bluuebunny/crossref_metadata_2025 huggingface dataset:
Synapses made by axons of callosal projection neurons in mouse somatosensory cortex: Emphasis on intrinsic connections
Authors: White Edward L. , Czeiger David
Published: January 2005

This is one of a series of papers aimed at identifying the synaptic output patterns of the local and distant projections of subgroups of pyramidal neurons. The subgroups are defined by the target site to which their main axon projects. Pyramidal neurons in areas 1 and 40 of mouse cerebral cortex were labeled by the retrograde transport of horseradish peroxidase (HRP) transported from severed callosal axons in the contralateral hemisphere. Terminals of the local axon collaterals of these neurons (“intrinsic” terminals) were identified in somatosensory areas 1 and 40, and their distribution and synaptic connectivity were examined. Also examined were the synaptic connections of “extrinsic” callosal axon terminals labeled by lesion induced degeneration consequent to the severing of callosal fibers. A post‐lesion survival time of 3 days was chosen because by this time the extrinsic terminals were all degenerating, whereas the intrinsic terminals were labeled by HRP.

Both intrinsic and extrinsic callosal axon terminals occurred in all layers of the cortex where they formed only asymmetrical synapses. Layers II and III contained the highest concentrations of both types of callosal axon terminal. Analyses of serial thin sections through layers II and III in both areas 1 and 40 yielded similar results: 97% of the extrinsic (277 total sample) and of the intrinsic (1215 total sample) callosal axon terminals synapsed onto dendritic spines, likely those of pyramidal neurons; the remainder synapsed onto dendritic shafts of both spiny and nonspiny neurons. Thus the synaptic output patterns of intrinsic vs. extrinsic callosal axon terminals are strikingly similar. Moreover, the high proportion of axospinous synapses formed by both types of terminal contrasts with the proportion of asymmetrical, axospinous synapses that occur in the surrounding neuropil where only about 80% of the asymmetrical synapses are onto spines. This result is in accord with previous quantitative studies of the synaptic connectivities of both extrinsic and intrinsic axonal pathways in the cortex (White and Keller, 1989: Cortical Circuits: Boston: Birkhauser): in all instances, axonal pathways are highly selective for the types of elements with which they synapse.
Factors determining the migration of astrocytes into the developing retina: Migration does not depend on intact axons or patent vessels
Authors: Chan‐Ling Tailoi , Stone Jonathan
Published: January 2005

Astrocytes migrate into the cat retina from the optic nerve, beginning from embryonic day (E) 52. Once they have entered the retina they concentrate along major axon bundles and fail to enter regions of the retina with high densities of neurones, in particular the area centralis region of the ganglion cell layer. These nonuniformities appear as the astrocytes spread over the retina during development, and in this study we have examined factors that might control their spread. First we examined astrocytes in a retina in which the axon bundles had degenerated following an optic nerve lesion at birth. The area over which astrocytes had spread was normal, suggesting that their spread does not depend on the presence of intact axons. Second, we noted that, despite the degeneration of all ganglion cells following the nerve lesion, astrocytes still did not spread over the area centralis. Their spread is apparently not inhibited by concentrations of neurones. Third, we examined astrocytes in retinas of animals raised in an atmosphere containing 70–80% oxygen, which prevents the formation of retinal vessels. Again, the area over which the astrocytes had spread was normal, suggesting that their spread does not depend on the presence of patent blood vessels. These negative findings led us to compare the distribution of spindle cells (precursors of retinal vasculature) and astrocytes in the cat during development. The close correspondence in their topographical distribution and the earlier spread of the spindle cells lead us to suggest that spindle cells provide a basal lamina component that may guide the migration of astrocytes.
Continuous growth of the motor system in the axolotl
Authors: Holder Nigel , Clarke J. D. W. , Stephens Nigel , Wilson Stephen W. , Orsi Claudia , Bloomer Timothy , Tonge D. A.
Published: January 2005

During growth of the axolotl, motor neurons, and muscle fibres are added to the motor system. By double labelling neurons with tritiated thymidine and retrogradely transported HRP, we show that some motor neurons are born at postembryonic stages. Further analysis of motor neurons with the aid of HRP reveals this population of newly, born cells relatively frequently in small (5–7 cm long) axolotls, but only rarely in large (7–13 cm long) axolotls. Evidence is presented that suggests that these immature cells are in the process of migrating from close to the ependyma out to the ventral horn. HRP transport also reveals growth cones of advancing axons within spinal nerves in animals up to 6 cm in length. Cell counts by light and electron microscopic methods show that muscle fibres are generated throughout larval life in the iliotibialis, a typical limb muscle. This analysis provides data consistent with the notion that new muscle fibres are added from a localised growth zone situated at the superficial edge of the muscle. These results are discussed in terms of the correlation between continuous growth of the motor system and the ability of the axolotl to functionally repair lesions to the peripheral nervous system.
Prefrontal cortical projections to the cholinergic neurons in the basal forebrain
Authors: Gaykema Ronald P. A. , Van Weeghel Rob , Hersh Louis B. , Luiten Paul G. M.
Published: January 2005

