Proportion of NADPH-diaphorase reactive sympathetic efferents innervating the normal and inflamed knee joint of the cat

To determine whether postganglionic sympathetic efferents may be a source of nitric oxide in normal and inflamed knee joints, the distribution of NADPH-diaphorase was studied in retrogradely labelled neurons of the paravertebral sympathetic ganglia in the cat. In these ganglia, a strong NADPH-diaphorase staining reaction was found in 3-7% (segments L2-L5) and 14-17% (segments L6 and L7) of the neurons. Only 2.5 +/- 1.2% (mean +/- SD, 4 normal joints), of 2207 labelled neurons showed a positive staining reaction. During a unilateral inflammation (32 h), this proportion slightly increased to 5.0 +/- 1.2% (unaffected joints of 4 animals, 2510 labelled perikarya) and 5.4 +/- 2.8% (inflamed joints of 4 animals, 2578 labelled perikarya). However, these increases only attained statistical significance between the values obtained from control animals and from the normal sides of animals with a monoarthritis. Thus, the data indicate that in the sympathetic innervation of the normal and inflamed knee in the cat, the release of nitric oxide has little or no importance.

Vagal modulation of the insulin secretory response to KCl loading in nephrectomized dogs

In K-loaded intact and nephrectomized control dogs there is a four-to five-fold increase of basal serum insulin. With beta receptor blockade in K-loaded intact animals the increase of basal serum insulin is less than 1/4 to that in controls; in those with nephrectomy, the increase is similar to that in controls. Cervical vagotomy in K-loaded intact dogs does not alter (influence) the increase of serum insulin; in those with nephrectomy there is a striking increase. In K-loaded intact dogs cervical vagotomy added to beta receptor blockade has no influence i.e., the response is the same as that to blockade alone; in those with nephrectomy, the increase produced by vagotomy is suppressed. Results suggest that in controls with nephrectomy, the insulin secretory response does not involve beta receptors of pancreatic islet B cells owing to restraint by efferent impulses in the cervical vagi. Interruption of the impulse by vagotomy releases the restraint, with resulting hyperactivity; the accompanying hyperinsulinemia may be the result of suppression of the hyperactive receptors by beta receptor blockade.

Oligodendrocytes differentiate in organotypic cultures of rat visual cortex and myelinate efferent axons

We have investigated the presence and function of glia cells, especially of oligodendrocytes (OL) in organotypic cultures of rat visual cortex grown for 1-6 weeks in vitro. OL identified by strong Galactocerebroside-immunoreactivity (GalC-ir) displayed rather small somata and elaborately ramified processes. They were most concentrated in layers VIa and VIb and the remnant of the white matter. Silver staining revealed long descending or oblique processes in layers V and VI, which were often arranged in patches, and horizontal processes in the white matter. Proximal processes of OL cell bodies were connected to these long processes. DiI-labeling revealed very similar patches of processes, termed OL domains. They were identified as membraneous sheaths formed by processes of single OL around axons passing the OL domain. Confocal microscopy revealed single axons running through the membrane sheaths. We compared the molecular differentiation of glial cells in cultures to the in vivo situation with protein blots and immunohistochemistry for glial cell marker molecules. In homogenates of visual cortex in vivo, protein blots revealed the increase in expression by OL of myelin basic protein (MBP) during the fourth postnatal week. The astrocytic marker glial fibrillary acidic protein (GFAP), blotted as a control, increased over time in vivo, beginning at P14, indicating the differentiation of astrocytes. In homogenates of organotypic cortex cultures, the times course of expression of GFAP was very similar: it increased dramatically during the first 10 DIV, and remained fairly constant in older cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

The lateral ganglionic eminence is the origin of cells committed to striatal phenotypes: neural transplantation and developmental evidence

