Examination of the effects of cholecystokinin 26-33 and neuropeptide Y on responses of visual cortical neurons of the cat

Bilateral multielectrode neurophysiological recordings coupled to local pharmacology in awake songbirds

Here we describe a protocol for bilateral multielectrode neurophysiological recordings during intracerebral pharmacological manipulations in awake songbirds. This protocol encompasses fitting adult animals with head-posts and recording chambers, and acclimating them to periods of restraint. The adaptation period is followed by bilateral penetrations of multiple electrodes to obtain acute, sensory-driven neurophysiological responses before versus during the application of pharmacological agents of interest. These local manipulations are achieved by simultaneous and restricted drug infusions carried out independently for each hemisphere. We have used this protocol to elucidate how neurotransmitter and neuroendocrine systems shape the auditory and perceptual processing of natural, learned communication signals. However, this protocol can be used to explore the neurochemical basis of sensory processing in other small vertebrates. Representative results and troubleshooting of key steps of this protocol are presented. Following the animal's recovery from head-post and recording chamber implantation surgery, the length of the procedure is 2 d.

Ultrastructural organization of transmitters in the cat lateralis medialis-suprageniculate nucleus of the thalamus: an immunohistochemical study

The lateralis medialis-suprageniculate nuclear (LM-Sg) complex of the cat's posterior thalamus receives a rather wide variety of inputs from diverse cortical and subcortical areas. Previous ultrastructural studies of this nucleus demonstrated the presence of four types of vesicle-containing profiles and characterized some of these as gamma-aminobutyric acid (GABA)-containing terminals (Norita and Katoh [1987] J. Comp. Neurol. 263:54-67; Norita and Katoh [1988] Prog. Brain Res. 75:109-118). The present study has extended these observations by examining the immunoreactivity (ir) of LM-Sg, with antibodies raised against aspartate (Asp), glutamate (Glu), GABA, the acetylcholine (ACh) marker, choline acetyltransferase (ChAT), and substance P (SP), by using light and electron microscopy. Neuronal somata immunopositive for the excitatory amino acids (EAAs) Asp and Glu, were of medium size. EAA-ir terminals also were of medium size and contained round synaptic vesicles; they made asymmetrical synaptic contacts with dendritic profiles. Neuronal somata immunopositive for GABA were small. GABA-positive terminals also were small and contained pleomorphic synaptic vesicles; they formed symmetrical synaptic contacts with dendritic profiles. No neurons immunolabeled for ChAT were found. Terminals immunopositive for ChAT were small and contained round synaptic vesicles; these made symmetrical synaptic contacts, asymmetrical synaptic contacts, or both, of the en passant type with dendritic profiles. SP-immunolabeled neuronal somata were not found. Immunolabeled terminals were small, contained round synaptic vesicles, and made asymmetrical synaptic contacts with dendritic profiles. ChAT-ir and SP-ir axon terminals were not expressed evenly within LM-Sg. This difference in distribution suggests that within the LM-Sg, there may be a difference in specific sensory processing functions which correlate with transmitter type.

The contribution of intracortical inhibition to dynamics of orientation tuning in cat striate cortex neurons

Orientation tuning of some neurons in cat visual cortex (area 17) revealed successive shifts of the preferred orientation and widening of tuning in time during the first 150 ms after onset of a flashing light bar. The mechanisms of these dynamics and the possible role of intracortical inhibition are still under discussion. In this study we analysed the dynamics using the time slice method before and during blockade of GABAergic inhibition by microiontophoretic application of bicuculline and observed two main types of neuronal behaviour. The first group of neurons (39 of 68 units or 57.4%) with relatively sharp tuning and absence or relatively small shifts of preferred orientation under control conditions increased or developed this shift during bicuculline application. Changes in tuning were observed between 30 and 150 ms after stimulus onset when inhibition was blocked. Neurons of the second group (29 units or 42.6% of cases) displayed pronounced shifts of preferred orientation under control conditions which was typically diminished or lost during blockade of inhibition. The results indicate different contributions of intracortical inhibition to different neurons distinguishing by stability or time dependence of their orientation preference during normal response generation. In one group of striate cells orientation tuning was kept narrow and constant in time by intracortical inhibition, while in another group orientation tuning dynamics are induced by inhibitory mechanisms.

