Auditory localization: role of auditory pathways in brain stem of the cat.

Cats were trained to localize sound in space. The animals' localization accuracy was determined before and after one of the following operations: 1) transection of the trapezoid body, 2) unilateral and 3) bilateral transection of the lateral lemniscus, 4) unilateral and 5) bilateral transection of the brachium of the inferior colliculus. The results after bilateral transections of the lateral lemniscus and the one deep bilateral transection of the brachium of the inferior colliculus indicate that some portion of the ascending auditory system must be intact above the medulla for an animal to be able to localize sound. A small loss in accuracy of localization was found after unilateral transection of the lateral lemniscus or brachium of the inferior colliculus. This loss, when compared with the much larger loss that monaural animals show, is an indication that binaural analysis, important for sound localization, occurs at the level of the medulla. Some transections of the trapezoid body resulted in a deficit in localization ability that appeared to be complete and permanent. The position of the lesions in the trapezoid body indicated that important encoding of the binaural cues to localization most likely occurs at the superior olivary complex, probably at the medial superior olive. But the trapezoid body or other commissures of the brain stem auditory system are probably also involved in transmission of information necessary for localization to higher centers.     

Contribution of auditory cortex to sound localization by the ferret (Mustela putorius)

Ferrets were tested in a semicircular apparatus to determine the effects of auditory cortical lesions on their ability to localize sounds in space. They were trained to initiate trials while facing forward in the apparatus, and sounds were presented from one of two loudspeakers located in the horizontal plane. Minimum audible angles were obtained for three different positions, viz., the left hemifield, with loudspeakers centered around -60 degrees azimuth; the right hemifield, with loudspeakers centered around +60 degrees azimuth; and the midline with loudspeakers centered around 0 degrees azimuth. Animals with large bilateral lesions had severe impairments in localizing a single click in the midline test. Following complete destruction of the auditory cortex performance was only marginally above the level expected by chance even at large angles of speaker separation. Severe impairments were also found in localization of single clicks in both left and right lateral fields. In contrast, bilateral lesions restricted to the primary auditory cortex resulted in minimal impairments in midline localization. The same lesions, however, produced severe impairments in localization of single clicks in both left and right lateral fields. Large unilateral lesions that destroyed auditory cortex in one hemisphere resulted in an inability to localize single clicks in the contralateral hemifield. In contrast, no impairments were found in the midline test or in the ipsilateral hemifield. Unilateral lesions of the primary auditory cortex resulted in severe contralateral field deficits equivalent to those seen following complete unilateral destruction of auditory cortex. No deficits were seen in either the midline or the ipsilateral tests.     

Hearing in the ferret (Mustela putorius): effects of primary auditory cortical lesions on thresholds for pure tone detection

1. Pure tone thresholds were determined for five adult male ferrets before and after bilateral ablation of primary auditory cortex. Complete audiograms ranging from 0.016 to 48 kHz were obtained for two animals. The remaining three animals were tested at five frequencies selected to assess hearing throughout the audible range (0.125, 0.5, 2.0, 8.0, and 32.0 kHz). 2. Shortly after surgery one animal had elevated thresholds across the entire frequency range with the most pronounced hearing loss above 12.0 kHz. Four other animals had no elevation of thresholds at low and midrange frequencies but suffered a hearing loss at very high frequencies (32 kHz). 3. Repeated testing over a period of several months revealed substantial recovery of sensitivity. There was complete recovery of sensitivity in the low- and middle-frequency range of the audiogram. Some hearing loss persisted at the extreme upper end of the audiogram (32 kHz), but in two cases there was evidence of recovery at this frequency as well. 4. Following determination of absolute thresholds all animals were assessed for their ability to localize sound in space. Minimum audible angles were obtained on midline as well as within both left and right hemifields, i.e., around 0, -60 and +60 degrees azimuth. All animals had severe and persistent deficits in their ability to localize brief sounds within the lateral fields, but were still capable of midline localization.     

