Fimbria Fornix Research Articles

Differential effects of drugs on the behaviour of rats with selective fimbria-fornix lesions and intrahippocampal septal cell transplants

Rats that had received two kinds of septo-hippocampal deafferentations, medial septum (MS) lesion and fimbria-fornix (FF) transection, were assayed for brain cholineacetyltransferase (ChAT) activity and spatial memory in an 8-arm radial maze task. Both lesions produced profound and long-lasting spatial memory impairments, which were characterized by a reduction in the numbers of correct arm choices and first correct choices, a reduction in the percent of correct choices and an increase in the number of errors. The degree of memory impairment was severer in FF- than in MS-lesioned rats, and paralleled that of decreases in ChAT activity in the hippocampus. MS lesion reduced ChAT activity in the hippocampus by approximately 45%, while FF lesion almost completely depleted the activity.An intraperitoneal injection of physostigmine (0.0032–0.32 mg/kg), an acetylcholinesterase (AChE) inhibitor, significantly ameliorated the spatial memory deficit induced by MS lesion, but hardly affected that by FF lesion. In contrast, intraperitoneal doses (0.032–3.2 mg/kg) of pilocarpine, a muscarinic agonist, showed a significant improvement of both types of memory deficit with bell shaped dose-response curves. The drug was more potent in the FF- than in the MS-lesioned rats.These results suggest that the septo-hippocampal cholinergic system plays a crucial role in the maintenance of spatial memory, and that the degree of septo-hippocampal deafferentation affects the efficacy of cholinergic drugs.

Nucleus basalis magnocellularis and medial septal area lesions differentially impair temporal memory

Functional dissociations between the medial septal area (MSA) and the nucleus basalis magnocellularis (NBM) were examined using the concepts and experimental procedures developed by scalar timing theory. Rats were tested in variations of a signalled discrete-trial peak-interval schedule of reinforcement in which the response rate functions identified the time when the rats expected reinforcement. The variations assessed aspects of both reference and working memory for information obtained from prior trials and from the current trial. A double dissociation was found in reference memory. Rats with NBM lesions, like those with frontal cortex (FC) lesions, remembered the time of reinforcement as having occurred later than it actually did; rats with MSA lesions, like those with fimbria-fornix (FF) lesions, remembered the time of reinforcement as having occurred earlier than it did. A single dissociation was found in working memory. MSA lesions and FF lesions impaired working memory, while NBM and FC lesions had no effect on it. These data begin to identify the brain mechanisms underlying temporal memory; they indicate that the frontal and hippocampal systems are both involved, but in complementary ways; and they provide information that helps specify more clearly the functions of the frontal and hippocampal systems.

Separation of hippocampal and amygdaloid involvement in temporal memory dysfunctions

The role of the hippocampus and the amygdala in timing and in the memory of previously timed events was investigated in rats. Two testing procedures used the peak time (the time at which the maximum response rate occurred) to identify the time at which the rat expected reinforcement. Amygdala (AMG) lesions had no effect on the remembered time of reinforcement or on the ability to remember the duration of a previous stimulus. Fimbria—fornix (FF) lesions had two effects: these rats remembered the time of reinforcement as occuring earlier than it really did, and could not remember the duration of a previous stimulus even after a gap of only 0.5 s. This behavior pattern endured throughout testing in spite of reinforcement contingencies designed to eliminate it. Atropine, 0.45 mg/kg, caused control rats to forget the duration of a previous stimulus, while haloperidol, 0.15 mg/kg, did not. Taken together, these data indicate that the hippocampus, but not the amygdala, has an important role in the memory for time. They suggest that alterations in temporal processes may be intimately involved in the amnesic syndrome seen following damage to temporal lobe structures.

Effects of fimbria-fornix transection and ganglioside treatments on histochemical staining for glucose-6-phosphate dehydrogenase in the lateral septum.

