摘要:

AbstractThe most prominent hypothesis of hippocampal function likens the hippocampus to a “cognitive map,” a term used by a famous learning theorist, E. C. Tolman, to explain maze learning. The usual application of this concept of cognitive map, as it applies to the hippocampus, is to what is called spatial learning, mainly in the radial‐arm maze of Olton and the Morris water maze. In a recentHippocampusForum, evidence for the cognitive map hypothesis was reviewed in a lead article by Nadel, followed by a series of commentaries by leading investigators of hippocampal function. This speculative commentary offers an alternative not represented in the forum—that the function of the hippocampus in spatial learning is not as a cognitive map, but that it subserves another function proposed by Tolman in his work on simple discrimination learning, vicarious trial and error, based on incipient, conflicting dispositions to approach an

ISSN:1050-9631    

DOI:10.1002/hipo.450030302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIn the present study, using Golgi and electron microscopy techniques, experimentally induced epilepsy (kindling and kainate treatment) elicited collateral sprouting of mossy fibers in rat hippocampus. Collateral branches invade the hilus, cross the granule cell layer, and distribute throughout the inner third of the molecular layer. These newly developed collaterals may acquire the typical features of mossy fibers including giant fiber varicosities (mousses), although the mean surface of these mousses was thinner in these collaterals than in terminal branches. Granule cell dendrites may develop giant thorny excrescences, suggesting that the targets of these collaterals are granule cells. Giant synaptic boutons appear in the inner third of molecular layer of epileptic rats. These boutons acquire the morphological features of mossy fiber boutons and made multiple synaptic contacts with dendritic spines. The analysis of the profile types suggests that some of the newly developed collateral mossy fibers made hypotrophic synaptic contacts.

ISSN:1050-9631    

DOI:10.1002/hipo.450030303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe present study usedin vitroautoradiography to examine the density of [3H]‐kainate (KA) binding in subregions of the hippocampal formation and certain cortical areas in young (7–8 months) and aged (27–29 months) Long‐Evans rats. In addition, the topography of KA binding in the dentate molecular layer was examined for evidence of reactive reorganization in the aged brain. This investigation of age‐related changes in [3H]‐KA binding included correlations with the animals' spatial learning performance in a Morris water maze. The results showed an age‐related decrease in the density of [3H]‐KA binding in several regions of the hippocampal formation (CA3, CA1, hilus) and within related cortical areas (subicular complex, entorhinal cortex, perirhinal cortex). In addition, an expanded zone of KA binding in the molecular layer of the dentate gyrus was observed in the aged group. This expansion of KA binding may reflect sprouting due to a loss of perforant path input to the dentate. The results of additional correlational analyses, however, indicated that these changes in the density and topography of [3H]‐KA binding were not strongly correlated with a decline in place

