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The aim of the present work was to identify the role of ATP acting on specific P2X receptors in the central mechanisms of thermoregulation. Immunohistochemical studies demonstrated that brainstem structures involved in controlling body temperature contained large number of nerve cells bearing P2X ATP receptors. Experiments on conscious rats involving intracerebroventricular administration of an ATP analog and P2X antagonists showed that both activation and blockade of central P2X receptors produced marked changes in body temperature. Analysis of the effects of these substances provided grounds for suggesting that ATP acting on P2X receptors fulfils an important function in the mechanisms of transmitting afferent information from peripheral thermal receptors to thermoregulatory centers in the brainstem with responsibility for heat loss, while in pyrogen-induced fever ATP acting on these receptors may be involved in the activity of the endogenous antipyretic system.

The hypothalamus is a key area for the integration of the autonomic features of affective behavior. Hypothalamic defence area (HDA) stimulation evokes major cardiorespiratory changes as well as modifications of general autonomic activity both in the anesthetized and conscious animal. Micturition is due to an increase in pelvic parasympathetic activity and, in the cat, the anterior hypothalamus has been implicated in urinary bladder control with the demonstration of a dorsolateral vesicoconstrictor pathway and a ventromedial inhibitory pathway. In this study we have investigated the effect of electrical and chemical stimulation of the HDA on bladder pressure and contractions in rat. Female rats (n = 15) were anesthetized, paralyzed and ventilated artificially. Arterial blood pressure, heart rate, urinary bladder pressure and pelvic nerve activity were recorded. HDA was electrically (1 ms, 100 Hz, 5-10 s train at intensities up to 150 micro A) and chemically (sodium glutamate, 50 nl, 2mM) stimulated. For statistical analysis the t-test was used, data were expressed as mean +/- SEM. Values of t were taken as significant when p0.05.HDA stimulation at 100-150 micro A evoked changes of both mean blood pressure (mBP) and bladder pressure (BlP). However, stimulation at30 micro A allowed a distinction within HDA of two different regions, at the same antero-posterior and lateral level, but separated 100-150 micro m in depth, which evoked differential effects on blood pressure and urinary bladder pressure. Results show that low intensity stimulation at ventral sites evoked a significant increase of mBP (from 102 +/- 5.9 to 127 +/- 8.6 mmHg, n = 10, p0.0001) with little changes of BlP (from 12 +/- 2.2 to 16 +/- 2.9 cmH(2)O, n = 10, p0.0005), whilst at more dorsal sites significant increases of BlP were elicited (from 12 +/- 8.3 to 38 +/- 4.6 cmH(2)O,n = 10, p0.0001) with only a small rise of mBP (from 102 +/- 6.2 to 111 +/- 9.8 mmHg, n = 10, p0.005). Glutamate injections at dorsal sites evoked a rise of BlP (from 11 +/- 2.2 to 30 +/- 3.0 cmH(2)O (n = 5; p0.0001) with small changes in BP, whilst at ventral sites (n = 4) glutamate microinjections evoked changes in BP but not of BlP. In conclusion stimulation at different sites within HDA can elicit separate changes in BP and BlP.

Compound action potentials evoked by electrical stimulation in the brainstem of anaesthetized, paralyzed cats and rabbits were recorded distally in the carotid sinus nerve. The latencies of the components of the responses were indicatives of fibres with conduction velocities between 0.5 and 32 m/s. These include both myelinated and unmyelinated fibres. Using histological reconstruction of the 'responsive sites', the termination of the primary afferent fibres of the sinus nerve within the medulla was mapped. In both cat and rabbit these responsive sites were restricted to the doromedial medulla in the vicinity of the NTS 0--3 mm rostral to the obex. Although in the cat the fast conducting myelinated fibres (conduction velocities greater than 12.5 m/s) were discretely localized to the ventrolateral area of the NTS, the slower conducting myelinated and unmyelinated fibres were found more diffusely, spreading into areas dorsal and medial to the NTS. In the the rabbit the terminals of all types of fibre were mainly confined to the NTS although some C fibres appeared to be grouped in the juxta-alar region. Responses were never evoked from the medial reticular formation or nucleus ambigus in either cats or rabbits. The organization of the sinus nerve input to the medulla is discussed in the light of these results.

1. Experiments have been undertaken on 11 decerebrate cats to investigate the effects of natural vestibular stimulation on the activity of cerebellar fastigial neurons. 2. From recordings in the rostral portion of the nucleus during sinusoidal lateral (roll) and horizontal (yaw) rotation, distinctive patterns of response were observed. 3. The majority of neurons sensitive to vestibular stimulation showed responses to a single modality of vestibular activation. During lateral tilt some neurones showed positional sensitivity, others gave responses related to the velocity of movement. Other neurones responded in phase with the velocity of movement in the horizontal plane. 4. Aside from these neuronal responses, others provided indications of a convergence of inputs from different sets of vestibular receptors. In particular, several neurons showed a pattern of response that indicated that they received inputs from otolith receptors and ampullar receptors of the vertical canal. At low velocities of movement their response was positional but with increasing velocity the magnitude of the response increased and there was a marked phase shift of the discharge towards head velocity. 5. Neurons responding to horizontal rotation often showed positional responses during lateral tilt. There were also indications of a convergence of ampullar inputs from both vertical and horizontal canals. 6. The neural pathways mediating these responses are discussed in consideration of previous neuroanatomical and neurophysiological data. We consider it likely that several pathways may act to evoke the patterns of response observed, and a role of the cerebellar cortex is indicated.