Effects of medial geniculate lesions on sound localization by the rat

Rats with bilateral lesions of the medial geniculate body were tested on a two-choice sound-localization task that required a directional response to a distant sound source. Stimuli included both broadband and filtered noise bursts presented singly or in repetitive trains. Separate tests were conducted with loudspeakers 180 and 60 degrees apart, centered around 0 degree azimuth. With complete bilateral destruction of the medial geniculate, rats could localize both trains and single bursts of noise and were capable of high levels of performance even at small angles of speaker separation. Some evidence of impaired performance was noted with high-frequency noise bursts, but generally the deficits were not severe. Animals with lesions that extended caudally into the brachium of the inferior colliculus and lateral tegmentum were severely impaired in their ability to localize sounds even at large angles of speaker separation. Three of the four animals in this group were incapable of localizing single bursts even with loudspeakers separated by 180 degrees, and the fourth was unable to perform above chance at 60 degrees. The effects of medial geniculate lesions were very similar to those reported previously for rats with lesions of the auditory cortex, but contrasted with reports of severe impairments in sound localization following damage to the auditory cortex in other mammalian species.     

Effects of altering spectral cues in infancy on horizontal and vertical sound localization by adult ferrets

We investigated the behavioral consequences of removing the pinna and concha of the external ear bilaterally in infancy on the sound localization ability of adult ferrets. Altering spectral cues in this manner has previously been shown to disrupt the development of the neural representation of auditory space in the superior colliculus. Using broadband noise stimuli, we tested pinnae-removed ferrets and normal ferrets in three sound localization tasks. In each case, we found that both groups of animals performed significantly better when longer duration noise bursts were used. In a relative localization task, we measured the acuity with which the ferrets could discriminate between two speakers in the horizontal plane. The speakers were placed symmetrically either around the anterior midline or around a position 45 degrees lateral to the midline. In this task, the pinnae-removed ferrets achieved very similar scores to the normal ferrets. By contrast, in another relative localization task that measured localization ability in the midsagittal plane, pinnae-removed ferrets performed less well than normals. In an absolute localization task, 12 speakers were spaced at 30 degrees intervals in the horizontal plane at the level of the ferrets' ears. Overall, the pinnae-removed ferrets also performed poorly in this task compared with normal ferrets: they made significantly fewer correct responses, larger localization errors and more front-back errors. Both normal and pinnae-removed animals showed an improvement in performance with practice, although the pattern of improvement differed for each group. The largest improvements in localization accuracy were achieved by the pinnae-removed ferrets, particularly at the frontal positions, and their performance eventually approached that of the normal animals. Nevertheless, some intergroup differences were still present. In particular, the pinnae-removed ferrets continued to make significantly more front-back errors than the normals. These deficits can be attributed to differences in the spectral localization cues available to the animals. Acoustical measurements showed that, compared with normal animals, the head-related transfer functions in the horizontal plane were largely ambiguous around the interaural axis and also contained fewer location-dependent features in the midsagittal plane.     

Role of auditory cortex in sound localization in the midsagittal plane

Although the auditory cortex is known to be essential for normal sound localization in the horizontal plane, its contribution to vertical localization has not so far been examined. In this study, we measured the acuity with which ferrets could discriminate between two speakers in the midsagittal plane before and after silencing activity bilaterally in the primary auditory cortex (A1). This was achieved either by subdural placement of Elvax implants containing the GABA A receptor agonist muscimol or by making aspiration lesions after determining the approximate location of A1 electrophysiologically. Psychometric functions and minimum audible angles were measured in the upper hemifield for 500-, 200-, and 40-ms noise bursts. Muscimol-Elvax inactivation of A1 produced a small but significant deficit in the animals' ability to localize brief (40-ms) sounds, which was reversed after removal of the Elvax implants. A similar deficit in vertical localization was observed after bilateral aspiration lesions of A1, whereas performance at longer sound durations was unaffected. Another group of ferrets received larger lesions, encompassing both primary and nonprimary auditory cortical areas, and showed a greater deficit with performance being impaired for long- and short-duration (500- and 40-ms, respectively) stimuli. These data suggest that the integrity of the auditory cortex is required to successfully utilize spectral localization cues, which are thought to provide the basis for vertical localization, and that multiple cortical fields, including A1, contribute to this task.     

