains greater in magnitude. During this time, the duration of the inhibitory period also decreases to near the adult value of 200-300 msec. In the third postnatal week the pattern was similar to that in the adult, but the inhibition was still clearly weaker than in adults. These results suggest a delayed maturation of the cortical inhibitory circuitry; this conclusion has also been suggested by previously published observations in the developing neocortex and hippocampus. In addition, the acceleration with age of the conduction velocity of axons in the LOT was analyzed. The adult value of 9.6 m/sec was not achieved until some time after postnatal day 15, which parallels the myelinization of the tract as observed with the light microscope.

Aging↗
PubMed1989

Deep neurons in piriform cortex. I. Morphology and synaptically evoked responses including a unique high-amplitude paired shock facilitation.

1. Synaptic responses of cells in layer III of the piriform cortex and the subjacent endopiriform nucleus (layer IV) were analyzed with intracellular recording techniques in a slice preparation from the rat, cut perpendicular to the pial surface. 2. Micropipettes containing Lucifer yellow (LY) were used to correlate response properties with morphology. An antiserum to LY was used to intensify staining and to prevent fading during detailed morphological study. Response properties were also examined with potassium acetate-containing electrodes. 3. Morphologically, two cell types were identified: pyramidal cells that were confined to layer III of the piriform cortex and multipolar cells that were in layer III and the endopiriform nucleus. 4. In morphology, deep pyramidal cells in layer III closely resembled superficial pyramidal cells in layer II, with the exception that primary apical dendritic trunks were longer and basal dendritic arborizations were more extensive than apical. Like superficial pyramidal cells, apical dendrites of all deep pyramidal cells stained extended through the afferent fiber termination zone in layer Ia and gave rise to local axonal arbors that were concentrated in layer III and the endopiriform nucleus. 5. Multipolar cells were morphologically indistinguishable in layer III and the endopiriform nucleus. All gave rise to nonvaricose spiny dendrites that never extended into layer II and local axonal arbors. 6. Response properties of deep pyramidal and multipolar cells were similar; responses of both of these populations were very different from those of superficial pyramidal cells. The primary difference between responses of deep pyramidal and multipolar cells was a shorter latency of postsynaptic potentials evoked in deep pyramidal cells by stimulation of afferent fibers, consistent with the extension of their dendrites into layer Ia. 7. Responses of most deep cells to stimulation of afferent and association fibers at sufficiently high strength consisted of an initial excitatory postsynaptic potential (EPSP), followed by a fast Cl- -mediated and a slow K+-mediated inhibitory postsynaptic potential (IPSP). 8. A characteristic feature of deep cells, which was only rarely observed in superficial pyramidal cells, was the presence of variable EPSPs evoked at long latencies (greater than 100 ms) by stimulation of afferent or association fibers. 9. A striking finding for deep pyramidal and multipolar cells, when studied with LY-containing pipettes, was a variable slowly rising depolarizing potential triggered at depolarized membrane potentials by stimulation of afferent or association fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Induction of Fos protein in the piriform cortex after brain injury in pentobarbital-anaesthetized rats: lack of effect of lactation.

The ability of lactation and progesterone administration to inhibit the induction of Fos protein in the piriform cortex after brain injury in pentobarbital-anaesthetized rats was assessed in three studies. Consistent with previous reports we found that brain injury-induced Fos expression in the piriform cortex could be eliminated by the administration of the non-competitive NMDA receptor antagonist MK 801 (4 mg/kg i.p.). Fos induction was not reduced, however, in lactating dams (days 7-9) post-partum or in progesterone-treated males. These results are not consistent with the hypothesis that suckling stimulation and progesterone have a direct effect at the NMDA receptor complex.

Anesthesia↗
PubMed2005

Analysis of calretinin immunoreactivity in the rat piriform cortex after open field stress during postnatal maturation.

