Postganglionic connections between sympathetic ganglia in the solar plexus of the cat demonstrated autoradiographically.

The anatomic substrate for postganglionic interaction between sympathetic ganglia was examined by autoradiography. In anesthetized cats, the left celiac ganglion was surgically isolated using a retroperitoneal approach and injected either hydraulically or electrophoretically with concentrated tritiated proline. Two to twenty-seven days after injection, the celiac and superior mesenteric ganglia, interganglionic connections, adrenal glands, nearby arteries, and splanchnic nerves were removed and prepared for autoradiography. Principal cell bodies in each injection site showed heavy incorporation of radiochemical with little, if any, spread to other regions of the ganglion. Occasionally, labeled processes resembling dendrites or axons were observed emerging from these cells. Small, radioactively labeled fibers streamed from the injected ganglion into the intermediate region between the celiac ganglia. Some of these elements entered “satellite ganglia” in the intermediate zone, and others could be traced to the contralateral celiac ganglion. In both types of ganglia, small fibers formed basket-like structures around the somata of principal cells. Labeled fibers also were observed entering the ipsilateral adrenal gland and terminating on, and around, blood vessels in the adrenal medulla.     

Effects of enkephalin, morphine, and naloxone on the electrical activity of the in vitro hippocampal slice preparation

The effects of infusion of low concentrations of d-Ala-d-Leu-enkephalin, morphine, or naloxone on electrical responses to stimulation of the in vitro hippocampal slice preparation were investigated. Concentrations of enkephalin as low as 10 nm and morphine as low as 1 μm dramatically increased the magnitude of the population spike response of pyramidal cells to Schaffer-commissural stimulation. The drug response had a rapid onset and was replicable several times after infusion of normal incubation medium. Enhancement of the population spike by either morphine or enkephalin was blocked by the opiate receptor antagonist naloxone. The response to antidromic stimulation was not altered by enkephalin, nor was the slope of the dendritic response, indicating that the enkephalin effect is not mediated by depolarization of the pyramidal cells themselves nor by facilitation of synaptic processes at the dendrites. The possibility that the enkephalin effect might be produced by alteration of either a feed-forward or a feedback mechanism mediated by basket cells was investigated. Feed-forward inhibition was demonstrated, but enkephalin did not alter its efficacy. Feedback inhibition induced by antidromic stimulation was also unaffected by enkephalin. On the basis of these results we suggest that enkephalin acts to alter the efficiency of a mechanism involved in coupling the dendritic EPSP with the spike initiation mechanism of the cell body.     

Development of responses of globus pallidus and entopeduncular nucleus neurons to stimulation of the caudate nucleus and precruciate cortex

Extracellular recordings were made from neurons in the globus pallidus and entopeduncular nucleus (GP-ENTO) of anesthetized kittens of 2 to 177 days of age and from four adult cats. Stimulation of the striatum and the precruciate cortex produced responses in GP-ENTO neurons of the youngest kittens tested (2 days of age). In kittens of 1 to 10 days, about 70% of the GP-ENTO neurons responded to either caudate or cortical stimulation with a purely excitatory response (i.e., an evoked action potential). With increasing age the frequency of occurrence of this type of response decreased and the occurrence of inhibitory responses or of sequences of excitation followed by inhibition increased. In addition to these changes in the form of the evoked responses, other response parameters exhibited age-dependent alterations. Latency to response decreased with age and the ability of GP-ENTO neurons to follow repetitive stimuli increased as the kittens became older. These findings suggest that although GP-ENTO neurons are functional as early as 2 days postnatally in the kitten, subsequent maturation of the responsiveness of these neurons continues for several postnatal months.     

Impairment of semantic memory after basal forebrain and fornix lesion

Semantic memory impairment is classically associated with lesion of the anterior temporal lobe. We report the case of a patient with severe semantic knowledge impairment and anterograde amnesia after bilateral ischemic lesion of the fornix and of the basal forebrain following surgical clipping of an aneurysm of the anterior communicating artery. Fluorodeoxyglucose positron emission tomography (FDG-PET) showed a temporal hypometabolism. Severe semantic impairment is a rare complication after rupture of an anterior communicating artery aneurysm and may result from disconnection of the temporal lobe.     