Orientation tuning and receptive field structure in cat striate neurons during local blockade of intracortical inhibition

The contribution of intracortical inhibition to orientation tuning in the cat striate cortex (area 17) was studied by responses to flashing light bars of different orientations and lengths in 68 single-units before and during microiontophoretical application of bicuculline, a GABAA antagonist, A three-fold increase in the background activity (13.3 +/- 1.3 vs 4.4 +/- 0.5 imp/s) and 4.4-fold increase in the maximal discharge frequency (264.4 +/- 22.3 vs 60.6 +/- 5.3 imp/s) was found in 96.0% of the cells studied during microiontophoresis. In most units all characteristics of orientation tuning significantly changed during application of bicuculline: i) tuning width increased in 76.3% of cells from 52.7 +/- 2.8 degrees in control to 85.2 +/- 4.6 degrees, ii) tuning selectivity diminished in 63.6% of cells by a factor of 1.5, and iii) tuning quality dropped in 68.5% of cases by a factor of 2.5. The threshold ejection current of bicuculline for widening of tuning was in 2/3 of the cells in the range from +10 to +40 nA (+31.0 +/- 4.5 nA) and the maximum effect was obtained in 3/4 of units with +30(-) + 100 nA (+67.1 +/- 6.0 nA). Unmasking of additional excitatory inputs to the studied cells due to blockade of the inputs from inhibitory interneurons in considered as the main mechanism of the described bicuculline effects.

Cholecystokinin-8 regulation of NGF concentrations in adult mouse brain through a mechanism involving CCK(A) and CCK(B) receptors

1. Nerve growth factor (NGF), a powerful agent for the growth, differentiation and regeneration of lesioned cells of the central and peripheral nervous systems, has in recent years been indicated as a potential therapeutic agent capable of reversing the processes of cell damage in neurodegenerative events in man. Since NGF does not cross the blood-brain barrier and central NGF administration requires invasive surgical procedures, the discovery of substances modulating in vivo NGF synthesis in the brain will be extremely useful for a possible clinical use of NGF. 2. The aim of the present study to analyse if the content of NGF in the brain of adult mice can be affected by peripheral administration of cholecystokinin-8 (CCK-8), a well known neuropeptide which has stimulant actions on neurons in the brain and promotes a variety of neurobehavioural effects both in man and rodents. 3. The dose-response and time course effects of an i.p. injection of CCK-8 on the NGF concentrations in the hippocampus, cortex, hypothalamus and pituitary of adult male mice were analysed by use of a sensitive immunoenzymatic assay for NGF. The effects of pretreatment with selective CCK(A) and CCK(B) receptor antagonists and atropine on the NGF response to CCK injection were also studied. 4. The effects of CCK-8 were dose- and time-dependent and the injection of 8 nmol kg(-1) resulted in a 3 fold increase of NGF levels in the hypothalamus and pituitary, and about a 60% increase in the hippocampus. No effects were observed in the cortex. Pretreatment with a selective CCK(A) receptor antagonist blocked the CCK-induced NGF increase in the hypothalamus and pituitary. In the hippocampus the same effect was obtained with a CCK(B) receptor antagonist. Pretreatment with atropine suppressed the CCK-induced effects on NGF levels in all the brain regions examined. 5. Our results showing that i.p. injection with CCK-8 can modulate NGF levels in the brain through a mechanism which seems, in part, to be mediated via the vagal afferents, indicate that this neuropeptide may represent a useful pharmacological approach to enhance endogenous NGF levels in neuropathologies associated with a neurotrophin deficit.