In our study we used c-Fos protein to identify whether cells containing calretinin (CR) in the rat piriform cortex are engaged in the response to stress stimulation and to find out how this expression changes during maturation (PC). The material consisted of Wistar strain rats of between 0 and 120 days of age divided into 9 groups. Each group consisted of 5 experimental and 3 control rats. Animals from the experimental groups were exposed to the open field test throughout 10 minutes. The control animals were kept in a home cage. In all age-related control rats weak c-Fos immunoreactivity was observed. Our results showed that cells containing c-Fos following an acute open field test were observed predominantly in layers II and III of the PC just after birth. Their number then increased and stabilised on P30. We had already observed immature CR-ir cells at birth. In the 4th week of life these neurons achieved maturity. Their number increased to P90 and decreased in older animals. CR-ir neurons were localised mainly in layer II and to a lesser degree in layers III and I of the PC. Double immunostaining c-Fos/CR revealed that the level of co-localisation was low. Only small differences were observed between the anterior and posterior parts of the PC. In the anterior part a higher number of CR-ir neurons was found. The difference in the level of co-localisation between the anterior and posterior parts was age-related and differentiated. Our results may suggest that during maturation CR-ir neurons of the piriform cortex are not the main population engaged in response to the open field test.

Age Factors↗
PubMed1992

Origin of the in vivo rat piriform cortex activity recorded with voltage-sensitive dyes: comparison of the optical signals and the field potentials.

The comparison of optical recordings and evoked field potentials recorded on the rat piriform cortex pointed out that both signals were strongly correlated. As the field potentials, the two waves of the optical signals originated from the mono- (direct olfactory bulb afferents) and polysynaptic (intrinsic association fibers) excitatory postsynaptic potentials. Such optical recordings will be used for studying spatiotemporal distribution of the piriform cortex activity.

Animals↗
PubMed1999

Biophysical and pharmacological diversity of high-voltage-activated calcium currents in layer II neurones of guinea-pig piriform cortex.

1. High-voltage-activated calcium currents were studied with the whole-cell, patch-clamp technique in acutely dissociated pyramidal neurones from guinea-pig piriform cortex layer II. Barium ions were used as charge carriers. 2. Barium currents (IBa) displayed a remarkable kinetic diversity in different neurones. The ratio between the current amplitude at the end of the test pulses and the peak amplitude (Re/p) showed two frequency-distribution peaks at approximately 0.4 and 0.8. The index of current activation speed (rise time 10-90 %) directly correlated with the index of current persistence, Re/p. 3. The half-activation potential (V ) of total IBas positively correlated with the Re/p of the corresponding currents. This implied that the high-decay IBas also had a more negative voltage range of activation than the more persistent ones. 4. The L- and N-type channel blockers nifedipine (10 microM) and omega-conotoxin GVIA (omega-CTx GVIA, 0.5-1 microM) additively blocked 20 and 25 % of the total IBa, respectively. The P/Q-type calcium channel blockers omega-agatoxin IVA (100 nM), omega-conotoxin MVIIC (1 microM) and 3.3 funnel toxin (1 microM), had little effect on IBa. 5. The nifedipine- and omega-CTx GVIA-sensitive current had a Re/p > 0.55 and their voltage dependence of activation was of the high-voltage-activated type (V approximately 0 mV). 6. High-, intermediate- and low-decay blocker-resistant currents were observed in different neurones. Their Re/p values highly correlated with those of the corresponding total IBas and with the voltage dependence of activation of the underlying conductances. Exponential fittings of the inactivation phase of blocker-resistant currents returned very fast time constants (lower than 30 ms) for high-decay currents (Re/p < 0.25). The intermediate-decay currents (Re/p approximately 0.55) could not derive from variable combinations of high- and low-decay current components. 7. Our data demonstrate a remarkable variety in voltage-activated calcium currents expressed by piriform cortex neurones, that include currents resistant to high-voltage-activated calcium-channel blockers.

Algorithms↗
PubMed1994

Presence of gonadotropin-releasing hormone mRNA in the rat olfactory piriform cortex.

Gonadotropin releasing hormone (GnRH) neurons are known to be originated from the olfactory placode and to enter the forebrain regions during embryonic development. The present study aims to ascertain whether GnRH is locally expressed in the olfactory cortex. Northern blot hybridization and reverse transcription-polymerase chain reaction revealed that GnRH mRNA was present in the rat olfactory cortex as well as in the olfactory bulb. The predicted size of GnRH mRNA is similar to that detected in the hypothalamus. In situ hybridization histochemistry also showed that GnRH mRNA is highly concentrated in the olfactory piriform cortex. The present data indicate that GnRH is synthesized in the olfactory piriform cortex.

