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PubMed1996

Indispensable amino acid deficiency and increased seizure susceptibility in rats.

Repeated subthreshold stimulation of limbic brain areas increases seizure susceptibility in experimental models of epilepsy. In addition, acute dietary indispensable amino acid (IAA) deficiency activates the anterior piriform cortex (APC), a seizure-prone limbic brain area in the rat. Based on these two findings, we hypothesized that activation of the APC by chronic exposure to IAA-deficient diets might increase seizure susceptibility. Several nonessential amino acid neurotransmitters are important in seizures, but deficiencies of nontransmitter IAAs have not been well studied in seizure models. In four trials, we made injections of pentylenetetrazole intraperitoneally or of bicuculline into the APC in histidine-, isoleucine-, or threonine-deficient rats and controls. Increased susceptibility to seizures in the deficient animals was observed as increased severity of the seizures, decreased threshold for the dose of the chemostimulant and time to seizure, or a combination thereof. Pair-fed controls showed that this effect was not due to an energy deficit. This novel but robust finding suggests that IAA deficiency may increase vulnerability to seizures by repeated activation of the APC.

Amino Acids↗
PubMed2001

Glial angiotensinogen regulates brain angiotensin II receptors in transgenic rats TGR(ASrAOGEN).

TGR(ASrAOGEN)680, a newly developed transgenic rat line with specific downregulation of astroglial synthesis of angiotensinogen, exhibits decreased brain angiotensinogen content associated with a mild diabetes insipidus and lower blood pressure. Autoradiographic experiments were performed on TGR(ASrAOGEN) (TG) and Sprague-Dawley (SD) control rats to quantify AT(1) and AT(2) receptor-binding sites in different brain nuclei and circumventricular organs. Dose-response curves for drinking response to intracerebroventricular injections of ANG II were compared between SD and TG rats. In most of the regions inside the blood-brain barrier [paraventricular nucleus (PVN), piriform cortex, lateral olfactory tract (LOT), and lateral preoptic area (LPO)], AT(1) receptor binding (sensitive to CV-11974) was significantly higher in TG compared with SD. In contrast, in the circumventricular organs investigated [subfornical organ (SFO) and area postrema], AT(1) receptor binding was significantly lower in TG. AT(2) receptors (binding sensitive to PD-123319) were detected at similar levels in the inferior olive (IO) of both strains. Angiotensin-binding sites sensitive to both CV-11974 and PD-123319 were detected in the LPO of SD rats and specifically upregulated in LOT, IO, and most notably PVN and SFO of TG. The dose-response curve for water intake after intracerebroventricular injections showed a higher sensitivity to ANG II of TG (EC(50) = 3.1 ng) compared with SD (EC(50) = 11.2 ng), strongly suggesting that the upregulation of AT(1) receptors inside the blood-brain barrier of TG rats is functional. Finally, we showed that downregulation of angiotensinogen synthesized by astroglial cells differentially regulates angiotensin receptor subtypes inside the brain and in circumventricular organs.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed2003

Beta and gamma oscillations in the olfactory system of the urethane-anesthetized rat.

Fast oscillations in the beta (15-40 Hz in awake rats) and gamma (50-100 Hz) frequency ranges are prominent in field potentials induced by odorants in the mammalian olfactory bulb (OB) and piriform cortex (PC). Whereas the gamma oscillation has been studied for >50 yr, the beta oscillation has attracted attention only recently, and its origin, mechanism, and relationship to gamma are unknown. To address these questions, we have examined responses induced by odorants in the urethane-anesthetized rat-a preparation well-suited for the analysis of mechanisms. We found that both oscillations could be induced by odorants in a concentration-dependent manner. Analysis with a concentration series and spectral methods revealed that the beta and gamma oscillations were distinct and not harmonically related, indicating generation by independent mechanisms. The beta oscillation was synchronous at sites < or =4 mm apart in the OB, the greatest distance tested. In contrast, the gamma oscillation was synchronous in some experiments and asynchronous in others (frequency differed slightly at different sites, resulting in progressive phase shifts). Current source-density analysis indicated that, for both oscillations, the field potentials in the OB were generated by synaptic currents in granule cells. The two oscillations were differently affected by surgical interruption of the lateral olfactory tract. This lesion abolished the beta oscillation, whereas the gamma oscillation was still induced in the OB. Our results confirm previous reports that the gamma oscillation is generated within the OB but indicate that the beta oscillation requires the participation of PC.

