Posterior Cortical Nucleus Research Articles

Projections from the amygdaloid complex to the piriform cortex: A PHA-L study in the rat.

Projections from the amygdala to the piriform cortex are proposed to provide a pathway via which the emotional system can modulate the processing of olfactory information as well as mediate the spread of seizure activity in epilepsy. To understand the details of the distribution and topography of these projections, we injected the anterograde tracer Phaseolus vulgaris-leucoagglutinin into different nuclear divisions of the amygdaloid complex in 101 rats and analyzed the distribution and density of projections in immunohistochemically processed preparations. The heaviest projections from the amygdala to the piriform cortex originated in the medial division of the lateral nucleus, the periamygdaloid and sulcal subfields of the periamygdaloid cortex, and the posterior cortical nucleus. The heaviest terminal labeling was observed in layers Ib and III of the medial aspect of the posterior piriform cortex. Lighter projections to the posterior piriform cortex originated in the dorsolateral division of the lateral nucleus, the magnocellular and parvicellular divisions of the basal and accessory basal nuclei, and the anterior cortical nucleus. The projections to the anterior piriform cortex were light and originated in the dorsolateral and medial divisions of the lateral nucleus, the magnocellular division of the basal and accessory basal nuclei, the anterior and posterior cortical nuclei, and the periamygdaloid subfield of the periamygdaloid cortex. The results indicate that only selective amygdaloid nuclei or their subdivisions project to the piriform cortex. In addition, substantial projections from several amygdaloid nuclei converge in the medial aspect of the posterior piriform cortex. Via these projections, the amygdaloid complex can modulate the processing of olfactory information in the piriform cortex. In pathologic conditions such as epilepsy, these connections might provide pathways for the spread of seizure activity from the amygdala to extra-amygdaloid regions.

Activin mRNA induced during amygdala kindling shows a spatiotemporal progression that tracks the spread of seizures.

The progressive development of seizures in rats by amygdala kindling, which models temporal lobe epilepsy, allows the study of molecular regulators of enduring synaptic changes. Neurotrophins play important roles in synaptic plasticity and neuroprotection. Activin, a member of the transforming growth factor-beta superfamily of growth and differentiation factors, has recently been added to the list of candidate synaptic regulators. We mapped the induction of activin betaA mRNA in amygdala and cortex at several stages of seizure development. Strong induction, measured 2 hours after the first stage 2 (partial) seizure, appeared in neurons of the ipsilateral amygdala (confined to the lateral, basal, and posterior cortical nuclei) and insular, piriform, orbital, and infralimbic cortices. Activin betaA mRNA induction, after the first stage 5 (generalized) seizure, had spread to the contralateral amygdala (same nuclear distribution) and cortex, and the induced labeling covered much of the convexity of neocortex as well as piriform, perirhinal, and entorhinal cortices in a nearly bilaterally symmetrical pattern. This pattern had filled in by the sixth stage 5 seizure. Induced labeling in cortical neurons was confined mainly to layer II. A similar temporal and spatial pattern of increased mRNA expression of brain-derived neurotrophic factor (BDNF) was found in the amygdala and cortex. Activin betaA and BDNF expression patterns were similar at 1, 2, and 6 hours after the last seizure, subsiding at 24 hours; in contrast, c-fos mRNA induction appeared only at 1 hour throughout cortex and then subsided. In double-label studies, activin betaA mRNA-positive neurons were also BDNF mRNA positive, and they did not colocalize with GAD67 mRNA (a marker of gamma-aminobutyric acidergic neurons). The data suggest that activin and BDNF transcriptional activities accurately mark excitatory neurons participating in seizure-induced synaptic alterations and may contribute to the enduring changes that underlie the kindled state.