In order to determine whether the lateral ganglionic eminence (LGE) of the fetal telencephalon is the primary source of striatal precursors in striatal transplants and tissue cultures, cells derived exclusively from the LGE of fetal rat brains were transplanted into the quinolinic-acid-lesioned striatum of adult rats. After 2-3 months they produced grafts that were almost entirely AChE-positive as well as DARPP-32-, TH-, and calbindin-immunoreactive. The grafts were integrated into the host striatum so that host corticofugal fiber tracts interdigitated with graft tissues similar to the way they penetrate the gray matter of the normal striatum. Fast Blue dye injected into the ipsilateral globus pallidus of LGE grafted produced retrogradely labeled neurons within the grafts, but Fluorogold dye injected into the ipsilateral substantia nigra did not. In a separate experiment using DARPP-32-immunohistochemstry as a striatal marker, fetal (E16) and neonatal (P2) rat brains showed DARPP-32 immunoreactivity in the LGE but not in the adjacent medial ganglionic eminence (MGE). In summary, both fetal LGE cells and LGE grafts express specific striatal markers, and LGE grafts integrate into the host striatum and innervate the major striatal efferent target within the host brain. These data suggest that the LGE is the origin of cells committed to striatal phenotypes in the developing brain.

Efferent connections from the external cuneate nucleus to the medulla oblongata in the gerbil

The present study revealed the efferent projections from the external cuneate nucleus (ECN) to various medullary nuclei in the gerbil as demonstrated in fresh living brainstem slices by using in vitro anterogradely tracing with the dextran-tetramethyl-rhodamine-biotin. The tracer-labelled ECN axon terminals were observed (1) in most of the vital autonomic-related nuclei: the nucleus solitary tractus, nucleus ambiguus, rostroventrolateral reticular nucleus and C2 adrenergic area, (2) in the reticular formation: the medullary, parvocellular, intermediate, gigantocellular, dorsal paragigantocellular and lateral paragigantocellular reticular nuclei and medullary linear nucleus, and (3) in sensory nuclei: the cuneate nucleus, spinal trigeminal nuclei caudalis and interpolaris, paratrigeminal nucleus, medial and spinal vestibular nuclei, inferior olive and prepositus hypoglossal nucleus. These new findings are discussed in relation to possible roles of the ECN in cardiovascular, respiratory and sensorimotor controls.

Diagonal ventral forebrain continuum has overlapping telencephalic inputs and brainstem outputs which may represent loci for limbic/autonomic integration

Growing evidence indicates that three areas within the mammalian basal forebrain share many common features. Based on the similarity of connections and their adjacent spacial proximity, three forebrain nuclei are referred to as a continuum. The components of this diagonal ventral forebrain continuum (DVFC) are the central nucleus of the amygdala, the sublenticular portion of the substantia innominata, and the lateral bed nucleus of the stria terminalis. A primary concern and terminal goal of this study is to determine whether the region of this continuum which projects to the brainstem autonomic nuclei such as the vagal nuclei or the parabrachial nuclei also receives inputs from the basolateral amygdala. The first phase of this study involved determining what autonomic regions receive projections from the basal forebrain. The vagal complex and the parabrachial nuclei were found to receive the densest inputs from the DVFC. The topographic distribution of the respective retrogradely labeled cells and their collateral status is described. The second phase involved looking at afferent inputs from brainstem nuclei. The parabrachial nucleus sends reciprocal projections back to the continuum, which generally overlap the neurons which project back to the brainstem visceral nuclei. The third phase of the study indicated that the cells of the basolateral amygdala contribute a major terminal field which overlaps those cells of the basal forebrain continuum which in turn project to either the nucleus of the solitary tract or the parabrachial nucleus. The possibility that the circuits implied in this study represent the neural circuitry whereby emotional stimuli result in changes in visceral activity is addressed.

[Effects of lateral habenular stimulation on nociceptive response of neurons in rat spinal dorsal horn]

Ipsilateral stimulation of the LHb produced a significant attenuation of nociceptive response of wide dynamic range (WDR) neurons in the rat spinal dorsal horn. The inhibitory effect produced by LHb stimulation was partially blocked by systemic cyproheptadine and phentolamine but not naloxone. No significant change was observed in the activity of WDR neurons after ipsilateral electrolytical lesions of the LHb. These results suggest that the LHb participates in the supraspinal descending control on nociceptive response of WDR neurons in the spinal dorsal horn. However, tonic inhibitory mechanism seems not to be involved.