Anesthesia, Intravenous↗
PubMed2005

Olfactory cortical adaptation facilitates detection of odors against background.

Detection and discrimination of odors generally, if not always, occurs against an odorous background. On any given inhalation, olfactory receptor neurons will be activated by features of both the target odorant and features of background stimuli. To identify a target odorant against a background therefore, the olfactory system must be capable of grouping a subset of features into an odor object distinct from the background. Our previous work has suggested that rapid homosynaptic depression of afferents to the anterior piriform cortex (aPCX) contributes to both cortical odor adaptation to prolonged stimulation and habituation of simple odor-evoked behaviors. We hypothesize here that this process may also contribute to figure-ground separation of a target odorant from background stimulation. Single-unit recordings were made from both mitral/tufted cells and aPCX neurons in urethan-anesthetized rats and mice. Single-unit responses to odorant stimuli and their binary mixtures were determined. One of the odorants was randomly selected as the background and presented for 50 s. Forty seconds after the onset of the background stimulus, the second target odorant was presented, producing a binary mixture. The results suggest that mitral/tufted cells continue to respond to the background odorant and, when the target odorant is presented, had response magnitudes similar to that evoked by the binary mixture. In contrast, aPCX neurons filter out the background stimulus while maintaining responses to the target stimulus. Thus the aPCX acts as a filter driven most strongly by changing stimuli, providing a potential mechanism for olfactory figure-ground separation and selective reading of olfactory bulb output.

Adaptation, Physiological↗
PubMed2006

Opposing inward and outward conductances regulate rebound discharges in olfactory mitral cells.

The olfactory bulb, a second-order sensory brain region, relays afferent input from olfactory receptor neurons to piriform cortex and other higher brain centers. Although large inhibitory postsynaptic potentials (IPSPs) are evident in in vivo intracellular recordings from mitral cells, the functional significance of these synaptic responses has not been defined. In many brain regions, IPSPs can function to either inhibit spiking by transiently suppressing activity or can evoke spiking directly by triggering rebound discharges. We used whole cell patch-clamp recordings from mitral cells in olfactory bulb slices to investigate the mechanisms by which IPSPs regulate mitral cell spike discharges. Mitral cells have unusual intrinsic membrane properties that support rebound spike generation in response to small-amplitude (3-5 mV) but not large-amplitude hyperpolarizing current injections or IPSPs. Rebound spiking occurring in mitral cells was dependent on recovery of subthreshold Na currents, and could be blocked by tetrodotoxin (TTX, 1 microM) or the subthreshold Na channel blocker riluzole (10 microM). Surprisingly, larger-amplitude hyperpolarizing stimuli impeded spike generation by recruiting a transient outward I(A)-like current that was sensitive to high concentrations of 4-aminopyridine and Ba. The interplay of voltage-gated subthreshold Na channels and transient outward current produces a narrow range of IPSP amplitudes that generates rebound spikes. We also found that subthreshold Na channels boost subthreshold excitatory stimuli to produce membrane voltages where granule-cell-mediated IPSPs can produce rebound spikes. These results demonstrate how the intrinsic membrane properties of mitral cells enable inhibitory inputs to bidirectionally control spike output from the olfactory bulb.

Animals↗
PubMed1992

Cholinergic modulation of cortical associative memory function.

