Membrane resistance increase induced in thalamic neurons by stimulation of brainstem cholinergic afferents

The synaptic response induced in thalamic relay cells by stimulation of peribrachial cholinergic afferents was studied in cats maintained under urethane anesthesia. Recordings were performed in the ventral lateral nucleus after destruction of the reticular thalamic complex and cortical lesion. Some animals were also pretreated with reserpine (1.2 mg/kg) 24 h before recording sessions. Repetitive stimulation (25-60 Hz for 200-600 ms) of the peribrachial area produced a slow depolarization and tonic firing in thalamic cells. The depolarization was associated with an increase in membrane resistance and its amplitude decreased during membrane hyperpolarization. The reactivity of thalamic relay cells to a corticothalamic volley was also increased during the slow depolarization. Similar results were obtained in reserpinized animals. On the basis of previous data obtained in vitro, it is concluded that the slow depolarization resulted from the activation of muscarinic receptors by brainstem cholinergic afferents.

Polyclonal B cell activation of IgG2a and IgG2b production by infection of mice with lactate dehydrogenase-elevating virus is partly dependent on CD4+ lymphocytes

Concentrations of IgM and IgG isotypes were determined by capture ELISA in plasma of Swiss, BALB/c and C58/M mice. Plasma IgG isotype concentrations, especially of IgM, IgG1 and IgG2a, varied considerably between mouse strains, batches of mice of the same strain and individual mice and as a function of age. Infection of the mice with LDV, which is known to replicate primarily in a subpopulation of macrophages, consistently resulted in a rapid elevation of plasma IgG2a (or of IgG2b in some Swiss nu/+ mice), but no plasma IgG increases were observed in mice immunized with inactivated LDV. Plasma IgG2a elevation after LDV infection was greatly delayed and reduced by depletion of the mice of CD4+, but not of CD8+, T cells by administration of protein-G-purified anti-CD4 or anti-CD8 mAbs, and completely inhibited by repeated treatment of the mice with cyclophosphamide. Treatment with anti-CD4 mAbs, or cyclophosphamide also greatly reduced the production of anti-LDV antibodies, while not significantly affecting the replication of LDV in these mice. Nude Swiss mice also failed to produce anti-LDV antibodies, though supporting normal LDV replication. Plasma IgM, IgG1, IgG2a and IgG2b levels increased in LDV-infected nu/nu mice, but similar changes were observed in uninfected mice. The results indicate that the LDV-induced polyclonal activation of B cells requires productive LDV infection of mice and is, at least partly, dependent on functioning CD4+ cells. They suggest that productive infection of the LDV-permissive subpopulation of macrophages leads to the activation of CD4+ T lymphocytes of subset 1 and their Spleen cells from 5-day LDV-infected BALB/c mice incorporated [3H]thymidine 2-3 times more rapidly in vitro than spleen cells from companion uninfected mice, whereas their responses to concanavalin A and lipopolysaccharide were reduced 60-70%.

The effects of brainstem peribrachial stimulation on perigeniculate neurons: the blockage of spindle waves

The mode of action of afferents arising from the brainstem peribrachial region at the midbrain-pontine junction on neurons recorded from the reticular thalamic sector adjacent to the lateral geniculate nucleus (perigeniculate cells) was investigated at the intracellular level in the cat. Experiments were performed in cats under barbiturate or urethane anaesthesia and in non-anaesthetized deafferented animals. Most cats were pretreated with reserpine (1-2 mg/kg) and were also acutely deprived of their retinal and cortical visual inputs. It was found that peribrachial stimulation produced a short train of fast-rising depolarizations followed by a long-lasting period of hyperpolarization in all perigeniculate neurons. Although the latest part of the early depolarizations preceding the hyperpolarization resulted from a parallel activation of lateral geniculate relay neurons by peribrachial afferents, those occurring at shortest latencies appear to result from a direct excitation produced by peribrachial afferents. Furthermore, these early excitatory postsynaptic potentials persisted under deep barbiturate anaesthesia, a condition that prevents activation of thalamic relay neurons by peribrachial stimulation. The evoked hyperpolarization decreased with membrane hyperpolarization, was associated with a 40-50% increase in membrane conductance and was insensitive to Cl injections. It was no longer observed within one hour after i.v. injection of scopolamine. However, the depolarizing responses were not depressed by this muscarinic antagonist. Iontophoretic applications of scopolamine also removed peribrachial-evoked inhibition of synaptic responses triggered by optic chiasma stimulation. The peribrachial input exerted a powerful control on the oscillatory behavior of perigeniculate neurons. Spindle oscillations which are generated within the reticular thalamic complex were readily blocked by peribrachial stimulation. It is then concluded that the transition from an oscillatory to a relay mode of operation in the thalamus is controlled at least in part by a muscarinic inhibition of reticular thalamic neurons. The synaptic mechanism responsible for the early depolarization remains to be elucidated.