The present study examined whether ganglioside treatments would affect an enzyme marker (glucose-6-phosphate dehydrogenase; G6PDH) of neural metabolism in an established model system (the hippocamposeptal projection) of deafferentation and sprouting. Rats were subjected to unilateral transections of the fimbria-fornix (FF) in order to (1) interrupt the hippocamposeptal projection, (2) deafferent the lateral septal nucleus (LSN) ipsilaterally, and (3) induce sprouting by the contralateral FF. In untreated rats which were killed at 2-4 days postlesion, histochemical staining for G6PDH was reduced by 35-40% in the deafferented LSN relative to the contralateral side. However, at 6-8 days (i.e., when sprouting begins), staining intensity returned toward contralateral values (i.e., recovered). This pattern of changes in G6PDH staining was not observed in the caudate nucleus adjacent to the LSN. In ganglioside-treated rats which were killed at 4 days, there was a significantly smaller reduction of G6PDH staining in the deafferented LSN (23%; P = .05). This effect was not observed in the LSN of treated rats killed at 2 days, nor in the caudate nucleus at either time point. The present data indicate that (1) FF transection results in a reduction and subsequent recovery of G6PDH staining in the deafferented LSN; and (2) ganglioside treatments may accelerate the onset of the recovery of G6PDH activity. We suggest that gangliosides' effect on G6PDH reflects an acute enhancement of biosynthetic events in deafferented neurons.

Chapter 16 Exogenous administration of neuronotrophic factors in vivo protects central nervous system neurons against axotomy induced degeneration

Publisher Summary The discovery and investigation of nerve growth factor (NGF) have opened the way to a search for other neuronotrophic factors capable of supporting survival and general growth of selected neurons in vitro and, potentially, in vivo. Recent studies by others have revealed that NGF can be selectively accumulated by the central nervous system (CNS) cholinergic neurons in vivo and can stimulate their choline acetyltransferase activity both in vivo and in vitro. The chapter describes an experimental septohippocampal model in the adult rat, which allows for (i) quantitative evaluation of cholinergic and other neuronal cell death in the septum, (ii) continuous infusion of the septum with exogenous agents, and (iii) the imposition of experimental lesions on the test system. By using such a model, scientists were able to obtain quantitative evidence that the survival of axotomized CNS neurons can be promoted in vivo by exogenously administered neuronotrophic factors. Specifically, continuous infusion of NGF either intraventricularly or intraparenchymally (i) drastically reduces the death of both cholinergic and noncholinergic neurons in the adult rat medial septum and vertical diagonal band regions, which would otherwise follow unilateral fimbria–fornix transection, and (ii) appears to promote massive intraseptal sprouting of cholinergic fibers unilaterally to the fimbria–fornix lesion.

Restoration of rhythmic slow activity (θ) in the subcortically denervated hippocampus by fetal CNS transplants

Solid pieces of the fetal septal region (SG) or hippocampus (HPC) were implanted in a cavity formed by aspiration of the fimbriafornix (FF) and the overlying cingulate cortex on one side in adult rats. In other lesioned animals cell suspensions obtained from the fetal septal area (SS) or the locus coeruleus region of the brainstem (LC) were injected stereotaxically into the deafferented host hippocampus. Six to 9 months after transplantation the animals had chronic recording electrodes implanted into both hippocampi. EEG and unit activity were monitored during running in a wheel, drinking and immobility. Unilateral fimbria-fornix lesions abolished rhythmic slow activity (RSA or theta, θ) in the ipsilateral hippocampus and no recovery was seen up to 9 months later in either the control FF-lesioned animals or in the rats with LC suspension grafts. Recovery of RSA, however,was observed in all animals with solid septal grafts and in some rats with solid HPC grafts. Similar to normal rats, RSA was present only during running and absent during drinking and sitting still. Coherence measurements of RSA between the transplanted and intact hemispheres resulted in high values (0.70–0.95). Concurrent with RSA, interneurons and granule cells in the host hippocampus fired rhythmically at RSA frequency (6–9 Hz). The depth profile and the antero-posterior distribution of the power of RSA correlated with the amount and distribution of the graft-induced acetylcholinesterase-positive reinnervation of the host hippocampus. In contrast to the animals with solid septal grafts, placed within the FF lesion cavity, the rats with intrahippocampal septal suspension grafts displayed only short duration bursts of RSA, and mainly during immobility. Based on these findings it is suggested that at least a proportion of the RSA ‘pacemaker’ cells of the host septum survives the transection of the fimbria-fornix fibers and that a graft of fetal septal or hippocampal tissue implanted into the lesion cavity may be capable of relaying this pacemaker activity to the host hippocampus. This effect may be due to the ability of the grafted tissue to promote the regeneration of new, direct or indirect, septo-hippocampal connections across the lesion cavity.