Effects of kainic acid lesions of the nucleus reticularis tegmenti pontis on fast and slow phases of vestibulo-ocular and optokinetic reflexes in the pigmented rat

Summary The nucleus reticularis tegmenti pontis (NRTP) and adjacent pontine reticular formation were lesioned chemically using the neurotoxic agent kainic acid, and the effects of these lesions on horizontal ocular optokinetic and vestibular nystagmus were examined. Eye position was measured in the alert, NRTP-lesioned animals with the electromagnetic search coil technique. Optokinetic and vestibular stimuli consisted of steps of rotations or sinusoidal oscillations of a fullfield visual pattern surrounding the animal or of the animal in total darkness, respectively. In a first group of animals, small unilateral NRTP lesions were produced by placing a single kainic acid injection in the area of the left NRTP. In one third of the animals, ipsilateral quick phases of optokinetic and vestibular nystagmus were abolished. In the remaining animals, quick phases were deficient to various degrees or not affected at all. There were no changes in the characteristics of optokinetic step responses to ipsilateral pattern rotations which activate predominantly optokinetic pathways on the side of the brainstem lesion. In animals with ipsiversive quick phase deficits, contralateral pattern rotations elicited tonic eye deviations. In a second group of animals, large uni- or bilateral lesions were produced by injecting kainic acid into three separate rostral, middle and caudal levels of the right NRTP. These animals had uni- or bilateral quick phase deficits during optokinetic and vestibular nystagmus. Optokinetic nystagmus in response to velocity steps of pattern rotation towards the lesion side was strongly reduced in gain even in those animals that had no apparent deficits in the fast contraversive reset phases. In four out of six animals, responses to sinusoidal optokinetic pattern oscillations were reduced in gain and showed increased phase lags compared to controls. Vestibulo-ocular responses to velocity steps of head rotations were of normal gain but reduced in duration (measured from onset of stimulation to reversal of nystagmus). Sinusoidal vestibulo-ocular responses evoked by head oscillations exhibited reduced gain values and strongly increased phase leads in the frequency range below 0.5 Hz. The vestibular time constant was found to be around 4.5 s in animals with NRTP lesions compared to about 7.5 s in control animals. The present results show that large kainic acid lesions of the NRTP (and adjacent area) do not abolish optokinetic eye movements in the rat, in contrast to what has been reported after electrolytic lesions. The data suggest, however, that there is a failure of slow build-up of OKN slow phase velocity as well as a shortening of the vestibular time constant which correlates with the kainic acid lesions extending into rostromedial and caudal parts of the NRTP. The implications of these findings with respect to an involvement of these structures in velocity storage are discussed.Abbreviations CN cochlear nucleus - DpSC decussation, peduncle, superior, cerebellar - ip interpeduncular nucleus - MLF medial longitudinal fasciculus - NOT nucleus of optic tract - NRTPc nucleus reticularis tegmenti pontis, central subdivision - NRTPp nucleus reticularis tegmenti pontis, pericentral subdivision - p pontine nuclei - ph praepositus hypoglossi nucleus - pMC peduncle, middle cerebellar - pSC peduncle, superior cerebellar - Pyr pyramidal tract - Rcs raphe central superior - Rm raphe magnus - rpc reticular nucleus, pontine, caudal - rpo reticular nucleus, pontine, oral - TB trapezoid body - tM trapezoid nucleus, medial - tGd tegmental nucleus of von Gudden, dorsal - tGv tegmental nucleus of von Gudden, ventral - 5 trigeminal tract or trigeminal nerve - 5m mesencephalic trigeminal nucleus - 5mt motor trigeminal nucleus - 6n abducens nucleus - 7 facial nerve Prof. W. Precht died on March 12, 1985     

Effects of LH kainic acid infusions on ingestion and autonomic activity

The effects of lateral hypothalamic (LH) infusions of kainic acid (KA) were determined on ingestive behavior, body weight, and motor and autonomic activity. In Experiment 1 male hooded rats received bilateral LH infusions of isotonic saline in volumes of 0.5 or 1.0 μl, 3.0 μg KA in volumes of 0.5 or 1.0 μl, or 6.0 μg of KA in a volume of 1.0 μl. All animals receiving 6.0 μg/1.0 μl of KA died. The 3.0 μg/0.5 μl dose resulted in transient decreases in food and water consumption and body weight. Animals receiving this dose no longer drank in response to 2 cc/kg 15% NaCl injections, exhibited attenuated drinking in response to 24 hr water and food deprivation, exhibited a transient decrease in eating following food deprivation and decreased eating following 750 mg/kg injections of 2-deoxy-D-glucose. Minimal effects on these measures were observed following the 3.0 μg/1.0 μl dose. In Experiment 2 rats received unilateral infusions of KA and the effects on motor and autonomic activity and ingestive behavior and body weight were compared to unilateral saline infused animals and animals with radiofrequency lesions. Only transient decreases in food consumption lasting 1–2 days were observed for both unilateral KA LH infused and lesioned animals. In KA infused rats contralateral exophthalamus, rapid shallow breathing, bilateral mydriasis, no contralateral pupillary constriction response, excessive salivation, body tremors, seizures, convulsions, teeth chattering, contralateral tail suspension induced spinning and turning, and elevated body temperature were observed for up to 6 hr following the infusion. Results are discussed in terms of lateral ventral diencephalic neurons involved in the more permanent deficits associated with bilateral LH damage.     

