Cerebellum mossy fibers

Regional distribution studies indicate that the highest density of kainate receptor occurs in the stratum lucidum of the hippocampus (mossy fiber system) and in the inner and outer layers of the neocortex. The highest density of NMDA receptors is found in the hippocampus, stratum radiatum, and in the striatum, thalamus, and cerebral cortex. The distribution of AMPA receptors is similar to that of NMDA receptors, but in the cerebellum AMPA receptors predominate in the molecular layer... 

PKA-dependent long-term potentiation and depression was initially discovered in the mossy-fiber synapses of the hippocampus, and later demonstrated in parallel fiber synapses of the cerebellum and corticothalamic synapses of the forebrain (Malenka and Siegelbaum, 2001). This widespread form of plasticity does not involve changes in Ca2+-influx, but operates via a direct increase or decrease, respectively, of the amount of vesicle exocytosis that can be triggered by a given Ca2+-signal. Interestingly, this form of plasticity appears to depend on the interaction... 

Ruiz A, Fabian-Fine R, Scott R, Walker MC, Rusakov DA, Kullmann DM (2003) GABAA Receptors at hippocampal mossy fibers. Neuron 39 961 Rusakov DA, Saitow F, Lehre KP, Konishi S (2005) Modulation of presynaptic Ca2+ entry by AMPA receptors at individual GABAergic synapses in the cerebellum. J Neurosci 25 4930-40 Rustioni A (2005) Modulation of sensory input to the spinal cord by presynaptic ionotropic glutamate receptors. Arch Ital Biol 143 103-12... 

Garthwaite J, Brodbelt AR (1990) Glutamate as the principal mossy fiber transmitter in rat cerebellum pharmacological evidence. Eur J Neurosci. 2 177-180. 

Fig. 79. Photomicrograph of camera lucida drawing (inset) of anterogradely labelled axons and terminal boutons in the crus I ansiform lobule of rat cerebellum after cholera toxin (b fragment) injection into the contralateral ventral tegmental area. Arrows point to rosettes characteristic of mossy fiber endings in the granular layer (G). P, Purkinje cell layer WM, white matter. Scale bar = 40 ixm. Ikai et al. (1992).

Barmack et al. (1992a) noted a dense population of small ChAT-positive mossy fiber-like terminals in the tip of lobules IXa,b of rat cerebellum that are significantly smaller than the other ChAT positive rosettes (Fig. 83). This type of labelling was not described by Ojima et al. (1989) but could be observed in their Fig. 4. The source and characteristics of this peculiar population of terminals is still unknown. 

Fig. 84. Illustrations of choline-acetyltransferase (ChAT)-like immunoreactivity in the rabbit cerebellum. A. Sagittal view of the rabbit cerebellum delineating the lobules according to Larsell (Larsell, 1970). Mean measurements of ChAT activity are indicated by numbers in parentheses. B. Magnified view of the ventral vermis. The vermis contains areas of ChAT-positive mossy fiber terminals (indicated by dots). These areas in lobules 1 and 9d are illustrated in C and D, respectively. E. View of the right paraflocculus of the rabbit. ChAT-like immunoreactivity and ChAT activity was highest in the ventral paraflocculus, particularly lobule 2. The numbers in parentheses are mean measurements of ChAT activity, expressed as mmol of Ach synthe-sized/hr. g tissue at 37°C, for each cerebellar lobule in six rabbits. Barmack et al. (1992a).

Fig. 85. A. Drawing displaying the distribution of mossy rosettes (dots) immunoreactive to monoclonal choline-acetyltransferase (ChAT) antibody. The section (40 fim thick) was cut sagittally through the middle vermis of rat cerebellum. A considerable number of immunoreactive mossy terminals are observed in lobules I through IXab, although they are much fewer than in lobules IXc and X. Calibration bar = 1 mm. B. Drawing of part of lobule IXab shows the overall distribution of immunoreactive fibers. Arrows indicate mossy fibers with glomerular rosettes. Small and large arrowheads point to some varicose fibers distributing in or near the Purkinje cell layer (PCL) and in the molecular layer (ML), respectively. The ML fibers are most frequently observed in this lobule and tend to be restricted to the inner half of the layer. Calibration bar = 200 jum. Ojima et al. (1989).

Summarizing it appears that the cellular and regional distribution of muscarine receptors in the cerebellum is different between different species. Golgi cells and subpopulations of mossy fibers seem to express muscarine receptors most constantly. An interesting aspect about the presence of muscarine receptors in parallel fibers in rat and rabbit, is that the lobular distribution of m2-containing parallel fibers, is the same as that of ChAT-positive mossy fiber rosettes (see above). This raises the possibility that muscarine m2 receptor are specifically expressed by those granule cells that are innervated by cholinergic mossy fibers. If this proves to be true, this would imply that there... 

Fig. 146. Parasagittal section of the rat cerebellar vermis immunostained with antiserum to calretinin. Folia are labelled with roman numerals according to Larsell. The pattern of immunoreactivity in the nodulus (lobule X) and portion of the ventral uvula (lobule IXd) differs from that in the other vermal folia. While in most of the vermis weak immunoreactivity is present in granule cell bodies within the granular layer and in parallel fibers within the molecular layer, in the folia X and IXd of the vestibulo-cerebellum the immunoreaction product is largely localized in unipolar brush cells and mossy fibers, MN, medial cerebellar nucleus. Bar = 1 mm. Floris et al. (1994).

