Dorsal Acoustic Stria Research Articles

Pathways and terminal fields of the cochlearofugal somatostatin tracts of very young rats

The cochlearofugal somatostatin (SRIF) neuron system of very young rats (between newborn and 1 week old) was investigated by means of the indirect immunofluorescence technique of Coons. Cochlear nuclei (both dorsal and ventral cochlear nuclei) of this stage contain numerous SRIF-positive cells which are scarcely found in adult rats. Based upon the experimental findings obtained by this study, the majority of SRIF-positive fibers originating from these nuclei reach the contralateral inferior colliculus via well-established cochlearo-inferior collicular tracts such as dorsal acoustic striae, intermediate acoustic striae and trapezoid body, respectively. The possible significance of SRIF in the development of the auditory system is briefly discussed.

Neuronal types in the deep dorsal cochlear nucleus of the cat: I. Giant neurons.

Large or "giant" neurons (average somatic diameter greater than 22 micron) of the dorsal cochlear nucleus (DCN) have been carefully described in this light (LM) and electron (EM) microscopic study of normal Nissl-stained and Golgi-impregnated cat brain stems. These neurons can be roughly classed by somatic shape (width:length ratio = r) as elongate (r less than 0.65), ovoid (0.65 less than or equal to r less than 0.75), or spherical (0.75 less than or equal to r less than or equal to 1.0) in Nissl-stained sections. However, orientation and location of somata, size, number, and distribution of basal dendrites and other cytological features seen in Nissl material provided five, easily recognized classes of large neurons: elongate bipolar, elongate multipolar, globular, radiate, and oriented multipolar giant cells. Further cytological details of the dendritic tree and axonal morphology of these neurons, observed in rapid Golgi impregnations of cat and kitten brain stems, extended these descriptive categories of giant neurons. These same deep DCN giant cells were identified in thick plastic sections and in subsequent thin sections. Thin sections showed further neuronal distinctions by relative density of somatic and dendritic synaptic inputs. All giant cells have dense synaptic inputs to basal and primary dendrites but only elongate multipolar and radiate giant cell somata have nearly continuous synaptic coverage of somata. Many axodendritic terminals and some axosomatic endings resemble cochlear endings as identified on fusiform cells of the DCN. Nauta preparations after ipsilateral cochlear ablations have confirmed (1) cochlear input to all giant cell types and (2) different patterns of input to each type. Hence, each giant cell type must process incoming auditory signals, but each cell must receive slightly different primary information. Since some giant cells of each type had observable axons heading into the dorsal acoustic stria, they must all carry encoded primary information to higher auditory centers.

The effect of lesions of the dorsal acoustic stria on the levels of glutamic acid decarboxylase and GABA transaminase in the inferior colliculus and cochlear nucleus of the guinea-pig

The levels of glutamic acid decarboxylase (GAD) and γ-amino butyric acid-α-oxoglutarate transaminase (GABA-T) have been investigated in the cochlear nucleus and inferior colliculus of the guinea-pig after hemilateral section of the dorsal acoustic stria. Animals were cerebellectomised and the stria on one side cut. Eleven days later the animals were killed and GAD and GABA-T assayed in the respective nuclei. There was no change in the enzyme levels of the inferior colliculi showing no direct GABA-ergic fibres ascending through the stria and terminating in the inferior colliculi. The levels of both GAD and GABA-T in the cochlear nucleus on the operated side decreased significantly. It is concluded that about 30% of the GAD containing terminals in the cochlear nucleus arise from fibres descending through the dorsal acoustic stria. The bulk of the GABA-ergic transmission in the cochlear nucleus is assumed to involve an intrinsic system of short axoned neurones, the majority of which have their nerve endings in the dorsal part of the nucleus.

Physiology of pathway from dorsal cochlear nucleus to inferior colliculus revealed by electrical and auditory stimulation.

The dorsal cochlear nucleus (DCN) projects axons to the contralateral central nucleus of the inferior colliculus (ICC) via the dorsal acoustic stria (DAS). In the anaesthetised cat, when brief electrical stimuli are applied to the caudal surface of DCN, single unit and field activity is evoked preferentially in the ventro-lateral region of ICC. Most single ICC units judged by electrical stimulation to have received a direct input from DCN are excited by contralateral tonal stimulation and inhibited or uninfluenced by ipsilateral tones. The sharp non-monotonic intensity functions of most of these units are similar to those of units in the dorsal cochlear nucleus, but ipsilateral inhibition is likely to be provided by a source other than DCN. Thus, although it is suggested that axons of DAS terminate preferentially in the ventro-lateral aspect of the contralateral ICC, it is likely that at least some neurones in this latter region receive additional input from another source - possibly the lateral superior olivary nucleus.