ISSN:1050-9631    

DOI:10.1002/hipo.450030304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAlthough the entorhinal cortex is a key structure connecting the hippocampal formation with the rest of the cerebral cortex, little is known about its early chemoanatomical development in primates. In the present study, a cytoarchitectonic analysis and immunocytochemical detection of somatostatin, neurotensin, parvalbumin, calbindin‐D 28K, DARPP‐32, as well as tyrosine hydroxylase, dopamine‐β‐hydroxylase, and serotonin, were carried out on serial sections of the entorhinal cortex of six rhesus monkey fetuses aged E47 to E90 (gestation period 165 days). At E56 the cortical plate of the entorhinal cortex already exhibited a sublamination; at E64 the lamina dissecans was partly formed, allowing the emergence of the lamina principalis externa and interna, and at E83 most of the regional and laminar subdivisions characteristic of the adult cortex could be identified, except for the rhinal sulcus restricted to a small dimple. The neurochemical development paralleled the early cytoarchitectonic differentiation, both largely preceding that of the neighboring cortical areas. The somatostatin‐like immunoreactive innervation, first detected at E56, was very dense as early as E64 and displayed by E83 a laminar distribution similar to that found in the adult. Labeled neurons indicated an intrinsic origin for this innervation but an extrinsic connection might be present as labeled fibers in the subplate of the entorhinal cortex were in continuity with positive fibers in the intermediate zone of the hippocampal formation. A faint neurotensin‐like immunoreactivity first detected at E64 became prominent at E83 in the entorhinal cortex but stopped abruptly at the anlage of the rhinal sulcus. The lack of neurotensin‐labeled neurons contrasted with their presence in other parts of the hippocampal region and suggested a precocious extrinsic connection. Only rare parvalbumin‐LIR neurons were detected at midgestation, whereas calbindin‐D 28K was expressed from E47 on in Cajal‐Retzius cells and from E56 on in various types of neurons in the cortical plate and subplate. Most characteristic was a category of medium‐sized, deeply stained calbindin‐LIR neurons, present only in the lamina principalis externa and possibly corresponding to the population of large neurons described by Kostovic et al. (1990, Soc Neurosci Abstr 16:846) in early developing entorhinal cortex of human fetuses. These and probably other neurons were also DARPP‐32‐positive, suggesting the possibility of an early dopaminergic regulation. Indeed, the monoaminergic innervation of the entorhinal cortex was detected from E56 on and gradually increased in density, displaying areal and laminar differences in the distribution of the dopaminergic, noradrenergic, and serotoninergic afferents. Each of the neuroactive substances under study also displayed a distinct pattern with respect to the mediolateral and rostrocaudal organization of the entorhinal cortex. These findings reveal a remarkably early maturation of the entorhinal cortex during the first half of gestation, compatible with the possibility of trophic effects. However, in keeping with the early neurochemical development of the hippocampal formation, it does not seem unreasonable to suggest that some functional circuits are already forming in the hippocampo‐entorhinal complex of primates duri

ISSN:1050-9631    

DOI:10.1002/hipo.450030305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe vulnerability of the human hippocampal complex to disease, trauma, and aging indicates the necessity to target this area therapeutically. The distribution and density of transmitter receptors provide a rational basis for this approach, and in this study the topography of 11 different pharmacological sites is compared with the cholinergic innervation, which is partcularly vulnerable in dementia. The regional distribution of cholinergic innervation to the normal adult human hippocampus and adjacent cortex, marked by acetylcholinesterase (AChE) fiber and terminal reactivity, is notable for its concentration in CA2/3 of Ammon's horn and the dentate fascia. Neither nicotinic (high‐affinity nicotine binding) nor muscarinic (“M1” or “M2”) cholinergic receptor binding paralleled this distribution. In Ammon's horn, 5‐HT2and kainate receptor binding more closely resembled the pattern of AChE, being concentrated in CA2–4 compared with CA1. By contrast, muscarinic M1and M2, 5‐HT1A, benzodiazepine (including zolpidem‐insensitive binding), NMDA (MK801), and AMPA/QUIS receptors were higher in CA1 and/or subiculum. Kainate binding, like AChE, was high in CA4. 5‐HT2and nicotinic binding partially mimicked the pattern of AChE around the granule layer. In the subicular complex and parahippocampal gyrus, where cholinergic activity is relatively lower, muscarinic, 5‐HT1A, and benzodiazepine binding were relatively high and the nicotinic receptor was remarkable for its highest density compared to other areas examined. In stratum lacunosum‐moleculare of CA1, which was relatively low in AChE activity, there was a dense band of nicotinic, M2, and benzodiazepine receptor binding. These observations, while reflecting the anatomical complexity of chemical signaling in the hippocampal region, indicate a unique distribution for the nicotinic receptor and suggest that the cholinergic input may specifically interact with 5‐HT and excitatory amino acid systems via 5‐HT2and kainate receptor subtypes in governing signaling to

