Technical contribution. Tungsten ball microelectrode for extracellular single-unit recording

Increased firing of neurons in the posterior hypothalamus which precede classically conditioned pupillary dilations

Paralyzed cats were used as subjects in a classical conditioning experiment where each subject was exposed to 40 explicitly unpaired 1-s bursts of white noise and 0.5-s paw shocks. This training was followed by 60 trials of the two stimuli paired, where the white noise immediately preceded the paw shock. Following this training, the subjects were re-exposed to 40 trials of the explicitly unpaired procedure. The pupil was monitored as the behavior and electrodes implanted in the thalamus, the dorsal hypothalamus and the posterior hypothalamus recorded the activity of clusters of cells. Only the cells in the posterior hypothalamus showed robust changes in firing rates that preceded the pupillary behavior, both (a) on any particular trial and (b) as the learned association was being demonstrated behaviorally across trials.

Fractured cutaneous projections to the granule cell layer of the posterior cerebellar hemisphere of the domestic cat

Snider 's pioneering studies of tactile responses in the cerebellar cortex of cats and monkeys suggested that posterior regions of the cerebellar hemispheres receive somatotopically organized projections. However, recent studies in rats, using high-density, in depth microelectrode mapping methods, have shown that tactile projections to the granule cell layer of the cerebellar hemispheres are somatotopically disrupted. We reexamined the organization of cutaneous projections to cerebellar hemispheric cortex in cats by using micromapping methods. Natural stimulation of cutaneous surfaces evokes short-latency (mossy-fiber-induced) multiple unit responses in the cerebellar granule cell layer of crus II and paramedian lobule in both ketamine- and barbiturate-anesthetized cats. Facial structures are represented in several of the most caudomedial folia of crus II as well as in three of the rostral folia of the paramedian lobule. In several of these paramedian folia, facial projections are interspersed with projections from the forelimb. Forelimb structures alone are represented in two intermediate folia of the paramedian lobule. No cutaneous projections were found from the trunk or hindlimb. All projections were from ipsilateral receptive fields. In four folia of crus II and six folia of the paramedian lobule, cutaneous projections form a mosaic of patchlike projections. Within single patches, projections are somatotopically organized, but projections to adjacent patches come from noncontiguous body regions. Within a single folium , a particular facial region may be represented in two or three spatially separated patches. Facial patches are small, usually less than 1 mm2. Forelimb patches are usually larger, often extending the full length and breadth of a folial crown. Patches with like receptive fields are not organized in zonal sagittal strips. Rather than being somatotopically organized, cutaneous mossy fiber projections to granule cells in cats, as in rats, reveal a more complex mosaic pattern of organization.

Reevaluation of motor cortex and of sensorimotor overlap in cerebral cortex of albino rats

The organization of motor cortex and the sensorimotor overlap zone was examined by in-depth electrical stimulation using micromapping procedures in rats. The cutaneous somatic sensory, as well as the efferent motor projections to the hindlimb and forelimb sensorimotor overlap zone were studied in the same animals. Low-threshold movements were elicited from portions of 3 architectonic areas: the lateral agranular, dysgranular and granular areas. Cutaneous light touch projections occur only within the granular area. Cutaneous projections to, and motor projections from individual punctures in the granular overlap zone did not always involve homologous body parts. The total motor cortex exhibits a general musculotopic pattern of organization.

Patterns of afferent projections to transitional zones in the somatic sensorimotor cerebral cortex of albino rats

The organization of somatosensory projections to the dysgranular areas of somatic sensory cortex was mapped in albino rats. Receptive fields that activate layer IV granule cells in these dysgranular zones were: cutaneous and deep (including muscle), roughly somatotopic, larger, and required stronger stimulation (tap) than the cutaneous light touch RFs of the adjacent granule cell zones.

Somatotopic organization of SI corticotectal projections in rats

The somatotopic organization of somatosensory (SI) cortical projections to the deep layers of the superior colliculus (SC) in rats was examined using neurophysiological micromapping methods. Electrical stimulation of SI produced SC unit responses at the same depths as did peripheral tactile stimulation, in SC laminae IV and VI; mapping of corticotectal projections was performed only in lamina IV. Antidromic activation of the pathway revealed that corticotectal cell bodies are located in SI layer V. Corticotectal projections were found to interconnect only those SI and collicular areas which have similar tactile receptive fields.