Damage to the amygdalo-hippocampal projection in temporal lobe epilepsy: A tract-tracing study in chronic epileptic rats

Both the amygdala and hippocampus are damaged in drug-resistant temporal lobe epilepsy (TLE), suggesting that amygdalo-hippocampal interconnectivity is compromised in TLE. Therefore, we examined one of the major projections from the amygdala to the hippocampus, the projection from the amygdala to the CA1 subfield of the hippocampus/subiculum border region, and assessed whether it is preserved in rats with spontaneous seizures. Male Wistar rats were injected with kainic acid (9 mg/kg, i.p.) to induce chronic epilepsy. The occurrence of spontaneous seizures was monitored 5 or 15 weeks later by video-recording the rats for up to 5 days. Saline-injected animals served as controls. Thereafter, the retrograde tracer Fluoro-gold was injected into the border region of the temporal CA1/subiculum. Rats were perfused for histology 1–2 weeks later and sections were immunohistochemically processed to detect Fluoro-gold-positive cells. Comparison of the labeling in control and epileptic tissue indicated that a large cluster of retrogradely labeled cells in the parvicellular division of the basal nucleus was well preserved in epilepsy, even when the neuronal damage in the amygdala was substantial. Another large cluster of retrogradely labeled cells in the lateral division of the amygdalo-hippocampal area, the posterior cortical nucleus (part of the vomeronasal amygdala), and the periamygdaloid cortex (part of the olfactory amygdala), however, had disappeared in epileptic brain in parallel to severe neuronal loss in these nuclei. These data demonstrate that a projection from the parvicellular division of the basal nucleus to the temporal CA1/subiculum region is resistant to status epilepticus-induced neuronal damage and provides a candidate pathway by which seizure activity can spread and propagate from the amygdala to the hippocampal formation.

Projections from the periamygdaloid cortex to the amygdaloid complex, the hippocampal formation, and the parahippocampal region: a PHA-L study in the rat.

The periamygdaloid cortex, an amygdaloid region that processes olfactory information, projects to the hippocampal formation and parahippocampal region. To elucidate the topographic details of these projections, pathways were anterogradely traced using Phaseolus vulgaris leukoagglutinin (PHA-L) in 14 rats. First, we investigated the intradivisional, interdivisional, and intra-amygdaloid connections of various subfields [periamygdaloid subfield (PAC), medial subfield (PACm), sulcal subfield (PACs)] of the periamygdaloid cortex. Thereafter, we focused on projections to the hippocampal formation (dentate gyrus, hippocampus proper, subiculum) and to the parahippocampal region (presubiculum, parasubiculum, entorhinal, and perirhinal and postrhinal cortices). The PACm had the heaviest intradivisional projections and it also originated light interdivisional projections to other periamygdaloid subfields. Projections from the other subfields converged in the PACs. All subfields provided substantial intra-amygdaloid projections to the medial and posterior cortical nuclei. In addition, the PAC subfield projected to the ventrolateral and medial divisions of the lateral nucleus. The heaviest periamygdalohippocampal projections originated in the PACm and PACs, which projected moderately to the temporal end of the stratum lacunosum moleculare of the CA1 subfield and to the molecular layer of the ventral subiculum. The PACm also projected moderately to the temporal CA3 subfield. The heaviest projections to the entorhinal cortex originated in the PACs and terminated in the amygdalo-entorhinal, ventral intermediate, and medial subfields. Area 35 of the perirhinal cortex was lightly innervated by the PAC subfield. Thus, these connections might allow for olfactory information entering the amygdala to become associated with signals from other sensory modalities that enter the amygdala via other nuclei. Further, the periamygdalohippocampal pathways might form one route by which the amygdala modulates memory formation and retrieval in the medial temporal lobe memory system. These pathways can also facilitate the spread of seizure activity from the amygdala to the hippocampal and parahippocampal regions in temporal lobe epilepsy.

Projections from the amygdaloid complex to the claustrum and the endopiriform nucleus: a Phaseolus vulgaris leucoagglutinin study in the rat.