Animals↗
PubMed1987

Structure of the piriform cortex of the adult rat. A Golgi study.

The piriform cortex (PC) was studied in the adult rat with anilines, rapid Golgi and Golgi-Colonnier techniques. As in other animals in the PC of the adult rat three layers can be distinguished: layer I or plexiform layer, layer II or superficial cellular layer and layer III or deep cellular layer. Golgi impregnations allowed to describe seven different types of cells. Pyramidal cells, in which it is possible to distinguish three subtypes (superficial, middle and deep pyramidal cells) by virtue of their morphology and location. Bipolar cells, a very little and scarce type of cell restricted to layer I and that has not been previously described. Fusiform cells, similar to those found in other species. Semilunar cells, also like those described in other animals but which are only found in the posterior PC. These cells resemble other type of cell, the ovoid cells that neither have been described in other animals and, on the contrary, are only located in the anterior PC. Stellate cells, which are a very wide population of cells with variable sizes, dendritic patterns and locations. Horizontal cells, similar to pyramidal cells but oriented in horizontal direction and polymorphic cells, whose the most striking feature is their smooth and beaded prolongations. Morphological features of these cells are compared with those described in the cells of the PC of other animals.

Animals↗
PubMed1991

Excitatory responses to serotonin (5-HT) in neurons of the rat piriform cortex: evidence for mediation by 5-HT1C receptors in pyramidal cells and 5-HT2 receptors in interneurons.

As a prerequisite to pharmacological analysis of the excitatory effects of serotonin (5-HT) on piriform pyramidal cells and interneurons, this study first examined the physiological characteristics of these two cell types. Intracellular recordings confirmed that the subpopulation of 5-HT-activated cells located at the border of layers II and III are indeed interneurons. Voltage clamp recordings in pyramidal cells showed that the increase in excitability produced by 5-HT in these cells was the result of voltage- and Ca(2+)-dependent outward currents with the characteristics of IM and IAHP. Pharmacological studies were designed to discriminate 5-HT2 from 5-HT1C responses in interneurons and pyramidal cells of piriform cortex. The 5-HT antagonist spiperone, which has a much higher affinity for 5-HT2 receptors than for 5-HT1C receptors, blocked the excitatory effect of 5-HT at lower concentrations in interneurons (IC50 = 31 nM) than in pyramidal cells (IC50 = 2.1 microM). Similarly, ritanserin, a drug which also has a higher affinity for 5-HT2 than 5-HT1C receptors, blocked the effect of 5-HT at lower concentrations in interneurons (IC50 = 400 nM) than in pyramidal cells (IC50 = 8.1 microM). In contrast, LY 53857, an antagonist with higher affinity for 5-HT1C than for 5-HT2 receptors, blocked the effect of 5-HT at lower concentrations in pyramidal cells (IC50 = 26 nM) than in interneurons (IC50 = 364 nM). The 5-HT1C partial agonist/5-HT2 antagonist mCPP produced agonist-like effects in only 66% of pyramidal cells tested indicating that not all pyramidal cells may express 5-HT1C receptors. In that both spiperone and ritanserin have higher affinity for 5-HT2 receptors than for 5-HT1C receptors and LY 53857 has a higher affinity for 5-HT1C receptors than for 5-HT2 receptors, these data suggest that in piriform cortex excitatory effects of 5-HT are mediated by 5-HT1C receptors in pyramidal cells an by 5-HT2 receptors in interneurons.

Animals↗
PubMed1988

Excitatory amino acid receptors in piriform cortex do not show receptor desensitization.

We have investigated the proposed role of transmitter receptor desensitization as an explanation for the excitotoxicity rank order of several excitatory amino acid agonists as compared to kainic acid, using a brain slice of rat piriform cortex. Responses to glutamate, aspartate, quisqualate, n-methyl aspartate and kainate showed no evidence of receptor desensitization when studied with very long and large ionophoretic pulses, repeated ionophoretic pulses or by bath perfusion. At least in rat piriform cortex, the suggestion that kainate receptors do not desensitize while those to glutamate and quisqualate do, does not apply to nor explain the more potent kainate excitotoxicity.

Animals↗