The cellular mechanism of thalamic ponto-geniculo-occipital waves

The cellular mechanisms underlying the genesis of thalamic ponto-geniculo-occipital waves were studied in reserpinized cats under urethane anaesthesia. Simultaneous field potential and intracellular recordings were performed in the lateral geniculate nucleus after acute lesions of retinal and visual cortical inputs. In most relay cells, reserpine-induced ponto-geniculo-occipital waves were associated with a transient depolarization that was often interrupted by a unitary inhibitory postsynaptic potential. The depolarization grew in size with membrane hyperpolarization and was accompanied by an increase in membrane conductance. The inhibitory postsynaptic potential is likely to have resulted from the activation of intrageniculate interneurons since perigeniculate cells were always inhibited during the occurrence of ponto-geniculo-occipital waves. Under reserpine, thalamic ponto-geniculo-occipital waves could also be triggered by peribrachial or auditory stimulation. These evoked ponto-geniculo-occipital waves were associated with intracellular events identical to those occurring spontaneously after reserpine administration. In addition, thalamic spindle oscillations were readily blocked by the occurrence of spontaneous or evoked ponto-geniculo-occipital waves. On the basis of the present results and those already published in the literature, the conclusion is reached that lateral geniculate ponto-geniculo-occipital waves result from a nicotinic activation of relay cells and from a parallel muscarinic inhibition of perigeniculate cells by peribrachial afferents. The functional significance of the ponto-geniculo-occipital activity is discussed on the basis of the antagonistic action of these signals on thalamic oscillations. It is proposed that these signals are the central correlates of orienting reactions elicited by sensory stimuli during waking (the so-called eye movement potentials) and by internally generated drives during paradoxical sleep.

The effects of brainstem peribrachial stimulation on neurons of the lateral geniculate nucleus

The intracellular effects of brainstem peribrachial stimulation on lateral geniculate neurons were investigated in the cat. Experiments were performed in cats under barbiturate or urethane anaesthesia and in non-anaesthetized deafferented animals. Most animals were pretreated with reserpine and were acutely deprived of their retinal and visual cortical inputs. Short trains of stimuli triggered a transient depolarization in most relay neurons (latency: 20-30 ms; duration: 200-300 ms). This depolarization could be interrupted by a short-duration unitary inhibitory postsynaptic potential. The depolarization increased with membrane hyperpolarization and was associated with an increase in membrane conductance. The inhibitory postsynaptic potential had an intrathalamic origin and likely resulted from parallel activation of intrageniculate interneurons. The above responses were largely enhanced in reserpinized cats and were completely abolished by small doses of barbiturates. Iontophoretic applications of the nicotinic blocker, hexamethonium, eliminated peribrachial-evoked discharges in these cells, while similar applications of the muscarinic antagonist, scopolamine, were devoid of any effect. The conclusion is reached that the depolarization of lateral geniculate relay neurons by peribrachial afferents represents a direct postsynaptic effect and does not result from a global disinhibitory mechanism involving inhibition of perigeniculate cells and intrageniculate interneurons. This peribrachial-evoked transient excitation of relay neurons results from a nicotinic mechanism.

The blockage of ponto-geniculo-occipital waves in the cat lateral geniculate nucleus by nicotinic antagonists

The cholinergic mechanism underlying the genesis of ponto-geniculo-occipital (PGO) waves recorded from the lateral geniculate (LG) nucleus was studied in reserpinized cats under urethane anesthesia. PGO field potentials and their related unit activities occurred spontaneously or were triggered by stimulation of the brainstem peribrachial (PB) area. It was found that PGO-related unit activities were strongly depressed by systemic or iontophoretic applications of nicotinic antagonists such as mecamylamine or hexamethonium but remained intact after similar applications of scopolamine. These results suggest that the genesis of thalamic PGO waves involves a nicotinic activation of relay neurons by PB cholinergic afferents.