The claustrum and the endopiriform nucleus contribute to the spread of epileptiform activity from the amygdala to other brain areas. Data of the distribution of pathways underlying the information flow between these regions are, however, incomplete and controversial. To investigate the projections from the amygdala to the claustrum and the endopiriform nucleus, we injected the anterograde tracer Phaseolus vulgaris leucoagglutinin into various divisions of the amygdaloid complex, including the lateral, basal, accessory basal, central, anterior cortical and posterior cortical nuclei, the periamygdaloid cortex, and the amygdalohippocampal area in the rat. Analysis of immunohistochemically processed sections reveal that the heaviest projections to the claustrum originate in the magnocellular division of the basal nucleus. The projection is moderate in density and mainly terminates in the dorsal aspect of the anterior part of the claustrum. Light projections from the parvicellular and intermediate divisions of the basal nucleus terminate in the same region, whereas light projections from the accessory basal nucleus and the lateral division of the amygdalohippocampal area innervate the caudal part of the claustrum. The most substantial projections from the amygdala to the endopiriform nucleus originate in the lateral division of the amygdalohippocampal area. These projections terminate in the central and caudal parts of the endopiriform nucleus. Lighter projections originate in the anterior and posterior cortical nuclei, the periamygdaloid cortex, the medial division of the amygdalohippocampal area, and the accessory basal nucleus. These data provide an anatomic basis for recent functional studies demonstrating that the claustrum and the endopiriform nucleus are strategically located to synchronize and spread epileptiform activity from the amygdala to the other brain regions. These topographically organized pathways also provide a route by means of which the claustrum and the endopiriform nucleus have access to inputs from the amygdaloid networks that process emotionally significant information.

Distribution of PSA-NCAM expression in the amygdala of the adult rat

Synaptic plasticity in the amygdala appears to be necessary for the generation of emotional memories. However, the molecular bases of this plasticity are not fully understood. Because the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) has been implicated in memory consolidation in the hippocampus and temporal cortex, we have studied in detail the expression of this molecule in the adult rat amygdala with an antibody against PSA-NCAM. Our results demonstrate for the first time the presence of PSA-NCAM in the adult rat amygdala. Immunoreactive somata and processes are abundant in the amygdalo-hippocampal transition area, central nucleus, intra-amygdaloid bed nucleus of the stria terminalis, anterior and posterior cortical nuclei, periamygdaloid cortex and medial nucleus of the amygdala. In addition PSA-NCAM immunoreactive neuronal somata and processes exist in the lateral, basal and accessory basal nuclei, anterior amygdaloid area and amygdalo-striatal area. The presence of this molecule in areas that receive olfactory or vomeronasal input could reflect the intrinsic plasticity of these chemosensory systems. PSA-NCAM expression in the lateral amygdala could indicate its participation in the plastic events that lead to the generation of emotional memories such as those related to fear conditioning.

Projections from the posterior cortical nucleus of the amygdala to the hippocampal formation and parahippocampal region in rat.

The posterior cortical nucleus of the amygdala is involved in the processing of pheromonal information and presumably participates in ingestive, defensive, and reproductive behaviors as a part of the vomeronasal amygdala. Recent studies suggest that the posterior cortical nucleus might also modulate memory processing via its connections to the medial temporal lobe memory system. To investigate the projections from the posterior cortical nucleus to the hippocampal formation and the parahippocampal region, as well as the intra-amygdaloid connectivity in detail, we injected the anterograde tracer phaseolus vulgaris-leucoagglutinin into different rostrocaudal levels of the posterior cortical nucleus. Within the hippocampal formation, the stratum lacunosum-moleculare of the temporal CA1 subfield and the adjacent molecular layer of the proximal temporal subiculum received a moderate projection. Within the parahippocampal region, the ventral intermediate, dorsal intermediate, and medial subfields of the entorhinal cortex received light to moderate projections. Most of the labeled terminals were in layers I, II, and III. In the ventral intermediate subfield, layers V and VI were also moderately innervated. Layers I and II of the parasubiculum received a light projection. There were no projections to the presubiculum or to the perirhinal and postrhinal cortices. The heaviest intranuclear projection was directed to the deep part of layer I and to layer II of the posterior cortical nucleus. There were moderate-to-heavy intra-amygdaloid projections terminating in the bed nucleus of the accessory olfactory tract, the central division of the medial nucleus, and the sulcal division of the periamygdaloid cortex. Our data suggest that via these topographically organized projections, pheromonal information processed within the posterior cortical nucleus can influence memory formation in the hippocampal and parahippocampal areas. Also, these pathways provide routes through which seizure activity can spread from the epileptic amygdala to the surrounding region of the temporal lobe.