Sound localization during homotopic and heterotopic bilateral cooling deactivation of primary and nonprimary auditory cortical areas in the cat

Although the contributions of primary auditory cortex (AI) to sound localization have been extensively studied in a large number of mammals, little is known of the contributions of nonprimary auditory cortex to sound localization. Therefore the purpose of this study was to examine the contributions of both primary and all the recognized regions of acoustically responsive nonprimary auditory cortex to sound localization during both bilateral and unilateral reversible deactivation. The cats learned to make an orienting response (head movement and approach) to a 100-ms broad-band noise stimulus emitted from a central speaker or one of 12 peripheral sites (located in front of the animal, from left 90 degrees to right 90 degrees , at 15 degrees intervals) along the horizontal plane after attending to a central visual stimulus. Twenty-one cats had one or two bilateral pairs of cryoloops chronically implanted over one of ten regions of auditory cortex. We examined AI [which included the dorsal zone (DZ)], the three other tonotopic fields [anterior auditory field (AAF), posterior auditory field (PAF), ventral posterior auditory field (VPAF)], as well as six nontonotopic regions that included second auditory cortex (AII), the anterior ectosylvian sulcus (AES), the insular (IN) region, the temporal (T) region [which included the ventral auditory field (VAF)], the dorsal posterior ectosylvian (dPE) gyrus [which included the intermediate posterior ectosylvian (iPE) gyrus], and the ventral posterior ectosylvian (vPE) gyrus. In accord with earlier studies, unilateral deactivation of AI/DZ caused sound localization deficits in the contralateral field. Bilateral deactivation of AI/DZ resulted in bilateral sound localization deficits throughout the 180 degrees field examined. Of the three other tonotopically organized fields, only deactivation of PAF resulted in sound localization deficits. These deficits were virtually identical to the unilateral and bilateral deactivation results obtained during AI/DZ deactivation. Of the six nontonotopic regions examined, only deactivation of AES resulted in sound localization deficits in the contralateral hemifield during unilateral deactivation. Although bilateral deactivation of AI/DZ, PAF, or AES resulted in profound sound localization deficits throughout the entire field, the cats were generally able to orient toward the hemifield that contained the acoustic stimulus, but not accurately identify the location of the stimulus. Neither unilateral nor bilateral deactivation of areas AAF, VPAF, AII, IN, T, dPE, nor vPE had any effect on the sound localization task. Finally, bilateral heterotopic deactivations of AI/DZ, PAF, or AES yielded deficits that were as profound as bilateral homotopic cooling of any of these sites. The fact that deactivation of any one region (AI/DZ, PAF, or AES) was sufficient to produce a deficit indicated that normal function of all three regions was necessary for normal sound localization. Neither unilateral nor bilateral deactivation of AI/DZ, PAF, or AES affected the accurate localization of a visual target. The results suggest that hemispheric deactivations contribute independently to sound localization deficits.     

Kainate and electrolytic lesions of the lateral habenula: effect on avoidance responses

Male Sprague Dawley rats (n = 24), which received either bilateral electrolytic lesions, kainic acid lesions or sham treatments in the lateral habenula, were tested for acquisition of a one-way, conditioned avoidance response. Animals with electrolytic lesions failed to learn the avoidance task within 15 trials. In contrast, rats with kainic acid lesions performed as well as the control group. The results indicate that the disruption of the septal-medial habenula-interpenduncular nucleus pathway may be responsible for the observed avoidance deficit in electrolytically lesioned animals.     