Response of medial septal neurons to the iontophoretic application of glucocorticoids

In view of the influence of glucocorticoids on adrenocortical activity, the iontophoretic effects of cortisol and corticosterone on the electrical activity of medial septal neurons were investigated. About one-half of these cells were steroid sensitive. The hormonal effect was short in the excitatory neurons; however, it persisted as long as 2 min in inhibitory units after cessation of iontophoretic current. This was contrary to the finding in the mediobasal hypothalamic neurons in which both in excitatory and inhibitory cells the effect lasted as long as 30 s. Autocorrelation analysis of the firing of septal neurons revealed that most cells showed a regular nonrhythmic, nonbursting spike activity. Only 10 of the 48 units studied changed their pattern of firing during hormone iontophoresis. These results are significant in relation to the role played by the septum in the neuroendocrine control of adrenocortical secretion.     

Influence of chronic prenatal ethanol on cholinergic neurons of the septohippocampal system

This study characterized the influence of full-term gestational ethanol exposure on choline acetyltransferase (ChAT)-immunoreactive neurons that project to the hippocampus, within the medial septal (MS) nucleus and the vertical limb of the diagonal band of Broca (DBv). On gestation days 1–22, pregnant dams were fed either a vitamin fortified ethanol-containing liquid diet, pair fed a calorically equivalent sucrose-containing diet, or given rat chow ad libitum. In a previous study, we found that chronic prenatal exposure to ethanol, in this manner, resulted in a significant decline in the ontogenetic upregulation of ChAT activity in the septal area during the second postnatal week, but was followed by recovery to control levels by adulthood. On postnatal days 14 and 60 (P14 and P60) the brains were prepared for ChAT immunocytochemistry. Ethanol exposure had little influence on the number of ChAT-positive neurons in the MS nucleus of animals at either age. Ethanol exposure had no effect on neuronal size or ChAT staining intensity of MS or DBv neurons when compared to chow-fed offspring. Although age-related increases in cholinergic neuronal numbers and decreases in neuronal size were observed between juvenile and adult animals, prenatal ethanol exposure did not appear to influence these postnatal changes in the population as a whole. Overall, these findings suggest that the anatomical maturation of septal cholinergic neurons may be relatively insensitive to prenatal ethanol exposure under conditions of a vitamin-rich dietary supplementation, while biochemical development within this region may be more susceptible to early ethanol influences. © 1996 Wiley-Liss, Inc.     

Distribution of gamma-aminobutyric acid-immunoreactive neurons in the septal region of the rat brain

The distribution of gamma-aminobutyric acid-immunoreactive (GABA-I) elements was examined in the septal region of the rat brain. The indirect peroxidase-antiperoxidase technique was used with anti-GABA antibodies in normal and colchicine-pretreated rats, with or without use of detergent in the incubation medium. Intraventricular injection of colchicine did not result in any change in the staining of neuronal perikarya. Intraseptal injections increased the intensity of labelling of GABA-I cell bodies in the lateral septal nucleus and increased the number of labelled cells in the medial septal nucleus and diagonal band of Broca (dbB). Triton X-100 added to the incubation media decreased the intensity of staining and number of GABA-I somata in all septal nuclei with a concentration-dependent effect. No change was observed concerning GABA-I varicosities. The septal area, including the lateral, medial, and triangular septal nuclei; the anterior rudiment of the hippocampus; the island of Calleja magna; the septofimbrial nucleus; the bed nucleus of the stria terminalis; and the dbB showed a strong reaction to anti-GABA antibodies with regard to GABA-containing surrounding structures. GABA-I axonal varicosities were observed in all the regions with an uneven distribution. The highest density was found in the dorsal and ventral parts of the lateral septal nucleus and in a band situated between the dbB and the nucleus accumbens. Labelled varicosities were frequently observed surrounding GABA-I and nonimmunoreactive cell bodies. GABA-I somata ranged from 10 to 30 micron in diameter. Small neurons were present in great number at the ventricular border and in the zona limitans. Medium-size and large neurons were mostly observed in the medial part of the dorsal lateral nucleus and in the intermediate lateral nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epileptogenic doses of penicillin do not reduce a monosynaptic GABA-mediated postsynaptic inhibition in the intact anesthetized cat

The hypothesis that penicillin (PCN) causes seizures by interfering with γ-aminobutyric acid (GABA)-mediated inhibition was investigated by observing the effect of epileptogenic doses of systemic PCN on the monosynaptic inhibition of Deiters neurons by cerebellar stimuli. After intravenous PCN, typical epileptic spikes in cerebral cortical surface recordings occurred and were correlated with various degrees of hyperactivity and Deiters nucleus. Intracellular recordings in five Deiters neurons with stable penetrations before and after PCN-induced cortical spikes showed no reduction of the evoked monosynaptic inhibitory postsynaptic potential (IPSP). These few long-duration recordings were supported by statistical analysis of IPSP amplitude in small populations of neurons recorded either before or after PCN in 11 cats; no significant trend was seen after PCN. Extracellular unit and antidromic field potential recordings in Deiters nucleus did show alterations of net inhibition after PCN but do not refute the intracellular data. The epileptic effects of PCN on the intact mammalian nervous system may involve mechanisms other than antagonism of GABA-mediated inhibition.     

Organization of cerebral cortical afferent systems in the rat. II. Magnocellular basal nucleus

The organization of the magnocellular basal nucleus (MBN) projection to cerebral cortex in the rat has been studied by using cytoarchitectonic, immunohistochemical, and retrograde and anterograde transport methods. The distribution of retrogradely labeled basal forebrain neurons after cortical injections of wheat germ agglutinin-horseradish peroxidase conjugate was essentially identical to that of neurons staining immunohistochemically for choline acetyltransferase. These large (20-30 micrometers perikaryon diameter) multipolar neurons were found scattered through a number of basal forebrain cell groups: medial septal nucleus, nucleus of the diagonal band of Broca, magnocellular preoptic nucleus, substantia innominata, and globus pallidus. This peculiar distribution mimics the locations of pathways by which descending cortical fibers enter the diencephalon. Each cortical area was innervated by a characteristic subset of MBN neurons, always located in close association with descending cortical fibers. In many instances anterogradely labeled descending cortical fibers appeared to ramify into diffuse terminal fields among MBN neurons which were retrogradely labeled by the same cortical injection. Double label experiments using retrograde transport of fluorescent dyes confirmed that MBN neurons innervate restricted cortical fields. Anterograde autoradiographic transport studies after injections of 3H-amino acids into MBN revealed that MBN axons reach cerebral cortex primarily via two pathways: (1) The medial pathway, arising from the medial septal nucleus, nucleus of the diagonal band, and medial substantia innominata and globus pallidus MBN neurons, curves dorsally rostral to the diagonal band nucleus, up to the genu of the corpus callosum. Most of the fibers either directly enter medial frontal cortex or turn back over the genu of the corpus callosum into the superficial medial cingulate bundle. Many of these fibers enter anterior cigulate or retrosplenial cortex, but some can be traced back to the splenium of the corpus callosum, where a few enter visual cortex but most turn ventrally and sweep into the hippocampal formation. Here they are joined by other fibers which, at the genu of the corpus callosum, remain ventrally located and run caudally through the dorsal fornix into the hippocampus. (2) The lateral pathway arises in part from medial septal, diagonal band, and magnocellular preoptic neurons whose axons sweep laterally through the substantia innominata to innervate primarily piriform, perirhinal, and endorhinal cortex. Some of these fibers may also enter the hippocampal formation from the entorhinal cortex via the ventral subiculum.(ABSTRACT TRUNCATED AT 400 WORDS)     

Intracellular potential of medullary reticular neurons during sleep and wakefulness

Intracellular records were obtained in the chronic cat from neurons of the nucleus reticularis gigantocellularis (NGC) during naturally occurring sleep and wakefulness. When wakefulness and quiet sleep was compared with active sleep, the membrane potential level of NGC neurons gradually decreased; a depolarized membrane potential was maintained tonically and selectively throughout active sleep. These data support the concept that NGC neurons assist in the generation of somatic atonia during active sleep and suggest that this state-dependent inhibitory function may be controlled by the nucleus pontis oralis as part of the general phenomenon of reticular response reversal.     