Retrograde labelling of mitral/tufted cells in the mouse accessory olfactory bulb following local injections of the lipophillic tracer DiI into the vomeronasal amygdala

It has recently become apparent that there are two classes of vomeronasal receptor neurons that project to functionally separate anterior and posterior sub-regions of the mammalian accessory olfactory bulb. However, anterograde tracing of the projections from these sub-regions, in the mouse, has revealed that the processing pathways are not segregated at the level of the vomeronasal amygdala. Both sub-regions have overlapping projections to the superficial lamina of the medial and posterior medial cortical nuclei of the amygdala. However, differential projections have been found in the opossum, in which only the posterior sub-region projects to the deeper laminae of the medial amygdala. Therefore, there may be species differences in these projections that are important for the control of reproductive behaviour. This study used an alternative approach of retrogradely tracing mitral/tufted cell projections from different nuclei of the vomeronasal amygdala back to the accessory olfactory bulb of mice. Local injections of the lipophillic tracer DiI were made into the antero-dorsal and postero-ventral divisions of the medial amygdala, and into the postero-medial cortical amygdala. In each case, provided the DiI affected the superficial lamina Ia, labelled mitral/tufted cells were found distributed throughout the anterior-posterior extent of the accessory olfactory bulb. These results confirm that mitral/tufted cells of the anterior and posterior sub-regions of the accessory olfactory bulb project to both the medial and postero-medial cortical nuclei of the amygdala. There was no evidence for differential projections from the anterior and posterior sub-regions accessory olfactory bulb in mice, as has been reported to occur in other species.

Reciprocal connections between the amygdala and the hippocampal formation, perirhinal cortex, and postrhinal cortex in rat. A review.

Recent anterograde and retrograde studies in the rat have provided detailed information on the origin and termination of the interconnections between the amygdaloid complex and the hippocampal formation and parahippocampal areas (including areas 35 and 36 of the perirhinal cortex and the postrhinal cortex). The most substantial inputs to the amygdala originate in the rostral half of the entorhinal cortex, the temporal end of the CA1 subfield and subiculum, and areas 35 and 36 of the perirhinal cortex. The amygdaloid nuclei receiving the heaviest inputs are the lateral, basal, accessory basal, and central nuclei as well as the amygdalohippocampal area. The heaviest projections from the amygdala to the hippocampal formation and the parahippocampal areas originate in the lateral, basal, accessory basal, and posterior cortical nuclei. These pathways terminate in the rostral half of the entorhinal cortex, the temporal end of the CA3 and CA1 subfields or the subiculum, the parasubiculum, areas 35 and 36 of the perirhinal cortex, and the postrhinal cortex. The connectional data are summarized and the underlying principles of organization of these projections are discussed.

Differential Distribution and Regulation of OX1 and OX2 Orexin/Hypocretin Receptor Messenger RNA in the Brain upon Fasting

To further understand the functions of the orexin/hypocretin system, we examined the expression and regulation of the orexin/hypocretin receptor (OX1R and OX2R) mRNA in the brain by using quantitative in situ hybridization. Expression of OX1R and OX2R mRNA exhibited distinct distribution patterns. Within the hypothalamus, expression for the OX1R mRNA was largely restricted in the ventromedial (VMH) and dorsomedial hypothalamic nuclei, while high levels of OX2R mRNA were contained in the paraventricular nucleus, VMH, and arcuate nucleus as well as in mammilary nuclei. In the amygdala, OX1R mRNA was expressed throughout the amygdaloid complex with robust labeling in the medial nucleus, while OX2R mRNA was only present in the posterior cortical nucleus of amygdala. High levels of OX2R mRNA were also observed in the ventral tegmental area. Moreover, both OX1R and OX2R mRNA were observed in the hippocampus, some thalamic nuclei, and subthalamic nuclei. Furthermore, we analyzed the effect of fasting on levels of OX1R and OX2R mRNA in the hypothalamic and amygdaloid subregions. After 20 h of fasting, levels of OX1R mRNA were significantly increased in the VMH and the medial division of amygdala. An initial decrease (14 h) and a subsequent increase (20 h) in OX1R mRNA levels after fasting were observed in the dorsomedial hypothalamic nucleus and lateral division of amygdala. Levels of OX2R mRNA were augmented in the arcuate nucleus, but remained unchanged in the dorsomedial hypothalamic nucleus, paraventricular hypothalamic nucleus, and amygdala following fasting. The time-dependent and region-specific regulatory patterns of OX1R and OX2R suggest that they may participate in distinct neural circuits under the condition of food deprivation.