ISSN:1050-9631    

DOI:10.1002/hipo.450030306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMany complex spike cells in the hippocampus of the freely moving rat have as their primary correlate the animal's location in an environment (place cells). In contrast, the hippocampal electroer cephalograph theta pattern of rhythmical waves (7–12 Hz) is better correlated with a class of movements that change the rat's location in an environment. During movement through the place field, the complex spike cells often fire in a bursting pattern with an interburst frequency in the same range as the concurrent electroencephalograph theta. The present study examined the phase of the theta wave at which the place cells fired. It was found that firing consistently began at a particular phase as the rat entered the field but then shifted in a systematic way during traversal of the field, moving progressively forward on each theta cycle. This precession of the phase ranged from 100° to 355° in different cells. The effect appeared to be due to the fact that individual cells had a higher interburst rate than the theta frequency. The phase was highly correlated with spatial location and less well correlated with temporal aspects of behavior, such as the time after place field entry. These results have implications for several aspects of hippocampal function. First, by using the phase relationship as well as the firing rate, place cells can improve the accuracy of place coding. Second, the characteristics of the phase shift constrain the models that define the construction of place fields. Third, the results restrict the temporal and spatial circumstances under which synapses in the hippocampus could be modif

ISSN:1050-9631    

DOI:10.1002/hipo.450030307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractTo examine the inhibitory postsynaptic potentials (IPSPs) elicited in pyramidal cells by interneurons situated at the stratum oriens/alveus border (O/A), glutamate was applied by micropressure to this area during intracellular recordings from CA1 pyramidal cells. Glutamate stimulation evoked IPSPs (glut‐IPSPs) of small amplitude (4 mV), delayed peak latency (100–110 ms), and long duration (300–400 ms). Recurrent activation of interneurons via glutamate stimulation of pyramidal cells by local application in stratum pyramidale (PYR) evoked recurrent IPSPs (PYR glut‐IPSPs) with similar amplitude and time course as O/A glut‐IPSPs. The mean equilibrium potential of O/A glut‐IPSPs (−77 mV) was significantly different from that of the PYR glut‐IPSPs (−71 mV), however, neither equilibrium potential was significantly different from that of the electrically evoked early IPSP in the same cells. Glutamate‐evoked IPSPs elicited from O/A displayed some response reversal (27% reversal) like those evoked from PYR (41% reversal). The early IPSP evoked by electrical stimulation displayed significantly more response reversal (67% reversal) than glut‐IPSPs. Both types of glut‐IPSPs (O/A and PYR) were associated with moderate increases in membrane conductance (5.9 and 6.6 nS, respectively), which were significantly less than the conductance change associated with the early IPSP (45.8 nS). In interneurons within PYR, glutamate stimulation in PYR readily elicited a flurry of excitatory postsynaptic potentials, whereas glutamate stimulation in O/A elicited IPSPs. The electrophysiological properties of IPSPs elicited in pyramidal cells by glutamate stimulation of interneurons in O/A were similar to those of recurrent IPSPs evoked from PYR. Given that both of these types of glutamate‐evoked IPSPs were mostly mediated via GABAAreceptor channels (Samulack DD, Lacaille J‐C, 1993, Hippocampus 3:345–358), the small differences observed between equilibrium potentials, response reversals, and conductance changes could be due to a more electrotonically distant location from the soma of the synapses involved in O/A glut‐IPSPs as compared to those of re