Interaction of cholecystokinin and glutamate agonists within the dLGN, the dentate gyrus, and the hippocampus

The interaction of sulfated cholecystokinin (CCK-8S) with excitatory amino acids (EAA) was studied on single units of the dorsal lateral geniculate nucleus (dLGN), the dentate gyrus, and the hippocampal CA3 region in rats anaesthetized with urethane. lontophoretic co-administration of small, individually ineffective currents of CCK-8S and kainic acid or N-methyl-D-aspartate repeatedly elicited an increase of the discharge rate in nearly all geniculate and half of the dentate neurons but not in those of the CA3 region. The effect could be reduced by the CCKB receptor antagonist PD 135,158 more often than by the CCKA antagonist KL 1001. The increased firing due to co-administration of CCK and kainate could also be suppressed by the non-NMDA antagonist CNQX but not by the NMDA antagonists CPP or AP-5, which were otherwise able to prevent the neuron from responding to co-administration of CCK and NMDA. It is suggested that in distinct brain regions the effectivity of the "low level" EAA transmission may be enhanced by small amounts of CCK-8S. This is thought to be mediated by a coactivation of CCK and EEA receptors.

Cholecystokinin excites neostriatal neurons in rats via CCKA or CCKB receptors

The effect of iontophoretically applied cholecystokinin (CCK) on neurons of the neostriatum was studied in rats anaesthetized with urethane. The most frequently observed effect of the sulphated octapeptide (CCK-8S) on striatal neurons was excitation. Spontaneously active neurons responded more often to CCK-8S than quiescent cells. Silent, primarily non-responsive neurons could often be stimulated with CCK-8S using glutamate to induce an ongoing discharge. Thus, 45.8% of the 177 neurons studied changed their discharge rate by more than 30%. Certain CCK receptor antagonists could prevent the effect of CCK-8S, fully or at least partly, in the majority of CCK-responsive neurons. The data suggest that cholecystokinin modulates the firing of active neostriatal neurons via the CCKA or the CCKB receptor type. Furthermore, we compared neuronal responses to glutamate with those recorded during concomitant administration of CCK-8S in order to study the interaction of both transmitters, which may be colocalized in striatal afferents. CCK-8S mainly enhanced the excitatory effect of glutamate on striatal neurons, but in several neurons the response to glutamate was reduced. The CCKB receptor antagonist could prevent CCK-8S from increasing the glutamate-induced activation.

Cholecystokinin-induced activity changes of dorsal lateral geniculate neurons in rats

The effects of iontophoretically applied cholecystokinin fragments and cholecystokinin antagonists on neurons of the dorsal lateral geniculate nucleus were investigated with extracellular recordings in rats anesthetized with urethane. The peptide cholecystokinin-8S, which has affinity for both cholecystokinin-A and -B receptors, altered the baseline firing as well as the responses to visual stimuli of about one half of the investigated neurons (90 out of 190). Excitatory effects predominated (P < 0.01, Wilcoxon test), although inhibitory effects were also observed. The effects of cholecystokinin-8S were dose-dependent. Neurons sensitive to cholecystokinin-8S could be found in all regions of the dorsal lateral geniculate nucleus, but they differed in their susceptibility to cholecystokinin in relation to their location. The B-agonist, BOC-cholecystokinin-4, also changed the baseline firing as well as the light-evoked activity of dorsal lateral geniculate nucleus neurons. The effects were either excitatory or inhibitory. Changes induced by cholecystokinin-8S could be effectively blocked by the cholecystokinin-B antagonist, CAM 1028 (19 out of 22 cholecystokinin-sensitive neurons tested). The cholecystokinin-A antagonist, Ge 410, blocked cholecystokinin-induced effects in 10 out of 16 neurons. These results indicate that the modulation of geniculate cell firing by cholecystokinin is mediated by both A-and B-receptor types.