Chapter 28 A functional analysis of connections between grafted septal neurons and host hippocampus

Publisher Summary This chapter discusses the efficacy of using neural grafting to restore physiological and behavioral functions following damage to the cholinergic septohippocampal system. It presents a study in which embryonic septal regions were injected into the hippocampi of fimbria–fornix (FF) transected rats. The grafts developed an extensive innervation of the host hippocampus and, when stimulated, produced a slow depolarizing response that was blocked by atropine and facilitated by physostigmine. There is evidence that the graft restored hippocampal theta rhythm, which had been eliminated by FF transactions or septal lesions. However, unlike unlesioned controls, theta in grafted animals is not correlated with movement. Performance in a water maze, which was markedly impaired by fornix transection, showed no improvement 6 months after transplantation, but was restored in septal lesioned, septal grafted rats. The results indicate that grafting may provide a useful tool for studying the action of neurotransmitter systems and their involvement in higher brain functions.

Nerve growth factor protein level increases in the adult rat hippocampus after a specific cholinergic lesion.

Nerve growth factor (NGF) is the best-characterized neurotrophic substance and has recently been shown to influence cholinergic neurons in the basal forebrain. Hippocampus and neocortex, the primary targets for these central neurons, have further been found to contain high levels of NGF. Using enzyme immunoassay and acetylcholine esterase (AChE) histochemistry we have now studied the levels of NGF and AChE after a specific cholinergic lesion, transection of the fimbria fornix comprising the major cholinergic input to hippocampus. Fimbriectomy in adult rats led to a marked decrease in AChE-positive nerve terminals in both hippocampus and neocortex 10 days later, and to an increase (40%) of NGF protein concentration in hippocampus. thirty days after surgery, NGF had returned to control levels and remained there after 90 days. Removal of superior cervical ganglion did not alter the results. The density of cholinergic terminals in both hippocampus and neocortex increased with time (90 days) after fimbrial transection. The results support the idea that cholinergic neurons in the basal forebrain take up and retrogradely transport NGF from their target areas and suggest that transection of the pathway interrupts the transport thereby increasing NGF distal to the lesion. The return of NGF to control levels probably reflects reestablished cholinergic contracts in the hippocampus.

Ganglioside-induced alterations in hippocampal cholinergic enzymes and Na,K-ATPase after fimbria-fornix transection.

Previous biochemical findings suggest that exogenous gangliosides enhance cholinergic sprouting in the hippocampus after partial lesions of the septohippocampal pathway. To assess whether GM1 ganglioside accelerates the onset of this sprouting after complete lesions, we measured cholinergic enzymes and Na,K-ATPase activity in the hippocampus of rats with unilateral fimbria-fornix transection. At 14 and 18 days postlesion, histochemical staining showed that acetylcholinesterase (AChE) was almost completely eliminated in the hippocampus ipsilateral to the transection in untreated and GM1-treated rats. Biochemical assays confirmed that GM1 treatments did not increase AChE activity in the denervated hippocampus. Rather, there were significant reductions of AChE and choline acetyltransferase activities in the ipsilateral hippocampus relative to the contralateral value (P less than .001); and the reductions were greater in GM1-treated rats than in untreated controls (P less than .001). Na,K-ATPase activity in the ipsilateral hippocampus increased by 10.1% in GM1-treated rats, whereas it decreased by 21.7% in untreated controls (P less than .05). Since Na, K-ATPase is enriched in synaptic membranes, the increased activity of this enzyme may indicate that GM1 treatments stabilize surviving synaptic membranes and/or accelerate the onset of sprouting in the denervated hippocampus. The reductions in cholinergic enzymes, however, imply that the sprouting pathway must be noncholinergic.