1. The effect of cholinergic modulation on associative memory function was studied in a computational model based on the physiology and anatomic structure of piriform cortex. Both the cholinergic suppression of intrinsic fiber synaptic transmission and the cholinergic changes in postsynaptic excitability described in the companion paper were examined. 2. Distributed input patterns representing odors were stored in the model with the use of a synaptic modification rule dependent on pre- and postsynaptic activity (i.e., Hebbian). Associative recall of these patterns was tested by presenting the model with degraded versions of the learned patterns and testing whether these degraded patterns evoked the same network response as the full learned input pattern. Storage was evaluated with the use of a performance measure designed to reflect how well degraded input patterns could be recognized as a particular learned input pattern. 3. When memory function was evaluated with a selective cholinergic suppression of intrinsic fiber synaptic transmission during learning, associative memory performance was greatly enhanced. Cholinergic suppression during learning prevents previously stored patterns from interfering with the storage of new patterns. 4. When memory function was evaluated with a cholinergic mediated enhancement in cell excitability during learning, the speed of learning increased, but so did the decay in performance due to interference during learning. 5. When suppression of intrinsic fiber synaptic transmission was coupled with an increase in cell excitability, the best memory performance was obtained. 6. These results provide a possible theoretical framework for linking the neuropharmacological effects of acetylcholine to behavioral evidence for a role of acetylcholine in memory function. This could help describe how memory deficits might arise from cholinergic dysfunction in diseases such as Alzheimer's dementia.

Association↗
PubMed1993

Organization of inhibition in the rat olfactory bulb external plexiform layer.

1. Intracellular recordings were made from the output neurons (mitral and tufted cells) of the rat olfactory bulb during electrical orthodromic stimulation of the olfactory nerve layer (ONL) and antidromic stimulation of the lateral olfactory tract and posterior piriform cortex (pPC) to test for physiological differences among the neuron types. Many of these neurons were identified by intracellular injections of biocytin, and others were identified by their pattern of antidromic activation. 2. Both marked and unmarked mitral cells showed large inhibitory postsynaptic potentials (IPSPs) in response to antidromic stimulation of the pPC, whereas tufted cells exhibited small IPSPs in response to pPC stimulation. Tufted cells, however, showed large IPSPs in response to ONL stimulation. In many cases, these tufted cell responses to ONL stimulation were larger than the mitral cell responses. The marked superficial tufted cells, those with basal dendrites in the superficial sublayer of the external plexiform layer (EPL), had the smallest IPSPs in response to pPC stimulation. These data support anatomic observations suggesting that the granule cell populations responsible for the IPSPs may be different for mitral and for superficial tufted cells. 3. The different types of output cells also showed differences in their responses to orthodromic stimulation. Type I mitral cells, which have basal dendrites confined to the deep sublayer of the EPL, were significantly less excitable by ONL stimulation than were the type II mitral cells, which have basal dendrites distributed within the intermediate sublayer of the EPL. Half of the type I mitral cells could not be excited at all by ONL stimulation. Superficial tufted cells showed even greater orthodromic excitability than type II mitral cells, usually responding to ONL stimulation with two or more spikes. 4. The ionic basis of the IPSPs in the superficial tufted cells appeared similar to those described for mitral cells. These IPSPs could be reversed by chloride injection and were associated with increased membrane conductance. 5. For both mitral and tufted cells, the number of ONL electrodes evoking IPSPs was greater than the number evoking spikes. These data suggest a kind of center-surround organization of inputs to these cells from the ONL, although this does not yet imply that the sensory receptive field of these output cells has a center-surround organization. 6. In conclusion, the properties of rat olfactory bulb output cells correlate with the sublayers of the EPL in which their basal dendrites lie.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Salamander olfactory bulb neuronal activity observed by video rate, voltage-sensitive dye imaging. II. Spatial and temporal properties of responses evoked by electric stimulation.