Slow rhythmic activity of caudate neurons in the cat: Statistical analysis of caudate neuronal spike trains

Spike trains of caudate neurons initially having mean interspike intervals of less than 4 ms were analyzed with progressive administration of pentobarbital (5 to 20 mg/kg). Among the neurons investigated, 77% (N = 79) showed evidence of a rhythmic basis of their activity in first-order interspike interval histograms and/or autocorrelation histograms in the course of becoming silent due to progressive administration of pentobarbital. Although the rhythmicies of given units varied depending on the level of anesthesia the most prominent cycle was almost always within the range of 200 to 320 ms; the majority were not discernable on visual inspection of the spike trains. Cortical stimuli reset the cycle. Cross-correlation histograms constructed from pairs of caudate neurons provided some evidence that their spontaneous firing was mutually inhibited. The possibility that the rhythmicities might arise from such mutual inhibition of spontaneously firing caudate neurons is discussed.     

Cholinergic neurons contain Calbindin-D28k in the monkey medial septal nucleus and nucleus of the diagonal band: an immunocytochemical study

The distribution patterns of choline acetyltransferase (CAT), as a marker for cholinergic neurons, and Calbindin-D_28k (CaBP) immunoreactivities in the forebrain basal ganglia of the Japanese monkeyMacaca fuscata were compared. Similar distribution patterns of CAT and CaBP immunoreactivities were found in the medial septal nucleus (MS) and the nucleus of the diagonal band of Broca (DBB). Double-labeling fluorescence immunocytochemistry revealed that most, but not all, cholinergic neurons were CaBP-immunoreactive in the MS and DBB. The results suggest that CaBP may play a role in the septohippocampal cholinergic neuron system of the monkey.     

Monosynaptic and disynaptic activation of pyriform cortex neurons by synchronous lateral olfactory tract volleys in the rabbit

To elucidate the organization of synaptic inputs to pyriform cortex neurons, intracellular and extracellular responses of single units were analyzed in urethane-anesthetized rabbits. The lateral olfactory tract (LOT) or the olfactory bulb (OB) was electrically stimulated. Intracellular recordings revealed two types of cells (type I and type II cells), according to the types of EPSP evoked by the LOT or OB shock. The EPSP in the type I cells had shorter latencies (0.0 to 0.9 ms) from the onset of the component 2 (C2) wave of the field potential (which signals the onset of the synaptic depolarization of the apical dendrites of the pyramidal cells in the PC), and that in the type II cells had longer latencies (1.0 to 6.0 ms). A conditioning LOT or OB shock did not suppress the testing EPSP in the type I cells, whereas the conditioning stimulation greatly suppressed the testing EPSP in most of the type II cells. Extracellular recordings from units responding synaptically to the LOT or OB shock revealed a group of units which had short latencies (0.7 to 1.9 ms) of spike discharges. Those units, which were likely to be the same cells as the type I cells, are believed to mediate excitatory synaptic inputs to the type II cells. On the basis of these results, we concluded that type I cells are monosynaptically activated by LOT volleys, whereas type II cells are activated di- or polysynaptically by way of a relay from type I cells. The type I cells were recorded in both the superficial and the deep parts of the pyriform cortex, although they were recorded more frequently in the superficial part. On the other hand, most of the type II cells were recorded in the deep part of the PC. These results support and extend the previous model, in which the monosynaptically activated superficial pyramidal cells give rise to excitatory inputs to other pyramidal cells and neurons in deep layers.     

Cholinergic neuropathology in a mouse model of Alzheimer's disease

Transgenic mice overexpressing mutant human amyloid precursor protein (PDAPP mice) develop several Alzheimer's disease (AD)-like lesions including an age-related accumulation of amyloid-beta (Abeta)-containing neuritic plaques. Although aged, heterozygous PDAPP mice also exhibit synaptic and glial cell changes characteristic of AD pathology, no evidence of widespread neuronal loss has been observed. The present study sought to determine whether homozygous PDAPP mice, which express very high levels of Abeta peptide, exhibit AD-like cholinergic degenerative changes, and whether the changes parallel the deposition of Abeta plaques. Mice were examined at 2 and 4 months and at 1 and 2 years of age. There was an age-related increase in the density of Abeta plaques in the cortex and hippocampus of the PDAPP animals; at 4 months of age there were very few plaques, and at 2 years there was a very high density of plaques. There was an age-related reduction in the density of cholinergic nerve terminals in the cerebral cortex; at 2 months there was a normal density of nerve terminals, but as early as age 4 months there was an approximately 50% reduction. However, at age 2 years there was no difference in the number or size of basal forebrain cholinergic somata compared with 2-month-old PDAPP mice. These data indicated that the homozygous PDAPP mouse exhibits cholinergic nerve terminal degenerative pathology and that the cortical neurodegenerative changes occur before the deposition of Abeta-containing neuritic plaques.     