Continuous infusion of nerve growth factor prevents basal forebrain neuronal death after fimbria fornix transection.

Neurons in the rat medial septum (MS) and vertical limb of the diagonal band of Broca (VDB) undergo a rapid and severe cell death after transection of their dorsal projection to the hippocampus by aspiration of the ipsilateral fimbria fornix and supracallosal striae. By 2 weeks posttransection, the extent of neuronal loss was 50% of the total neurons and 70% of the cholinergic neurons in the MS and 30% of the total neurons and 40% of the cholinergic neurons in the VDB. We hypothesized that (i) the death was due to the loss of a hippocampus-derived neuronotrophic factor, and (ii) exogenous nerve growth factor (NGF) might provide trophic support to the MS/VDB cholinergic neurons, in light of recent reports that the septal diagonal band cholinergic neurons are responsive to NGF and that NGF is present and produced in the hippocampus. In the present study, we attempted to prevent the transection-induced neuronal death by continuous infusion of exogenous 7S NGF (1 microgram/wk) through an intraventricular cannula device. We report here that NGF treatment significantly reduces both the total neuronal and cholinergic neuronal death found 2 weeks after fimbria fornix transection; there was a sparing of 50% of the neurons in the MS and essentially 100% of those in the VDB that otherwise would have died. We conclude that NGF also has a protective effect on noncholinergic neurons since calculations indicate that 80% of the NGF-affected neurons are noncholinergic.

Induced homotypic sprouting of serotonergic fibers in hippocampus. II. An immunocytochemistry study

The dorsal hippocampus of the rat normally receives its 5-HT innervation from two homologous groups of cells in the median raphe nucleus via the cingulum bundle-induseum griseum (CB-IG) and the fornix-fimbria (FF) ( J. Comp. Neurol., 179 (1978) 641–667 and Brain Res. Bull., 10 (1983) 445–451). 5-HT immunoreactive (IR) fibers are distributed in a laminar pattern in the hippocampus. These fibers have large varicosites and are densely distributed in the infragranular layer of dentate gyrus, in the stratum lacunosum-moleculare of the cornu Ammonis and in the are fasciola cinerea (FC). The present study provides evidence that the density of the 5-HT-IR fibers in the dorsal hippocampus is greatly decreased but maintained a similar laminar pattern 3 days after lesioning by microinjection of 4 μg of 5,7-dihydroxytryptamne (5,7-DHT) into the CB-IG. An apparently normal density and distribution pattern of the 5-HT-IR fiber is seen by 42 days postlesion. The FC in the hippocampus is among the first regions reinnervated by 5-HT-IR fibers with very dense and large varicosities. The restitution of 5-HT-IR fibers in the dorsal hippocampus after the 5,7-DHT lesion in the CB-IG is accompanied by a marked increase in the number and intensity of 5-HT-IR fibers in the FF. No evidence of a regeneration of 5-HT-IR fibers is seen distal to the injection site in the CB-IG. These observations provide direct evidence for homotypic collateral sprouting in the CNS induced by removal of a single fiber type.

Septal deafferentation enhances the neurotrophic effects of rat hippocampus on cultured neural cells from the central nervous system

Neurotrophic effects (NTEs) of various brain regions of 4-week-old rats were examined in primary culture of rat embryonic cerebral hemispheres. Extracts of the hippocampus, brainstem and septal nucleus highly enhanced the survivability of neuronal cells and the division of non-neuronal cells by 9 days. The septohippocampal tract (fimbria fornix) was cut and the effect on the neurotrophic activity in the hippocampus was examined. The NTEs of hippocampal extracts remained unchanged 3 days after septal deafferentation, was significantly increased by 7 days, peaked at 14 days and returned to the basal level by 21 days.