Distribution of mRNAs encoding CRF receptors in brain and pituitary of rat and mouse.

Two G protein-coupled receptors have been identified that bind corticotropin-releasing factor (CRF) and urocortin (UCN) with high affinity. Hybridization histochemical methods were used to shed light on controversies concerning their localization in rat brain, and to provide normative distributional data in mouse, the standard model for genetic manipulation in mammals. The distribution of CRF-R1 mRNA in mouse was found to be fundamentally similar to that in rat, with expression predominating in the cerebral cortex, sensory relay nuclei, and in the cerebellum and its major afferents. Pronounced species differences in distribution were few, although more subtle variations in the relative strength of R1 expression were seen in several forebrain regions. CRF-R2 mRNA displayed comparable expression in rat and mouse brain, distinct from, and more restricted than that of CRF-R1. Major neuronal sites of CRF-R2 expression included aspects of the olfactory bulb, lateral septal nucleus, bed nucleus of the stria terminalis, ventromedial hypothalamic nucleus, medial and posterior cortical nuclei of the amygdala, ventral hippocampus, mesencephalic raphe nuclei, and novel localizations in the nucleus of the solitary tract and area postrema. Several sites of expression in the limbic forebrain were found to overlap partially with ones of androgen receptor expression. In pituitary, rat and mouse displayed CRF-R1 mRNA signal continuously over the intermediate lobe and over a subset of cells in the anterior lobe, whereas CRF-R2 transcripts were expressed mainly in the posterior lobe. The distinctive expression pattern of CRF-R2 mRNA identifies additional putative central sites of action for CRF and/or UCN. Constitutive expression of CRF-R2 mRNA in the nucleus of the solitary tract, and stress-inducible expression of CRF-R1 transcripts in the paraventricular nucleus may provide a basis for understanding documented effects of CRF-related peptides at a loci shown previously to lack a capacity for CRF-R expression or CRF binding. Other such "mismatches" remain to be reconciled.

Quantitative Autoradiography of Mu-Opioid Receptors in the CNS of Alcohol-Naive Alcohol-Preferring P and -Nonpreferring NP Rats

M cBRIDE, W. J., E. CHERNET, D. L. M cKINZIE, L. LUMENG AND T.-K. LI. Quantitative autoradiography of mu-opioid receptors in the CNS of alcohol-naive alcohol-preferring P and -nonpreferring NP rats. ALCOHOL 16(4) 317–323, 1998.–The densities of mu-opioid binding sites in the CNS of alcohol-naive adult male P and NP rats ( N = 9 each line) were examined using quantitative autoradiography. Coronal sections (20 μm) were prepared from frozen brains and incubated in 5 nM [ 3H]DAMGO to label mu-opioid receptor sites. Nonspecific binding was determined in the presence of 1 μM DAMGO. The amount of [ 3H]DAMGO binding was (a) 20–25% higher in the olfactory tubercle, nucleus accumbens shell and core, and basolateral and lateral amygdaloid nuclei; (b) 15% higher in the lateral septal intermediate nucleus and caudate-putamen patches; and (c) 10–30% lower in the pyramidal and radiatum layers in the CA1 region of the anterior dorsal hippocampus, ventral dentate gyrus and CA1 pyramidal layer of the posterior hippocampus, and posterior medial cortical amygdaloid nucleus of the P compared to the NP rat. No line differences were found in any of the other regions examined (e.g., the cerebral cortical subregions and layers, thalamic nuclei, ventral tegmental area, ventral pallidum, lateral hypothalamus, other regions of the hippocampus, and several subcortical structures). The innate differences in the amount of binding to mu-opioid recognition sites in certain limbic structures, such as the nucleus accumbens, amygdala, and olfactory tubercle, of the P and NP lines may be factors contributing to their disparate alcohol drinking characteristics.