Electrophysiological studies of the septal nuclei: I. The lateral septal region

Electrophysiological studies of the lateral septal region were performed on acutely prepared cats. The data indicate that the lateral septal region consists of two functionally distinct zones: a dorsal zone (i.e., dorsal septal nucleus) and a ventral zone (i.e., lateral septal nucleus). The dorsal septal nucleus receives a heavy ipsilateral fimbria projection, but receives no projection via the ventral septal afferent system. There is no return projection through the fimbria. Test responses recorded from the dorsal septal nucleus show prolonged periods of suppression. The lateral septal nucleus receives a lesser share of the ipsilateral fimbria input, but does receive input via the ventral septal afferent system. Convergence upon single cells between ipsilateral fimbria and ventral septal afferent input was an outstanding feature of lateral septal nucleus organization. Cells in the lateral septal nucleus project out of the lateral septal region in both dorsal and ventral directions.     

The cholinergic system in the basal forebrain of the Atlantic white‐sided dolphin (Lagenorhynchus acutus)

The basal forebrain (BFB) cholinergic neurotransmitter system is important in a number of brain functions including attention, memory, and the sleep‐wake cycle. The size of this region has been linked to the increase in encephalization of the brain in a number of species. Cetaceans, particularly those belonging to the family Delphinidae, have a relatively large brain compared to its body size and it is expected that the cholinergic BFB in the dolphin would be a prominent feature. However, this has not yet been explored in detail. This study examines and maps the neuroanatomy and cholinergic chemoarchitecture of the BFB in the Atlantic white‐sided dolphin (Lagenorhynchus acutus). As in some other mammals, the BFB in this species is a prominent structure along the medioventral surface of the brain. The parcellation and distribution of cholinergic neural elements of the dolphin BFB was comparable to that observed in other mammals in that it has a medial septal nucleus, a nucleus of the vertical limb of the diagonal band of Broca, a nucleus of the horizontal limb of the diagonal band of Broca, and a nucleus basalis of Meynert. The observed BFB cholinergic system of this dolphin is consistent with evolutionarily conserved and important functions for survival.     

Neuroanatomical distribution of vasotocin in a urodele amphibian (Taricha granulosa) revealed by immunohistochemical and in situ hybridization techniques

Immunohistochemical and in situ hybridization techniques were used to investigate the neuroanatomical distribution of arginine vasotocin-like systems in the roughskin newt (Taricha granulosa). Vasotocin-like-immunoreactive neuronal cell bodies were identified that, based on topographical position, most likely, are homologous to groups of vasopressin-immunoreactive neuronal cell bodies described in mammals, including those in the bed nucleus of the stria terminalis, medial amygdala, basal septal region, magnocellular basal forebrain—including the horizontal limb of the diagonal band of Broca, paraventricular and supraoptic nuclei, suprachiasmatic nucleus, and dorsomedial hypothalamic nucleus. Several additional vasotocin-like-immunoreactive cell groups were observed in the forebrain and brainstem regions; these observations are compared with previous studies of vasotocin- and vasopressin-like systems in vertebrates. Arginine vasotocin-like-immunoreactive fibers and presumed terminals also were widely distributed with high densities in the basal limbic forebrain, the ventral preoptic and hypothalamic regions, and the brainstem ventromedial tegmentum. Based on in situ hybridization studies with synthetic oligonucleotide probes for vasotocin and the related neuropeptide mesotocin, as well as double-labeling studies with combined immunohistochemistry and in situ hybridization, we conclude that the vasotocin immunohistochemical procedures used identify vasotocin-like, but not mesotocin-like, elements in the brain of T. granulosa. The distribution of arginine vasotocin-like systems in T. granulosa is greater than the distribution previously reported for any other single vertebrate species; however, it is consistent with an emerging pattern of distribution of vasotocin- and vasopressin-like peptides in vertebrates. Complexity in the vasotocinergic system adds further support to the conclusion that this peptide regulates multiple neurophysiological and neuroendocrinological functions. J. Comp. Neurol. 385:43–70, 1997. © 1997 Wiley-Liss, Inc.     