[Role of paraventriculo-spinal pathway in the inhibition of renal sympathetic nerve activity induced by blood volume expansion in rabbits]

In anesthetized and bilateral sinoaortic denervated rabbits with either intact or ascorbic acid injected paraventricular nucleus (PVN), the inhibition of renal sympathetic nerve activity (RSNA) induced by blood volume expansion (VE) all decreased by approximately 48%. However, 3-4 h and 3-4 d after kainic acid lesion of PVN, the inhibition of RSNA was attenuated respectively to -28.0 +/- 4.5% and -25.7 +/- 4.1% (P < 0.05) with considerably shortened time course (P < 0.01). Also such inhibition could be significantly attenuated (P < 0.05) by intrathecal injection of vasop ressinergic V1 receptor antagonist in spinal T10-T12 segments. There was no significant difference with the slight and brief increase of mean arterial pressure induced by VE in the control and the experimental group. Thus it can be concluded that the inhibition of RSNA induced by VE is partly mediated by a vagal afferent triggered PVN-spinal pathway.

[Responses of motoneurons to ventrolateral funiculus stimulation in neonate rat spinal cord slices]

Intracellular recordings were made from 25 antidromically identified motoneurons (MNs) in the transverse thoracolumbar spinal cord slices (500 microns) of neonate rats (7-16 d). In more than 80% MNs, depolarization potentials (EPSP) with latency of 1.2 +/- 0.2 ms could be evoked by focal stimulation (0.1 ms, 1-20 V, 0.1 Hz) of ventrolateral funiculus. When recorded at resting potential of -70 +/- 6 mV, the time-to-peak, amplitude, half-decay time and duration of EPSPs to suprathreshold stimuli were respectively, 2.6 +/- 0.4 ms, 13 +/- 3 mV, 5.3 +/- 1.6 ms and 31 +/- 8 ms. The EPSPs were graded in consummate to stimulus intensity and upon reaching threshold depolarization, action potentials were initiated. Relatively constant latency of EPSPs was observed in spite of varying stimulus frequency from 0.1 to 5 Hz. Upon increasing stimulation frequency > 20 Hz, EPSPs began to decrease and finally disappeared. In 3 MNs tested, the mean reversal potential of EPSPs was -8 mV. Low Ca/high Mg solution consistently attenuated but Mg-free solution enhanced the EPSPs. EPSPs were reversibly depressed by kynurenic acid (0.5-1 mmol/L) and partially inhibited by ketamine (50-100 mumol/L). The findings of the present investigation suggest that MNs are excited by the descending fibers in ventrolateral funiculus possibly via excitatory amino acid transmitters.

[Descending pathways mediating the effect of stimulating cerebral peduncle on the spinal nociceptive transmission in the rat]

The descending pathways for the effects of stimulation of cerebral peduncle (CP) on the nociceptive neurons of spinal cord dorsal horn were analyzed by subtotal spinal cord lesions in anesthetized rats. Inhibition was the predominant effect of CP stimulation on the C-fiber elicited nociceptive responses of dorsal horn neurons, in 30.7% of such neurons, the inhibition was preceded by some initial excitation. In most neurons the inhibitory effect was mediated by both dorsal funiculus (DF) and dorsolateral funiculus (DLF), that of DF usually predominated. It seemed that DLF played a more important role than DF. However, the excitatory effect was mediated by DF alone. Since in the rat the corticospinal tract (CST) is situated in the DF, the results suggest that cerebral cortex can modulate spinal nociceptive transmission not only by the CST, but also through a relay in some supraspinal structure(s) sending descending fibers into the DLF.