Identification of response properties of ascending axons from dorsal cochlear nucleus

Electrical stimulation in the dorsal acoustic stria (DAS) and the posterior and dorsal part of the ventral cochlear nucleus (VCN) was used to identify the response properties of efferent axons from the dorsal cochlear nucleus (DCN) in unanesthetized, decerebrate cats. Responses recorded in the DCN of this preparation can be divided into two broad classes, type II/III and type IV. Results of previous studies suggest that one subclass of type II/III units, those without spontaneous activity, are inhibitory interneurons terminating on type IV cells. Most type IV units (34/43) could be antidromically activated from the DAS and most units which could be activated from the DAS were of this type (34/39), suggesting that type IV responses are recorded from the projection cells of the DCN. Few type II/III cells without spontaneous activity could be activated from the DAS (1/30). A few cells of this type (6/32) could be antidromically stimulated from regions of the posterior AVCN or dorsal PVCN through which axon collaterals of some small cell interneurons of the DCN have been reported to pass. No type IV cells could be activated from the VCN (0/22). Thus the results are consistent with some type II/III responses originating in DCN interneurons. Spontaneously active type II/III units had intermediate properties.

Auditory brain stem responses in the cat. II. Effects of lesions

Discrete lesions of the brain stem auditory pathway in cats were found to have complex effects on the auditory brain stem response (ABR). These effects ranged from an amplitude change on only a single component of the ABR to latency and amplitude changes for that component plus some or all of the subsequent components. Lesions of certain portions of the classical primary auditory pathway (i.e., the dorsal cochlear nucleus, the dorsal acoustic stria, the lateral superior olivary nucleus, the posterior portion of the lateral lemniscus and the inferior colliculus) were not associated with changes in the ABR prior to component P5. Except for midline lesions, the effects of a brain stem lesion on the ABR were quite different for ipsilateral and contralateral stimulation. The predominant effect of brain stem lesions on the ABR was an attenuation of the amplitudes of the components and only an occasional increase in their latency. Opposite effects, i.e., increases in amplitude or decreases in latency, were rare. The acute effects of brain stem lesions on the ABR could be transient and not persist in chronic recordings. The components of the ABR were primarily affected by the following lesions. Component P0.8 was attenuated by a lesion of the eighth nerve. N1.0, P1.2 and N1.5 were unaffected by lesions of the cochlear nucleus but were affected by lesions of the eighth nerve, suggesting that the eighth nerve was the generator of these components. Except for one lesion of the trapezoid body component P1.7 was only affected by lesions of the cochlear nucleus or eighth nerve, suggesting its origin in one or both of these structures. N2.0 was affected by lesions of the ventral cochlear nucleus, the region of the superior olivary complex and the trapezoid body. P3 was affected by lesions in the region of the superior olivary complex and the trapezoid body. N3 and N4 were affected primarily by lesions of the lateral lemniscus, but also by lesions of the superior olivary complex and trapezoid body. The results suggest that except for the first few components (P0.8, N1.0, P1.2 and N1.5) each of the components has substantial contributions from more than one auditory brain stem structure. Component P0.8 was determined to have substantial contributions from both cochlear microphonic and neural activity.

Identification of the response properties of efferent axons of the dorsal cochlear nucleus

The response properties of cells in the dorsal cochlear nucleus (DCN) of unanesthetized, decerebrate cats fall into two broad classes: type II/III units are excited by best frequency tones at all levels above threshold; type IV units are inhibited at most levels [Young and Brownell, J. Neurophysiol. 39, 282 (1976)]. By using antidromic stimulation, the response properties of cells whose axons travel in two output pathways of the DCN have been identified. It was possible to antidromically stimulate occasional type II/III cells from the posterior, dorsal part of the AVCN, but never type IV cells. In contrast, almost all type IV cells can be antidromically stimulated from the dorsal acoustic stria (DAS). Most type II/III cells cannot be stimulated from the DAS. Thus, the ascending axons from DCN to higher brainstem nuclei originate largely in type IV cells and the association fibers from DCN to AVCN originate in type II/III cells. These results will be discussed in terms of the known morphological features of the DCN and the previously described response properties of its cells.

Descending connections between superior olivary and cochlear nuclear complexes in the cat studied by autoradiographic and horseradish peroxidase methods.

The descending pathways from the superior olivary complex (SO) to the cochlear nuclear complex (CN) were investigated in 58 cats using labelled aminoacid and horseradish peroxidase transport techniques. Descending connections were found coursing bilaterally through the trapezoid body (TB) and ipsilaterally in the intermediate and dorsal acoustic striae. The dorsolateral periolivary nucleus (DLPO) sends fibres through both the intermediate and dorsal striae, which are joined by others from the lateral preolivary nucleus (LPO). Both the latter nucleus and the medial preolivary nucleus (MPO) give rise to a bilateral descending projection which traverses TB. The distribution of these descending pathways within CN is described (although the technique did not permit precise synaptic identification). The possible implications of these pathways for response patterns at the level of CN are discussed.

Single unit studies on the dorsal and intermediate acoustic striae.