Fig. 191. Schematic line drawings of the unfolded opossum cerebellum modified after Larsell and Jansen (1972). The broken lines indicate the boundaries of the corticonuclear zones A-D after Klinkhachorn et al. (1984a). The distribution of the three types of enkephalinergic axons is indicated by the frequency and size of the symbols the beaded axons by asterisks (C), the mossy fibers by dots (A), and the climbing fibers by triangles (B). I-X indicate vermal lobules CR I, II, crura I and II, F, flocculus LS, lobulus simplex PFL, paraflocculus PML, paramedian lobule. D. Distribution of enkephalinergic axons in a horizontal section through the cerebellar nuclei. D, dentate nucleus, F, fastigial nucleus IPA, anterior interposed nucleus IPP, posterior interposed nucleus. From King et al. (1987).

Fig. 194. Three transverse sections through the cerebellum of the cat showing corticotrophin releasing factor (CRF)-like immunoreactivity in climbing fibers in the molecular layer (radial lines) and mossy fibers (dots) in the granular layer. Note corresponding positions (arrows) of strongly labelled climbing fibers and mossy fibers (arrows). Abbreviations CR I, II, Crus I and II FL, flocculus LS, simple lobule NIP, posterior interposed nucleus NL, lateral cerebellar nucleus NM, medial nucleus PFL, paraflocculus PML, paramedian lobule I-X, lobules I-X of Larsell. Cummings (1989).

Mossy fiber systems within the cerebellum display a concentric arrangement vestibulocerebellar fibers are located most centrally, and terminate in the cortex in the bottom of the fissures spino-, cuneo-, and reticulocerebellar fibers extend more peripherally and... 

Vestibulocerebellar mossy fibers take their origin from neurons in all vestibular nuclei, with the exception of the Deiters nucleus and a sparse projection from the magnocellular medial vestibular nucleus (Figs 200 and 201). The distribution of neurons projecting to either flocculus or caudal vermis or to both is rather similar and is bilaterally symmetrical. Most neurons were found in the medial, superior and descending vestibular nuclei in this order. Neurons projecting to lobules IX and X, to the flocculus and to both parts of the cerebellum occur in a ratio of 12 4 1 (Epema et al.,... 

Fig. 202. Cuneocerebellar projection to ipsilateral cerebellum in the cat. Left side diagrams from antegrade axonal transport of [ Hjleucine in transverse sections. Borders of compartments in adjacent Haggqvist-stained sections are indicated on the right. Abbreviations A(l-3) = A( 1-3) compartment A = concentration of mossy fibers in A compartment B = B compartment bp = brachium pontis Cl -tC2 = concentration of mossy fibers in Cl and C2 compartments Cl-3 = Cl-3 compartment C3 = concentration of mossy fibers in C3 compartment cr = restiform body D = Dcompartment D = concentration of mossy fibers in D compartment F = fastigial nucleus FL = flocculus HVI = hemisphere of lobule VI (simple lobule) lA = anterior interposed nucleus L = dentate nucleus PAR = paramedian lobule PFLD = dorsal paraflocculus PFLV = ventral paraflocculus X = X compartment X/B = concentration of mossy fibers in border region of X and B compartments. Gerrits et al. (1985b).

Correlations between the terminations of mossy fibers and cytochemical maps are rare. Gerrits et al. (1985b) mapped the localization of cuneocerebellar fibers with respect to the borders of white matter compartments in adjacent, Haggqvist-stained sections (Fig. 202). The projections of low thoracic-lumbar cord to the cerebellum of the rat were compared to the localizations of Zebrin 1-immunoreactive Purkinje cells in surface maps of all relevant cerebellar lobules by Gravel and Hawkes (1990). These authors noticed... 

Fig. 205. Distribution of spinocerebellar and pontocerebellar mossy fibers in surface reconstructions of the cerebellum of Tupaia gli.s, based on the sections depicted in Fig. 200. Voogd, unpublished.

P2- (i.e. the B zone) extending into P3+ (Fig. 207). Matsushita et al. (1991), who mapped fibers from the cervical cord in Zebrin-I stained sections of rat cerebellum found less correspondence of the concentrations of rosettes with the borders of the im-munoreactive Purkinje cell zones. Ji and Hawkes (1994) showed that cuneocerebellar mossy fiber terminals are located between the concentrations of lumbar spinocerebellar mossy fiber rosettes in P1+, PI - and P2- of lobules II and III of the rat cerebellum (Fig. 207). A close correspondence between multiple patches of mossy fibers with vibrissal receptive fields and the Zebrin-negative P1-, P2- and P3- zones of lobule IX of the rat cerebellum, was observed by Chockkan and Hawkes (1994). 

Fig. 206. Plots of the distribution of mossy fibers on the dorsal (caudal) surface of lobule IV in the cat. A. Fibers from the central cervical nucleus (Matsushita and Tanami, 1987). B. Fibers from the medial vestibular nucleus (Matsushita and Wang, 1987). C. Fibers from the thoracic cord (Yaginuma and Matsushita, 1987). D. Fibers from the spinal border cells (Yaginuma and Matsushita, 1986). E. Fibers from the external cuneate nucleus (Gerrits, 1985). F. Fibers from the basal pontine nuclei (Gerrits, 1985). G. Localization of AChE in the molecular layer on the dorsal surface of lobule IV. Inset sagittal section of the cerebellum of the cat.

Fig. 208. Diagram of the fractured somatotopy of the mossy fiber projections in the cerebellum of the rat. Patches with similar receptive fields are indicated with abbreviations for the stimulation sites on the head and the extremities. Redrawn from Welker (1987). Cr = crown El = eyelids Fbp = furry buccal pad FL = forelimb and hand G = gingiva HL = hindlimb I, II = crus I and II Li = lower incisor LI = lower lip Lob.ant. = anterior lobe lob.sim = lobulus simplex N = nose Nk = neck P = pinna PFL = paraflocculus PML = paramedian lobule PY = pyramis Rh = rhinarium Ui = upper incisor U1 = upper lip UV = uvula.

---