Bulbospinal neurons of the cat that co-contain serotonin and methionine enkephalin

The present study utilizes a combined retrograde transport of Fast Blue (or rhodamine-labeled latex microspheres) and simultaneous immunofluorescence technique to demonstrate directly the coexistence of serotonin and methionine enkephalin in bulbospinal neurons of the cat. The bulbospinal neurons that immunostained for both serotonin and enkephalin were observed, without any distinct somatotopic organization, in the nuclei raphe pallidus, obscurus and magnus. They were also observed in the nucleus reticularis magnocellularis and the ventrolateral medulla (cell group B1/3). Among the bulbospinal neurons encountered within individual 5-HT-rich medullary nuclei, high proportions of these neurons co-containing serotonin and methionine enkephalin were evidenced in the nucleus raphe obscurus (64%) and nucleus raphe pallidus (56%), less so in cell group B1/3 (41%), nucleus raphe magnus (39%), and the nucleus reticularis magnocellularis (29%). Physiological significance of such a morphological substrate is discussed.

The central organization of the vagus nerve innervating the colon of the rat

BACKGROUND

The extent to which the vagus nerve innervates the colon remains controversial.

METHODS

In 29 rats the tracer cholera toxin-horseradish peroxidase was injected into the cecum, the ascending, transverse, or descending colon or the rectum. For comparison, control injections were made into the stomach.

RESULTS

For all areas of colon except the rectum, brainstem motoneuronal labeling was limited to the lateral third of the dorsal motor nucleus of the vagus nerve bilaterally. In contrast, gastric injections resulted in motoneuronal labeling limited to the medial portions of the nucleus. The number of labeled motoneurons was greatest following injection of the cecum, and it significantly decreased for the more distal areas of the colon. Colonic motoneuron dendrites projected into the nucleus of the solitary tract and within the dorsal motor nucleus of the vagus nerve. Sensory afferent terminal labeling was limited to the commissural and medial subnuclei of the nucleus of the solitary tract. For the rectum, sensory and motor labeling was limited to the spinal cord.

CONCLUSIONS

The distribution of labeling within the vagal complex indicates that all regions of the colon, except the rectum, are innervated by the celiac and accessory celiac branches of the vagus nerve.

Ultrastructural organization of calcitonin gene-related peptide immunoreactive efferent axons and terminals in the vestibular periphery

The ultrastructural distribution of calcitonin gene-related peptide immunoreactivity (CGRPi) was examined in sections of decalcified temporal bones in order to study the complex peptidergic innervation patterns of this efferent neuromodulator in the peripheral vestibular system of the rat. A new method of preembedding immunoelectron microscopy was developed to accomplish this study. Unmyelinated CGRPi axons, measuring 1 to 3 microns in diameter, passed among the primary afferent fibers in Scarpa's ganglion, and these fibers continued through the subepithelial regions of the vestibular end-organs. Within the neurosensory epithelia of the maculae and cristae, the CGRPi axons ramified to produce numerous CGRPi terminals. Immunoelectron microscopic localization of CGRPi terminals in the maculae and cristae revealed an extensive innervation pattern on the afferent vestibular pathway. Calcitonin gene-related peptide immunoreactive terminals made synaptic contacts with the unmyelinated portions of the primary afferent vestibular fibers innervating both type I and type II hair cells. Abundant synaptic contact between CGRPi terminals and the chalices surrounding type I hair cells was observed. Rare direct contact between CGRPi terminals and type I or type II hair cells was observed. In addition, vesiculated efferent terminals without CGRPi were seen contacting type II hair cells. These data suggest that the efferent vestibular system has a much more complex innervation pattern on the afferent vestibular pathway than previously believed.

Beta-endorphin-induced inhibition of rumen contractions in sheep. The effect of hypothalamic de-efferentiation

In conscious sheep, beta-endorphin (1 and 2 micrograms/kg) administered into the third cerebral ventricle caused psychomotor excitability and a significant inhibition of the frequency of rumen contractions. The amplitude of the first rumen contractions, following immediately after the end of endorphin infusion, and the average amplitude of primary rumen contractions were also inhibited. De-efferentiation at the level of the hypothalamus prevented both the inhibitory effect of beta-endorphin on the frequency of rumen contractions and the drug-induced psychomotor excitability. However, de-efferentiation did not prevent beta-endorphin-induced inhibition of the mean amplitude of rumen contractions. The character of pathohistological changes induced by de-efferentiation showed descending degenerative changes of the nerve tracts connecting the hypothalamus with the pons and the medulla oblongata. These results, together with previously published evidence, do suggest that de-efferentiation at the level of the hypothalamus causes degeneration of inhibitory descending opioid-noradrenergic pathways connecting the hypothalamus with the gastric centres in the medulla oblongata.