Studies were made of the fiber compositon and of single unit dischage characteristics in the dorsal and intermediate acoustic straie. Counts of fibers and cells revealed more than twice as many fibers as cochlear nucleus cells of the types known to contribute axons to these tracts. Recordings were made in the striae to confirm the classes of discharge patterns which are transmitted from the posterior cochlear nucleus to more central structures and to seek evidence for descending activity entering the cochlear nucleus through the striae. Discharge patterns of the majority of units resembled those seen in previous studies when recordings were made from regions of the cochlear nucleus which are known to contribute fibers to the striae. Some patterns, however, were unlike any which have been reported in the cochlear nucleus on the same side as the recording site, but resembled activity of other auditory structures, suggesting that these were descending inputs. To confirm the presence of descending activity, recordings were made in the dorsal acoustic stria at a point medial to where the stria had been completely severed. Recordings made under these conditions demonstrated the presence of descending activity. The physiological findings help explain the disparity between the counts of fibers and cells, and point out a need for more detailed descriptions of the origins of descending inputs through the striae.

The origins, course and distribution of the dorsal and intermediate acoustic striae in the rhesus monkey.

AbstractAttempts were made to produce discrete stereotactic lesions in the dorsal cochlear nucleus (Dc) in a series of rhesus monkeys. Anterograde degeneration was studied using Nauta and Fink‐Heimer techniques. Following lesions confined to the caudal pole of Dc, a few degenerated fibers projected to the contralateral lateral superior olivary nucleus via the dorsal acoustic stria. Degeneration was distributed to the contralateral ventral and to a lesser extent dorsal nuclei of the lateral lemniscus. The contralateral central nucleus of the inferior colliculus was a major site of termination of second order auditory fibers; a small number of degenerated fibers ascended to this nucleus ipsilaterally, and a few crossed in its commissure. A few degenerated fibers also were present in the contralateral magnocellular division of the medial geniculate body.When Dc was damaged at levels which overlie the posteroventral cochlear nucleus (Pv), or after lesions involving both subdivisions, degeneration was seen in the intermediate as well as in the dorsal acoustic stria. Fibers arising in Pv coursed through Dc and were interrupted by lesions in the latter. In addition to degeneration described above, fibers projected to the ipsilateral lateral superior olivary nucleus, contralateral medial trapezoid nucleus, and bilaterally to dorsal retroolivary and to preolivary cell groups. No degeneration was seen in the trapezoid body. Lesions involving the posteroventral and anteroventral (Av) cochlear nuclei produced degeneration in the intermediate acoustic stria and in the trapezoid body, but not in the dorsal stria. Degeneration in the intermediate acoustic stria was similar to that present after lesions affecting Dc and Pv. Thus, since Av does not project crossed fibers to this structure, these findings indicate that Pv sends some fibers to the contralateral as well as ipsilateral lateral superior olivary nucleus.

Second-Order Auditory Pathways to the Superior Olivary Complex in the Rhesus Monkey

Unilateral stereotactic lesions were made in the cochlear nuclei as follows: restricted to the caudal pole of the dorsal cochlear nucleus (Dc) (N = 2); restricted to the posterior end of Dc (N = 2); involving Dc and the posteroventral nucleus (Pv) (N = 2); confined to the anteroventral nucleus (Av) (N = 4); involving Av and Pv (N = 1); and involving Av together with Dc (N = 3). Monkeys were sacrificed after 6–17 days. Material was stained by the Nauta-Gygax (1954) technique and as described by Fink and Heimer (1967). Data indicate that fibers from Dc, Pv, and Av enter the dorsal acoustic stria, intermediate stria, and trapezoid body, respectively. Regarding the superior olivary complex, Dc projects only to the contralateral lateral superior olive (SOL) and fibers are scant; Pv projects bilaterally to the SOL, preolivary nuclei (PON), and dorsal retro-olivary group, and to the contralateral medial trapezoid nucleus (MTN); and Av projects bilaterally to the PON and medial superior olive (SOM), to the ipsilateral SOL, and to the contralateral MTN. Av efferents terminate on laterally oriented processes of ipsilateral SOM and medial processes of contralateral SOM, and are topographically organized in the vertical dimension. [Supported by NIH grants.

Ascending connections of the anterior ventral cochlear nucleus in the rat

AbstractThe purpose of the experiment was to determine the connections of the three regions of the anterior ventral cochlear nucleus in the rat. Lesions were placed in the regions of the nucleus in 11 rats. After 25 days each animal was sacrificed and its brain impregnated by the protargol method of Bodian. The superior olivary complex, the lateral lemniscus and the dorsal acoustic stria were examined for diminution of synaptic endings, thinning of neuropil and debris of degeneration.Complete destruction of region III of the anterior ventral cochlear nucleus produced degeneration in the ipsilateral lateral superior olive and in the medial superior olive of both sides. Destruction of other regions of the anterior ventral cochlear nucleus, region III remaining intact, had no effect upon the lateral or medial superior olive.Destruction of region II of the anterior ventral cochlear nucleus produced degeneration in the anterior halves of the ipsilateral lateral nucleus of the trapezoid body and the contralateral medial nucleus of the trapezoid body. Complete destruction of other regions of the anterior ventral cochlear nucleus, region II remaining intact, was without effect upon the lateral and medial nuclei of the trapezoid body.No degeneration was detected following destruction of region I of the anterior ventral cochlear nucleus.