The effect of aging on the subcellular distribution of estrogen receptor-alpha in the cholinergic neurons of transgenic and wild-type mice

The degeneration of the basal forebrain cholinergic system plays an important role in cognitive deterioration in aging and Alzheimer's disease. Brain cholinergic neurons and their projections are affected by changes in the circulating levels of estrogens, which exert their effects mainly through the estrogen receptors. In this study, we investigated the effect of aging, estrogen status and transgenic genotype on the number of cholinergic neurons and the estrogen receptor alpha (ERalpha) content in the medial septum-vertical limb of the diagonal band of Broca. We used 6- and 12-month-old female double transgenic mice carrying mutated human amyloid precursor protein (APPswe) and presenilin-1 (PS1-A246E), and their nontransgenic littermate controls, which had been sham-operated or ovariectomized at the age of 3 months. Brain sections were double immunostained for choline acetyltransferase (ChAT) and ERalpha and used for stereological cell counting. We found that the number of ChAT-immunoreactive (ir) neurons containing nuclear ERalpha-ir was significantly lower in 12- than in 6-month-old mice. However, the age of the mice, the transgenic genotype or ovariectomy had no effect on the total number of ChAT-ir neurons, or on the number and percentage of all ChAT-ir neurons that contained ERalpha. These results indicate that aging is associated with translocation of ERalphas from the nucleus to the cytoplasm. We propose that this phenomenon is linked to those age-related processes known to be involved in inhibiting ERalpha binding to nuclei.     

A study of the transition from spindles to spike and wave discharge in feline generalized penicillin epilepsy: Microphysiological features

The microphysiological features underlying the evolution of spike and wave discharge from spindles in feline generalized penicillin epilepsy were investigated using extracellular microelectrode recordings. Action potentials generated by single cortical neurons were related to the EEG features of the transition from spindles to spike and waves using statistical methods of analysis on a computer. The probability of an action potential being discharged by a spindle wave was weak. It progressively increased after penicillin during the transformation of the spindle wave into the spike of the spike and wave complex. As this occurred, periods of decreased firing probability coinciding with the slow wave of the spike and wave complex developed immediately after each period of enhanced firing probability. The spike and wave pattern was thus characterized by a remarkable oscillation between periods of increased excitation of cortical neurons corresponding to the spike, and periods of markedly decreased firing probability corresponding to the wave of the spike and wave complex. This was associated with increased synchronization of discharge of neighboring cortical neurons. We propose that the transformation of spindles to spike and waves is the consequence of a single feature: increased excitability of cortical neurons to spindle-inducing thalamocortical volleys. Under those conditions cortical cells discharge action potentials more consistently with each thalamocortical volley. Because of this the high threshold intracortical recurrent inhibitory pathway is recruited into the discharging process and induces recurrent periods of powerful inhibition of cortical neurons.     

Inputs of the pulvinar and lateral posterior nucleus into the abducens nucleus of the cat

Intracellular potentials in anesthetized cats were recorded in abducens motoneurons after stimulation of the ipsilateral and contralateral pulvinar-lateral posterior nuclei (Pul-LPs). The contralateral superior colliculus was ablated to determine the dependence of the ocular input of the Pul-LP on this structure. Stimulation of the contralateral Pul-LP produced predominately excitatory responses in abducens motoneurons. The excitatory responses occurred as an early and/or late EPSP and demonstrated a variability of latency and amplitude characteristic of Pul-LP-evoked saccades. Stimulation of the ipsilateral Pul-LP produced inhibition more frequently than the contralateral Pul-LP. Stimulation of identical, bilateral sites in the Pul-LP suggests the ipsilateral and contralateral Pul-LP have reciprocal input into the abducens motoneurons. The polysynaptic pathway to the abducens nucleus is not dependent on the integrity of the superior colliculus. We conclude in agreement with Crommelinck et al. that although the Pul-LP definitely has an input into the oculomotor system, it is not closely linked to the final common pathway.