Effects of auditory cortical lesions on pure-tone sound localization by the albino rat

Two-choice and three-choice tests were used to evaluate the effects of bilateral auditory cortical lesions on pure-tone sound localization by the albino rat. Both tests required that animals approach a distant sound source to obtain water reinforcement. Stimuli were single noise and tone bursts, 65 ms in duration including 20-ms rise and fall times. Tone frequencies were 2, 4, 8, 16, and 32 kHz adjusted to 40 dB (SPL) above the rat's absolute threshold. Five animals were tested in the two-choice situation following bilateral ablation of auditory cortex. Some reduction in performance was observed relative to normals, but impairments were not severe. Similar results were obtained for 2 brain-damaged animals tested in the three-choice situation. Thus, the ability to localize sounds in space remained intact after complete destruction of auditory cortex, and there was no indication of a frequency-dependent deficit.     

Cochlear efferent feedback balances interaural sensitivity

Neurons in the lateral superior olive (LSO) compute sound location based on differences in interaural intensity, coded in ascending signals from the two cochleas. Unilateral destruction of the neuronal feedback from the LSO to the cochlea, the lateral olivocochlear efferents, disrupted the normal interaural correlation in response amplitudes to sounds of equal intensity. Thus, lateral olivocochlear feedback maintains the binaural balance in neural excitability required for accurate localization of sounds in space.     

Development of sound localization mechanisms in the mongolian gerbil is shaped by early acoustic experience

Sound localization is one of the most important tasks performed by the auditory system. Differences in the arrival time of sound at the two ears are the main cue to localize low-frequency sound in the azimuth. In the mammalian brain, such interaural time differences (ITDs) are encoded in the auditory brain stem; first by the medial superior olive (MSO) and then transferred to higher centers, such as the dorsal nucleus of the lateral lemniscus (DNLL), a brain stem nucleus that gets a direct input from the MSO. Here we demonstrate for the first time that ITD sensitivity in gerbils undergoes a developmental maturation after hearing onset. We further show that this development can be disrupted by altering the animal's acoustic experience during a critical period. In animals that had been exposed to omnidirectional white noise during a restricted time period right after hearing onset, ITD tuning did not develop normally. Instead, it was similar to that of juvenile animals 3 days after hearing onset, with the ITD functions not adjusted to the physiological range. Animals that had been exposed to omnidirectional noise as adults did not show equivalent abnormal ITD tuning. The development presented here is in contrast to that of the development of neuronal representation of ITDs in the midbrain of barn owls and interaural intensity differences in ferrets, where the representations are adjusted by an interaction of auditory and visual inputs. The development of ITD tuning presented here most likely depends on normal acoustic experience and may be related to the maturation of inhibitory inputs to the ITD detector itself.     

Temperature activation of courtship behavior in the male red-sided garter snake (Thamnophis sirtalis parietalis): role of the anterior hypothalamus-preoptic area

Adult male red-sided garter snakes (Thamnophis sirtalis parietalis) received radio-frequency lesions prior to 17 weeks of low-temperature hibernation. Animals found to have bilateral lesions of the anterior hypothalamus-preoptic area (AH-POA) failed to exhibit courtship behavior on emergence from hibernation. Those individuals in which the major portion of the destruction was centered in the anterior POA also exhibited deficits in thermoregulatory behavior. Animals that received unilateral lesions of the AH-POA initiated courtship behavior after controls and had an abbreviated period of courtship; these animals exhibited normal responses to thermal stimuli. Male snakes with lesions outside the AH-POA courted normally and demonstrated no differences in thermoregulatory behavior compared with the surgical controls. These results indicate that in male red-sided garter snakes, an intact AH-POA is critical for the integration of thermal stimuli that activate seasonal courtship behavior.     

Midline and lateral field sound localization in the albino rat (Rattus norvegicus)

Six albino rats were used in tests of sound localization around midline and in left and right lateral field positions (i.e., 0 degree, -60 degrees, and +60 degrees azimuth). Each of the animals performed at high levels on the midline task but had great difficulty with tests in the left and right fields. Minimum audible angles for midline localization were obtained for 2 subjects and were estimated as 11.5 degrees and 13.5 degrees. Performance levels on the hemifield tests for each of the 6 animals, however, were too low to permit estimates of threshold even with speakers separated by 60 degrees. The differences between midline and lateral field sound localization are discussed.     

Induction of somatic sensory inputs to the lateral geniculate nucleus in congenitally blind mice and in phenotypically normal mice.

