Brain research
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The anticonvulsant, trimethadione (TMO), was tested for effects on cholinergic responses to iontophoretic application of ACh on identified neurons in Aplysia. TMO (1--10 mM) depressed the amplitudes of depolarizing responses mediated by Na+ and hyperpolarizing responses mediated by Cl- but did not affect hyperpolarizing responses mediated by K+. Such a combination of effects on cholinergic responses distinguishes the action of this anti-absence drug from agents effective against tonic-clonic seizures and from convulsive drugs.
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This study demonstrates that capsaicin exerts a selective neurotoxic action to induce degeneration of glomerular C-type nerve terminals in adult rats. Since the C terminals may be essential components of the circuitry for modulation of pain, it is suggested that capsaicin induced analgesia is the result of this neurotoxic action.
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Spontaneous respiratory neuronal activities within cervical spinal cord were investigated in two groups of 36 adult cats: cervical spinalized and non-spinalized preparations. In the first group of 18 animals, spontaneous breathing was abolished after total spinal transection at C1. However, spontaneous rhythmic breathing reappeared within 2 h after transection in 13 animals. ⋯ The recording sites were histologically located in the intermediate zone of the spinal gray matter of C1-C2 cervical cord. These results suggested the possible existence of some intrinsic respiratory rhythm generators within the cervical cord. Possible neuronal mechanisms for generation of spontaneous respiratory rhythm were discussed.
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The spontaneous discharge of cerebellar Purkinje neurons was studied in 3-, 12-, 15-, and 20-month-old rats. Fluphenazine and haloperidol administered intraperitoneally produced a dose-dependent increase in the spontaneous discharge in 3-month-old animals, but were ineffective in 12-, 15- and 20-month-old rats. Intraperitoneal administration of amphetamine resulted in a dose-dependent decrease in spontaneous Purkinje neuron discharge in 3-month-old rats without affecting neurons from the older animals. ⋯ Similar application of GABA did not reveal a differential sensitivity. For locus coeruleus activation to produce 50% inhibition in Purkinje neuron discharge, significantly higher stimulation currents were required in 15-month-old rats than in 3-month-old animals. Our results suggest a decreased postsynaptic sensitivity to norepinephrine in 12-, 15- and 20-month-old rats as compared to 3-month-old animals.
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We have extended our previous description at the dorsal horn level of Diffuse Noxious Inhibitory Controls (DNIC) to the trigeminal nucleus caudalis of the intact anaesthetized rat. These controls produce powerful long-lasting inhibitions of all activities of convergent neurones and can be elicited by noxious stimuli applied to widespread areas of the body unrelated to the receptive fields of the neurones under study. In nucleus caudalis, 39/40 convergent neurones were found to be under DNIC produced from the tail, paws, viscerae, nose and ears. ⋯ DNIC strongly inhibited both the A fibre and C fibre related activities of trigeminal convergent neurones whether evoked electrically or naturally with the degree of inhibition ranging between 55 and 100% in the most cases. Of 43 non-convergent neurones, noxious only, innocuous, proprioceptive and cold responsive, 42 were unaffected by DNIC. The results demonstrate that both the neuronal responses and DNIC at the trigeminal nucleus caudalis level in the rat are similar to those reported for the dorsal horn.