1. Video imaging of changes in voltage-sensitive dye (VSD) fluorescence was used to analyze spatial and temporal properties of activity patterns in the in vivo salamander olfactory bulb and primordium piriform cortex after electric stimulation. Distribution of activity among and within the neuronal layers was analyzed after orthodromic stimulation of the whole olfactory nerve (ON), isolated fascicles, or local epithelial sites, and after antidromic stimulation of the medial olfactory tract (OT). 2. Optical signals propagated through the bulbar layers with a sequence that correlates with electrophysiological responses. After orthodromic stimulation, VSD responses started in the glomerular layer, spread to the deeper laminae, and, after reaching the region of mitral/tufted somata, were observed as a brief burst of activity in the OT. Compound action potentials in the ON were associated with short-duration, rapidly depolarizing optical responses in the ON layer. Responses in glomerular layer and external plexiform layer (EPL) first showed in some recordings a brief, small-amplitude hyperpolarization, followed by a period of depolarization, followed by a second, longer-lasting hyperpolarization. The periods of optical hyperpolarization could be related to events observed in intracellular mitral/tufted cell recordings. 3. With shocks delivered to the entire ON, depolarizing responses were nonhomogeneously distributed, appearing as multiple foci or bands of activity. Spatial patterns within each bulbar layer had poorly defined borders. Sites showing short-latency responses were often those with the largest and longest-lasting activity. 4. Increasing the intensity of stimulation to the ON enhanced the size and duration of the depolarizing and hyperpolarizing responses. The short-latency, early hyperpolarization was best seen with low-intensity, peripherally placed stimuli. 5. ON stimulation also elicited activity in the contralateral bulb. Activity started at the innermost layers and spread in patches to regions of the EPL just beneath the glomeruli. These had durations similar to ipsilateral responses, but longer latencies. A period of early hyperpolarization, longer than that on the ipsilateral side, was followed by prolonged depolarization and then by a second, later hyperpolarization. 6. Antidromic stimuli applied to the OT evoked optical responses consisting of a period of depolarization followed by hyperpolarization, similar to the components elicited by orthodromic stimuli. These responses had short time courses, began in the deeper layers, and spread to the superficial region of the bulb usually without reaching the glomerular region. 7. Punctate stimulation of the mucosa or nerve elicited depolarizing and hyperpolarizing events that depended on the stimulation site.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Similarity of granular-induced inhibitory periods in pairs of neighboring mitral/tufted cells.

1. Neighboring mitral/tufted cells have been previously shown to present temporal correlations of their firings related to the respiratory rhythm, particularly under odor stimulation. This occurs despite the existence of a powerful inhibitory control exerted by granule cells onto mitral/tufted cells. In the present study, we hypothesized that neighboring mitral cells can present granular induced inhibitory periods with similar latencies and durations and that such a similarity would preserve them from a possible suppression of their temporal correlations. 2. To test this hypothesis, we analyzed the latencies and durations of the inhibitory periods induced by granular activation in pairs of simultaneously recorded neighboring mitral cells. The activation of granule cells was achieved by electrical stimulation of the different pathways known to directly activate granule cells [lateral olfactory tract (LOT), anterior limb of the anterior commissure (AC), and piriform cortex (PC)]. Data from this group were compared with those of a control group composed of distant cells also recorded simultaneously. 3. Results first show that the latencies to onset of inhibition or to recovery were more frequently similar in neighboring cells than in control cells and that this similarity was enhanced by odor stimulation. Second, the probability that two cells exhibit similar inhibitory periods (i.e., similar latencies to both onset and to recovery) in response to electrical stimulation of LOT, AC, or PC was significantly higher in neighboring than in control cells. Third, only neighboring cells were found to present similar inhibitory periods in response to the stimulation of all of the three structures. 4. Granular activation was also found to modify the temporal patterns of individual mitral cells. However, although these patterns were not systematically modified similarly in neighboring mitral cells, they remained perfectly synchronized with zero delay if they were already synchronous without electrical stimulation. On the contrary, if patterns were spontaneously uncorrelated, electrical stimulation never produced a synchronization of their firings, even if their temporal relationships could be profoundly modified. 5. These results show that neighboring mitral cells can receive granular-induced inhibition with similar latencies and durations with a probability much higher than control cells. Such similarities allow neighboring mitral cells to preserve their temporal correlation despite the powerful inhibitory input from granule cells. Functional hypotheses about the role of the cortical feedback projections onto the bulb are discussed.

Animals↗
PubMed2000

Functional role of NMDA autoreceptors in olfactory mitral cells.