The incidence of aberrant innervation of the lateral geniculate nucleus by ascending somatic sensory axons was examined following injections of wheat germ agglutinin conjugated with horseradish peroxidase into the dorsal column nuclei of adult mice which were: (1) normal; (2) normal, but bilaterally enucleated on the day of birth; (3) normal, but received a large unilateral lesion of the rostral cortex on the day of birth; (4) normal, bilaterally enucleated, as well as unilaterally lesioned in the rostral cortex on the day of birth; (5) homozygous for an ocular retardation mutation (orj/orj); or (6) homozygous for the orj mutation and received a large unilateral lesion of the rostral cerebral cortex on the day of birth. In the phenotypically normal animals which were untreated, no somatic sensory inputs enter into the dorsal lateral geniculate nucleus. A few labeled axons enter into and arborize within the dorsal lateral geniculate nucleus in normal animals which received bilateral enucleations or unilateral rostral cortical lesions on the day of birth. However, in congenitally blind animals and in phenotypically normal animals which received bilateral enucleations as well as unilateral rostral cortical lesions on the day of birth, a significant number of labeled axons enter into and arborize within the dorsal lateral geniculate nucleus. Among all these experimental groups, the densest innervation of the lateral geniculate nucleus occurred in congenitally blind animals which received rostral cortical lesions on the day of birth. In these, robust arborizations of labeled somatic sensory axons occupy a substantial extent of the lateral geniculate nucleus. These results not only demonstrate that ascending somatic sensory axons can be rerouted to the lateral geniculate nucleus, but also indicate that the ability of a thalamic afferent pathway to undergo extensive reorganization and to innervate inappropriate thalamic targets following early perturbations is not unique to the retinal projection (in which this has previously been demonstrated), and may be a more general characteristic of the major thalamic afferent systems.     

Sound localization deficits during reversible deactivation of primary auditory cortex and/or the dorsal zone

We examined the contributions of primary auditory cortex (A1) and the dorsal zone of auditory cortex (DZ) to sound localization behavior during separate and combined unilateral and bilateral deactivation. From a central visual fixation point, cats learned to make an orienting response (head movement and approach) to a 100-ms broadband noise burst emitted from a central speaker or one of 12 peripheral sites (located in front of the animal, from left 90 degrees to right 90 degrees, at 15 degrees intervals) along the horizontal plane. Following training, each cat was implanted with separate cryoloops over A1 and DZ bilaterally. Unilateral deactivation of A1 or DZ or simultaneous unilateral deactivation of A1 and DZ (A1/DZ) resulted in spatial localization deficits confined to the contralateral hemifield, whereas sound localization to positions in the ipsilateral hemifield remained unaffected. Simultaneous bilateral deactivation of both A1 and DZ resulted in sound localization performance dropping from near-perfect to chance (7.7% correct) across the entire field. Errors made during bilateral deactivation of A1/DZ tended to be confined to the same hemifield as the target. However, unlike the profound sound localization deficit that occurs when A1 and DZ are deactivated together, deactivation of either A1 or DZ alone produced partial and field-specific deficits. For A1, bilateral deactivation resulted in higher error rates (performance dropping to approximately 45%) but relatively small errors (mostly within 30 degrees of the target). In contrast, bilateral deactivation of DZ produced somewhat fewer errors (performance dropping to only approximately 60% correct), but the errors tended to be larger, often into the incorrect hemifield. Therefore individual deactivation of either A1 or DZ produced specific and unique sound localization deficits. The results of the present study reveal that DZ plays a role in sound localization. Along with previous anatomical and physiological data, these behavioral data support the view that A1 and DZ are distinct cortical areas. Finally, the findings that deactivation of either A1 or DZ alone produces partial sound localization deficits, whereas deactivation of either posterior auditory field (PAF) or anterior ectosylvian sulcus (AES) produces profound sound localization deficits, suggests that PAF and AES make more significant contributions to sound localization than either A1 or DZ.     

