Intracellular and extracellular recordings were performed in lateral thalamic nuclei (ventroanterior-ventrolateral, ventroposterolateral, centralis, lateralis, and reticularis) of cats under barbiturate anesthesia. Neurons were driven antidromically and/or synaptically by stimulating cortical projection areas and prethalamic afferent pathways. Three neuronal populations were identified on the basis of electrophysiological and anatomical criteria: thalamic relay neurons, local interneurons, and reticularis thalami neurons. At rest, two coexistent rhythms were observed in thalamic neurons. Brief episodes (1-2 s) of membrane-potential oscillations at frequencies of 8-12 Hz appeared with a periodicity of about 10 s. In relay neurons, each episode was characterized by a sequence of hyperpolarizations and burst discharges. These rhythmic episodes of hyperpolarization recurring about every 10 s could be reversed in sign by hyperpolarizing currents or by Cl injection, hence suggesting that they were mainly composed of rhythmic inhibitory postsynaptic potentials (IPSPs). This result also indicated that the slow 0.1-Hz rhythm was imposed on relay neurons by other neuronal pools. Following a complete isolation of the thalamus by cortical and high brain stem lesions, the slow 0.1-Hz rhythm was still present, and it was concluded that this rhythm was generated within the thalamus by inhibitory elements. In thalamic interneurons (identified by electrophysiological criteria) brief episodes (1-2 s) of repetitive depolarizations (8-12 Hz) and burst discharges recurred every 10 s. In the interval, the membrane potential of interneurons slowly hyperpolarized, contrasting with the rhythmic phasic hyperpolarizations observed in relay neurons. Electrophysiological properties shared by most relay neurons included a) afterspike hyperpolarizing potentials of long duration, which were blocked by injections of a Ca chelator; b) a pacemaker potential in the vicinity of the spike trigger level; and c) a low-threshold somatic Ca conductance that underlies burst discharges. As a general rule, prethalamic volleys induced faster rising and shorter lasting EPSPs than cortical volleys. Moreover prethalamic afferent-evoked responses could be associated with production of fast prepotentials, some of which appeared to result from dendritic spiking. It appears that synaptic and intrinsic membrane properties of thalamic neurons allow them to function under two modes: a relay mode and an oscillatory mode; the oscillatory mode being intrinsic to the thalamus and the relay mode being commanded and maintained by cortical and brain stem structures.

Background and Objectives -These guidelines were written by an international group of specialists with the aim to provide veterinarians with current recommendations for the diagnosis and treatment of canine demodicosis.Methods -Published studies of the various treatment options were reviewed and summarized. Where evidence in form of published studies was not available, expert consensus formed the base of the recommendations.

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Hereditary nasal dermatitis is reported in 14 Labrador Retrievers and 4 Labrador Retriever crosses. This appears to be a newly described inherited disorder for which an autosomal recessive mode of inheritance is suspected. The lesions were first noted between 6 and 12 months of age. Histopathological analysis revealed parakeratotic hyperkeratosis, often with marked multifocal accumulation of proteinaceous fluid between keratinocytes within the stratum corneum and superficial stratum spinosum. There was also a sub-basal lymphoplasmacytic infiltration within the superficial dermis. Immunohistochemistry staining for IgG (n = 4), distemper and papillomaviruses (n = 4) were negative, as were serum antinuclear antibody serology (n = 4) and fungal culture (n = 7). Electron microscopy revealed an altered cornification process: retention of nuclear chromatin, absence of lamellar bodies and marked intercellular oedema. Dogs did not respond to oral administration of zinc methionin (n = 3), cephalexin (n = 4), vitamin A alcohol (n = 1) or topical tretinoin (n = 1). Improvement of the lesions was obtained with topical vitamin E (n = 2), petroleum jelly (n = 2), and propylene glycol (n = 5).

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