For the past decade, the dopamine hypothesis of schizophrenia has been the predominant biochemical theory of schizophrenia. Despite the extensive study of tissue samples obtained from schizophrenics, indirect pharmaco...
For the past decade, the dopamine hypothesis of schizophrenia has been the predominant biochemical theory of schizophrenia. Despite the extensive study of tissue samples obtained from schizophrenics, indirect pharmacological evidence still provides the major support for the hypothesis. Direct support is either uncompelling or has not been widely replicated. The dopamine hypothesis is limited in theoretical scope and in the range of schizophrenic patients to which it applies. No comprehensive biological scheme has yet been proposed to draw together the genetic, environmental, and clinical features of schizophrenia. Recent refinements of the dopamine hypothesis may aid in the delineation of biologically homogeneous subgroups. Positive symptoms (e.g., hallucinations, delusions) and negative symptomatology (e.g., affective flattening, social withdrawal) may result from different pathophysiological processes. Schizophrenia research might benefit from an increased attention to neurophysiological adaptations.
Whether the phasic bursting activity, characteristic of certain magnocellular neuropeptidergic neurons in rat hypothalamus, is dependent on chemical synaptic input was studied. Slices of hypothalamus were placed in an...
Whether the phasic bursting activity, characteristic of certain magnocellular neuropeptidergic neurons in rat hypothalamus, is dependent on chemical synaptic input was studied. Slices of hypothalamus were placed in an in vitro chamber with hippocampal slices. The synaptic response in the CA1 cell layer from Schaffer collateral stimulation was monitored before, during and after synaptic transmission was blocked by superfusion of medium containing high Mg2+ (either 18.7 or 9.3 mM) and low Ca2+ (0.05 mM). This well studied pathway was chosen as an assay of synaptic blockade because hypothalamic circuitry is relatively unknown. The electrical activity of 22 phasic phasic bursting neurons in the lateral portion of the paraventricular nucleus (PVN) was recorded. Of 22 phasic PVN neurons, 19 were recorded only after synaptic transmission was blocked. The remaining 3 cells were firing phasically in standard medium when first encountered and continued to display phasic bursting activity for up to 1.25 h after synaptic blockade. Active cells in nearby hypothalamic areas did not show phasic bursting patterns either before or after synaptic transmission was blocked. The phasic bursting activity of the PVN neurons in this study and that of previously reported PVN cells in vivo were similar in firing rate within bursts, burst length and silent period duration. Phasic bursting in PVN magnocellular neuropeptidergic cells is not dependent upon synaptically mediated excitation or recurrent inhibition as was hypothesized earlier. Alternative hypotheses, based upon acute changes in [K+]o, [extracellular concentration of K+], endogenous membrane currents and electrotonic coupling are discussed as possible explanations of phasic bursting in these magnocellular neuropeptidergic cells.
AVERY AND BOWMAKER REPLY- Bridges presents data from partial bleaching experiments to show that the rod pigment of Anableps (Amax = 506-507 nm) is actually a mixture of rhodopsin (Amax = 498 nm) and a porphyropsin (Am...
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AVERY AND BOWMAKER REPLY- Bridges presents data from partial bleaching experiments to show that the rod pigment of Anableps (Amax = 506-507 nm) is actually a mixture of rhodopsin (Amax = 498 nm) and a porphyropsin (Amax = 519nm), and is not a pure rhodopsin as reported by Schwanzara1. In our recent investigation of the dorso-ventral distribution of visual pigments in Anableps2, we suggested from the shape of the absorbance spectra of the rods, obtained by microspectrophotometry, that the pigments were probably rhodopsins, but we are not surprised to find that they are rhodopsin-porphyropsin *** suggests that we found no difference between the visual pigments of the dorsal and ventral parts of the retina possibly due to a change in the rhodopsin-porphyropsin ratio caused by keeping the fish in artificial light. Our value of the mean Amax of the rods is, however, within 1 nm of the value he and Schwanzara1 obtained for extracts of the rod pigment, inferring that the rhodopsin-porphyropsin ratio in the rods we measured in both regions of the retina was the same as that of their extracts. If Anableps does have higher proportions of porphyropsin in the dorsal retina in its natural habitat, we would have expected the Amax of Bridges' extract to have been longer than our rod mean Amax. Unfortunately, extracts normally contain only rod pigments and give no information about the distribution of pigments across the retina or the nature of the cone pigments. Thus, further microspectrophotometric studies are required.
Administration of d-amphetamine sulfate (7.5 mg/kg i.p.) twice daily to cats produces an initial large increase in both locomotion and behavioral stereotypy. As this regimen continues beyond 3 days, both measures show...
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Administration of d-amphetamine sulfate (7.5 mg/kg i.p.) twice daily to cats produces an initial large increase in both locomotion and behavioral stereotypy. As this regimen continues beyond 3 days, both measures show large significant decreases. This tolerance to the behavioral effects of amphetamine may be attributable to the concomitant decrease (approximately 70%) in presynaptic stores of dopamine and norepinephrine.
The passive electrical cable properties of CA3 pyramidal neurons from guinea pig hippocampal slices were investigated by applying current steps and recording the voltage transient from 25 CA3 neurons, using a single i...
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The passive electrical cable properties of CA3 pyramidal neurons from guinea pig hippocampal slices were investigated by applying current steps and recording the voltage transient from 25 CA3 neurons, using a single intracellular microelectrode and a 3-kHz time-share system. Two independent methods were used for estimating the equivalent electrotonic length of the dendrites, L, and the dendritic to somatic conductance ratio, .rho.. The first method is similar to that used by Gorman and Mirolli and gave an average L of 0.96;the average .rho. was 2.44. The 2nd method, derived for the 1st time, assumes a finite-length cable with lumped soma. It is an exact solution for L and .rho., using the slopes and intercepts of the first 2 peeled exponentials. The average L was 0.94;the average .rho. was 1.51. The results, using both methods, are in close agreement. The average membrane time constant for all 25 CA3 neurons was 23.6 ms, suggesting a large (23,600 .***2) average membrane resistivity. CA3 neurons are electronically short.
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