The prefrontal cortex (PFC) projections to the basal forebrain cholinergic cell groups in the medial septum (MS), vertical and horizontal limbs of the diagonal band of Broca (VDB and HDB), and the magnocellular basal nucleus (MBN) in the rat were investigated by anterograde transport of Phaseolus vulgaris leuco‐agglutinin (PHA‐L) combined with acetylcholinesterase (AChE) histochemistry or choline acetyltransferase (ChAT) immunocytochemistry. The experiments revealed rich PHA‐L‐labeled projections to discrete parts of the basal forebrain cholinergic system (BFChS) essentially originating from all prefrontal areas investigated. The PFC afferents to the BFChS display a topographic organization, such that medial prefrontal areas project to the MS, VDB, and the medial part of the HDB, whereas the orbital and agranular insular areas predominantly innervate the HDB and MBN, respectively. Since the recurrent BFChS projection to the prefrontal cortex is arranged according to a similar topography, the relationship between the BFChS and the prefrontal cortex is characterized by reciprocal connections. Furthermore, tracer injections in the PFC resulted in anterograde labeling of numerous “en passant” and terminal boutons apposing perikarya and proximal dendrites of neurons in the basal forebrain, which were stained for the cholinergic marker enzymes. These results indicate that prefrontal cortical afferents make direct synaptic contacts upon the cholinergic neurons in the basal forebrain, although further analysis at the electron microscopic level will be needed to provide conclusive evidence.
Ontogeny of the F8Famide‐like (morphine‐modulating) peptides in the central nervous system of rats
Authors: Kivipelto L. , Panula P. , Rubenstein J. , Yang H.‐Y. T.
Published: January 2005

FLFQPQRF‐NH2 (F8Famide; FMRFamide‐like peptide; morphine‐modulating peptide) is a peptide isolated from bovine brain. It has some opiate analgesia modulating effects. In an adult rat central nervous system, F8Famide‐like immunoreactivity is found in high concentrations in the posterior pituitary, hypothalamus, pons, medulla, and dorsal spinal cord.

By using immunohistochemistry and radioimmunoassay, we studied the development of the F8Famide‐immunoreactive system in the rat central nervous system during the ontogeny. F8Famide‐immoreactive fibers and terminals first appeared in the median eminence on the twentieth embryonal day. Postnatally the F8Famide‐immunoreactive system developed rapidly both in the brain and spinal cord, the immunoreactive structures having an adultlike distribution by the age of 1 week. A transient increase of the F8Famide‐immunoreactive material was observed during the third and fourth postnatal weeks. By the age of 4 weeks, the F8Famide‐containing neuronal system was adultlike both in distribution and quantity.

The results suggest that the F8Famide‐like peptides may act as neurotransmitters or neuromodulators from the time of their appearance in the brain and spinal cord. The early appearance and the distribution of the F8Famide‐like immunoreactivity suggest that these peptides may participate, in addition to nociceptive mechanisms, in the regulation of blood pressure, feeding behaviour, and endocrine functions.
Patterns of synaptic input on corticocortical and corticothalamic cells in the cat visual cortex. II. The axon initial segment
Authors: Fariñas Isabel , DeFelipe Javier
Published: January 2005

In the present study we examined the synaptology of the axon initial segments (AISs) of three populations of retrogradely labeled pyramidal cells: callosal, corticothalamic, and ipsilateral corticocortical projecting cells. The cells were labeled by horseradish peroxidase injected into the contralateral visual cortex, the ipsilateral lateral geniculate nucleus, or area 19 of the ipsilateral hemisphere. The AISs of these cells were completely reconstructed from tracings of serial electron micrographs and the number and type of synapses ending on them determined, These data were compared with that described in the companion paper (Fariñas and DeFelipe, J Comp Neurol 1991; 304:53–69), in which the ultrastructure and synaptology of the somata of callosal and corticothalamic cells was investigated. Together, these data permit comparisons to be made between the somatic and axonic innervation of the same cells.

Our results show that each population of efferent cells examined received a characteristic and rather homogeneous number (in comparison with the number of axosomatic synapses) of axoaxonic synapses: 16 to 23 for AISs of callosal cells, 22 to 28 for ipsilateral corticocortical cells, and 1 to 5 for corticothalamic cells. Since most axoaxonic synapses are likely to be GABAergic, it is concluded that each population of pyramidal cells receives a distinct GABAergic inhibitory synaptic profile.
Topography of projections from the auditory cortex to the inferior colliculus in the rat
Authors: Herbert Horst , Aschoff Andreas , Ostwald Joachim
Published: January 2005

We examined the organization of descending projections from auditory and adjacent cortical areas to the inferior colliculus (IC) in the rat by using the retrograde and anterograde transport of wheat germ agglutinin‐horseradish peroxidase.

Small tracer injections were placed into cytologically defined subnuclei of the IC. On the basis of the resulting pattern of retrogradely labeled neurons in the cortex, different cortical areas and fields were defined. Two secondary areas located ventrocaudally (Te2) and ventrally (Te3) to the primary auditory area (Te1) were delineated. The primary auditory area was subdivided into a posterior (Te1.p), a medial (Te1.m), and an anterior (Te1.a) auditory field. In addition, we outlined an area located rostrally to the auditory areas comprising a part of the secondary somatosensory cortex, as well as a dorsal belt surrounding dorsally the auditory areas.