Trigeminocerebellar mossy fiber branching to granule cell layer patches in the rat cerebellum

Recent micromapping studies of tactile areas in rat cerebellum have revealed a spatially precise mosaic of granule cell layer areas termed 'patches', with multiple patches on several folia resulting in multiple representations of the same body part. The research reported in the present paper tested the hypothesis that trigeminocerebellar mossy fiber branching is patch-related, so that collaterals terminate only within the boundaries of one or more of the tiny (often less than 1 sq. mm) patches having similar receptive fields. This hypothesis was supported by 3 separate series of electrophysiological experiments: (1) electrical stimulation in a patch resulted in short latency, low threshold responses confined within the boundaries of a second patch having a similar receptive field; (2) antidromic collison tests demonstrated that collaterals of axons originating in nucleus interpolaris reach pairs of patches with similar receptive fields; and (3) micromapping of the area from which a particular interpolaris neuron could be antidromically activated revealed that local terminal branching of a given mossy fiber axon appeared to be confined within the boundaries of a single patch. Together these results indicate that trigeminocerebellar mossy fiber branching is related to the fractured somatotopical organization of the granule cell layer. Possible functional implications of such mossy fiber branching are discussed.

Superior colliculus projections to tactile areas of rat cerebellar hemispheres

The spatial organization of the projections of the superior colliculus (SC) to the contralateral cerebellar hemisphere and posterior vermis was examined using micromapping techniques in barbiturate or ketamine anesthetized rats. Electrical stimulation of the tactile-responsive intermediate layers of SC evoked responses in tactile regions of the contralateral granule cell (GC) layer of cerebellar cortex. In most experiments, the SC stimulating electrode remained stationary while the cerebellar electrode mapped the region of the GC layer activated by SC stimulation. In a few experiments, the cerebellar recording electrode remained fixed while the SC electrode mapped the area of effective stimulation. Puncture densities up to 60/sq.mm were necessary to fully determine the spatial pattern of these projections. Major results are: (1) cerebellar responses to SC stimulation are found in the GC layer of contralateral crus I, crus II, lobulus simplex, and the paramedian lobule; no responses were seen in the uvula. The anterior lobe was not examined; (2) peripheral receptive fields (RFs) of the interconnected SC and GC loci consist exclusively of facial structures (especially vibrissae, crown, bridge of nose, and eyelid); (3) SC sources project within the confines of GC layer patches with similar RFs; (4) GC layer responses typically consist of an early, low amplitude potential, followed by a multiple-unit response; and (5) latencies of GC layer responses to SC stimulation are 2.2-2.5 msec for the early potential, and 2.5-3.5 msec for the multiple-unit response. This is the first physiological demonstration of projections from the superior colliculus to the cerebellar hemispheres. The results of this and other studies in our laboratory indicate that the tactile areas of the cerebellar hemispheres receive convergent inputs from peripheral, tectal, and SI cortical tactile sources.

Organization and development of brain stem auditory nuclei of the chicken: tonotopic organization of n. magnocellularis and n. laminaris

Extracellular recordings of responses to tone-burst stimulation were used to determine the tonotopic organization of n. magnocellularis (NM) and n. laminaris (NL) in hatching chickens. NM cells show "primary-like" response patterns to ipsilateral stimulation, and are arranged in dorso-ventral isofrequency columns. Units responding to the highest frequency tones (about 4,100 Hz) are situated at the rostromedial pole of the medial division. Units with lower characteristic frequencies (CF's) are found at successively caudal and lateral sites, until extremely low CF's ( less than 500 Hz) are represented dorsoventrally in the daudolateral tail of the lateral division. No evidence was found of auditory input to the region which receives projections from the macula lagena. NL receives polarized, binaural, excitatory input. Units have similar CF's and thresholds to tones presented to either ear. The tonotopic organization in NL matches that found in NM--high CF's rostromedially and low CF's caudal and lateral. Quantitative procedures were developed for relating CF to the position of a unit within either nucleus. These analyses account for 79% and 89% of the frequency variance found within NM and NL, respectively, and predict the CF of a neuron by its position within each nucleus.