Differential expression of tyrosine hydroxylase mRNA in the developing rat mesencephalon

1. With respect to the mesostriatal projection, the mesencephalon is composed of two dopaminergic (DA) cell populations, called dorsal tier and ventral tier. Strong evidence suggests differences in both the spatial and the temporal sequence of the innervation of the striatum between the two groups, with the ventral tier neurons innervating striatal patches prenatally and dorsal tier cells innervating striatal matrix postnatally. 2. Using in situ hybridization, we have examined the expression of the gene coding for tyrosine hydroxylase (TH) in mesencephalic DA neurons with respect to their postnatal development. Two ontogenic patterns of expression were observed: (a) dorsal tier neurons of the medial mesencephalon exhibited a sharp increase in expression beginning after birth, peaking on day 14, then decreasing and, finally, stabilizing; and (b) ventral tier neurons and dorsal tier cells from the lateral and the medial-dorsal mesencephalon showed only a slight increase in TH mRNA, reaching a plateau at P10. 3. The time course of the observed increase in TH gene expression in the first group, generally parallels the innervation of their target cells in the striatal matrix, suggesting that TH gene expression in these cells may be influenced by their postsynaptic cells or by the innervation process.

Allatostatin-immunoreactive neurons projecting to the corpora allata of adult Diploptera punctata

A monoclonal antibody against allatostatin I was used to demonstrate the allatostatin-immunoreactive pathways between the brain and the corpus cardiacum-corpus allatum complex in the adult cockroach Diploptera punctata. The antibody was two to three orders of magnitude more sensitive to allatostatin I than to the other four known members of the allatostatin family. Whole and sectioned brains in which immunoreactivity was localized with horseradish peroxidase-H2O2-diaminobenzidine reaction showed strongly immunoreactive cells in the pars lateralis of the brain with axons leading to and arborizing in the corpus cardiacum and the corpus allatum. Although many neurosecretory cells of the pars intercerebralis project to the corpora allata only, four strongly immunoreactive cells were evident here (two pairs on either side), and these did not project to the corpus cardiacum and corpus allatum but rather terminated within the protocerebrum in areas in which lateral cells also formed arborizations. Immunoreactivity was found in many other cells in the brain, especially in the tritocerebrum.

Characterization of peptidergic efferents from the lateral parabrachial nucleus to identified neurons in the rat dorsal raphe nucleus

The peptidergic content of the lateral parabrachial nucleus (LPB) efferents to the dorsal raphe nucleus (DRN) was studied by combining visualization of the anterogradely transported tracer Phaseolus vulgaris leucoagglutinin within fibers that were immunocytochemically stained for neurotensin (NT), calcitonin gene-related peptide (CGRP) or galanin (GAL). The identity of DRN target neurons was determined with simultaneous immunocytochemical labelling for serotonin, the major transmitter within the nucleus. Within the DRN, we estimated that about two-thirds of the anterogradely labelled fibers arising from the LPB also showed peptidergic immunoreactivity. NT was the most commonly observed neuropeptide in LPB neuronal efferents directed to the DRN, followed by CGRP and GAL. The peptidergic afferents in the DRN were oriented preferentially in the dorsoventral plane. Peptidergic fibers from the LPB possessed varicosities (diameters not exceeding 3 microns) and were apposed on serotoninergic neuronal somata. Some of the anterogradely labelled peptidergic fibers were not associated with cells showing immunoreactivity for serotonin. The present results suggest that NT-ergic, CGRP-ergic and GAL-ergic neurons within the LPB are in contact with serotoninergic and non-serotoninergic neurons within the DRN. Since the DRN is known to project to the LPB, it is likely that bi-directional interconnections between these nuclei exist. Such linkages may provide anatomical substrates for coordinated autonomic responses.

Effect of dietary potassium chloride in borderline hypertensive rats

The borderline hypertensive rat is the first filial offspring of the spontaneously hypertensive rat and the Wistar-Kyoto rat. With increased dietary sodium chloride intake, the borderline hypertensive rat develops hypertension and exaggerated cardiovascular and renal responses to acute environmental stress, similar to those observed in the hypertensive spontaneously hypertensive rat parent. In other models of sodium chloride-sensitive hypertension with different genetic background (Dahl rat), dietary potassium chloride supplementation protects against the development of hypertension, increased sympathetic nervous system activity, and exaggerated responses to acute environmental stress. This investigation sought to determine whether the dietary sodium chloride-induced development of both the hypertension and the exaggerated responses to acute environmental stress could be reversed or prevented by increased dietary potassium chloride intake. Dietary potassium chloride intake was increased with a 1% potassium chloride drinking solution either after 12 wk of 8% sodium chloride intake (reversal) or concomitant with the onset of 12 wk of 8% sodium chloride intake (prevention). An increase in dietary potassium chloride intake did not reverse or prevent the development of either the hypertension or the exaggerated cardiovascular and renal responses to acute environmental stress in borderline hypertensive rats fed 8% sodium chloride. It is concluded that the difference in genetic background between borderline hypertensive rats and other models of sodium chloride-sensitive hypertension is an important determinant of the protective effect of dietary potassium chloride supplementation.

Actions of cholinergic agonists and antagonists on the efferent synapse in the frog sacculus

Intracellular recordings were made from hair cells in the frog saccular epithelium isolated with its innervating nerves. Inhibitory post-synaptic potentials (IPSPs) were recorded from hair cells when the efferent fibers were activated by electrical stimulation. The effects of acetylcholine (ACh), cholinomimetics, and cholinergic antagonists on the efferent synapse were studied in a preparation where the IPSPs can be observed directly. ACh or carbachol (CCh) produced a transient membrane hyperpolarization with a decrease in input resistance followed by an abolition or reduction of the IPSP. In a low Ca2+ medium where efferent synaptic activity was abolished, ACh or CCh still induced hyperpolarization, though the response appeared to be smaller than that in normal medium. Neither nicotinic (dimethyl-4-phenyl-piperazinium (DMPP), phenyltrimethylammonium (PTMA) and nicotine) nor muscarinic (muscarine, methacholine, bethanechol and oxotremorine) agonists induced the membrane hyperpolarization, but the former drugs inhibited the IPSPs while the latter drugs did not. Both d-tubocurarine and atropine inhibited the IPSP, but the d-tubocurarine was more potent, causing inhibition even at a dose of 0.5 microM while 2 microM or more atropine was needed. The ACh- or CCh-induced hyperpolarization was inhibited completely by d-tubocurarine (5 microM), but only slightly by atropine (5 microM). These results may indicate that the IPSP and the effects of ACh or CCh are based on a direct interaction between ACh or CCh and ACh receptors on the hair cells.

Surgical treatment of clinical stage A nonseminomatous testis cancer

Until clinical staging improves, patients presenting with clinical stage A nonseminomatous testis cancer should be offered the option of initial nerve-sparing RPLND versus surveillance. Either method of management may be successful in the individual patient. We feel each patient with clinical stage A disease must be informed of alternative methods of management and be allowed to choose the method of management that he feels best suits his needs in terms of risk benefit.

The origin of ovarian neuropeptide Y (NPY)-immunoreactive nerve fibres from the inferior mesenteric ganglion in the pig

Applying a double-immunofluorescence technique, the porcine ovary is demonstrated to receive two populations of NPY-immunoreactive nerve fibres originating from the inferior mesenteric ganglion: one with colocalized tyrosine hydroxylase and supplying predominantly the ovarian vasculature, and a second, solely NPY-immunoreactive and almost exclusively associated with growing follicles. A third group of tyrosine hydroxylase- and dopamine-beta-hydroxylase-positive, but NPY-negative nerve fibres is associated with ovarian blood vessels and, to a minor extent, with ovarian follicles. As revealed by retrograde tracing, the vast majority of postganglionic neurons projecting to the ovary is located in a discrete area of the ganglion, suggesting a somatotopic organization of the porcine inferior mesenteric ganglion. Moreover, the findings indicate that three subpopulations of postganglionic sympathetic neurons with different chemical codes supply different target components of the porcine ovary. The physiological relevance of the described neurons in the nervous control of ovarian functions remains to be elucidated.

A comparative study of the behavioral deficits following lesions of various parts of the zebra finch song system: implications for vocal learning

Song production in song birds is controlled by an efferent pathway. Appended to this pathway is a "recursive loop" that is necessary for song acquisition but not for the production of learned song. Since zebra finches learn their song by imitating external models, we speculated that the importance of the recursive loop for learning might derive from its processing of auditory feedback during song acquisition. This hypothesis was tested by comparing the effects on song in birds deafened early in life and birds with early lesions in either of two nuclei--Area X and the lateral magnocellular nucleus of the anterior neostriatum (LMAN). These nuclei are part of the recursive loop. The three treatments affected song development differently, as reflected by various parameters of the adult song of these birds. Whereas LMAN lesions resulted in songs with monotonous repetitions of a single note complex, songs of Area X-lesioned birds consisted of rambling series of unusually long and variable notes. Furthermore, whereas song of LMAN lesioned birds stabilized early, song stability as seen in intact birds was never achieved in Area X-lesioned birds. Early deafness also resulted in poorly structured and unstable song. We conclude that Area X and LMAN contribute differently to song acquisition: the song variability that is typical of vocal development persists following early deafness or lesions of Area X but ends abruptly following removal of LMAN. Apparently, LMAN plays a crucial role in fostering the kinds of circuit plasticity necessary for learning.

Rat muscle spindle immunocytochemistry revisited

The expression of myosin heavy chain isoforms in muscle spindle fibres has been the subject of a number of immunocytochemical studies, some of them with discordant results. In order to assess whether these discrepancies are due to differences in the specificity and sensitivity of the antibodies used, we have compared the reactivity of rat muscle spindle fibres to two pairs of antibodies presumed to be directed against slow tonic (ALD 19 and ALD 58) and neonatal (NN5) and neonatal/fast (MF30) myosin heavy chains. Adult, developing and neonatally de-efferented muscle spindles from the rat hind limb muscles were studied in serial cross-sections processed for the peroxidase-antiperoxidase method. Important differences in the staining profiles of intrafusal fibres were noted when ALD 19 and ALD 58 were compared. ALD 19 stained the muscle spindle precursors from the seventeenth day in utero, whereas ALD 58 only did so by the twentieth day of gestation. In adult spindles ALD 19 stained the nuclear bag1 fibres along their entire length, whereas ALD 58 did not stain these fibres towards their ends. ALD 19 stained the nuclear bag2 fibres along the A, B and inner C region, but ALD 58 stained these fibres only in the A and the inner B regions. ALD 19 stained some nuclear chain fibres along a short equatorial segment, whereas ALD 58 did not stain the nuclear chain fibres at all. NN5 stained the nascent nuclear bag1 and chain fibre precursors at earlier stages of development than MF30. Clear differential staining between primary and secondary generation of both extra- and intrafusal myotubes was seen with NN5, whereas MF30 stained all myotubes alike. However, in postnatal spindles, MF30 was a very good negative marker of nuclear bag1 fibres. The staining profile of the adult fibres with NN5 and MF30 was rather similar. The staining pattern of neonatally de-efferented bag fibres obtained with ALD 19 and ALD 58 was practically identical and it differed from that of control spindles, confirming that motor innervation participates in the regulation of the expression of slow tonic MHC along the length of the nuclear bag2 fibres, as we have previously shown with ALD 19. The distinct staining patterns obtained with ALD 19 versus ALD 58 and with NN5 versus MF30 reflect differences in antibody sensitivity and specificity. These differences account, in part, for the discrepancies in the results of previous studies on muscle spindles, published by Kucera and Walro using ALD 58 and MF30, and by us using ALD 19 and NN5.