The following basic patterns of corticocollicular projections are revealed: (1) layers 2 and 3 of the dorsal cortex of the IC (DC2, DC3) are differentially innervated by the primary auditory fields (Te1.p and Te1.a project bilaterally to DC2, while Te1.m projects bilaterally and in topographical order to DC3); cells in Te1.m, arranged in caudal to rostral sequence, project to corresponding loci in DC3 arranged from dorsolateral to ventromedial; (2) the fibrocellular capsule of the IC, comprising layer 1 of the dorsal and external cortex of the IC, receives input from the secondary auditory area Te2; (3) layers 2 and 3 of the external cortex of the IC are only weakly innervated by the primary and secondary auditory cortex; (4) the intercollicular zone receives its major input from the secondary auditory area Te3, the secondary somatosensory cortex, and the dorsal belt; and (5) finally, the central nucleus of the IC receives no input from the temporal cortex at all.

Our results demonstrate that the corticocollicular projections are highly organized. These pathways may modulate auditory processing in different functional circuits of the inferior colliculus.
All peroneal motoneurons of the rat survive crush injury but some fail to reinnervate their original targets
Authors: Swett John E. , Hong Chang‐Zern , Miller Peter G.
Published: January 2005

This is a quantitative study of the motoneuronal population of the rat's common peroneal nerve following severe crush injury of the sciatic nerve or its component branches. The crush was performed unilaterally under anesthesia for 60 seconds with hemostat jaws covered with tubing to form a smooth, 2 mm long, injured zone. Recovery from injury was allowed for 14 to 188 days. It was measured behaviorally using the sciatic functional index (SFI) and electrophysiologically by comparing the conduction velocity and amplitudes of evoked muscle action potentials prior to injury, and again after injury just before the nerve was labeled with horseradish peroxidase (HRP), and/or its wheat germ agglutinin conjugate (WGA‐HRP), 48–72 hours before sacrifice. The motoneurons were retrogradely labeled on both sides so that the uninjured side might serve as a control. On the injured side the nerves were labeled either distal or proximal to the crush site, The tibialis anterior muscles on both sides were removed and weighed. Spinal segments L2 to L6 were cut in serial, frozen cross‐sections. HRP reaction products were formed using TMB as the chromogen. The normal peroneal nerve was found to contain 634 ± 26 motoneurons (22 cases). The number of motoneurons labeled 5–15 mm distal to the injury site (22 cases) was 535 ± 69 or 84.4% of normal. In 12 cases in which the nerve was labeled 5 mm proximal to the injury normal population numbers (648 ± 30) were found. These counts demonstrated that the unlabeled 15.6% in the distal labeled cases had not vanished as a result of cell death. Instead, the unlabeled group was composed mainly of small motoneurons whose axons probably had not regenerated distal to the crushed zone. Mean soma size of injured neurons increased to maximum 3–6 weeks after injury and then gradually decreased in size over the following weeks to nearly normal values. This transient increase in size was due to two factors: (1) soma swelling in response to axonal injury, and (2) absence of many small motoneurons, presumably γ‐motoneurons, which were either incapable of, or prevented from, regenerating beyond the injury zone long after larger motoneurons had reinnervated their targets. SFI scores, muscle weights, and amplitude ratios of evoked potentials recovered to control values by 70–80 days post‐injury. Conduction velocities remained 20–25% below normal at the end of 80 days. These data suggest that because all motoneurons survived injury, it is possible for all of them to reinnervate their original targets under certain conditions providing that proper pathguides are available.
Projection of the mammalian superior colliculus upon the dorsal lateral geniculate nucleus: Organization of tectogeniculate pathways in nineteen species
Authors: Harting John K. , Huerta Michael F. , Hashikawa T. , van Lieshout David P.
Published: January 2005

Anterograde and retrograde transport methods have been used to analyze the projection of the superior colliculus upon the dorsal lateral geniculate nucleus in 19 mammalian species. Our retrograde findings reveal that tectogeniculate neurons are relatively small, and lie dorsally within the superficial gray. These small tectogeniculate neurons are spatially related to a dense tier of W‐cell retinal input.

Our anterograde tracing results show that tectogeniculate axons are visuotopically distributed to small‐celled regions of the lateral geniculate in all nineteen species. In the majority of these species, the small‐celled, tectally innervated regions of the lateral geniculate lie adjacent to the optic tract and contain W‐cell‐like neurons. Our findings suggest that neuroanatomical demonstration of the tectogeniculate projection is a relatively simple and straightforward way of revealing regions of the lateral geniculate which contain W‐cells. This is true even in species in which the lateral geniculate lacks obvious cellular laminae, and in regions of the lateral geniculate where W‐cells are few in number.

The present data are especially interesting in light of the cortical projections of tectally innervated, small‐celled regions of the lateral geniculate to the patches or puffs within layer III of area 17. Since these regions of small‐celled geniculocortical axons are co‐extensive with zones (“blobs”) rich in cytochrome oxidase, it might be that information carried over the tectogeniculate circuitry plays an important role in the functions of the blob system.
Distribution of vasoactives intestinal peptide‐ and substance P‐containing nerves originating from neurons of airway ganglia in cat bronchi
Authors: Dey Richard D. , Altemus Jeffrey B. , Michalkiewicz Mieczyslaw
Published: January 2005

This study examined the possibility that vasoactive intestinal peptide (VIP)‐ and substance P (SP)‐containing nerve fibers in bronchial smooth muscle, glands, epithelium, and blood vessels originate from neurons of airway ganglia. Explants of airway walls were maintained in culture with the expectation that nerve fibers from neurons of airway ganglia would remain viable, whereas fibers originating from neurons not present in the airway walls would degenerate. Airways were dissected and placed into culture dishes containing CMRL 1066 medium for 3, 5, and 7 days. In controls (noncultured), VIP‐ and SP‐like immunoreactivity was observed in nerve fibers associated with bronchial smooth muscle, glands, and blood vessel walls and in nerve cell bodies of airway ganglia. Nerve fibers containing SP were also observed within the bronchial epithelium. After 3,5, and 7 days in culture, VIP‐ and SP‐containing fibers were identified in all of the same locations except in the airway epithelium where SP‐containing fibers could not be demonstrated. VIP and SP were frequently colocalized in the same nerve fibers of bronchial smooth muscle and glands in controls and cultured airways. There were no statistically significant differences in nerve fiber density for either VIP‐ or SP‐containing fibers in bronchial smooth muscle between controlled and cultured airways. VIP concentrations in cultured airways were significantly less than in controls. The results suggest that a large proportion of VIP‐ and SP‐containing nerve fibers supplying bronchial smooth muscle, glands, and blood vessels in the airways originate from neurons of airway ganglia.
Projections of physiologically characterized globular bushy cell axons from the cochlear nucleus of the cat
Authors: Smith Philip H. , Joris Philip X. , Carney Laurel H. , Yin Tom C. T.
Published: January 2005

We made intraaxonal recordings from 30 individual globular bushy cell axons in the trapezoid body of the cat using HRP‐filled glass microelectrodes. With subsequent HRP injection, we determined their axonal projection patterns.

For cells with characteristic frequencies (CFs) above 3 kHz, short‐tone peristimulus time histograms (PSTHs) at CF were typically primarylike at low tone intensities and primarylike with notch (PLN) or onset with low sustained activity (OL) at higher stimulus levels. Cells with CFs between 1 and 3 kHz showed the same response features with the spikes in the sustained region of the response phase‐locked to the stimulus tone. Cells with CFs below 1 kHz showed phase‐locked PSTHs with exceptionally high levels of synchrony compared to eighth nerve fibers with comparable CFs. This exceptional phase‐locking was also noted when cells with CFs of 1–3 kHz were presented with tones below 1 kHz.

Although the globular bushy cell axons were not completely filled from the soma of origin to terminal fields in the contralateral brainstem, a number of consistent anatomical features were distinguished in the population. All but one of the myelinated axons crossed the midline in the middle, large fiber component of the trapezoid body. Ipsilaterally, the axon always gave off from one to four collateral branches whose major targets were the posterior periolivary nucleus (PPO) and the lateral nucleus of the trapezoid body (LNTB). Minor termination sites for ipsilateral collateral branches were the dorsolateral periolivary nucleus (DLPO) and the lateral superior olive (LSO). Contralaterally the axon gave rise to one or two calyces of Held in the medial nucleus of the trapezoid body (MNTB). Three other major collateral branches arose from the contralateral axon and innervated a consistent set of areas. One headed caudally to innervate an area just ventromedial to the facial nucleus. Another followed the sixth nerve dorsally to innervate the dorsomedial periolivary nucleus (DMPO). A third collateral headed rostrally toward the ventral nucleus of the lateral lemniscus (VNLL), giving off occasional small sidebranches. Although each injected axon gave rise to a collateral that innervated the MNTB, it did not necessarily give rise to all three of the other collateral branches.
Enrichment of cholinergic synaptic terminals on GABAergic neurons and coexistence of immunoreactive GABA and choline acetyltransferase in the same synaptic terminals in the striate cortex of the cat
Authors: Beaulieu Clermont , Somogyi Peter
Published: January 2005

The synaptic circuits underlying cholinergic activation of the cortex were studied by establishing the quantitative distribution of cholinergic terminals on GABAergic inhibitory interneurons and on non‐GABAergic neurons in the striate cortex of the cat. Antibodies to choline acetyltransferase and GABA were used in combined electron microscopic immunocytochemical experiments.

Most of the cholinergic boutons formed synapses with dendritic shafts (87.3%), much fewer with dendritic spines (11.5%), and only occasional synapses were made on neuronal somata (1.2%). Overall, 27.5% of the postsynaptic elements, all of them dendritic shafts, were immunoreactive for GABA, thus demonstrating that they originate from inhibitory neurons. This is the highest value for the proportion of GABAergic postsynaptic targets obtained so far for any intra‐ or subcortical afferents in cortex. There were marked variations in the laminar distribution of targets. Spines received synapses most frequently in layer IV (23%) and least frequently in layers V–VI (3%); most of these spines also received an additional synapse from a choline acetyltransferase‐negative bouton, The proportion of GABA‐positive postsynaptic elements was highest in layer IV (49%, two‐thirds of all postsynaptic dendritic shafts), and lowest in layers V–VI (14%). The supragranular layers showed a distribution similar to that of the average of all layers. The quantitative distribution of targets postsynaptic to choline acetyltransferase‐positive terminals is very different from the postsynaptic targets of GABAergic boutons, or from the targets of all boutons in layer IV reported previously. In both cases the proportion of GABA‐positive dendrites was only 8–9% of the postsynaptic elements. At least 8% of the total population of choline acetyltransferase‐positive boutons, presumably originating from the basal forebrain, were also immunoreactive for GABA. This raises the possibility of cotransmission at a significant proportion of cholinergic synapses in the cortex.

The present results demonstrate that cortical GABAergic neurons receive a richer cholinergic synaptic input than non‐GABAergic cells. The activation of GABAergic neurons by cholinergic afferents may increase the response specificity of cortical cells during cortical arousal thought to be mediated by the basal forebrain. The laminar differences indicate that in layer IV, at the first stage of the processing of thalamic input, the cholinergic afferents exert substantial inhibitory influence in order to raise the threshold and specificity of cortical neuronal responses. Once the correct level of activity has been set at the level of layer IV, the influence can be mainly facilitatory in the other layers.
Topography of the projection from the central complex of the thalamus to the sensorimotor striatal territory in monkeys
Authors: François C. , Percheron G. , Parent A. , Sadikot A. F. , Fenelon G. , Yelnik J.
Published: January 2005

The distribution of axons arising from the central complex (or centre médian‐parafascicular complex) and terminating in the striatum was studied in seven macaques and one squirrel monkey. Deposits of anterograde tracers were made in the two lateral‐most subdivisions of the central complex, i.e., the middle part (or pars media) and the lateral part (or pars paralateralis). All injections avoided the pars parafascicularis. The intrastriatal distribution of labeled axonal endings was mapped in relation to the standard ventricular (CA‐CP) system of coordinates. Labeled endings were observed in the major posterior and dorsal parts of the putamen (excluding its anteromedial and ventral parts) and also in a restricted ventrolateral part of the caudate nucleus. The topography of the central territory of the striatum, denned as the striatal space receiving axons from the central complex, was found to correspond exactly to that of the cortical sensorimotor territory delineated after cortical injections. The termination pattern of the central axons within the striatum was patchy. Viewed as a whole, the irregular and hazy patches formed oblique streaks, parallel one with the other. The three‐dimensional reconstructions of data from transverse sections revealed that the streaks were bi‐dimensional pictures of three‐dimensional parasagittal layers covering the whole anteroposterior extent of the cortical sensorimotor territory of the striatum. Our work shows that the pars media of the central complex, which receives selectively pallidal afferent axons (Francois et al., '88: Brain Res. 473:181–186), is the main source of the centroputaminal projection. The probable implication of this in a closed sensorimotor loop of the basal ganglia is discussed.
Synaptic connections of the auditory nerve in cats: Relationship between endbulbs of held and spherical bushy cells
Authors: Ryugo David K. , Sento Seishiro
Published: January 2005

This report focuses on a class of large synaptic endings, the endbulbs of Held. These endings are located in the anteroventral cochlear nucleus and arise from the axons of type I spiral ganglion neurons. Axons were stained with horseradish peroxidase (HRP) using intracellular injections of single fibers or extracellular injections into the auditory nerve. Individual endbulbs or pairs of endbulbs that converged onto the same spherical bushy cell were examined with the aid of a light microscope and subjected to morphometric analyses. Endbulbs of fibers having low spontaneous discharge rates (SR, ≤ 18 spikes/sec) have a more complex shape than those of high SR fibers (> 18 s/s), a feature represented by systematic differences in endbulb silhouette perimeter without differences in endbulb silhouette area. Consequently, the ratio, silhouette area divided by silhouette perimeter, yields a “form factor” separating endbulbs of high SR from those of low SR. High SR fibers had ratios > 0.52 (mean = 0.63 ± 0.09), whereas low SR fibers had ratios <.52 (mean = 0.45 ± 0.06). Pairs of endbulbs with unknown physiological properties had similar form factor values, despite the wide range of values observed in the endbulb population. These data imply that endbulbs converging upon the cell body of a spherical bushy cell arise from fibers of the same SR group.

Electron microscopic examination was conducted on the endbulb of one physiologically characterized and intracellularly stained auditory nerve fiber (CF = 1.4 kHz; SR = 55 s/s) and its unstained endbulb mate with the aid of serial ultrathin sections. In addition to the well‐known axosomatic synapses, these endbulbs formed axodendritic synapses: 11.7% for the HRP‐labeled endbulb and 13.3% for the unlabeled endbulb. The axodendritic synapses appear to occur on dendrites of nearby spherical bushy cells and may represent a mechanism whereby single endbulbs can disperse activity to multiple neurons in the cochlear nucleus. We propose that axosomatic synapses preserve fiber SR groupings, whereas axodendritic synapses may not.
Species‐specific distribution of aromatic L‐amino acid decarboxylase in the rodent adrenal gland, cerebellum, and olfactory bulb
Authors: Baker Harriet , Abate Cory , Szabo Aniko , Joh Tong H.
Published: January 2005

Aromatic L‐amino acid decarboxylase (AADC), the enzyme that converts L‐dopa to dopamine, displayed species‐specific differences in both activity and immunoreactivity in the cerebellum, olfactory bulb, and adrenal glands of three rodent species, the hamster, rat, and mouse. Specifically, in the hamster but not the rat or mouse, AADC immunoreactive cells were observed in the cerebellum and adrenal cortex. The unusual distribution of the enzyme was confirmed biochemically. AADC activity was greater in the adrenal gland and the cerebellum in the hamster than in the mouse or rat. In addition, by Western blot analysis, one band of appropriate molecular weight was observed both in the hamster adrenal gland and cerebellum. The rat adrenal gland displayed a similar immunoreactive protein on the Western blot; however, the protein could not be detected in the rat cerebellum by the technique utilized. Tyrosine hydroxylase (TH) immunoreactivity in these same tissues did not differ among the species. In the main olfactory bulb of the mouse, juxtaglomerular cells exhibited very limited immunoreactivity for AADC, but TH‐immunoreactivity in these cells was robust. In contrast, juxtaglomerular cells in the rat displayed a similar intensity of immunostaining for both AADC and TH. AADC activity in the mouse, consistent with the reduced immunostaining for the enzyme, was 50% of that in the rat and the hamster. These data demonstrate that AADC protein, which is contained in cells of diverse function, also displays qualitative and quantitative species specific variations in both distribution and amount.
Inputs to spinocerebellar tract neurones located in Stilling's nucleus in the sacral segments of the rat spinal cord
Authors: Edgley S. A. , Grant G. M.
Published: January 2005

Spinocerebellar neurones located in the sacral segments of the rat spinal cord have been identified electrophysiologically. The neurones studied were located 0.7–1.1 mm. deep to the cord dorsum, lateral and dorsal to the central canal in the medial part of lamina VII. Neurones were identified as spinocerebellar by antidromic activation from the cerebellar surface, the lowest threshold stimulation sites being near the midline on the posterior lobe vermis (lobule VIII). Estimates of conduction velocities of the axons ranged from 15–32 m/s (mean 22.8 m/s) and are directly comparable to velocities of presumed ventral spinocerebellar tract neurones recorded in the same animals. In intact animals, activity was most strongly influenced by passive movement of the tail. Activation by proprioceptors was confirmed with nerve stimulation: all of the neurones studied were discharged by stimulation of nerves which innervate ipsilateral tail muscles. In many cases responses appeared close to the threshold of the nerve, indicating that the largest, fastest conducting afferents (group la muscle spindle primary afferents) were responsible for them. Latencies of EPSPs or spikes were brief and in many cases indicative of a monosynaptic connection. We conclude that this group of neurones is powerfully and monosynaptically excited by group I muscle afferents and thus resemble the cells of Clarke's column and cells of the central cervical nucleus, both of which occupy a similar location in the grey matter of more rostral segments.
Distribution of cholecystokinin‐like immunoreactivity within the stomatogastric nervous systems of four species of decapod crustacea
Authors: Turrigiano G. G. , Selverston A. I.
Published: January 2005

The distribution of cholecystokinin‐like immunoreactivity was studied in the stomatogastric nervous systems, pericardial organs, and haemolymph of four species of decapod Crustacea, by using immunocytochemical and radioimmunoassay techniques. Whereas cholecystokinin‐like immunoreactivity was found within the stomatogastric nervous systems of all four species, its distribution in each is unique. Two species (Panulirus interruptus and Homarus americanus) have cholecystokinin‐like immunoreactivity within fibers and neuropil of the stomatogastric ganglion (STG); two other species (Cancer antenarius and Procambarus clarkii) do not. Further, the cholecystokinin‐like immunoreactivity within the STGs of Panulirus and Homarus arise from distinct structures; from a projection of anterior ganglia in Panulirus, and from somata within the posterior motor nerves in Homarus. The staining in the other ganglia of the stomatogastric nervous system also shows some interspecies variability, although it appears to be more highly conserved than staining within the STG. These differences in staining were confirmed by measuring the amount of CCK‐like peptide present in tissue extracts of ganglia by radioimmunoassay.

In contrast to the variable staining within the STG, all four species have cholecystokinin‐like immunoreactivity within the neurosecretory pericardial organs and thoracic segmental nerves. This cholecystokinin‐like immunoreactivity is contained within fibers and within varicosities that coat the surface of these structures. The location of this staining and the presence of detectible levels of CCK‐like peptide in the haemolymph suggests that CCK‐like peptides in decapod Crustacea may be utilized as neurohormones.
Afferent and efferent connections of the olfactory bulbs in the lizard Podarcis hispanica
Authors: Martinez‐Garcia Fernando , Olucha Francisco E. , Teruel Vicent , Lorente Maria J. , Schwerdtfeger Walter K.
Published: January 2005

The connections of the olfactory bulbs of Podarcis hispanica were studied by tract‐tracing of injected horseradish peroxidase. Restricted injections into the main olfactory bulb (MOB) resulted in bilateral terminallike labeling in the medial part of the anterior olfactory nucleus (AON) and in the rostral septum, lateral cortex, nucleus of the lateral olfactory tract, and ventrolateral amygdaloid nucleus. Bilateral retrograde labeling was found in the rostral lateral cortex and in the medial and dorsolateral AON. Ipsilaterally the dorsal cortex, nucleus of the diagonal band, lateral preoptic area, and dorsolateral amygdala showed labeled cell bodies. Retrogradely labeled cells were also found in the midbrain raphe nucleus.

Results from injections into the rostral lateral cortex and lateral olfactory tract indicate that the mitral cells are the origin of the centripetal projections of the MOB.

Injections in the accessory olfactory bulb (AOB) produced ipsilateral terminallike labeling of the ventral AON, bed nucleus of the accessory olfactory tract, central and ventromedial amygdaloid nuclei, medial part of the bed nucleus of the stria terminalis, and nucleus sphericus. Retrograde labeling of neurons was observed ipsilaterally in the bed nucleus of the accessory olfactory tract and stria terminalis, in the central amygdaloid nucleus, dorsal cortex, and nucleus of the diagonal band. Bilateral labeling of somata was found in the ventral AON, the nucleus sphericus (hilus), and in the mesencephalic raphe nucleus and locus coeruleus.

Injections into the dorsal amygdala showed that the mitral neurons are the cells of origin of the AOB centripetal projections. Reciprocal connections are present between AOB and MOB.

To our knowledge, this is the first study to address the afferent connections of the olfactory bulbs in a reptile. On the basis of the available data, a discussion is provided of the similarities and differences between the reptilian and mammalian olfactory systems, as well as of the possible functional role of the main olfactory connections in reptiles.
The fine structure of the Purkinje cell and its afferents in lurcher chimeric mice
Authors: Caddy Keith W. T. , Herrup Karl
Published: January 2005

Lurcher is an autosomal dominant mutation in the mouse. Heterozygote (+/Lc) animals lose 100% of their cerebellar Purkinje cells during the first postnatal month. Aggregation chimeras made between +/Lc and wild‐type embryos have been used to demonstrate that this neuronal cell death is a cell autonomous property of the +/Lc Purkinje cells. In lurcher chimeras, all +/Lc PCs die while wild‐type Purkinje cells survive in the numbers expected. Although they are normal in number, previous work from our laboratories has shown that when the genetically wild‐type Purkinje cells are present in the mosaic environment of the lurcher chimeric mouse they develop a very unusual morphology. Their dendritic trees are small, and the caliber of their dendrites is increased. This paper examines the fine structure of these unusual cells as well as their afferent fibers. Purkinje cell somas in the lurcher chimera have an increased number of lysosomes and the rough endoplasmic reticulum is improperly configured. In the majority of the Purkinje cell dendrites the organelles are disorganized; it is not certain whether this is a cause or a consequence of the increase in dendritic caliber previously reported. Presynaptic fibers have been examined and, while all classes of expected synapses can be observed, the numbers of synaptic profiles visible in any one thin section are reduced. Climbing fiber terminations on the Purkinje cells were smaller than normal with a greatly diminished number of constituent vesicles. Unexpectedly, we found unusual morphologies among the Bergmann glial fibers and the presence of unusual (or ectopic) astrocytic like glial cells near the pial surface. These changes in turn were accompanied by an increase in the number of glial‐like fibers near the pia in some parts of the chimeric cerebellar cortex. The results are discussed in light of our knowledge of other mutant mice, and a hypothesis is put forward to explain some of our results.
Expression of glial fibrillary acidic protein by müller cells in rd chick retina
Authors: Semple‐Rowland Susan L.
Published: January 2005

Accumulation of glial fibrillary acidic protein (GFAP) in Müller cells has been observed in retinas of several mammalian species secondary to genetically induced degeneration and neuronal injury. In the present series of experiments, I have examined the effects of the rd (retinal degeneration) mutation on the expression of GFAP in retinas of chicks homozygous for the mutation (rd/rd) prior to and following the onset of photoreceptor degeneration, which first appears approximately 7 days posthatch (7dph). Carrier (+/rd) and wild‐type (+/+) retinas served as controls.

Retinas taken from 1, 7, 21, and 33 dph rd/rd, +/rd, and +/+ chicks were analyzed for the presence of GFAP by immunocytochemical and SDS‐PAGE/Western blot techniques. The following immunocytochemical observations were made: (1) GFAP immunostaining was limited to and located throughout the Müller cells. (2) The intensity of GFAP immunostaining increased with age in all three retina types in tissue sections, as well as on immunoblots. (3) The distribution of GFAP staining within rd/rd Müller cells following the onset of degeneration was slightly different from that observed in +/+ and +/rd retinas and was distinguished by increased staining of the cell bodies and the cell processes forming the outer limiting membrane.

The results of these experiments show that Müller cells in chick retina contain GFAP. In addition, they suggest that, in contrast to Müller cells in degenerating mammalian retina, Müller cells in rd chick retina do not accumulate large amounts of GFAP in response to degeneration.
Somatosensory cortex of the neonatal pig: II. Topographic organization of the secondary somatosensory cortex (SII)
Authors: Craner Sandra L. , Ray Richard H.
Published: January 2005

Multiunit microelectrode recording techniques were used to delineate the somatotopic organization of the secondary somatosensory cortex (SII) of the neonatal pig. Barbiturate anesthetized piglets ranging in age from 7 days preterm to 2 months postpartum were used. The SII area, located lateral to the rostral and middle suprasylvian sulci, was found to contain a complete somatotopic representation of the contralateral body surface with a significant proportion of bilateral input for all body regions except the forehoof and forelimb. The SII forelimb and hindlimb representations were found to possess a “striplike” orientation in a rostral to caudal sequence, and the trunk representation was located posterolateral to the hindlimb representation, giving SII an inverted appearance. Two apparently separate face representations were delineated; one posterolateral to the projection from the trunk and the other anterior to the forehoof region.

Unlike SI, which possesses a disproportionately large representation of the rostrum, SII has no specialized representation of the rostrum. The overall organization of SII supports the contention that this cortical region provides a more generalized representation of the entire body surface than does SI.
Subregional topography of capillaries in the dorsal vagal complex of rats: I. Morphometric properties
Authors: Shaver Steven W. , Pang Judy J. , Wall Katharine M. , Sposito Nadine M. , Gross Paul M.
Published: January 2005

Cytoarchitectonic and neurochemical studies of the dorsal vagal complex in the caudal medulla oblongata of rats indicate the existence of distinct anatomical and functional compartments within its components. We applied morphometric methods to discern whether capillary networks differed quantitatively between subregions and zones of area postrema, nucleus tractus solitarii (NTS), and dorsal motor nucleus of the vagus nerve (DMN) of rats. Analysis of 11 subdivisions of area postrema identified both “true” (range in luminal diameter of 3–7.5 μm) and sinusoidal (luminal diameter > 7.5 μm) capillaries that, together, made the capillary density for most of area postrema 75% greater than that found in NTS and DMN (526/mm2 vs about 300/mm2). The rank order of true capillary density in area postrema along its rostracaudal axis was caudal > central < rostral, whereas the reverse order was true for sinusoidal capillaries. Dorsal (periventricular) and medial zones of area postrema throughout its rostrocaudal axis tended to have higher values for capillary density, volume, surface area, luminal diameter, and pericapillary space volume than lateral or ventral zones bordering NTS. Within 200 μm of obex, the ventral zone of rostral area postrema was distinct, having a relatively sparse capillary density that may indicate morphological specializations limiting blood‐tissue communication in this subregion. There were no quantitative differences in capillary dimensions between DMN and three subnuclei of NTS. These studies add to extant evidence that the dorsal vagal complex is differentiated for specific functions. Area postrema, especially, has topographical diversity in its capillary organization that likely corresponds to complex roles in neuroendocrine, autonomic, and chemosensory mechanisms.
Organization of the cerebellum in the pigeon (Columba livia): III. Corticovestibular connections with eye and neck premotor areas
Authors: Arends J. J. A. , Allan Robert W. , Zeigler H. Philip
Published: January 2005

The connections of the cerebellar cortex with vestibular premotor neurons of the oculomotor and collimotor systems in the pigeon were delineated in experiments using WGA‐HRP as an anterograde and retrograde tracer. Putative premotor neuron pools were identified by injections into the oculomotor (mIII) and trochlear nuclei (mIV) and into the most rostral portion of the cervical neck motor nucleus, nucleus supraspinalis (SSp). The retrograde data indicate that ipsilateral projections upon oculomotor neurons arise from the medial portions of the superior (VeS) and tangential (Ta) nuclei. Contralateral projections originate from the infracerebellar nucleus, the interstitial vestibular region including the main (lateral) portion of the tangential nucleus, and from the descending and medial vestibular nuclei (VeD, VeM). These projections were confirmed in anterograde studies that also denned the connections of these vestibular premotor regions with specific subnuclear divisions of the pigeon's “oculomotor” nuclei (mill, mIV, mVI). The organization of projections from the vestibular nuclei to the pigeon's extraocular motoneurons is similar to that reported in mammals.

Projections upon neck premotor neurons arise primarily from neurons in the interstitial region of the vestibular nuclear complex. After injections in SSp, retrogradely labeled neurons were found, contralaterally, in the lateral part of the tangential and superior vestibular nuclei and in the dorsolateral vestibular nucleus (VDL). Ipsilateral labeling was seen in the medial interstitial region (VeM, VeD, and medial Ta). These projections were confirmed in anterograde experiments. With the exception of VDL, vestibular nuclei projecting to neck motoneurons also project to extraocular motoneurons. Thus the infracerebellar nucleus projects exclusively, and the superior vestibular nucleus predominantly, upon oculomotor (mill, mIV) nuclei; VDL projects predominantly upon the neck motor nucleus, whereas the interstitial vestibular regions (medial Ta, rostral VeD, intermediate VeM) project upon both collimotor and oculomotor neurons.

The pattern of retrograde labeling seen in the cerebellar cortex after injections into vestibular premotor nuclei was used to define the projections of specific cerebellar cortical zones upon vestibular eye and neck premotor neurons. Corticovestibular projections upon these regions arise from the auricle and lateral unfoliated cortex, the posterior lobe components of cortical zones B and E, and from the vestibulocerebellum. Each of these cortical zones projects upon components of the vestibular nuclear complex, which are premotor to either oculomotor nuclei or collimotor nuclei.

The hodological findings are related to the functional organization of the oculomotor and collimotor systems in the pigeon and compared with the mammalian data.