Effect of vasopressin, oxytocin and peptides derived from these hormones on field potential induced in lateral septum of rats by stimulation of the fimbria fornix

Superfusion of the dorsal surface of the septum with artificial cerebrospinal fluid containing 10 −10 M [Arg 8]-vasopressin (VP) significantly increased the negative (N) wave in field potentials (FPs) elicited in the lateral septum (LS) of rats by stimulation of the fimbria-fornix. A similar increase in the FPs negativity was also observed following superfusion of the septum with [pGlu 4, Cyt 6] VP(4–9), [pGlu 4, Cyt 6] VP(4–8), [Cyt 6] VP(5–9), desglycinamide 9-VP and 1-deamino, 8-D-arginine-VP. However, for obtaining the effect with these peptides 10 3–4 times higher concentrations had to be used. Superfusion of the septum with 10 −8 M oxytocin (OX) elicited nearly the same N-wave increase as the 10 −8 M VP septal superfusion. The 10 −10 M concentration of OX as well as 10 −7 M [pGlu 4, Cyt 6] OX(4–9) and [pGlu 4, Cyt 6] OX(4–8) had little effect on the FPs negativity. The significance of these findings for the elucidation of the VP function in the LS is discussed.

Site of interaction of serotonin and desglycinamide-arginine-vasopressin in maintenance of ethanol tolerance

Rats trained to walk in a moving belt apparatus were subjected to a partial (fornix-fimbria (FF)) or total (fornix-fimbria + cingulum bundles (FF + CB) chemical denervation of the dorsal serotonergic afferent pathways to the hippocampus. After chronic alcohol treatment that resulted in tolerance development to the motor-impairing effects of ethanol, desglycinamide-arginine 8-vasopressin (DGAVP) or saline treatment was started and the residual tolerance measured at several intervals after ethanol withdrawal.DDGAVP administration resulted in a virtually complete retention of ethanol tolerance when given to sham-operated controls or FF-lesioned rats. The peptide treatment failed, however, to prolong tolerance in rats bearing a complete FF + CB lesion, that reduced serotonin (5-HT) levels in the hippocampus and overlying parietal cortex to 10 and 45% of controls respectively. These results suggest that the serotonergic innervation of these areas in necessary for the action of DGAVP in the maintenance of ethanol tolerance.

Induced homotypic collateral sprouting of serotonergic fibers in the hippocampus of rat

The organization of the raphe cells efferent to the dorsal hippocampus (DHipp) has been shown to consist of two homologous groups of cells in the median raphe nucleus (MRN). Their axons project by way of the cingulum bundle (CB) and the fornix-fimbria (FF)58. A group of neurons located in the interfascicular part of the dorsal raphe nucleus (IFN) was found to use the CB route exclusively. Quantitation of the HRP-labeledd cells in the MRN neurons projecting to the DHipp decreased by 55% and 92% 3 days following CB and CB-FF 5, 7-DHT injections respectively.There was a significant increase in HRP-labeled neurons in the MRN at 21 and 42 days compared to 3 days after CB injection (a 2% decrease at 21 days and 38% increase at 42 days compared to sham injected). No change in the number of labeled MRN cells was seen at these long-term time points after combined CB-FF 5, 7-DHT microinjections. The labeled cells in the MRN increased in size in the long survival group of CB lesioned animals. The labeled cells localized in the IFN which were lost after CB 5, 7-DHT injections did not reappear after loong-term survival. These results indicate that CB 5-HT fibers do not regenerate into the DHipp, but FF 5-HT fibers increase their terminal territory by collateral sprouting in response to homotypic denervation.

Properties of the internal clock.

Evidence has been cited for the following properties of the parts of the psychological process used for timing intervals: The pacemaker has a mean rate that can be varied by drugs, diet, and stress. The switch has a latency to operate and it can be operated in various modes, such as run, stop, and reset. The accumulator times up, in absolute, arithmetic units. Working memory can be reset on command or, after lesions have been created in the fimbria fornix, when there is a gap in a signal. The transformation from the accumulator to reference memory is done with a multiplicative constant that is affected by drugs, lesions, and individual differences. The comparator uses a ratio between the value in the accumulator (or working memory) and reference memory. Finally, there must be multiple switch-accumulator modules to handle simultaneous temporal processing; and the psychological timing process may be used on some occasions and not on others.