The output of the olfactory bulb is governed by the interaction of synaptic potentials with the intrinsic conductances of mitral cells. While mitral cells often are considered as simple relay neurons, conveying activity in olfactory receptor cells to the piriform cortex, there is strong physiological and behavioral evidence that local synaptic interactions within the olfactory bulb modulate mitral cell discharges and facilitate odorant discrimination. Understanding the circuitry of the olfactory bulb is complicated by the fact that most dendrites in this region are both pre- and postsynaptic. Feedback inhibition is mediated through reciprocal dendrodendritic synapses between the secondary dendrites of mitral cells and GABAergic granule cells. Here we show that glutamate released from mitral cell dendrites also activates local N-methyl-D-aspartate (NMDA) autoreceptors, generating an inward tail current following depolarizing voltage steps. Autoreceptor-mediated self-excitation is calcium dependent, can be evoked by single action potentials in the presence of magnesium, and is graded with the number of spikes in a train. We find that dendrodendritic inhibition also is evoked by single action potentials but saturates rapidly during repetitive discharges. Self-excitation also underlies the prolonged afterdischarges apparent in mitral cells following potassium channel blockade. Both afterdischarges and autoreceptor-mediated tail currents persist in TTX, suggesting that they are produced by local rather than polysynaptic actions of glutamate. Blockade of NMDA autoreceptors with 2-amino-5-phosphonovaleric acid (APV) reduces the firing frequency within action potential cluster. The rapid kinetics of self-excitation suggests a functional role of NMDA autoreceptors in prolonging periods of phasic firing in mitral cells.

2-Amino-5-phosphonovalerate↗
PubMed2000

Functional mapping of human brain in olfactory processing: a PET study.

This study describes the functional anatomy of olfactory and visual naming and matching in humans, using positron emission tomography (PET). One baseline control task without olfactory or visual stimulation, one control task with simple olfactory and visual stimulation without cognition, one set of olfactory and visual naming tasks, and one set of olfactory and visual matching tasks were administered to eight normal volunteers. In the olfactory naming task (ON), odors from familiar items, associated with some verbal label, were to be named. Hence, it required long-term olfactory memory retrieval for stimulus recognition. The olfactory matching task (OM) involved differentiating a recently encoded unfamiliar odor from a sequentially presented group of unfamiliar odors. This required short-term olfactory memory retrieval for stimulus differentiation. The simple olfactory and visual stimulation resulted in activation of the left orbitofrontal region, the right piriform cortex, and the bilateral occipital cortex. During olfactory naming, activation was detected in the left cuneus, the right anterior cingulate gyrus, the left insula, and the cerebellum bilaterally. It appears that the effort to identify the origin of an odor involved semantic analysis and some degree of mental imagery. During olfactory matching, activation was observed in the left cuneus and the cerebellum bilaterally. This identified the brain areas activated during differentiation of one unlabeled odor from the others. In cross-task analysis, the region found to be specific for olfactory naming was the left cuneus. Our results show definite recruitment of the visual cortex in ON and OM tasks, most likely related to imagery component of these tasks. The cerebellar role in cognitive tasks has been recognized, but this is the first PET study that suggests that the human cerebellum may have a role in cognitive olfactory processing as well.

Adolescent↗
PubMed1998

Enhanced epileptogenicity of area tempestas in the immature rat.

Age-related differences in kindling have been previously observed in terms of behavioral manifestations, seizure generalization and intensity of postictal refractory period. In the present study the development of kindling in the area tempestas (specifically the dorsal endopiriform nucleus) was examined in developing rats (15-16 days of age). Results indicate that kindling can be easily elicited from the immature area tempestas. Rats kindled from area tempestas reached the early kindling stages significantly faster, had longer afterdischarges and a greater number of severe stage 6 seizures than rats kindled from areas above the area tempestas or in the piriform cortex proper. This study indicates that the area tempestas is particularly epileptogenic in the immature rat.

Animals↗
PubMed1998

Differential expression and regulation of leptin receptor isoforms in the rat brain: effects of fasting and oestrogen.