Progressive pathology of the caudate nucleus, the substantia nigra pars reticulata and the deeper layers of the colliculus superior: acute behavioural and metabolic effects of intrastriatal kainic acid

The acute behavioural and metabolic consequences of functional changes following unilateral intracaudate kainic acid at the level of the feline caudate nucleus, the substantia nigra pars reticulata and the deeper layers of the colliculus superior were investigated. The present study became possible since it was previously found that unilateral changes in neurotransmission processes in these structures all result in behavioural alterations that can be distinguished from each other. During the first 17 min after kainic acid, all animals displayed contralateral forced staccato head turning; these movements are characteristic for an activation of dopamine receptors and/or inhibition of GABA receptors in the rostromedial caudate nucleus. Between 15 and 50 min, all animals displayed fast, uninterrupted contralateral forced head, torso or body turning; these movements are characteristic for an activation of nigral GABA receptors. From about 48 min, all animals displayed sequences of short contralateral forced ear, head, torso and body turnings; these movements are characteristic for an inhibition of collicular GABA receptors. Furthermore, most cats displayed ipsilateral orofacial dyskinetic movements during the whole 180 min observation period. Metabolism was analysed in three cats that received [14C]2-D-deoxyglucose immediately before, 5 min after, or 70 min after kainic acid. Metabolism was increased in the ipsilateral caudate nucleus; this effect was most pronounced in the cat that received deoxyglucose immediately before kainic acid. Metabolic activity was increased in the ipsilateral substantia nigra pars reticulata; this effect was most pronounced in the cat treated with deoxyglucose 5 min after kainic acid. Metabolism was increased in the ipsilateral deeper layers of the colliculus superior in the cat that received deoxyglucose 70 min after kainic acid. The present behavioural and metabolic data suggest that kainic acid produces an increasing pathology resulting successively in functional changes in the caudate nucleus, its output-station the substantia nigra pars reticulata and the nigral output-station the deeper layers of the colliculus superior. It is suggested that the successive appearance of the latter effects is inherent in the hierarchical order of the brain structures under study. The occurrence of orofacial dyskinetic movements during the whole observation period suggests that the former movements were not mediated via the striato-nigro-collicular pathway. Finally, apomorphine injected in the ipsilateral caudate nucleus 1 week after kainic acid was significantly less effective compared to apomorphine injected 1 week before kainic acid. The c     

Maternal behavior in rats: evidence for the involvement of preoptic projections to the ventral tegmental area

This study provides evidence that a neural system extending from the preoptic region to the ventral tegmental area (VTA) of the midbrain is important for the normal expression of maternal behavior in lactating rats. In the first experiment, bilateral electrolytic lesions of the VTA severely disrupted the maternal behavior of postpartum rats. In the second experiment, lactating rats that received a unilateral knife cut severing the lateral connections of the medial preoptic area (MPOA) paired with a contralateral lesion of the VTA showed more severe maternal behavior deficits than females that received one of the following treatments: (a) a unilateral knife cut severing the lateral connections of the MPOA paired with an ipsilateral VTA lesion; (b) a unilateral knife cut severing the lateral connections of the MPOA paired with a contralateral lesion of the medial hypothalamus posterior to the MPOA; (c) a unilateral knife cut severing the lateral connections of the lateral preoptic area paired with a contralateral VTA lesion. The oral components of maternal behavior (retrieving and nest building) were particularly affected as a result of bilateral damage to the system extending from the preoptic area to the VTA.     

Binaural response properties of low-frequency neurons in the gerbil dorsal nucleus of the lateral lemniscus

Differences in intensity and arrival time of sounds at the two ears, interaural intensity and time differences (IID, ITD), are the chief cues for sound localization. Both cues are initially processed in the superior olivary complex (SOC), which projects to the dorsal nucleus of the lateral lemniscus (DNLL) and the auditory midbrain. Here we present basic response properties of low-frequency (< 2 kHz) DNLL neurons and their binaural sensitivity to ITDs and IIDs in the anesthetized gerbil. We found many neurons showing binaural properties similar to those reported for SOC neurons. IID-properties were similar to that of the contralateral lateral superior olive (LSO). A majority of cells had an ITD sensitivity resembling that of either the ipsilateral medial superior olive (MSO) or the contralateral LSO. A smaller number of cells displayed intermediate types of ITD sensitivity. In neurons with MSO-like response ITDs that evoked maximal discharges were mostly outside of the range of ITDs the gerbil naturally experiences. The maxima of the first derivative of their ITD-functions (steepest slope), however, were well within the physiological range of ITDs. This finding is consistent with the concept of a population rather than a place code for ITDs. Moreover, we describe several other binaural properties as well as physiological and anatomical evidence for a small but significant input from the contralateral MSO. The large number of ITD-sensitive low-frequency neurons implicates a substantial role for the DNLL in ITD processing and promotes this nucleus as a suitable model for further studies on ITD-coding.