Effects of 5,7-dihydroxytryptamine on HRP retrograde transport from hippocampus to midbrain raphe nuclei in the rat

The combination of horseradish peroxidase (HRP) retrograde tracing and specific lesioning using 5,7-dihydroxytryptamine (5,7-DHT) was applied to the midbrain raphe-hippocampal system. Serotonergic fibers from the median raphe nucleus (MRN) of the rat reach the dorsal hippocampus (HIPP) through the cingulum bundle (CB) and the fornix-fimbria (FF). Intracerebral microinjections of 5,7-DHT in these two bundles were made at various times before HRP injections into the dorsal HIPP. After both CB and FF lesion, the number of labeled cells in MRN is reduced to 49.6% at zero time (HRP injected immediately after 5,7-DHT) and to 6.5% after 2 days. There was no significant effect on the number of labeled cells in the locus ceruleus. Selective lesioning of 5-HT fibers in the CB or the FF revealed that raphe-CB-HIPP neurons and raphe-FF-HIPP neurons have a similar distribution pattern in the MRN, but that a dorsal group of neurons at the junction of MRN and dorsal raphe nucleus took the CB route exclusively to innervate the HIPP. The CB pathway was used by more neurons (55% of total number of labeled neurons) than was the FF (21%). An appreciable number of fibers (23%) appear to have branches in both pathways. Our findings are discussed with regard to the recovery of HIPP function seen after long term destruction of 5-HT fibers in the CB.

Neuropeptides derived from pro-opiocortin: behavioral, physiological, and neurochemical effects.

Neuropeptides derived from pro-opiocortin: behavioral, physiological, and neurochemical effects.

The organization of the fimbria, dorsal fornix and ventral hippocampal commissure in the rat.

The morphological organization of the two principal efferent pathways of the hippocampal formation — the fimbria and the dorsal fornix — and of the interhippocampal fibers that cross in the ventral hippocampal commissure, has been studied autoradiographically following injections of 3H-amino acids into the relevant cytoarchitectonic fields. To a considerable extent the rostrally-directed fibers from each cytoarchitectonic field remain topographically segregated within the fimbria or dorsal fornix, their locations being determined by the relative levels at which they join these bundles. Thus, the fibers from the subicular region tend to be aggregated along the ependymal border of the fimbria while those from the hilar region of the dentate gyrus are medially-placed along its pial margin. Similarly, the efferents from the septal and temporal parts of the various fields are distributed along the proximo-distal dimension of the fimbria, from its base (adjacent to field CA3) to its tip. The dorsal fornix contains fibers from the septal (dorsal) part of the subiculum and field CA1; although there appears to be some overlap, the subicular efferents tend to be more medially placed while those from CA1 are further lateral. The topographic organization of the fibers in the fimbria is reflected in the arrangement of the crossed components in the hippocampal commissure. Those arising at more temporal levels cross most rostrally while those from the septal pole of field CA3 cross in the caudal part of the commissure; those from the hilar region of the dentate gyrus cross most ventrally, while those from the more lateral parts of field CA3 (CA3b and CA3a) cross at successively more dorsal levels.

Differential contribution of fimbria and fornix fibers to behavior

Rats with lesions severing either the subcallosal fornix (Fo) or medial half of the fimbria (Fi) were compared to sham-operated and intact animals in a series of behavioral tasks. Acquisition of Y-maze learning proceeded equally in all groups; the total number of rearing was, however, significantly lower in the lesioned subjects. Place-vs-cue test revealed that all rats utilized place hypothesis. In the cue guided spatial reversal task Fi and Fo rats were equally impaired. In the one trial passive avoidance problem Fo rats were inferior to both Fi and control animals. Open-field test failed to distinguish between the groups. Fo lesions destroyed, while Fi lesions did not affect rhythmic slow activity of the dorsal hippocampus. The results indicate differential involvement of the fibers of the fimbria—fornix complex in behavior.