Leptin affects body weight and reproduction mainly via receptors in the central nervous system. Different isoforms of the leptin receptor (leptin-R) exist, including a long isoform (leptin-RL) with signalling capacity and short isoforms (leptin-RS) with unknown function. The aim of this study was to examine leptin-R gene expression in different regions of the brain under conditions with altered body weight, in the female rat, including ovariectomy (OVX), oestradiol (E2) treatment, fasting and a genetic model of obesity (Zucker fa/fa). Leptin-R gene expression was analysed by in situ hybridization using probes recognizing all receptor isoforms (leptin-R) or specifically leptin-RL. Transcripts recognized by the leptin-R probe were abundant in the choroid plexus (CP), arcuate nucleus (ARC), ventromedial nucleus (VMN), thalamus (TH) and piriform cortex (PC). Leptin-RL transcripts were detected in the ARC, VMN, TH and PC but not in the CP. Although no sex difference was observed, leptin-R gene expression was reduced by E2 administration and increased by OVX. Administration of E2 reduced leptin-RL gene expression in the ARC and VMN but did not alter the expression in the TH or PC. OVX had no effect on the expression of leptin-RL mRNA. Fasting also caused a differential regulation of leptin-R mRNAs, with an increase in abundance of leptin-RL transcripts in the TH despite a decrease in leptin-R in this area. Obese Zucker rats had a similar pattern of expression with an increased expression of leptin-RL transcripts in all brain areas analysed and a decrease in leptin-R gene expression. These results demonstrate a differential regulation of leptin-RL and leptin-RS which could provide a mechanism for regulating access to, and sensitivity of, discrete regions of the brain for circulating leptin. We suggest that fasting and E2 alter the balance between leptin-RL and leptin-RS and that this could increase tissue sensitivity to leptin.

Animals↗
PubMed2000

Cloning, pharmacological characterization and brain distribution of the rat apelin receptor.

The peptide apelin, recently isolated from bovine stomach tissue extracts, has been identified as an endogenous ligand of the human putative receptor protein related to the angiotensin receptor AT(1) (APJ). In this article, we report cloning of the rat apelin receptor cDNA. The sequence shares 90% identity with the human APJ receptor and 31% with the rat AT(1A) angiotensin receptor. Subsequently a stable CHO cell line expressing the receptor fused at its C-terminal part with the enhanced green fluorescent protein (EGFP) was established, allowing to verify its cell surface distribution and to determine the affinity of various apelin and angiotensin fragments on the cloned receptor. As shown for the human APJ receptor, the rat apelin receptor expressed in the cell line was negatively coupled to adenylate cyclase. The apelin fragment K17F (Lys(1)-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe(17)) inhibited forskolin-stimulated cAMP production at sub-nanomolar concentrations whereas angiotensin II and angiotensin III were inactive. N-terminal elongation of K17F with a tyrosine or the N-terminal deletion of the first four amino acids did not modify the inhibitory action of K17F on cAMP production. In contrast, deletion of the first seven amino acids of K17F or substitution of phenylalanine by an alanine residue at the C-terminus completely abolished the activity of the peptide. In situ hybridization analysis of apelin receptor mRNA expression in the adult rat brain showed intense labeling in the hypothalamus, especially in the supraoptic and the paraventricular nuclei. The anterior and intermediate lobes of the pituitary were also highly labeled, as well as the pineal gland. Labeling was also found in extrahypothalamic structures such as the piriform cortex, the nucleus of the lateral olfactory tract, the central grey matter, the pars compacta of the substantia nigra, the dorsal raphe nucleus, the entorhinal cortex, the dentate gyrus and the Ammon's horn. The hypothalamic and hypophyseal distribution of the receptor suggests an involvement of apelin in the control of neuro- and adenohypophyseal hormone release, whereas its presence in the pineal gland and in discrete higher brain structures points out to possible roles in the regulation of circadian rhythms and of water and food intake behavior.

Amino Acid Sequence↗
PubMed2005

Cyto- and chemoarchitecture of the monotreme olfactory tubercle.

This study was undertaken to determine whether the olfactory tubercles of two monotremes (platypus and echidna) showed cyto- or chemoarchitectural differences from the tubercles of therian mammals. Nissl staining was applied in conjunction with enzyme reactivity for NADPH diaphorase and acetylcholinesterase, and immunoreactivity for calcium binding proteins (parvalbumin, calbindin and calretinin) and tyrosine hydroxylase (echidna only). Golgi impregnations of the tubercle were also available for the echidna. The olfactory tubercle is a poorly laminated structure in the echidna, despite the pronounced development of other components of the echidna olfactory system, and the dense cell layer of the olfactory tubercle was found to be discontinuous and irregular. Granule cell clusters (islands of Calleja) were present, but were small, poorly defined and did not show the intense NADPH diaphorase activity seen in marsupial and placental mammals. A putative small island of Calleja magna was seen in only one echidna out of four. In Golgi impregnations of the echidna olfactory tubercle, the most abundant neuron type was a medium-sized densely spined neuron similar to that seen in the olfactory tubercle of some therians. Large spine-poor neurons were also seen in the polymorphic layer. In the platypus, the olfactory tubercle was very small but showed more pronounced lamination than the echidna, although no granule cell clusters were seen. In both monotremes, the development of the olfactory tubercle was poor relative to other components of the olfactory system (bulb and piriform cortex). The small olfactory tubercle region in the platypus is consistent with poor olfaction in that aquatic mammal, but the tubercle in the echidna is more like that of a microsmatic mammal than other placentals occupying a similar niche (e.g., insectivores).

Animals↗
PubMedDate not supplied

c-fos expression as a marker of central cardiovascular neurons.

Immunohistochemical detection of Fos, the protein product of the immediate-early gene c-fos, was evaluated as a functional marker of central neurons sensitive to a change of blood pressure/blood volume. Controlled hemorrhage and infusion of the hypotensive agent nitroprusside or hydralazine induced the appearance of Fos-immunoreactivity (Fos-IR) in several prominent groups of central neurons: the piriform cortex, bed nucleus of the stria terminalis, islands of Calleja, subfornical organ, central nucleus of the amygdala, parabrachial nucleus, supraoptic and paraventricular nuclei, pontine A5, locus ceruleus, ventrolateral medulla, the nucleus of the solitary tract, area postrema, and intermediolateral cell column in the spinal cord. Elevation of blood pressure by infusion of phenylephrine caused the appearance of Fos-IR in fewer groups of neurons: the bed nucleus of the stria terminalis, central nucleus of the amygdala, parabrachial nucleus, the nucleus of the solitary tract and area postrema. The differential distribution of Fos neurons in hypotensive versus hypertensive animals underscores the potential application of Fos as a metabolic marker in identifying a network of neurons responding to a specific cardiovascular challenge. Further, simultaneous characterization of the transmitter phenotype of Fos-containing neurons offers an additional advantage of this method over other conventional tract-tracing techniques.

Animals↗
PubMedDate not supplied

Localization of prostaglandin G/H synthase gene expression in rat brain by in situ hybridization.

Prostaglandin G/H synthase (PGH synthase; EC 1.14.99.1, cyclooxygenase) is a key enzyme in prostanoid biosynthesis. The cellular sites for PGH synthase gene expression have not been identified in any tissue. We have mapped the expression of PGH synthase in rat brain by in situ hybridization and have found large quantities of PGH synthase mRNA in the granular cell layer of the cerebellum, pyramidal layer of the hippocampus and granular cells of the dentate gyrus, moderate levels in pyramidal cells of the piriform cortex, cellular layers of the cerebral cortex, central nucleus of the amygdala, paraventricular, supraoptic and suprachiasmatic nuclei and cells of pituitary body, and low levels in most other regions of the rat brain. These results may provide a basis for an understanding of possible roles of PGH synthase in the central nervous system of adult rats.

Animals↗
PubMed1990

Effects of treatment with estradiol and parental experience on the number and distribution of estrogen-binding neurons in the ovariectomized mouse brain.

The effects of a treatment with estradiol benzoate alone (EB, for 2 weeks) and combined with parental experience (for 5 days) on the number and regional distribution of estrogen receptor-containing cells (ER+ cells) in the brain of ovariectomized mice were studied using an immunocytochemical staining technique. Treatment with EB alone significantly reduces the average density of ER+ cells (labeled cells/mm3) in the ventromedial hypothalamic nucleus (VMH) and in the anterior hypothalamic area (AHA). Parental experience of EB-treated females (achieved by co-caring for 12 pups together with the mother for 5 days), however, leads to a significant increase in the absolute number and relative density of ER+ cells in the VMH. Moreover, ER+ cells are found in the entorhinal and piriform cortex in experienced females only. Generally, a trend of decrease in both the number and density of labeled cells is observed after EB treatment in all regions of the brain where immunostaining is observed in ovariectomized mice (amygdaloid and hypothalamic nuclei, preoptic area), whereas an increase in the above quantitative variables is found in experienced females. The hypothesis is put forward that olfactory cues from the young, experienced during the co-caring period promote the increase in ER+ cells in the above brain regions, which all receive input from the olfactory and/or vomeronasal systems.

Animals↗