Multisystemic chromatolytic neuronal degeneration in Cairn terriers. A case with generalized cataplectic episodes.

Multisystemic chromatolytic neuronal degeneration, a newly recognized disease of Cairn Terriers, is described in a second affected North American puppy. In this puppy, the early onset of hind limb weakness at 11 weeks and rapid development of signs of diffuse CNS involvement were distinctive. Signs of cerebellar dysfunction were prominent, but bouts of cataplectic collapse in this puppy constituted the most distinguishing clinical feature. Although electroencephalograph (EEG) recordings lacked a true rapid eye movement (REM) pattern during cataplectic episodes, cervical electromyograph (EMG) potentials ceased or diminished, and imipramine injection was associated with arousal. Postmortem studies revealed that chromatolytic degeneration was very widespread, affecting many neuronal populations in the brain and spinal cord as well as neurons in sensory ganglia. Although the pattern of chromatolysis varied among affected perikarya, chromatolysis was consistently related to dispersion and loss of ribosomes. In this puppy, as opposed to six studied previously, thoracolumbar myelomalacia also occurred symmetrically in the dorsal horns and adjoining funicular white matter. The metabolic derangement underlying this chromatolytic neuronal degeneration and myelomalacia remains unknown.

Interictal afterdischarge in focal penicillin epilepsy: block by thalamic cooling.

Interictal spikes recorded from a penicillin focus in the precruciate cortex of urethane-anesthetized cats were followed by brief afterdischarge oscillations that occurred at a delay of 170 to 220 ms from the interictal spike and consisted of as many as five cycles at 16 to 22/s. The origin of this afterdischarge was investigated by cooling different subcortical sites and thus blocking them reversibly. At none of the sites did cooling result in a block of the interictal spike whereas cooling of the ventrolateral nucleus of the thalamus resulted in block of the afterdischarge. Other subcortical sites had either no or less reliable effects on it. We conclude that afterdischarge but not the interictal spike depends on thalamic input, either as a generator of the rhythm or as a trigger for a cortically maintained oscillation.

Interictal afterdischarge in focal penicillin epilepsy: thalamocortical unit activity.

The involvement of thalamic versus cortical structures for the initiation and maintenance of brief interictal afterdischarge was evaluated by recording extracellularly units and field potentials from different subcortical and cortical sites. Afterdischarge oscillations at 16 to 22/s that followed interictal spikes with a delay of 170 to 220 ms usually appeared 10 to 30 min after the topical application of penicillin to the cat's precruciate cortex. Units in the ventrolateral nucleus of the thalamus fired in burst discharges during cortical afterdischarge and less reliably during the cortical interictal spike. In contrast, units recorded at the cortical penicillin focus and homologous contralateral site remained silent during afterdischarge but had a typical burst discharge during the interictal spike. Although these data support a thalamic basis for the rhythm, the lack of an afterdischarge-like oscillation in the thalamic field potential and the independent appearance of afterdischarge and cortical recruiting waves elicited by stimulation of the nucleus reticularis would favor its cortical origin. In accordance with its frequency characteristics and data gained from earlier cooling studies we suggest a cortical mechanism requiring thalamic triggering for the generation of afterdischarge.

Caudate unit activity and somal diameters in intact and nigral lesioned cats.

In a search for morphofunctional relationships in the head of the caudate nucleus (CN), we recorded extracellular unit activity in intact cats and in cats that had received bilateral injections of 6-OHDA into the substantia nigra (SN) 30 days previously. Only units firing spontaneously and continuously for 2 min were studied. In dorsal regions, potentials were small and iterative at almost constant intervals; the somal diameters were relatively small. In the ventrolateral region, potentials were bigger and appeared in bursts; somal diameters were significantly larger (p less than 0.05). For the centromedial region a histogram of numbers of neurons as a function of diameters revealed a Gaussian distribution extending from small to large neurons. Most dorsal neurons increased their firing rate to radial nerve, visual, SN, and/or nucleus centralis medialis (NCM) stimulation. Ventral neurons usually responded with excitation followed by long lasting inhibition, particularly to SN and NCM stimulation. A few neurons responded to all four inputs and some showed long-lasting potentiation in response to low frequency stimulation, suggesting a more general function. Greatest convergence (65%) was found for NCM and SN inputs. In lesioned cats, there was no SN driving, NCM's inhibitory actions almost disappeared, and the excitatory action of the other stimuli was reduced.

Plant "primary perception": electrophysiological unresponsiveness to brine shrimp killing.

A test of the "primary perception" hypothesis proposed by Backster in 1968 was made by recording electrical activity from the leaves of Philodendra scandentia while randomly ejecting the contents of micropipettes filled with brine shrimp or distilled water into boiling water. Test conditions conformed to those published by Backster or communicated in personal exchanges. Data were analysed from five experiments, in each of which recordings were made from four plants in the presence of three brine shrimp killings and two control water ejections. Inspection of the data and analysis by two statistical methods revealed no relationship between brine shrimp killing and electrical "responsiveness" of philodendron.

X-ray detection by the olfactory system: ozone as a masking odorant.

The technique of masking was used to test the hypothesis that x-ray detection is mediated by an odorant produced in irradiated air. Rats conditioned to cease licking during exposure to x-ray (conditioned suppression) did not display this conditioned response in the presence of ozone and strong volatile oxidants.