Amygdala damage in experimental and human temporal lobe epilepsy.

The amygdala complex is one component of the temporal lobe that may be damaged unilaterally or bilaterally in children and adults with temporal lobe epilepsy (TLE) or following status epilepticus. Most MR (magnetic resonance) imaging studies of epileptic patients have shown that volume reduction of the amygdala ranges from 10-30%. In the human amygdala, neuronal loss and gliosis have been reported in the lateral and basal nuclei. Studies in rats have more specifically identified the amygdaloid regions that are sensitive to status epilepticus-induced neuronal damage. These areas include the medial division of the lateral nucleus, the parvicellular division of the basal nucleus, the accessory basal nucleus, the posterior cortical nucleus, and portions of the anterior cortical and medial nuclei. Otherwise, other amygdala nuclei, such as the magnocellular and intermediate divisions of the basal nucleus and the central nucleus, remain relatively well preserved. Amygdala kindling studies in rats have shown that the density of a subpopulation of GABAergic inhibitory neurons that also contain somatostatin may be reduced even after a low number of generalized seizures. While analyses of histological sections and MR images indicate that in approximately 10% of TLE patients, seizure-induced damage is isolated to the amygdala, more often amygdala damage is combined with damage to the hippocampus and/or other brain areas. Moreover, recent data from rodents and nonhuman primates suggest that structural and functional alterations caused by seizure activity originating in the amygdala are not limited to the amygdala itself, but may also affect other temporal lobe structures. The information gathered so far on damage to the amygdala in epilepsy or after status epilepticus suggests that local alterations in inhibitory circuitries may contribute to a lowered seizure threshold and greater excitability within the amygdala. Furthermore, damage to select nuclei in the amygdala may predict impairment of performance in behavioral tasks that depend on the integrity of the amygdaloid circuits.

Status epilepticus causes selective regional damage and loss of GABAergic neurons in the rat amygdaloid complex.

In human epilepsy, the amygdala is often a primary focus for seizures. To analyse the status epilepticus-induced alterations in the amygdaloid circuitries which may later underlie epileptogenesis, we studied the amygdaloid damage in kainic acid and perforant pathway stimulation models of status epilepticus in the rat. We also studied the damage to inhibitory GABAergic neurons. In both models, the medial division of the lateral nucleus, the parvicellular division of the basal nucleus and portions of the anterior cortical and medical nuclei were damaged. In the kainate model, where the seizure activity was more severe, the accessory basal nucleus, amygdalohippocampal area, posterior cortical nucleus and periamygdaloid cortex were also damaged. Two weeks after kainate-induced seizures, 56% of the GABA-immunoreactive neurons remained in the lateral nucleus (P < 0.05) and 25% in the basal nucleus (P < 0.01). Further analysis showed that one subpopulation of damaged GABAergic neurons was immunoreactive for somatostatin (48% remaining in the lateral nucleus, P < 0.01; 33% in the basal nucleus, P < 0.01). In the perforant pathway stimulation model, the damage to somatostatin neurons was milder. According to our data, the initial insult, such as status epilepticus, selectively damages amygdaloid nuclei. The loss of inhibition may underlie the spontaneous generation of seizures and epileptogenesis. On the other hand, many amygdaloid output nuclei (magnocellular and intermediate division of the basal nucleus, the central nucleus) remained relatively undamaged, providing pathways for seizures spread and generation of seizure-related behavioural manifestations such as motor convulsions and fear response.

In vivo regulation of neurotensin receptors following long-term pharmacological blockade with a specific receptor antagonist

Adaptive changes in brain neurotensin (NT) receptors were investigated in rats after repeated administration of SR 48692, a potent and selective non-peptide NT receptor antagonist. Administration of SR 48692 (1 mg/kg i.p.) for 15 days did not alter NT content in the brain but highly enhanced the expression of NT receptor mRNA as shown by quantitative in situ hybridization. The increase of the signal was observed in numerous areas of the brain, such as the anterior cingulate, perirhinal and retrosplenial cortices, the suprachiasmatic nucleus, the ventral tegmental area, the substantia nigra and the posterior cortical nucleus of the amygdaloid complex. Moreover, the SR 48692 treatment induced the expression of NT receptor mRNA in several nuclei of the diencephalon where it could not be detected in basal conditions. Immunoblot analysis with a specific antibody directed against the rat cloned NT receptor revealed an important increase in NT receptor protein in the brain of SR 48692-treated rats, correlating well with the increase in NT receptor mRNA levels. Surprisingly, the number and the affinity constant of NT binding sites determined on brain membrane homogenates remained unchanged after SR 48692 treatment, even after membrane permeabilization with low concentrations of digitonin. These results suggest that chronic treatment with a specific NT antagonist induces an up-regulation of NT receptors at the level of mRNA and protein. Moreover, they indicate that after a chronic treatment with SR 48692, the number of NT binding sites remains stable in contrast to what is observed after 5-day treatment or with central monoaminergic receptor following their long-term blockade.

Estrogen regulation of preproenkephalin messenger RNA in the forebrain of female mice

We studied the effects of 10 μg of 17- β-estradiol-3-benzoate treatment on preproenkephalin (PPE) mRNA expression in female ovariectomized (OVX) Swiss Webster mice after 0, 1, 6, 12, 24, or 48 h, using the in situ hybridization technique. The VMH showed a 1.6- and 3.3-fold increase in PPE mRNA levels after 24 and 48 h of estrogen treatment (respectively) when compared to OVX females. No differences at 1, 6 or 12 h of estrogen treatment groups were observed compared to control groups. PPE mRNA levels were also increased at 24 and 48 h after estrogen treatment in the posterior medial nucleus of the amygdala (MeAmyg) by 3.3- and 2.5-fold, respectively, and in the arcuate nucleus (ARC) by 2- and 1.9-fold, respectively. No effects of estrogen were observed on PPE mRNA levels in the caudate-putamen (CPu) or the posterior lateral cortical nucleus of the amygdala (plCoAmyg). Furthermore, basal levels of PPE mRNA expression in the VMH and MeAmyg of female mice were lower than those observed in rats, although levels in the CPu, plCoAmyg, and ARC were similar between females of the two species. In conclusion, we have found two differences between the species. First, Swiss mice demonstrated a slower time course of estrogen induction of PPE mRNA in the VMH, ARC, and MeAmyg compared to female rats. Second, there are differences in basal levels of PPE in the MeAmyg and VMH.

Intrinsic connections of the rat amygdaloid complex: projections originating in the accessory basal nucleus.

The amygdaloid complex plays an important role in the detection of emotional stimuli, the generation of emotional responses, the formation of emotional memories, and perhaps other complex associational processes. These functions depend upon the flow of information through intricate and poorly understood circuitries within the amygdala. As part of an ongoing project aimed at further elucidating these circuits, we examined the intra-amygdaloid connections of the accessory basal nucleus in the rat. In addition, we examined connections of the anterior cortical nucleus and amygdalahippocampal area to determine whether portions of these nuclei should be included in the accessory basal nucleus (as some earlier studies suggest). Phaseolus vulgaris leucogglutinin was injected into different rostrocaudal levels of the accessory basal nucleus (n = 12) or into the anterior cortical nucleus (n = 3) or amygdalahippocampal area (n = 2). The major intra-amygdaloid projections from the accessory basal nucleus were directed to the medial and capsular divisions of the central nucleus, the medial division of the amygdalohippocampal area, the medial division of the lateral nucleus, the central division of the medial nucleus, and the posterior cortical nucleus. The projections originating in the anterior cortical nucleus and the lateral division of the amygdalohippocampal area differed from those originating in the accessory basal nucleus, which suggests that these areas are not part of the accessory basal nucleus. The present findings and our previous data suggest that each of the deep amygdaloid nuclei have different intra-amygdaloid connections. The pattern of these various connections suggests that information entering the amygdala from different sources can be integrated only in certain amygdaloid regions.

Calbindin-D28k-immunoreactive cells and fibres in the human amygdaloid complex

The distribution of calbindin-D28k-immunoreactive cells and fibres in five human amygdalae was analysed from sections that had been stained immunohistochemically with a monoclonal antibody raised against calbindin-D28k. The highest density of calbindin-D28k-positive neurons were found in the anterior cortical, medial, posterior cortical and accessory basal nuclei, in the parvicellular division of the basal nucleus and in the amygdalohippocampal area. The lowest densities of immunopositive neurons were found in the paralaminar nucleus, in the periamygdaloid cortex (PAC1 and PACo) and in some of the intercalated nuclei. The deep nuclei (lateral, basal and accessory basal nuclei) contained a high density of calbindin-D28k-immunoreactive fibres and terminals. The cortical nuclei and the central nucleus were characterized by intense neuropil labelling. Morphologically, a large majority of the calbindin-D28k-immunoreactive neurons were aspiny or sparsely spiny and resembled inhibitory local circuit neurons. A small population of lightly-stained, pyramidal-shaped neurons was also observed. In most of the amygdaloid nuclei, calbindin-D28k-immunoreactive fibres travelled close to each other and formed bundles, which suggests that some of the immunostained neurons were double-bouquet cells. In the paralaminar nucleus, the calbindin-D28k-immunoreactive axons formed tortuous plexus (100–200mm in diameter) that surrounded several unstained somata.This study provides baseline information on the morphology and distribution of calcium-binding protein-containing inhibitory cells and fibres immunoreactive for calbindin-D28k in the human amygdaloid complex. This information can be used in future studies on the pathogenesis of diseases known to damage the amygdala, such as Alzheimer's disease and temporal lobe epilepsy.

Regional induction of fos immunoreactivity in the brain by anticonvulsant stimulation of the vagus nerve.

Electrical stimulation of the vagus nerve exerts an antiepileptic effect on human partial-onset epilepsy, but little is known about the brain structures that mediate this phenomenon. Fos is a nuclear protein that is expressed under conditions of high neuronal activity. We utilized fos immunolabeling techniques on Sprague-Dawley rat brains to identify regions that are activated by antiepileptic stimulation of the left vagus nerve. Vagus nerve stimulation (VNS) induced specific nuclear fos immunolabeling in several forebrain structures, including the posterior cortical amygdaloid nucleus, cingulate and retrosplenial cortex, ventromedial and arcuate hypothalamic nuclei. In the brainstem, there was specific immunolabeling in vagus nerve nuclei, in the A5 and locus ceruleus noradrenergic nuclei, and in the cochlear nucleus. No labeling of these structures occurred in sham-operated, unstimulated control animals. Intense labeling also occurred in habenular nucleus of thalamus after vagus nerve stimulation, whereas only mild staining occurred in unstimulated animals. Several of the brain structures activated by VNS are important for genesis or regulation of seizures in the forebrain. These structures may mediate the antiepileptic effect of VNS.

Intrinsic connections of the rat amygdaloid complex: Projections originating in the lateral nucleus

The amygdaloid complex receives sensory information from a variety of sources. A widely held view is that the amygdaloid complex utilizes this information to orchestrate appropriate species-specific behaviors to ongoing experiences. Relatively little is known, however, about the circuitry through which information is processed within the amygdaloid complex. The lateral nucleus is the major recipient of extrinsic sensory information and is the origin of many intra-amygdaloid projections. In this study, we reinvestigated the organization of intra-amygdaloid projections originating from the lateral nucleus using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). The lateral nucleus has highly organized intranuclear connections. Dense projections interconnect rostral and caudal levels of the lateral and the medial divisions of the nucleus, and the lateral and medial divisions of the lateral nucleus are also interconnected. The major extranuclear projections of the lateral nucleus are (in descending order of magnitude) to the accessory basal nucleus, the basal nucleus, the periamygdaloid cortex, the dorsal portion of the central division of the medial nucleus, the posterior cortical nucleus, the capsular division of the central nucleus, and the lateral division of the amygdalohippocampal area. The pattern of extranuclear projections varied depending on the rostrocaudal or mediolateral location of the injection site within the lateral nucleus. These findings indicate that intra-amygdaloid projections originating in the lateral nucleus are both more widespread and more topographically organized than was previously appreciated.