ISSN:1050-9631    

DOI:10.1002/hipo.450030308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe receptor type mediating the inhibitory postsynaptic potentials (glut‐IPSPs), recorded in CA1 pyramidal cells, as a result of glutamate stimulation of interneurons in stratum oriens near the alveus (O/A) was assessed and compared to the type mediating recurrent IPSPs evoked by recurrent activation of interneurons through glutamate stimulation of pyramidal cells in stratum pyramidale (PYR). In response to repetitive electrical stimulation, the peak amplitude of both the O/A glut‐IPSP and the PYR glut‐IPSP was attenuated (n = 5) in parallel to the reduction in amplitude of the early and late components of the electrically evoked response (stimulus‐evoked disinhibition). This suggested the involvement of GABAergic receptors and attested that the interneurons activated during glut‐IPSPs were also involved in the circuitry of the electrically evoked IPSPs. The local application of the selective GABAAantagonist bicuculline (100–200 μM) to the slice resulted in a significant reduction in the amplitude of both the O/A (by 76.5%; n = 9) and PYR (by 86.2%; n = 5) glut‐IPSPs, in parallel to a decrease of the electrically evoked early IPSP, but not of the late IPSP. The presence of the GABABantagonist 2‐hydroxy‐saclofen (1 mM) was able to significantly reduce the amplitude of the O/A glut‐IPSPs (by 27.5%; n = 7) and of the electrically evoked late IPSP, but not the PYR glut‐IPSP (n = 3). Although the application of phaclofen (20 mM) to the slice reduced the amplitude of the O/A glut‐IPSPs (n = 3), the reduction was not statistically significant. These results suggest that recurrent IPSPs elicited from activation of interneurons by stimulation of pyramidal cells are mediated solely via GABAAreceptors. Inhibitory postsynaptic potentials elicited from stimulation of interneurons in O/A were also mediated mostly by GABAAreceptors, but in addition, displayed a minor component mediated by GABABreceptors. Therefore, since a large proportion of interneurons in O/A are recurrently excited by pyramidal cells (Lacaille J‐C et al., 1987, J Neurosci 7:1979–1993), and since recurrent IPSPs appeared mediated by GABAAreceptors, a subpopulation of interneurons activated from O/A might exist that do not receive recurrent excitation but can inhibit pyrami

ISSN:1050-9631    

DOI:10.1002/hipo.450030309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAdrenalectomy (ADX) of normal adult rats causes selective hippocampal dentate granule cell degeneration that is prevented by corticosterone. The ability to destroy this one hippocampal cell type noninvasively made it possible to address the role of the dentate granule cells in learning and memory. Four months after ADX, 31 of 45 rats failed to show obvious granule cell loss and displayed behavior in the Morris water maze that was similar to 16 sham‐operated control rats and 16 ADX rats maintained on corticosterone throughout the study. Conversely, 14 of the 45 ADX rats experienced a loss of granule cells that varied from minimal to extensive. Although there were no obvious differences between groups in motoric and motivational characteristics or search strategies, ADX rats with moderate to extensive granule cell loss acquired place learning slightly slower than controls or ADX rats with minimal or no obvious cell loss. Furthermore, the ADX rats with moderate to extensive cell loss were temporarily impaired following alteration of either intramaze or extramaze cues compared to controls. In contrast, the rats with granule cell loss remembered an old place and learned a new place as quickly as controls. These results suggest that a normal complement of dentate granule cells may not be necessary for the acquisition or retention of spatial information in the Morris water maz

ISSN:1050-9631    

DOI:10.1002/hipo.450030310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractRats transport food from exposed areas to covered areas where they eat it or leave it. Although there is evidence that limbic structures play a role in food transport, their role is controversial. Here it was found that although many rats with large hippocampal, septal/diagonal band of Broca or dorsomedial thalamic lesions did not carry food but ate it where they found it, a few presentations of an auditory stimulus could restore food carrying. Once restored, most features of food carrying in hippocampal rats were normal in relation to food presentation schedules, deprivation levels, ambient illumination, circadian cycles, food size, and eating times. Nevertheless, food carrying impairments reemerged when the testing environment was changed. Hippocampal rats were also excessively responsive to increases in travel distance and stopped carrying food at distances over which control rats would still carry large food pellets. Auditory stimulation did not restore food carrying over long travel distances. The findings that sensory stimulation, environmental change, and travel distance influence food carrying probabilities in rats with limbic system lesions is discussed in relation to research on limbic control of food hoarding and theories of limbic system function.

ISSN:1050-9631    

DOI:10.1002/hipo.450030311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY